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MUKAI ToshijiGraduate School of Medicine / Department of Medical Device EngineeringProfessor
Research activity information
■ Award- Feb. 2010 The Minerals, Metals and Materials Society (TMS), MAGNESIUM BEST PAPER AWARD- FUNDAMENTAL RESEARCH, Directionally controlled precipitation on twin-boundaries in Mg-Zn-Y alloysInternational society
- Mar. 2008 日本金属学会, 日本金属学会 功績賞（力学特性）, "Ductility Enhancement in AZ31 Magnesium Alloy by Controlling its Grain Structure"などJapan society
- Jan. 2003 Committee of Platform Science and Technology in Advanced Magnesium, Highly Contribution Paper Award at PSTAM2003, Guide for Enhancement of Room Temperature Ductility in Mg Alloys at High Strain RatesInternational society
- Jun. 2001 日本マグネシウム協会, 日本マグネシウム協会賞, 延性を阻害しないマグネシウム合金の高強度化に関する研究Japan society
- Purpose: The optimal hinge position to prevent hinge fractures in medial closing wedge distal femoral osteotomy (MCWDFO) based on the biomechanical background has not yet been well examined. This study aimed to examine the appropriate hinge position in MCWDFO using finite element (FE) analysis to prevent hinge fractures. Methods: Computer-aided design (CAD) models were created using composite replicate femurs. FE models of the MCWDFO with a 5° wedge were created with three different hinge positions: (A) 5 mm proximal to the proximal margin of the lateral epicondylar region, (B) proximal margin level and (C) 5 mm distal to the proximal margin level. The maximum and minimum principal strains in the cortical bone were calculated for each model. To validate the FE analysis, biomechanical tests were performed using composite replicate femurs with the same hinge position models as those in the FE analysis. Results: In the FE analysis, the maximum principal strains were in the order of Models A > B > C. The highest value of maximum principal strain was observed in the area proximal to the hinge. In the biomechanical test, hinge fractures occurred in the area proximal to the hinge in Models A and B, whereas the gap closed completely without hinge fractures in Model C. Fractures occurred in an area similar to where the highest maximal principal strain was observed in the FE analysis. Conclusion: Distal to the proximal margin of the lateral epicondylar region is an appropriate hinge position in MCWDFO to prevent hinge fractures. Level of Evidence: Level V.Apr. 2024, Journal of Experimental Orthopaedics, 11(2) (2)Scientific journal
- PURPOSE: Non-absorbable clips are widely used in urologic surgery and they may come in contact with an open urinary tract intraoperatively. As a result, stray clips in the urinary tract and associated intractable infections have been reported. We developed a bioabsorbable metal and evaluated whether it would dissolve if it strayed into the urinary tract. METHODS: We prepared four types of alloys mainly comprising zinc (Zn) with small amounts of magnesium (Mg) and strontium (Sr), and the biological effects, degradability, strength, and ductility were investigated. Each alloy was implanted in the bladder of five rats for 4, 8, and 12 weeks. The alloys were removed and evaluated for degradability, stone adhesion, and tissue changes. The Zn-Mg-Sr alloy had degradability and no stone adhesion in the rat experiments, and it was implanted in the bladders of five pigs for 24 weeks. The Mg and Zn levels in the blood were measured, and staple changes were confirmed by cystoscopy. RESULTS: Zn-Mg-Sr alloys showed the best degradability of 6.51% at 12 weeks. In pig experiments, the degradation rate was 3.72% at 24 weeks. None of the pigs had changes in the Zn or Mg concentrations in the blood. Overall, the bladder incision was healed and the gross pathology showed wound healing. CONCLUSIONS: The Zn-Mg-Sr alloys were safely used in animal experiments. Furthermore, the alloys are easy to process and can be formed into various shapes, such as staples, making them useful in robotic surgery.Apr. 2023, World journal of urology, 41(4) (4), 1181 - 1186, English, International magazineScientific journal
- Biodegradable magnesium-based composites have recently attracted considerable attention for use in orthopedic implants on account of not only their biocompatibility but also the possibility of tuning their mechanical and corrosion properties. In this study, the effects of the fraction of tricalcium phosphate (TCP) and its crystal structure on the electrochemical properties in Eagle's minimal essential medium as well as the mechanical properties were examined using high-strength Mg–Ca/TCP composites with a fine-grained matrix (grain size: 1.2 µm) and relatively uniform TCP particle dispersion. The composites were prepared by extruding mixtures of the component powders at 540 K and exhibited high compressive yield strengths exceeding 290 MPa. Electrochemical tests revealed that the corrosion parameters were insensitive to both the fraction of TCP particles and their crystal structure. The fine-grained matrix may have overwhelmed the ability of the TCP dispersion to serve as a corrosion inhibitor. The chemical compositions of the cracked surface layer on the matrix and the white discontinuous corrosion products of the composites formed after the electrochemical tests were similar to those of the parent alloy.Mar. 2023, Materialia, 27Scientific journal
- Magnesium is a metal material with both bioabsorbability and biocompatibility, and the fine wire is expected to be applied to bioabsorbable implants. It is desirable that the alloy composition is composed only of bioessential elements such as calcium and zinc, and the composition does not form the second phase precipitate of unknown biological toxicity. However, there are few studies on magnesium fine wires, and their degradability. In the case of surgical clips, staples, sutures, etc., it is necessary to consider bending deformation during ligation. In this study, fine wires of Mg-0.3 mol%Ca and Mg-0.3 mol%Zn were fabricated, and the coil was formed by the winding tester to evaluate the bending deformation. As a result, it was confirmed that Mg-0.3 mol%Zn was hard to crack, while Mg-0.3 mol%Ca was easy to crack after the deformation. In addition, an in vitro test was conducted using the prepared coil to investigate the effect of alloying elements on the degradability. After the tension bending deformation, surface appearance was inspected to know the effect of the trace alloying on the deformability. Continious observation revealed that the alloying element affect the degradability, since the shape of coil using Mg-0.3 mol%Ca and Mg-0.3 mol%Zn remained for 21 days and 35 days, respectively.2022, Keikinzoku/Journal of Japan Institute of Light Metals, 72(12) (12), 708 - 710Scientific journal
- We investigated the effect of grain refinement on the fatigue properties of biodegradable Mg0.3 at%Ca alloy, which is expected to be applied in bone fixation devices. Mg0.3 at%Ca alloy had poorer fatigue properties in simulated body fluid than in air, even after grain refinement. However, the alloy maintained mechanical properties similar to those of human cortical bone. Based on the fatigue fracture surface, the fracture modes of the Mg0.3 at%Ca alloy differ markedly in air and simulated body fluid. In air, both transgranular and intragranular fractures occurred frequently, whereas in the simulated body fluid, intergranular fracture was the dominant mode. Although the effect of grain refinement on fatigue life was less pronounced in simulated body fluid than in air, the Mg0.3 at%Ca alloy with grain refinement is considered a promising material for orthopedic devices.Japan Institute of Metals, Jan. 2022, MATERIALS TRANSACTIONS, 63(1) (1), 69 - 72Scientific journal
- Objective: In this study, autologous bone grafts using bone-fixing nails made of magnesium-zinc-calcium ternary alloys were performed using rabbit skulls. Material and methods: Two types of nails for bone fixation were prepared: 2.5 mm width, 3 mm length and 2.5 mm width, 2 mm length. A disk-shaped bone with a diameter of 5 mm was resected from the parietal bone and fixed with a 3 mm long nail. As a control group, a 2 mm long nail was driven into the existing bone. The rabbits were sacrificed at 1, 4, 12, and 24 weeks after surgery. The resected samples were observed with micro X-ray CT, and embedded in methyl methacrylate to prepare non-decalcified specimens. The in vivo localization of elements was examined using energy-dispersive X-ray spectroscopy (EDS). Results: Micro X-ray CT images of samples showed volume reduction due to degradation in both the bone graft and control groups. No significant difference in the amount of degradation between the two groups was observed, however characteristic degradation processes were observed in each group. The samples stained with alizarin red S showed amorphous areas around the nails, which were considered as corrosion products and contacted directly with the newly formed bones. EDS analysis showed that corrosion products were mainly composed of magnesium and oxygen at an early stage, while calcium and phosphorus were detected on the surface layer during the long-term observation. Conclusions: The degradation speed of the magnesium alloy nails varied depending on the shapes of the nails and surrounding tissue conditions. A calcium phosphate layer was formed on the surface of magnesium alloy nails, suggesting that the degradation rate of the nail was slow.2022, J Appl Biomater Funkt Mater., 20[Refereed]Scientific journal
- This study aimed to investigate the effects of alloying elements on the fatigue properties of magnesium in simulated body fluids. The fatigue life of the Mg-Zn alloy in air was longer than that of Mg-Ca. This result is in accordance with the tensile yield stress. Crack propagation occurred along the grain boundaries in Mg-Ca and among the grains in Mg-Zn because zinc addition significantly effects grain boundary strengthening. In contrast, the fatigue life in simulated body fluid was longer for the Mg-Ca alloy than for the Mg-Zn alloy at a lower stress amplitude. These results suggest that the use of both calcium and zinc as additives contributes to the further improvement of the fatigue life of magnesium in simulated body fluids as the immersion time is prolonged.Japan Institute of Metals, Dec. 2021, MATERIALS TRANSACTIONS, 62(12) (12), 1806 - 1809Scientific journal
- (一社)日本泌尿器科学会総会事務局, Dec. 2021, 日本泌尿器科学会総会, 109回, PP22 - 07, Japanese生体分解性亜鉛マグネシウム合金の開発及び、尿路手術での使用の検討
- Addition of Al to equiatomic high entropy alloy CrMnFeCoNi alloy with a single phase FCC structure is known to promote formation of a BCC phase. In addition, tetragonal intermetallic phase σ was also found to form in a (CrMnFeCoNi)92Al8 alloy when subjected to processing by caliber rolling (8 passes) at room temperature followed by annealing at 800 ∘C. Microstructure of the as-rolled alloy is complex, containing a high dislocation density and planar faults (including twins) which can be parallel and perpendicular to the rolling direction. Morphological features of the transformations induced by straining by caliber rolling have been determined by transmission electron microscopy (TEM). Two main morphologies have been determined. In one type of morphology, bundles of elongated domains of B2 ordered BCC phase form preferentially on {111} matrix planes, inside which σ phase particles nucleate on interface with the matrix. In another type of morphology called “aggregate” here, “spines” of elongated grains of σ phase form, over which domains of B2 phase nucleate driven by change in solute concentration ahead of the interface. The σ phase forms by nucleation on planar faults in the matrix with its (001) plane, forming the known orientation relationship (OR) {001}σ ∥ {111}FCC and 〈110〉σ ∥ 〈110〉FCC. Since the planar faults in a caliber rolled alloy form parallel as well as perpendicular to the rolling direction, spines of the σ phase elongated in three mutually perpendicular directions are shown to exist. OR of the B2 phase with the matrix is Kurdjumov-Sachs. The B2 phase matched pairs of close packed planes with σ phase, but no particular OR was found. Elemental concentration profiles across interfaces suggests that σ and B2 phases grow into the matrix. All the evidence suggests that the σ phase nucleates on the planar faults in the matrix, and then B2 phase forms by elemental concentration changes in the matrix caused by growth of the σ phase, forming the aggregate morphology.Elsevier {BV}, Dec. 2021, Materials Characterization, 182, 111556 - 111556, English[Refereed]Scientific journal
- Magnesium specimens were impacted by a spherical alumina projectile at a velocity around 7 km/s under two environment temperatures of room temperature (3300 K) and low temperature (3173 K). To clarify deformation and fracture mechanisms, macro- and micro-structure were inspected by using micro-X ray computed tomography and scanning electron microscope (SEM) with electron back scattering diffraction (EBSD). In addition, simulation of the hyper-velocity impact was conducted using Smoothed Particle Hydrodynamics method to investigate the cumulative strain and temperature rise during the deformation. After a projectile impacted a target, a crater was formed on the target together with several cracks. In a closed portion below the crater formed at room temperature, fine grains and subgrains were observed by SEM/EBSD. From the calculation results, a temperature rise around 0.5 Tm (Tm melting temperature of magnesium) and cumulated strain over 0.6 was suggested at 0.5 mm away from the edge of the crater. Therefore, the microstructure evolution was expected to be induced by the recrystallization and recovery due to the strain cumulated during the impact and the resultant temperature rise. On one hand, inspection of microstructure near the cracks revealed that microcracks were tended to propagate along grain boundary.Japan Institute of Metals (JIM), Sep. 2021, Materials Transactions, 62(9) (9), 1401 - 1406, EnglishScientific journal
- The microstructural changes and flow behavior under hot compression at a temperature of 1173 K were examined for a six-component (CoCrFeMnNi)92Al8 high-entropy alloy. The homogenized alloy, which was a single-phase solid solution with a face-centered cubic (fcc) structure, possessed a deformation microstructure with shear bands after hot compression and exhibited steady-state flow over a wide strain range. In contrast, the thermomechanically processed alloy, which was composed of an unrecrystallized fcc matrix and second phases (bcc and σ), comprised fully recrystallized matrix grains of 0.8 µm diameter after hot compression and displayed gradual strain softening from the early stages of deformation. The results demonstrated that the dense dispersion of the second phases in the thermomechanically processed alloy was quite effective for attaining fine grains by dynamic recrystallization upon hot deformation.Elsevier BV, Aug. 2021, Materialia, 18, 101172 - 101172Scientific journal
- An equiatomic CrMnFeCoNi alloy is usually a single-phase solid-solution with a face-centered cubic (fcc) structure. However, a Cr-rich σ phase with a tetragonal structure is formed in coarse-grained alloys after extended heat treatment between 873 K and 1073 K, which is indicative of metastability of the CrMnFeCoNi alloy. In this study, it was demonstrated that cold-working facilitated σ-phase formation during heat treatment at 1073 K in (CrMnFeCoNi)100−xAlx (x = 8 and 9 at%). More specifically, the heat treatment produced a unique σ–body-centered cubic (bcc) aggregate morphology in the unrecrystallized fcc matrix. Each aggregate was composed of σ-phase spine and bcc particles at the fcc/σ interface, and formed in a short period (0.5 h). It is suggested that aggregates precipitated on dislocations that were introduced by cold-working.Elsevier BV, Aug. 2021, Journal of Alloys and Compounds, 872, 159668 - 159668Scientific journal
- This study was designed to examine osteoconductive effects of Mg in rats tibia. The animals were sacrificed after 1, 2, and 8 weeks. The elemental analysis was performed using SEM/EDX at week 1. Following X-ray micrography at weeks 2 and 8, samples were embedded in paraffin. The expression of osteocalcin was observed by immunohistochemical staining. The element concentrations of fibrous capsules around the specimens were also measured by ICP-MS. The concentrations of Ca and P on the surface of the Mg specimen increased in SEM/EDX. The tissue specimen showed new bone formation on the bone surface near the implanted area. The concentrations of Mg, Ca, and P were high in the fibrous capsules surrounding Mg. Implantation induced differentiation of osteoblasts, and this process was considered to be associated with new bone formation. Induction of cell differentiation may be influenced by corrosion products in addition to corroding magnesium.Mar. 2021, Dental materials journal, 40(2) (2), 498 - 507, English, Domestic magazineScientific journal
- Drawing is suitable for manufacturing fine metal wire. This study was designed to clarify the effects of additive elements, calcium or zinc, on mechanical properties of drawn magnesium wires. Binary alloys of Mg-0.3 at. % Ca and Mg-0.1 at. % Zn were cast followed by extrusion. The extrusion bars were drawn to fabricate a fine wire with a diameter of 0.2 mm. Tensile tests were conducted for the wires. The results of the tensile tests confirmed that yield stress increased as the content of the solute element increased, while the work hardening rate and tensile ductility differed depending on the types of additive element. Inspection of the drawn microstructure revealed that the additive element plays an important role in microstructure evolution in magnesium.Springer Science and Business Media Deutschland GmbH, 2021, Minerals, Metals and Materials Series, 135 - 140, EnglishInternational conference proceedings
- In recent years, magnesium is expected to be used as a structural material in vehicles. Since limited slip systems in magnesium induces marked yield anisotropy and poor deformability at room temperature, there is a specific demand for developing magnesium alloys with reduced plastic anisotropy. In this study, we focused on the Mg–Al system alloy, which is widely used in commerce, and examined the third element contributing to the reduction of the plastic anisotropy. Generalized stacking fault energy (GSFE), which corresponds to the energy for sliding atomic layer along a slip plane, was calculated in the first-principles calculations to estimate deformability of ternary Mg–Al-X alloys adding the third element X, to the Mg–Al binary alloy. As the third element X, Zn, Zr, and Gd were selected. The slip properties were evaluated using the unstable stacking fault energy (USFE), which represents the maximum value of GSFE. The result suggested that the addition of zirconium contributes most to the reduction of plastic anisotropy.Springer Science and Business Media Deutschland GmbH, 2021, Minerals, Metals and Materials Series, 37 - 44, EnglishInternational conference proceedings
- Purpose: To develop a novel biocompatible solid fiducial marker that prevents radiopaque imaging artifacts and also maintains high imaging contrast for kilovoltage x-ray image-guided radiation therapy.Methods: The fiducial marker was made of pure zinc. An in-house water-equivalent phantom was designed to evaluate artifacts and visibility under various simulated treatment scenarios. Image artifacts were quantitatively assessed in terms of the metal artifact index (MAI) on kilovoltage computed tomography (CT) and cone-beam CT (CBCT) scans. Marker visibility was evaluated on two types of kilovoltage planar x-ray images in terms of the contrast-to-background ratio (CBR). Comparisons with a conventional gold fiducial marker were conducted.Results: The use of zinc rather than a gold marker mitigates imaging artifacts. The MAI near the zinc marker decreased by 76, 79, and 77 % in CT, and by 77 (81), 74 (80), and 79 (85) % in CBCT full-fan (half-fan) scans, when using one-, two-, and three-marker phantom settings, respectively. The high-contrast part of the zinc marker exhibited CBRs above 2.00 for 28/32 exposures under four (lung, tissue, low-density bone, and high-density bone) different simulation scenarios, making its visibility comparable to that of the gold marker (30/32 exposures with CBRs > 2.00).Conclusions: We developed a biocompatible, artifact-robust, and highly visible solid zinc fiducial marker. Although further evaluation is needed in clinical settings, our findings suggest its feasibility and benefits for kilovoltage x-ray image-guided radiation therapy. (C) 2020 American Association of Physicists in MedicineWILEY, Oct. 2020, MEDICAL PHYSICS, 47(10) (10), 4703 - 4710, EnglishScientific journal
- PURPOSE: Metallic medical devices are typically constructed from non-bioabsorbable metals that remains in the body and causes considerable complications. Particularly in the urinary tract, calculus, intractable infection, and misdiagnosis as calculus are often caused by non-bioabsorbable metals. Here, we developed a zinc-magnesium alloy as a new bioabsorbable metal and sought to evaluate the bioabsorbable behavior of zinc and zinc-magnesium alloy in a rat bladder implantation model. METHODS: We prepared zinc-magnesium alloy wires with various proportions of magnesium and investigated the strength, shape retention, formability, and absorbability of these novel materials. Then, we implanted zinc and zinc-magnesium alloy rings formed by the wires into rat bladder. Rats were euthanized at the end of the observation period, and the rings were removed for volume evaluation. Extracted bladder tissues were subjected to histological analysis. RESULTS: The strength of the zinc wire was enhanced by more than fourfold upon the addition of magnesium, without loss of ductility. Linear reduction of ring volume in urine was observed based on the concentration of magnesium within the ring. Nearly all rings were covered with a thin layer of calculus. Histological findings of the transected urinary bladder tissues did not differ among groups. CONCLUSIONS: Zinc-magnesium alloy is a promising candidate for use as a bioabsorbable medical device in the urinary tract.Feb. 2020, World journal of urology, 39(1) (1), 201 - 208, English, International magazine[Refereed]Scientific journal
- An equiatomic high entropy CoCrFeMnNi alloy has been processed by caliber rolling and its microstructure studied by transmission electron microscopy (TEM). The cast dendritic structure and compositional inhomogeneity was reduced to a nanoscale microstructure. Domains as thin as 50 nm elongated in the rolling direction were formed after 19 rolling passes. Boundaries on {111} plane perpendicular to the rolling direction were also observed. FCC twins were observed in the cross-section of the rolled rods, about 50 nm in thickness. A stack of twins and other planar faults result in a periodicity of three times the interplanar spacing of the {111} twinning plane to about 6.2 Å. Lattice imaging shows interference fringes and diffraction effects which can be attributed to domain formation at a very fine scale. These give rise to diffraction streaks and additional spots. Extra diffraction spots and associated diffuse intensity also point to an underlying lattice not fully ordered. The nanoscale domain boundaries are often on {111} planes which are not simple stacking faults but complex in structure.Jan. 2020, Journal of Alloys and Compounds, 812Scientific journal
- Magnesium alloys are promising lightweight structural materials. However, their practical utilization requires improvement of strength and ductility. Adding manganese as a solute improves the room-temperature ductility of magnesium alloys by facilitating grain boundary sliding, but its effects on deformation behavior under dynamic loading remain unclear. Accordingly, we investigated the strain rate dependence of both the flow stress and the deformation mechanism of Mg–Mn alloys via tensile tests over a wide range of strain rates. Grain boundary sliding induced relatively larger elongation under quasi-static conditions. On the contrary, the Mg–Mn alloy exhibited limited necking in the high strain rate regime dominated by intergranular fracture.Jan. 2020, Minerals, Metals and Materials Series, 381(385) (385), 381 - 385[Refereed]International conference proceedings
- BACKGROUND: The use of surgical metal clips is crucial for ligating vessels in various operations. The currently available metal clips have several drawbacks; they are permanent and interfere with imaging techniques such as computed tomography (CT) or magnetic resonance (MR) imaging and carry the potential risk of endo-clip migration. We recently developed a novel magnesium (Mg) alloy for biodegradable clips that reduces artifacts on CT imaging. This study aimed to examine the tolerance, biodegradability, and biocompatibility of the Mg alloy clips compared with those of standard titanium (Ti) clips in hepatectomy. METHODS: Thirty Wistar rats were divided into two groups based on the clip used (groups A and B). The vascular pedicle, including hepatic artery, portal vein, bile duct, and hepatic vein of the left lateral lobe, was ligated with the Ti clip in group A or the Mg alloy clip in group B, and then the left lateral lobe was removed. The rats were sacrificed at 1, 4, 12, 24, and 36 weeks after surgery. Clinical and histological evaluations were performed. Absorption rate was calculated by measuring the clip volume. RESULTS: Although the Mg alloy clips showed biodegradability over time, there were no significant differences in the serum concentration of Mg between the two groups. The remaining volume ratio of Mg alloy clips was 95.5, 94.3, 80.0, 36.2, and 16.7% at 1, 4, 12, 24, and 36 weeks, respectively. No side effects occurred. Most of the microscopic changes were similar in both groups. CONCLUSIONS: The new biodegradable Mg alloy clips are safe and feasible in vessel ligation for hepatectomy in a rat model and reduce artifacts in CT imaging compared with the standard Ti clips.Sep. 2019, BMC surgery, 19(1) (1), 130 - 130, English, International magazine[Refereed]Scientific journal
- Hot deformation behaviors accompanied with the development of new fine grains (NFGs) and microtexture were studied experimentally and numerically in a binary Mg-2.2 at% Y alloy by using compression test, SEM/OIM microscopy and full field crystal plasticity finite element modelling (CPFEM) method. NFGs are evolved along at original grain boundaries at low to medium strains and subsequently in grain interiors through grain fragmentation by frequent formation of kink bands in high strain. Such a series of strain-induced reactions occur in-situ during deformation. The addition of Y atoms to Mg results effectively in the appearance of much higher flow stress and also the slow development of NFGs even in high strain. Lattice orientations of NFGs are distributed almost randomly. The CPFEM results confirms that the dominant deformation mode changed from the combination of basal and prismatic slip system to the combination of pyramidal and basal slip system when deformation temperature increased from 673 K to 723 K, leading to a different microtexture between these two temperatures. Both mechanical and microstructural events are analyzed in detail and the operating mechanisms discussed.May 2019, Journal of Alloys and Compounds, 786, 118 - 125Scientific journal
- May 2019, 軽金属, 69(5) (5), 287 - 292, JapaneseMicrostructural evolution in magnesium after hyper-velocity impact of alumina projectile[Refereed]
- To apply magnesium in biodegradable bone fixation devices, it is favorable to improve its properties through approaches such as by forming composites between magnesium and calcium phosphate. In this study, a powder metallurgical method was used to prepare composites of a magnesium–calcium alloy and α-tricalcium phosphate (α-TCP). Refinement of the α-TCP particle size caused more uniform distribution and microstructure. Consequently, the composite with finer α-TCP particle size had better ductility to the alloy lacking α-TCP. The biodegradation properties were improved by the addition of α-TCP, and the refinement of the α-TCP particles led to a slower degradation rate in electrochemical and immersion tests.Apr. 2019, Materials Letters, Vol. 241, 96 - 99, English[Refereed]Scientific journal
- The present study was designed to investigate the biodegradation behavior of Mg alloy plates in the maxillofacial region. For in vitro analysis, the plates were immersed in saline solution and simulated body fluid. For in vivo, the plates were implanted into the tibia, head, back, abdominal cavity, and femur and assessed at 1, 2, and 4 weeks after implantation. After implantation, the plate volumes and the formed insoluble salt were measured via micro-computed tomography. SEM/EDX analysis of the insoluble salt and histological analysis of the surrounding tissues were performed. The volume loss of plates in the in vitro groups was higher than that in the in vivo groups. The volume loss was fastest in the abdomen, followed by the head, back, tibia, and femur. There were no statistically significant differences in the insoluble salt volume of the all implanted sites. The corrosion of the Mg alloy will be affected to the surrounding tissue responses. The material for the plate should be selected based on the characteristic that Mg alloys are decomposed relatively easily in the maxillofacial region.Feb. 2019, Dental materials journal, 38(1) (1), 11 - 21, English, Domestic magazine[Refereed]Scientific journal
- Japan Institute of Metals, Jan. 2019, Materials Transactions, 60(1) (1), 105 - 110, English[Refereed]Scientific journal
- Jul. 2018, Materials Letters, 223(15) (15), 65 - 68, English[Refereed]Scientific journal
- The Effect of the solidification conditions and subsequent extrusion of a Mg-3.0Zn-0.5Y (at. %) alloy containing quasicrystalline icosahedral (i-) phase was studied. Solidification was carried out by three methods using a chill casting mold, a conventional steel mold and a water-cooled mold. Subsequently, castings were extruded in the temperature range of 235–270°C at an extrusion ratio of 25:1. The solidification molds showed different characteristics. The water-cooled mold was most effective in cooling through the walls, but least effective at the center of the mold. The conventional cast mold was the most effective in cooling at the mold center. All the castings had an interdendritic eutectic structure of the i-phase, and a supersaturation of the matrix in zinc. As a result, all the extrusions had similar grain size close to 1 µm and very fine nano-size precipitation. Yield strengths in tension were in the range of 376 and 404 MPa, and from 300 to 330 MPa in compression. All elongations to fracture were about 13%. It is concluded that supersaturation of the matrix during solidification is the main factor, resulting in the dynamic precipitation of very fine precipitates and fine grain size during extrusion.MDPI AG, May 2018, Metals, 8(5) (5), English[Refereed]Scientific journal
- Magnesium (Mg) alloys are considered promising materials for biodegradable medical devices however, the initial effects and distribution of released Mg2+ ions following implantation are unclear. This is addressed in the present study, using two types of Mg alloys implanted into rats. An in vitro immersion test was first carried out to quantify Mg2+ ions released from the alloys at early stages. Based on these data, we performed an in vivo experiment in which large amounts of alloys were subcutaneously implanted into the backs of rats for 1, 5, 10, and 25 h. Mg2+ accumulation in organs was measured by inductively coupled plasma mass spectrometry. In vivo, blood and urine Mg2+ concentrations were higher in rats receiving the implants than in controls after 1 h however, the levels were within clinically accepted guidelines. The Mg2+ concentration in bone was significantly higher in the 25 h implanted group than in the other groups. Our results suggest that homeostasis is maintained by urinary excretion and bone accumulation of released Mg2+ ions in response to sudden changes in Mg2+ ion concentration in the body fluid in a large number of Mg alloy implants at the early stages.Institute of Physics Publishing, Mar. 2018, Biomedical Materials (Bristol), 13(3) (3), 035006, English[Refereed]Scientific journal
- Due to the excellent balance of strength and ductility exhibited by some Mg-Zn-RE (Y subgroup rare earth element) alloys, which contain icosahedral quasicrystalline precipitates, it is of interest to examine their deformation mechanisms. The internal strain evolution Mg-3at%Zn-0.5 at%Y with 4 vol% i-phase was measured using in-situ neutron diffraction. The extruded samples exhibit an initially weak <10.0> parallel to extrusion direction "rod texture," distinct from the normally strong texture of extruded Mg alloys, but the grain size is unexceptional (16.7 +/- 2.1 mu m). The initially weak texture contributes to a nearly symmetric yielding response between tension and compression. The hardening responses are asymmetric, however, since {10.2} extension twinning is significantly more active during compressive straining, despite the initially weak texture. In-situ neutron diffraction tension and compression experiments parallel to the extrusion direction, together with elasto-plastic self-consistent (EPSC) crystal plasticity modeling, reveal the strength and hardening behavior of individual slip and twinning modes. The previously published twinning-detwinning (TDT) model is implemented within the EPSC framework, and it is proven effective for describing the observed, mild tension-compression asymmetry. This is not possible with previous EPSC-based models of twinning. Finally, the description of hardening within the TDT model is modified, in order to accurately describe the evolution of internal strains within the twins. (C) 2017 Elsevier Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Jan. 2018, INTERNATIONAL JOURNAL OF PLASTICITY, 100, 34 - 51, English[Refereed]Scientific journal
- A magnesium matrix composite made of Mg-1mass%Ca and 10 vol% hydroxyapatite (HAp) particles was synthesized. The alloy powder was processed by pulverization of the small blocks of the alloy ingot using a high-speed blade grinder. Unreacted composite was successfully produced by extruding the two component powders at a temperature of 538 K. In the extruded compos-ites, the grains of the magnesium matrix were equiaxed and the matrix grain size was 3.9 μm. As for the HAp particles, both thin clustering and severe agglomeration with the size of ~30 μm were observed. The Young's modulus, tensile yield strength and tensile strength of the extruded composite were 39 GPa, 101 MPa and 153 MPa, respectively. The damping capacity of the composite was higher than that of extruded magnesium. The composite also showed good forgeability at a temperature of 523 K. However, quite high impurity contents of Fe (0.130 mass%) and Ni (0.010 mass%) were introduced in the magnesium matrix of the composite, probably as a result of contamination that accumulates during the processing (pulverization) of the alloy powder.Japan Institute of Metals (JIM), 2018, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 82(1) (1), 18 - 24, Japanese[Refereed]Scientific journal
- Fine and coarse grained (5-20 mu m) and ultra-fine-grained (down to 1 mu m) samples of a binary Mg-Al alloy were fabricated by extrusion at various temperatures. When tested in compression, a slight stress drop was observed after yielding, followed by a plateau in flow stress. This behavior is typical of textured fine-grained samples. Examination of deformed structures within the ultra-fine-grained samples at various levels of deformation showed that the stress drop after yielding is due to an occurrence of long, thin twins across low angle boundaries and in unrecrystallized regions. In the plateau region, extensive twinning occurs inside individual grains. Then, in a rapid strain hardening region that follows the plateau region, stress concentrations were found to build up on boundaries. Such pile-ups could be responsible for a lowering of fracture strain. (C) 2017 Elsevier B.V. All rights reserved.ELSEVIER SCIENCE SA, Dec. 2017, JOURNAL OF ALLOYS AND COMPOUNDS, 726, 651 - 657, English[Refereed]Scientific journal
- Equal channel angular extrusion (ECAE) was applied to an extruded Mg-1.0mass%Ca alloy to achieve a high strength and high damping capacity. Microstructure observations revealed that the texture and local misorientation distribution depend on the ECAE temperature. ECAE at a low temperature of 260 degrees C resulted in a high average Schmid factor of basal slip and a high kernel average misorientation in the processed alloy. Consequently, the alloy processed by ECAE showed a high yield strength without sacrificing the damping capacity. (C) 2017 Elsevier B.V. All rights reserved.ELSEVIER SCIENCE BV, Aug. 2017, MATERIALS LETTERS, 201, 144 - 147, English[Refereed]Scientific journal
- Equal channel angular extrusion (ECAE) was applied to an extruded Mg-1.0mass%Ca alloy to achieve a high strength and high damping capacity. Microstructure observations revealed that the texture and local misorientation distribution depend on the ECAE temperature. ECAE at a low temperature of 260 degrees C resulted in a high average Schmid factor of basal slip and a high kernel average misorientation in the processed alloy. Consequently, the alloy processed by ECAE showed a high yield strength without sacrificing the damping capacity. (C) 2017 Elsevier B.V. All rights reserved.ELSEVIER SCIENCE BV, Aug. 2017, MATERIALS LETTERS, 201, 144 - 147, English[Refereed]Scientific journal
- (一社)日本消化器外科学会, Jul. 2017, 日本消化器外科学会総会, 72回, O3 - 6, Japanese消化器外科の診断・手技・治療に役立つ先進技術 マグネシウム合金を用いた新規生体吸収性外科クリップの開発 イヌ胆嚢摘出モデルでの安全性と忍容性の検討
- Deformation structures have been examined by transmission electron microscopy after 4% plastic deformation in tension and compression in a Mg-2.2 at%Y alloy extruded at 698 K to obtain a recrystallized grain size of about 20 The extruded alloy showed similar yield stresses of about 240 MPa in both tension and compression at room temperature. Dislocations formed by tensile stress showed a tendency of < a > type dislocations to cross slip to prismatic planes, resulting in long continuous dislocation loops. Dislocation loops with < c > components were also observed. Occasionally, [1021] type twinning was also observed in grains with large orientation away from basal texture. These grains contained predominantly basal slip. Compression deformed samples showed a limited number of [1012] type twins. The matrix contained loops of non-basal < a > type dislocations, together with basal dislocations with < c > component. Inside the twins occurred stacking faults and loops of < c > type dislocations with segments perpendicular to the basal plane. Activation of several deformation modes and complex dislocation structures explains the strain hardening behavior and low anisotropy of the alloy.ELSEVIER SCIENCE SA, Jun. 2017, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 698, 238 - 248, English[Refereed]Scientific journal
- Background. Operative clips used to ligate vessels in abdominal operation usually are made of titanium. They remain in the body permanently and form metallic artifacts in computed tomography images, which impair accurate diagnosis. Although biodegradable magnesium instruments have been developed in other fields, the physical properties necessary for operative clips differ from those of other instruments. We developed a biodegradable magnesium-zinc-calcium alloy clip with good biologic compatibility and enough clamping capability as an operative clip. In this study, we verified the safety and tolerability of this clip for use in canine cholecystectomy. Methods. Nine female beagles were used. We performed cholecystectomy and ligated the cystic duct by magnesium alloy or titanium clips. The chronologic change of clips and artifact formation were compared at 1, 4, 12, 18, and 24 weeks postoperative by computed tomography. The animals were killed at the end of the observation period, and the clips were removed to evaluate their biodegradability. We also evaluated their effect on the living body by blood biochemistry data. Results. The magnesium alloy clip formed much fewer artifacts than the titanium clip, and it was almost absorbed at 6 months postoperative. There were no postoperative complications and no elevation of constituent elements such as magnesium, calcium, and zinc during the observation period in both groups. Conclusion. The novel magnesium alloy clip demonstrated sufficient sealing capability for the cystic duct and proper biodegradability in canine models. The magnesium alloy clip revealed much fewer metallic artifacts in GT than the conventional titanium clip.MOSBY-ELSEVIER, Jun. 2017, SURGERY, 161(6) (6), 1553 - 1560, English[Refereed]Scientific journal
- Recently, biodegradable bone fixation devices have been demanded when considering the patient's quality of life (QOL). During the fracture healing, the devices must support the repeated load due to daily performance. At the same time, surface of the magnesium devices was affected by body fluid. Thus in this research, in vitro fatigue properties of biodegradable Mg-0.3at.% Ca alloy was evaluated by using simulated body fluid. Though there was fatigue limit when the test was conducted under the ambient condition, it cannot be confirmed during the test in the simulated body fluid. Inspection of fracture surface revealed that crack propagated along the grain boundary after both the fatigue tests.SPRINGER INTERNATIONAL PUBLISHING AG, 2017, MAGNESIUM TECHNOLOGY 2017, 533 - 535, English[Refereed]International conference proceedings
- (一社)日本消化器外科学会, Jul. 2016, 日本消化器外科学会総会, 71回, P1 - 10, Japanese新しい生体吸収性マグネシウム合金クリップの開発とラット肝切除モデルにおける応用
- (一社)日本消化器外科学会, Jul. 2016, 日本消化器外科学会総会, 71回, P1 - 10, Japanese新規マグネシウム合金を用いた生体吸収性外科クリップの開発
- Biodegradable magnesium (Mg) alloys are the most promising candidates for osteosynthesis devices. However, their in vivo corrosion behaviour has not been fully elucidated. The aim of this study was to clarify the influence of the physiological environment surrounding Mg alloys on their corrosion behaviour. A Mg-1.0Al alloy with a fine-grained structure was formed into plates using titanium (Ti) as a control. These plates were implanted into the subperiosteum in the head, subcutaneous tissue of the back, and in the muscle of the femur of rats for 1, 2 and 4 weeks. The volumes of the remaining Mg alloy and of the insoluble salt deposition and gas cavities around the Mg alloy were determined by microtomography, and the volume losses were calculated. Then, the tissue response around the plates in each implantation site was examined histopathologically, and its relation to the respective volume loss was analyzed. These analyses determined that the Mg alloy was corroded fastest in the head, at an intermediate level in the back, and slowest in the femur. The insoluble salt deposition at the Mg alloy surface had no influence on the volume loss. Gas cavities formed around the Mg alloy at all implantation sites and decreased after 4 weeks. Histopathological examination revealed that the Mg alloy exhibited good biocompatibility, as was seen with Ti. In addition, vascularized fibrous capsules formed around the plates and became mature with time. Notably, the volume loss in the different anatomical locations correlated with capsule thickness. Together, our results suggest that, to facilitate the successful clinical application of Mg alloys, it will be necessary to further comprehend their interactions with specific in vivo environments.IOP PUBLISHING LTD, Apr. 2016, BIOMEDICAL MATERIALS, 11(2) (2), English[Refereed]Scientific journal
- We measured the impact toughness of three alloys (Mg, Mg-0.3 at%Ca-0.6 at%Zn, and Mg-0.3 at%Ca-0.6 at %Al) by the impact three-point bending test The plastic deformability and impact toughness were higher in the ternary alloys than in pure Mg. The generalized stacking fault energy and grain boundary cohesive energy were estimated by first-principles calculations for Mg, binary Mg-Ca, ternary Mg-Ca-Zn, and ternary Mg-Ca-Al alloys. The calculation results agreed with the trend in the experimental results. We suggest that addition of Ca along with Zn or Al reduced plastic anisotropy and strengthened the grain boundaries, leading to higher in impact toughness of Mg alloys. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Feb. 2016, ACTA MATERIALIA, 104, 283 - 294, English[Refereed]Scientific journal
- Lattice Ordering and Microstructure of Ultra-high Strength Mg-Ca-Zn AlloysMagnesium alloying with calcium is very promising for mechanical strength. One of the promising alloys systems is ternary Mg-Zn-Ca. Recent results by the first principles calculation suggest that, the combination of calcium and zinc possibly enhances the cohesive energy of grain boundary. In this work, Mg-Zn-Ca alloys with low alloying amounts of 0.1-0.3at% Ca and 0.2-0.6at% Zn were studied. Very fine grain size of smaller than 0.5 micron was achieved after extrusion, with finer substructure of the order of 100 nm. Microstructure showed sharp grain boundaries A possible ordering of atoms in the matrix was observed. These ultra-fine and complex grain structures have been studied with the aid of advanced transmission electron microscopy techniques.JOHN WILEY & SONS INC, 2016, MAGNESIUM TECHNOLOGY 2016, 83 - 88, EnglishInternational conference proceedings
- The Japan Society of Mechanical Engineers, 2016, The Proceedings of the Materials and Mechanics Conference, 2016(0) (0), PS - 41, Japanese
Today, there is a demand for bio-stapler which gradually degraded in the body and disappeared after healing from the medical field. Magnesium is noted as the material with biodegradability and biocompatibility. However, compared with the current material, magnesium have too poor mechanical properties to apply to the stapler. Therefore, it is necessary to improve its mechanical properties. It is known that addition of Ca improves the strength and corrosion resistance. To investigate the effect of alloying element on formability of Mg-Ca alloys, the generalized stacking fault energy was estimated by first-principles calculations for binary Mg-Ca, ternary Mg-Ca-Na, ternary Mg-Ca-K and ternary Mg-Ca-Sr alloys. We suggest that addition of Na, K or Sr reduced plastic anisotropy of binary Mg-Ca alloys.
- Mechanical properties of magnesium alloys under dynamic loading are still unclear. To evaluate the impact fracture behavior of magnesium alloys, we constructed a novel impact three-point bending test apparatus using three elastic bars with Charpy standard-size specimen, and investigated the impact fracture properties of as-cast Mg-3%Al-1%Zn (hereafter denoted as AZ31) alloy. Finite element (FE) analysis were carried out to estimate the effect of inertial force of the specimen during the impact three-point bending. Based on the FE analysis, we successfully developed a small-scale apparatus for examining a quarter-size specimen, which was capable of carrying out the impact three-point bending test with minimized influence of the inertial force. Impact fracture behavior of Mg-6%Al-1%Zn-2%Ca (hereafter denoted as AZX612) alloy was estimated and compared by using small-scale apparatus. The experimental results pointed out that the AZX612 had had similar energy absorption capability to AZ31 against the dynamic loading, however, the crack propagation speed of the Ca bearing alloy was almost twice as fast as that of the AZ31 alloy.Japan Institute of Light Metals, 2016, Keikinzoku/Journal of Japan Institute of Light Metals, 66(5) (5), 258 - 265, Japanese[Refereed]Scientific journal
- The impact of alloying elements on the room temperature tensile behaviour was investigated for a wide range of strain rates using eight types of extruded Mg-0.3at.% X (X=Ag, Al, Li, Mn, Pb, Sn, Y and Zn) binary alloys with an average grain size of 2-3m. The solid solution alloying element affected not only tensile plasticity but also rate-controlling mechanism for these fine-grained magnesium alloys. Most of the alloys exhibited an elongation-to-failure of 20-50% , while the alloys with a high m-value exhibited large tensile plasticity, such as an elongation-to-failure of 140% in a strain rate of 1x10(-5)s(-1) for the Mg-Mn alloy. This elongation-to-failure is more than two times larger than that for pure magnesium. This is due to the major contribution of grain boundary sliding (GBS) on the deformation. Microstructural observations reveal that grain boundary segregation, which is likely to affect gain boundary energy, plays a role in the prevention or enhancement of GBS. The present results are clearly expected to open doors to the development of magnesium alloys with good secondary formability at room temperature through the control of alloying elements.TAYLOR & FRANCIS LTD, 2016, PHILOSOPHICAL MAGAZINE, 96(25) (25), 2671 - 2685, English[Refereed]Scientific journal
- Superplastic deformation behavior was investigated for a dual-phase Mg-Ca alloy. The elongation-to-failure reached more than 120% with the strain rate sensitivity, m, over 0.4. The activation energy required for the deformation was estimated to be 98 kJ/mol which is close to the activation energy for grain boundary diffusion in magnesium. Therefore, the superplastic deformation mechanism was suggested to be the grain boundary sliding, which is controlled by boundary diffusion.Trans Tech Publications Ltd, 2016, Materials Science Forum, 838-839, 256 - 260, English[Refereed]International conference proceedings
- The magnesium composites containing hydroxyapatite (HA) particles were synthesized. Unreacted Mg/HA composites were successfully fabricated by extruding the two component powders. The Young's modulus and strength of the extruded composites were lower than that of extruded magnesium, whereas the damping capacity of the composite was superior to that of extruded magnesium over the entire strain range examined. Microstructural observation of the composite containing 10 vol%HA revealed that HA agglomerates with the size of 10-15 μm were formed during the fabrication. The mechanical properties of the composites were closely associated with the HA agglomeration.Japan Institute of Light Metals, 2016, Keikinzoku/Journal of Japan Institute of Light Metals, 66(6) (6), 318 - 323, Japanese[Refereed]Scientific journal
- To develop a biodegradable clip, the equivalent plastic strain distribution during occlusion was evaluated by the finite element analysis (FEA) using the material data of pure Mg. Since the PEA suggested that a maximum plastic strain of 0.40 is required to allow the Mg clips, the alloying of magnesium with essential elements and the control of microstructure by hot extrusion and annealing were conducted. Mechanical characterization revealed that the Mg-Zn-Ca alloy obtained by double extrusion followed by annealing at 673 K for 2 h possessed a fracture strain over 0.40. The biocompatibility of the alloy was confirmed here by investigating its degradation behavior and the response of extraperitoneal tissue around the Mg-Zn-Ca alloy. Small gas cavity due to degradation was observed following implantation of the developed Mg-Zn-Ca clip by in vivo micro-CT. Histological analysis, minimal observed inflammation, and an only small decrease in the volume of the implanted Mg-Zn-Ca clip confirmed its excellent biocompatibility. FEA using the material data for ductile Mg-Zn-Ca also showed that the clip could occlude the simulated vessel without fracture. In addition, the Mg-Zn-Ca alloy clip successfully occluded the renal vein. Microstructural observations using electron backscattering diffraction confirmed that dynamic recovery occurred during the later stage of plastic deformation of the ductile Mg-Zn-Ca alloy. These results suggest that the developed Mg-Zn-Ca alloy is a suitable material for biodegradable clips. Statement of significance Since conventional magnesium alloys have not exhibited significant ductility for applying the occlusion of vessels, the alloying of magnesium with essential elements and the control of microstructure by hot extrusion and annealing were conducted. Mechanical characterization revealed that the Mg-Zn-Ca alloy obtained by double extrusion followed by annealing at 673 K for 2 h possessed a fracture strain over 0.40. The biocompatibility of the alloy was confirmed by investigating its degradation behavior and the response of extraperitoneal tissue around the Mg-Zn-Ca alloy. Finite element analysis using the material data for the ductile Mg-Zn-Ca alloy also showed that the clip could occlude the simulated vessel without fracture. In addition, the Mg-Zn-Ca alloy clip successfully occluded the renal vein. Microstructural observations using electron backscattering diffraction confirmed that dynamic recovery occurred during the later stage of plastic deformation of the ductile Mg-Zn-Ca alloy. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.ELSEVIER SCI LTD, Jan. 2016, ACTA BIOMATERIALIA, 29, 468 - 476, English[Refereed]Scientific journal
- Today, stent is employed to expand the narrowed tubular organ such as blood vessel, esophagus and bile duct. The major of materials used for the stent is stainless steel or Ni-Ti alloy which remains in the body permanently and prevents the second application. Accordingly, this research targets on developing the biodegradable magnesium stent. Magnesium is, however, inferior to the conventional materials in mechanical properties. Therefore, it is required to improve the mechanical properties of magnesium and design the stent considering poverty of strength and ductility. To improve the mechanical properties, strengthening by solid solution due to adding Zn and Ca and by grain refining due to doubly hot extrusion were conducted. As a result, the extruded Mg-Ca-Zn alloy showed the superior mechanical properties compared with the conventional magnesium alloys. Furthermore, finite element analysis (FEA) based on the material data was conducted to investigate mechanical performance of a stent model. As a result of the FEA, it was indicated that Mg alloy stent has sufficient ductility for expansion and strength for restenosis. Examination for expanding a fabricated stent revealed that the FEA was reasonable and the present alloy was a good candidate for the stent application.Japan Institute of Light Metals, 2016, Keikinzoku/Journal of Japan Institute of Light Metals, 66(6) (6), 312 - 317, Japanese[Refereed]Scientific journal
- Mechanical properties of magnesium alloys under dynamic loading are still unclear. To evaluate the impact fracture behavior of magnesium alloys, we constructed a novel impact three-point bending test apparatus using three elastic bars with Charpy standard-size specimen, and investigated the impact fracture properties of as-cast Mg-3Al-1Zn (hereafter denoted as AZ31) alloy. Finite element (FE) analysis were carried out to estimate the effect of inertial force of the specimen during the impact three-point bending. Based on the FE analysis, we successfully developed a small-scale apparatus for examining a quarter-size specimen, which was capable of carrying out the impact three-point bending test with minimized influence of the inertial force. Impact fracture behavior of Mg-6Al-1Zn-2Ca (hereafter denoted as AZX612) alloy was estimated and compared by using small-scale apparatus. The experimental results pointed out that the AZX612 had similar energy absorption capability to AZ31 against the dynamic loading, however, the crack propagation speed of the Ca bearing alloy was almost twice as fast as that of the AZ31 alloy.JAPAN INST METALS, 2016, MATERIALS TRANSACTIONS, 57(11) (11), 1872 - 1879, English[Refereed]Scientific journal
- マグネシウムは実用金属材料の中で最軽量であり、次世代の移動用構造部材として注目を浴びている。本解説では、移動用部材として安全・信頼性の観点から重要な機械的特性であるマグネシウムの強度・靭性について注目し、これらの特性値に影響を及ぼす材料組織学的因子（結晶粒径や集合組織、析出粒子形態など）についてや、数値解析法を利用した高性能マグネシウム合金創製の可能性について紹介する。The Japan Society for Technology of Plasticity, Jun. 2015, Journal of the Japan Society for Technology of Plasticity, 50(579) (579), 291 - 295, Japanese[Refereed]Scientific journal
- Magnesium alloys are very promising structural material, especially because of their low density, but their poor deformability at room temperature is making their commercial application impractical. Some alloying elements have been shown to improve the ductility dramatically, and a search for the yet better alloying elements is now a pressing task. In this study, we investigated the effects of several alloying elements on the mechanical and deformation behaviour of magnesium alloys using both first-principles calculations as well as experiments. The first-principles calculations indicate that the influential key factor for the activation of non-basal slips is the electronegativity and atomic radius. The experimental result proves that the alloys with a similar electronegativity as magnesium and a little larger atomic radius than that of magnesium, such as Ca, Sr and some rare earth elements, show superior ductility due to activation of non-basal dislocation slips. These results propose a promising design principle for the alloys with the improved deformability at room temperature ranges.TAYLOR & FRANCIS LTD, Mar. 2015, PHILOSOPHICAL MAGAZINE, 95(8) (8), 869 - 885, English[Refereed]Scientific journal
- The damping capacity, which was characterized by bending vibration decay, was examined in extruded pure magnesium to understand the role played by pre-existing twins introduced by pre-strain. For materials without pre-strain, the damping capacity consisted of the strain-independent and the strain-dependent parts, which emerged above a critical strain. The critical strain observed for the damping capacity corresponded to the proportional limit observed for the tensile or compressive curves. For materials pre-strained to 1% and 8% in the extrusion direction, the damping capacity began to increase at low strains below the proportional limit and was higher than that without pre-strain. The higher damping capacity is thought to occur because of the alternate shrinkage and growth of pre-existing twins. (C) 2014 Elsevier B.V. All rights reserved.ELSEVIER SCIENCE SA, Mar. 2015, JOURNAL OF ALLOYS AND COMPOUNDS, 626, 60 - 64, English[Refereed]Scientific journal
- TMS, Mar. 2015, Proceedings of TMS 2015 Annual meeting, EnglishEffect of Solute Segregation on Fracture Behavior of Mg Alloy[Refereed]International conference proceedings
- TMS, Mar. 2015, Proceedings of TMS 2015 Annual meeting, EnglishDegradation Behavior of Mg-Ca Nail after Penetration into Artificial Bone[Refereed]International conference proceedings
- The effect of minor yttrium atom addition on deformation behavior was investigated using Mg-X at %Y (X = 0.01, 0.02, 0.03, 0.04 and 0.05) dilute alloys and pure magnesium with an average grain size of about 50 mu m. The stress and strain curves in all the alloys showed a sigmoidal shape in the compression tests, which suggested the formation of {10 (1) over bar2}-type twinning due to the lack of slip system. On the other hand, yttrium atom addition of more than 0.03 at% was effective to affect the deformation behavior: a large compressive strain of 0.5 was possible to obtain, and the sub-grained and fine-grained structures were formed even at room temperature in three kinds of alloys. The dominant deformation mechanism in these alloys was the twinning at the beginning of the state and the dislocation slip with further imposed strain.JAPAN INST METALS, Feb. 2015, JOURNAL OF THE JAPAN INSTITUTE OF METALS, 79(2) (2), 35 - 40, Japanese[Refereed]Scientific journal
- The effects of grain size and strain rate on tension behavior at ambient temperature were investigated for several extruded magnesium with an average grain size in the range between 1 and 20 mu m. In quasi-static strain rate regimes (1 x 10(-2) to 10(-4) s(-1)), the activation volume was similar to 20b (3) (b is the Burgers vector), which suggested that the major contribution of deformation was cross-slip and/or multiple slips. In contrast, in low strain rate regimes (< 1 x 10(-4) s(-1)), the ductility increased with grain refinement, and the maximum elongation-to-failure was 230 pct for a grain size of 1.2 mu m and a strain rate of 1 x 10(-5) s(-1); such ductility was never observed in magnesium at room temperature. In addition, the activation volume was also reduced to similar to 5b (3). Observations of the deformed surface revealed plentiful traces of grain boundary sliding. This mechanism played an important role in deformation. As a result, while the yield strength was aligned on the Hall-Petch relation in quasi-static strain rate regimes, an inverse Hall-Petch effect was observed in low strain rate regimes.SPRINGER, Feb. 2015, METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 46A(2) (2), 894 - 902, English[Refereed]Scientific journal
- Weight reduction of automobiles and aircrafts improves fuel economy and reduces greenhouse gas emissions. Use of Mg alloys may allow weight reduction because of their low densities, but adoption is hindered because they exhibit limited ductility at ambient temperatures [1], In a previous study of fracture toughness in a Mg alloy, crack readily propagated near twin boundaries and resulted in poor durability [2]. It has been shown that pile-up of dislocations at the interface between the matrix and deformation twins caused stress concentration to form cracks [2]. Another study suggested that the ductility of Mg alloys is further limited under dynamic loading due to lowered activity of dislocations [3]. It has also been reported that a Mg-AI-Mn alloy had pronounced mechanical anisotropy at high strain rates of around 1.0×103 s-1 [4], Therefore, the mechanical properties of Mg alloys should be evaluated accurately for applications involving possible dynamic loading.Minerals, Metals and Materials Society, 2015, Magnesium Technology, 2015-, 189, EnglishInternational conference proceedings
- Earlier, we reported very high yield strengths of 400 MPa accompanied by total elongations of over 12% in Mg-6xZn-xY alloys, where x=1.0, 0.5, 0.35 and 0.2 in at%, dispersed with quasicrystalline phase and processed by extrusion. Here we report on the effect of low amount of alloying elements zinc and yttrium on the texture and anisotropy of the Mg-Zn-Y alloys. With decreasing amount of the alloying elements, the yield strength of the extruded alloys remains close to 400 MPa with total elongation to failure of about 12%, while the anisotropy keeps increasing. Thus very high tensile strengths with moderate ductility are achieved even in very dilute alloys. With lesser amount of alloying elements the degree of dynamic recrystallization is reduced and the intensity of the basal texture is increased, resulting in higher yield anisotropy.Minerals, Metals and Materials Society, 2015, Magnesium Technology, 2015-, 215 - 220, EnglishInternational conference proceedings
- The damping capacity and mechanical response under uniaxial tension and compression were examined for specimens of extruded magnesium inclined by 0 degrees, 15 degrees and 30 degrees relative to the extrusion direction. It was found that both the microyielding under uniaxial deformation and the occurrence of strain-dependent damping capacity pertain to the same physical event: the breaking away of basal (a) dislocations from weak pinning points and the subsequent sweeping motion of dislocations between strong pinning points. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Sep. 2014, SCRIPTA MATERIALIA, 87, 1 - 4, English[Refereed]Scientific journal
- Recently, magnesium alloys with a dispersion of quasicrystalline icosahedral i-phase have been shown to exhibit very high strengths combined with ductility. However, effect of the i-phase and its amount has not been investigated comprehensively. To make a systematic investigation, two alloys of composition Mg-6x Zn-x Y, where x=0.5 and 1 at%, were chill cast and extruded at three different temperatures to produce various grain sizes with a dispersion of i-phase. The extruded alloys were tested in tension and compression. Very fine grains of micron and submicron size have been obtained, resulting in very high yield strengths of up to about 400 MPa accompanied by total elongations of over 12%. Microstructural features such as precipitation and texture have been studied, and mechanical properties such as strength and ductility in tension and compression have been determined. As the grain size is refined, depending on the alloy composition and extrusion temperature, the texture is also modified, such that a higher strength resulting from finer grain size is accompanied by a reasonable elongation, of over 12%. In aged condition the Hall-Petch plots for tensile and compressive yield strengths are nearly parallel, with slopes in the range of 237-307 MPa mu m(-1/2). The Hall-Petch slopes of critically resolved shear stress of slip and twinning are nearly the same at about 63 MPa mu m(-1/2). (C) 2014 Elsevier B.V. All rights reserved.ELSEVIER SCIENCE SA, Aug. 2014, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 611, 242 - 251, English[Refereed]Scientific journal
- Coarse grained Mg-0.3 at.% Al (0.33 in wt.%) alloy was processed by direct extrusion with a reduction ratio of 25:1 at a temperature of similar to 433 K. The extrusion remainder was removed from the die and analysed in three distinct zones: the cast billet, the conical zone of extrusion die, and the as-extruded rod. The zones were characterized by electron backscatter diffraction (EBSD) and light microscopy techniques to identify the processes responsible for grain refinement. Complex networks of {10-12} twins in practically all grains produced a noticeable microstructural fragmentation even before the material reached the conical zone of the die. Deformation twinning extended up to the entrance zone of the conical die where it was followed by a continuous dynamic recrystallization (CDRX) that gradually changed low angle boundaries to high angle boundaries. It is apparent that geometrically necessary dislocations play a crucial role in the formation of new grain boundaries. CDRX results in a bimodal structure with grain diameters similar to 3 and similar to 30 mu m. As a material flows through the conical zone, the ratio of large to small grains is progressively decreased by CDRX in favour of fine grains. The as-extruded microstructure (a rod 8 mm in diameter), with an average grain diameter of similar to 2.1 mu m, shows a strong texture where the vast majority of grains (99.99%) have the c-axis oriented at least 30 degrees from the extrusion direction. (C) 2014 Elsevier Inc. All rights reserved.ELSEVIER SCIENCE INC, Jul. 2014, MATERIALS CHARACTERIZATION, 93, 102 - 109, English[Refereed]Scientific journal
- Very high strengths, with tensile yield strength from 377 to 405 MPa, combined with elongation to failure of over 12 pct, have been achieved in Mg-Zn-Y dilute alloys by direct extrusion. Alloys Mg-6xZn-xY, where x = 0.2, 0.35, and 0.5 (at. pct) were chill cast in a steel mold and direct extruded at a temperature in the range 508 K to 528 K (235 A degrees C to 255 A degrees C), which produced an average grain size of about 1 mu m. Quasicrystalline i-phase particles were dispersed in the matrix with size ranging from 50 nm to 1 mu m. In addition, high density of nano-precipitates of average size 15 nm was dispersed in matrix. Thus we have developed magnesium alloys of very high strength combined with ductility by a simple process using extrusion with very little addition of yttrium. (C) The Minerals, Metals & Materials Society and ASM International 2013SPRINGER, Jul. 2014, METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 45A(8) (8), 3232 - 3240, English[Refereed]Scientific journal
- Tensile response at low strains and damping capacity were characterized in pure magnesium and Mg-1 mass%Ca alloy with the aim of revealing the effect of extrusion process and Ca addition. The damping capacity of extruded magnesium and solution treated Mg-1 mass%Ca alloy was lower than that of cast magnesium in the strain range examined. The proportional limit in the stress-strain relation of extruded magnesium and solution treated Mg-1 mass%Ca alloy was higher than that of cast magnesium. For all materials examined, the proportional limit corresponded to the critical strain, above which damping capacity begins to increase with strain. This suggests that dislocations breaking away from weak pinning points such as impurity/solute atoms causes the deviation from linearity in the stress-strain relation.JAPAN INST METALS, Jun. 2014, JOURNAL OF THE JAPAN INSTITUTE OF METALS, 78(6) (6), 230 - 234, Japanese[Refereed]Scientific journal
- The effect of solid-solution alloying on grain boundary sliding (GBS) was investigated using pure magnesium and six kinds of Mg-X (X = Ag, Al, Li, Pb, Y and Zn) dilute binary solid solutions with an average grain size of 10 mu m. A sharp increase in damping capacity caused by GBS was observed above a certain temperature. The temperature at which a sharp increase in damping capacity occurred depended on the alloying element. The addition of Y and Ag markedly increased the onset temperature (more than 100 K) for a sharp increase in damping capacity, whereas the addition of Zn, Al and Li slightly increased the onset temperature (less than 50 K) as compared with that for pure magnesium. Tensile tests at a temperature of 423 K revealed that the higher the onset temperature, the lower the strain rate sensitivity of the flow stress. It is suggested that the former elements (Y and Ag) are more effective in suppressing GBS in magnesium alloys than the latter ones (Zn, Al and Li). The suppression of GBS was associated with low grain boundary energy, and the extent to which the energy is reduced depended on the alloying element. It was suggested that the change in the lattice parameter (the so-called c/a ratio) affects the grain boundary energy, and thus, the occurrence of GBS.TAYLOR & FRANCIS LTD, Apr. 2014, PHILOSOPHICAL MAGAZINE, 94(12) (12), 1345 - 1360, English[Refereed]Scientific journal
- Weight reduction is effective for improving fuel efficiency of automobiles. Although magnesium is widely recognized as the lightest structural metal, applications for the automobile are limited because of the relatively low ductility, toughness, impact resistance and fatigue resistance. The aim of this research was to evaluate the impact energy absorption capability of a magnesium alloy pipe by a numerical simulation. First of all, finite element (FE) analysis of impact compression of magnesium alloy pipes was performed to design the shape of anvils for a dynamic compression experiment. The compression tests were conducted at a high strain rate on two Mg alloys, AZ31 and Mg-0.6Y, to examine the deformation response. The load-displacement data obtained were compared with the results of FE analysis to validate the simulation. The FE analysis revealed that the AZ31 pipe fractured at an early stage of deformation, while the Mg-0.6Y pipe fractured at about 90% compressed. As a result, Mg-0.6Y pipe exhibited lower yield strength, but a higher absorption energy capability than AZ31 pipe due to a weakened basal texture.JAPAN INST METALS, Apr. 2014, JOURNAL OF THE JAPAN INSTITUTE OF METALS, 78(4) (4), 142 - 148, Japanese[Refereed]Scientific journal
- Precipitation strengthening in Mg-Zn-Y alloys occurs via the formation of a fine dispersion of β'< inf> 1< /inf> (Mg< inf> 4< /inf> Zn< inf> 7< /inf> ) rods aligned parallel to the hexagonal axis. In this study, texture and controlled deformation have been used to control the directionality and morphology of the precipitates and their effect on the ageing response. The resulting precipitates were studied via conventional and high-resolution transmission electron microscopy. Texture was developed through extrusion at 300°C, followed by controlled room-temperature deformation to generate microstructures where yield occurred either with, or without, twinning. The ageing response was monitored using hardness testing. Both compressive and tensile deformation accelerated the ageing response. Compression parallel to the extrusion axis generated a high volume fraction of twins. Precipitates on the twin boundaries assumed a low aspect-ratio morphology different from the usual high-aspect ratio rods.Wiley Blackwell, Mar. 2014, Essential Readings in Magnesium Technology, 319 - 324, English[Refereed]In book
- Transmission electron microscopic study of crack propagation in a fine-grained Mg-Zn alloy shows a complex interplay of slip and twinning, leading to formation of twin-related nano-sized domains of 50nm size related by {101} and {102} twin orientations. Subgrain formation with low angle boundaries is followed by formation of {101} twins and twin multiplication by nucleation and growth. Basal and prismatic slip play an important role in the growth and formation of new domains of twins and boundaries. These basal and prismatic slip occur in the matrix as well as inside the {101} twins. Steps on these twin boundaries indicate interaction with slip, leading to their growth. Evidence of nucleation of twins on grain boundaries is found. Most interesting is the indication of nucleation of {101}-type twins. String or stacks of nano-sized domains related to each other by {101} twinning were found in the matrix, where the matrix contained basal, prismatic as well as pyramidal dislocations. It appears that a localization of slip or formation of low angle boundaries to accommodate stress from surrounding domains leads to nucleation of these twins.TAYLOR & FRANCIS LTD, Mar. 2014, PHILOSOPHICAL MAGAZINE, 94(9) (9), 898 - 913, English[Refereed]Scientific journal
- This study examines Mg-Y binary alloys at a high strain rate of approximately 1 x 10(3) s(-1) in compression by using a split Hopkinson pressure bar to elucidate the effect of yttrium in magnesium on mechanical anisotropy and other properties. As a result of high strain rate compression, Mg-0.6 at.%Y alloy showed less mechanical anisotropy, a lower strain hardening rate, and a larger compressive strain to failure of approximately 0.4, as compared with pure magnesium. Microstructure analysis by scanning electron microscopy/electron backscatter diffraction revealed that the addition of yttrium could release the stress concentration at the interface between the matrix and the {} c-axis tension twins by the formation of subgrains and lattice rotation around the c-axis during dynamic compression.SPRINGER, Feb. 2014, JOM, 66(2) (2), 305 - 311, English[Refereed]Scientific journal
- The wear and friction properties of the Mg-Zn-Y alloys with a dispersion of the quasi-crystalline phase were investigated using the pin-on-disk configuration. The wear loss rates and the friction coefficient were obtained to be 1.95 x 10(-5)mm(3)/mm and 0.26 in the casted alloy, 1.75 x 10(-5)mm(3)/mm and 0.24 in the heat-treated alloy, 2.40 x 10(-5)mm(3)/mm and 0.24 in the extruded alloy, respectively, under the dry wear condition. An effective method to enhance the wear properties in the magnesium alloys was determined to be a homogenous distribution of the quasi-crystalline phase in the coarse-grained matrix. Meanwhile, the grain refinement was not suitable due to grain boundary sliding, i.e., materials softening.JAPAN INST METALS, Jan. 2014, MATERIALS TRANSACTIONS, 55(1) (1), 216 - 219, English[Refereed]Scientific journal
- The mechanical properties of magnesium alloys under dynamic loading have not been explored in sufficient depth. This research aims to estimate the impact fracture toughness of AZ31 magnesium alloy by finite element (FE) analysis. An FE model of impact three-point bending with three elastic bars is developed. FE analysis is presented for AZ31 magnesium alloy and compared with the results for 7075-T6 aluminum alloy as a reference. The FE analysis showed that the plastic deformation region is wider and the crack propagating rate is lower in the AZ31 specimen than in the 7075-T6 specimen. Moreover, the energy absorption capability and impact fracture toughness of AZ31 alloy were found to be higher than those of 7075-T6 alloy. © (2014) Trans Tech Publications, Switzerland.Trans Tech Publications Ltd, 2014, Applied Mechanics and Materials, 566, 316 - 321, English[Refereed]International conference proceedings
- The effect of minor addition of yttrium element on deformation behavior was investigated using Mg-Xat%Y (X = 0.01, 0.02, 0.03, 0.04 and 0.05) dilute alloys and pure magnesium with an average grain size of about 50 mu m. The stress and strain curves in all the alloys showed a sigmoidal shape in the compression tests, which suggested the formation of {10 (1) over bar2}-type twinning due to the lack of slip system. On the other hand, yttrium atom addition of more than 0.03 at% was effective to affect the deformation behavior: a large compressive strain of 0.5 was possible to obtain, and the sub-grained and fine-grained structures were formed even at room temperature in three kinds of alloys. The dominant deformation mechanism in these alloys was the twinning at the beginning of the state and the dislocation slip with further imposed strain.JAPAN INST METALS, Jan. 2014, MATERIALS TRANSACTIONS, 55(1) (1), 182 - 187, English[Refereed]Scientific journal
- In Mg alloys, the most favorable deformation mechanism is the basal slip, and extension twinning also contributes to plastic deformation. Other mechanisms such as prismatic slips, pyramidal slips and twinning except for extension twinning scarcely occur. However, these slip systems also contribute to the plastic deformation of poly crystal Mg alloys, so the determination of CRSS of such non-basal slip systems are inevitable as a basis for the prediction of the deformation behavior of poly-crystal Mg alloys. Because of the difficulty of the evaluation of CRSS for non-basal slip by conventional compression test, newly designed "Pure shear test" is applied to evaluate the CRSS of the prismatic slip Mg alloy single crystals containing Y. Also a modification of Bridgman method using LiF + LiCl is attempted to obtain a pure-Mg single crystal.JAPAN INST METALS & MATERIALS, Oct. 2013, JOURNAL OF THE JAPAN INSTITUTE OF METALS AND MATERIALS, 77(10) (10), 466 - 472, Japanese[Refereed]Scientific journal
- The deformation behavior at the grain boundary was investigated by the molecular dynamics simulation using two models based on different kinds of [1 - 100] symmetric tilt boundaries (Sigma 25 with a tilt angle of theta = 23 degrees and Sigma 10 with theta = 78 degrees) in magnesium. Grain boundary migrations occurred in both models due to the reduction in the internal energy during deformation. The deformation mechanism at the grain boundary was shown to be the twinning induced grain boundary migration. The grain boundary migration was affected by the grain boundary structures, and it was enhanced in the grain boundaries with high energies. On the other hand, the grain boundary migration was suppressed by the addition of solute atoms, i.e., aluminum and silver. The silver atoms were found to be more effective for suppression than the aluminum atoms. These behaviors occurred in both the molecular dynamics simulation and the experiments. (c) 2013 Elsevier B.V. All rights reserved.ELSEVIER SCIENCE BV, Sep. 2013, COMPUTATIONAL MATERIALS SCIENCE, 77, 424 - 429, English[Refereed]Scientific journal
- Informa {UK} Limited, Jul. 2013, Materials Science and Technology, 16(11-12) (11-12), 1314 - 1319Scientific journal
- 東北大学歯学会, Jun. 2013, 東北大学歯学雑誌, 32(1) (1), 30 - 31, Japanese医療用デバイスのための生体吸収性マグネシウム合金の開発
- The effect of pre-ageing deformation on the size and distribution of beta'(1) precipitates and subsequently on the resulting strength and ductility have been measured in a Mg-3.0at.%Zn-0.5at.%Y alloy. The alloy was extruded and then subjected to a T8 heat treatment comprised of a solution-treatment, cold-work and artificial ageing. Extrusion was used to introduce texture, ensuring that deformation occurred via slip rather than twinning. Samples were subjected to controlled uniaxial deformation and then isothermally aged to peak hardness. Precipitate length, diameter and number density were measured and evaluated in terms of the strength and ductility of the alloy. The nucleation of the beta'(1) precipitates in peak-aged condition without pre-ageing deformation (i.e. T6 treatment) was poor, with only 0.5% volume fraction, compared to approximately 3.5% in T6 treated binary Mg-3.0at.%Zn alloy. The microstructure of the Mg-Zn-Y alloy was less refined, with larger diameter precipitates and lower beta'(1) number densities than a binary Mg-3.0at.%Zn alloy. Deformation to 5% plastic strain increased the volume fraction of beta'(1) precipitates to approximately 2.3% and refined the beta'(1) precipitate length and diameter. The combination of these effects increased the yield strength after isothermal ageing from 217 MPa (0% cold-work) to 287 MPa (5% cold-work). The yield stress increased linearly with reciprocal interparticle spacing on the basal and prismatic planes and the alloy showed similar strengthening against basal slip to Mg-Zn. The elongation increased linearly with particle spacing. The ductility of Mg-Zn-Y alloys was similar to that of Mg-Zn for equivalently spaced particles. (C) 2012 Elsevier B.V. All rights reserved.ELSEVIER SCIENCE SA, Feb. 2013, JOURNAL OF ALLOYS AND COMPOUNDS, 550, 114 - 123, English[Refereed]Scientific journal
- The effect of grain size and alloying elements on the yield strength in compression was investigated using pure magnesium and its diluted solid solution alloys (Mg-Zn and Mg-Y alloys). The yield strength in compression was closely related to the {10-12} twinning, and followed the Hall-Petch relation in all the alloys. The value of σ0 increased in the following order, Mg-Y> Mg-Zn> pure magnesium, indicating solid solution strengthening however, the slope in the Hall-Petch relation was not influenced much by the alloying elements. The twinning formed frequently at the grain boundaries with a low misorientation angle, and even occurred in the parent grains with a low Schmid factor in all the alloys. These results indicated that one of the most influential parameters for the Hall-Petch slope was not the Schmid factor but the grain boundary characteristics. All the stress and strain curves in the compression showed a plateau region referring to the expansion/propagation of {10-12} twinning after the yielding behavior. The length of the plateau region increased with a decrease in the grain size and the Schmid factor of the basal slip in the parent grains. © 2012 Elsevier B.V.Jan. 2013, Materials Science and Engineering A, 561, 378 - 385, English[Refereed][Invited]Scientific journal
- The friction and wear properties of pure magnesium and the Mg-Y alloy were investigated using the pin-on-disk configuration. The friction and wear resistance of the Mg-Y alloy was superior to those of pure magnesium. The wear mechanism was abrasion under all the conditions. The deformed microstructural evolutions near the surface region were observed by transmission electron microscopy and electron backscatter diffraction. The stress and strain states were also evaluated by finite element analysis (FEA). The deformed microstructures of both alloys consisted of the {10-12} twinning formation and the FEA results showed the occurrence of plastic deformation even at the beginning of the test. The formation of low angle grain boundaries was also confirmed with an increase in the applied load in the Mg-Y alloy. On the other hand, grain refinement due to dynamic recrystallization was observed in pure magnesium as the wear test progressed. The different microstructures resulted from difference in the surface temperature during the wear test, which was estimated to be around 393 K and 363 K for pure magnesium and the Mg-Y alloy, respectively. The high increment temperature in the fine-grained alloys brought about the occurrence of grain boundary sliding, i.e., material softening, which led to a decrease in the friction and wear properties. The present results indicated that one of the methods for enhancing the friction and wear properties is to increase the dynamic reaystallization temperature. (C) 2012 Elsevier B.V. All rights reserved.ELSEVIER SCIENCE SA, Jan. 2013, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 561, 371 - 377, English[Refereed][Invited]Scientific journal
- 2013, Magnesium Technology, 323 - 328, English[Refereed][Invited]International conference proceedings
- 2013, Magnesium Technology, 317 - 322, English[Refereed][Invited]International conference proceedings
- The effect of grain boundary structures on the deformation behavior at the grain boundaries in magnesium was examined by the nanoindentation creep test. The results of the nanoindentation creep test showed that the dominant deformation mechanism around the grain boundary was grain boundary sliding; however, the occurrence of grain boundary sliding was closely related to the grain boundary energy. The grain boundary with high energy showed high strain rate sensitivity, which was the same tendency as that of the other metallic materials. Furthermore, the addition of aluminum atoms into magnesium tended to prevent the grain boundary sliding due to the decrease in grain boundary energy. (C) 2012 Elsevier B.V. All rights reserved.ELSEVIER SCIENCE BV, Jun. 2012, MATERIALS LETTERS, 76, 32 - 35, English[Refereed]Scientific journal
- We report on a quantitative investigation into the effect of size and distribution of rod-shaped 13; precipitates on strength and ductility of a Mg-Zn alloy. Despite precipitation strengthening being crucial for the practical application of magnesium alloys this study represents the first systematic examination of the effect of controlled deformation on the precipitate size distribution and the resulting strength and ductility of a magnesium alloy. Pre-ageing deformation was used to obtain various distributions of rod-shaped beta'(1) precipitates through heterogeneous nucleation. Alloys were extruded to obtain a texture so as to avoid formation of twins and thus to ensure that dislocations were the primary nucleation site. Pre-ageing strain refined precipitate length and diameter, with average length reduced from 440 nm to 60 nm and diameter from 14 nm to 9 nm. Interparticle spacings were measured from micrographs and indicated some inhomogeneity in the precipitate distribution. The yield stress of the alloy increased from 273 MPa to 309 MPa. The yield stress increased linearly as a function of reciprocal interparticle spacing, but at a lower rate than predicted for Orowan strengthening. Pre-ageing deformation also resulted in a significant loss of ductility (from 17% to 6% elongation). Both true strain at failure and uniform elongation showed a linear relationship with particle spacing, in agreement with models for the accumulation of dislocations around non-deforming obstacles. Samples subjected to 3% pre-ageing deformation showed a substantially increased ageing response compared to non-deformed material; however, additional deformation (to 5% strain) resulted in only modest changes in precipitate distribution and mechanical properties. (C) 2012 Elsevier B.V. All rights reserved.ELSEVIER SCIENCE SA, Mar. 2012, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 539, 230 - 237, English[Refereed]Scientific journal
- An ultrafine-grained (UFG) ZK60 Mg alloy with an average grain size of similar to 1.0 mu m was processed by extrusion at relatively low temperature (488 K) with a high area reduction ratio (similar to 25). The mechanical behavior of the UFG Mg alloy is investigated over strain rates spanning nearly eight decades (10(-4)-10(4) s(-1)). The stress-strain responses in the quasi-static (similar to 10(-4) s(-1)) and high rate (10(4) s(-1)) regimes exhibit the characteristic sigmoidal profile that is a signature of {10 (1) over bar2}< 10 (1) over bar(1) over bar > extension twinning. Further, this sigmoidal profile is accentuated at high rates, suggesting a rate effect of twinning induced hardening. X-ray diffraction (XRD) and analysis of the as-received and deformed microstructures indicate the occurrence of twinning even at the quasi-static rates of loading. This observation is contrary to some of the theoretical predictions that suggest suppression of twinning in Mg below critical grain sizes much larger than in the present work. From the XRD analysis we infer that the twin volume fraction increases with increasing applied strain rate. Transmission electron microscopy observations of the tested specimens reveal high density non-basal dislocations that may result from the activation of these slip systems following twinning-induced lattice reorientation. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Feb. 2012, ACTA MATERIALIA, 60(4) (4), 1818 - 1826, English[Refereed]Scientific journal
- FORMATION OF NANO-SCALE TWINS AND LOW ANGLE GRAIN BOUNDARIES DURING FRACTURE OF A FINE GRAINED MAGNESIUM ALLOYSFine grained magnesium alloys show high fracture toughness, associated with void formation. Detailed microstructural evolution during a fracture toughness test of a fine grained Mg-Zn alloy has been studied here by transmission electron microscopy (TEM). Focused ion beam (FIB) technique was used for obtaining samples near crack. Initially, subgrain structures form ahead of the crack tip, after which {10 (1) over bar1} type twins of width of about 400nm form. They further twin by {10 (1) over bar2} twinning. Subsequent twinning occurs at a finer scale near the crack, forming configurations of {10 (1) over bar1}-{10 (1) over bar2} double twins and low angle boundaries. The scale of the twin domains became progressively finer to less than 50nm. In absence of enough dislocations to pile up causing fracture, deformation continues to occur by the twinning.JOHN WILEY & SONS, 2012, MAGNESIUM TECHNOLOGY 2012, pp.93-97, 93 - 97, English[Refereed]International conference proceedings
- Evaluating the effect of pre-ageing deformation on beta ' precipitate size and distribution in Mg-Zn(-Y) AlloysThe effect of pre-ageing deformation on the precipitate diameter and length distribution in Mg-Zn(-Y) alloys was examined. Extrusion and pre-ageing deformation were used to introduce dislocations while precluding twin formation. Dislocations provided nucleation sites for rod-like beta(1)' precipitates, resulting in a refinement of the precipitate size distribution. In the binary alloy 5% strain reduced the average precipitate length from approximately 450nm to 60nm, and average diameter from 14 to 9 nm. Substantial reductions in precipitate size were also observed in the Mg-Zn(-Y) alloy. The average interparticle spacing of the rod-like precipitates was measured by Delaunay triangulation. The precipitate distribution was found to be significantly inhomogeneous, with measured interparticle spacings approximately 32% greater than predicted. For 5% pre-ageing deformation the yield strength of the binary alloy approached 95% of the ultimate tensile strength.JOHN WILEY & SONS, 2012, MAGNESIUM TECHNOLOGY 2012, pp.191-196, 191 - 196, English[Refereed]International conference proceedings
- Development of High Strength and Toughness Magnesium Alloy by Grain Boundary ControlThe mechanical properties, such as strength and fracture toughness, were investigated using caliber rolled Mg-6wt.% Al-1wt.% Zn (AZ61) alloy, which is the material consists of a constrained plane other than the rolling direction plane and is compressed non-simultaneously from two directions. The initial microstructural observations showed that the caliber rolled AZ61 alloy had a high fraction of low-angle grain boundaries and an average grain size of 2.2 mu m. In addition, particles with an average size of 100 nm existed in the matrix. This alloy showed a yield strength of 423 MPa and a fracture toughness of 34.1 MPam(1/2). A combination of grain refinement, formation of low-angle grain boundaries and dispersion of fine particles is one of the effective microstructural controls to produce the magnesium alloys with fracture toughness similar to the conventional high strength aluminum alloys.JOHN WILEY & SONS, 2012, MAGNESIUM TECHNOLOGY 2012, pp.345-347, 345 - 347, English[Refereed]International conference proceedings
- The effect of the interface structure between the matrix and the particle on the damping capacity was investigated using Mg-Zn and Mg-Zn-Y alloys in this study. The damping capacity was not affected by the interface structure at room temperature. However, the onset of temperature, which was higher in the Mg-Zn-Y alloy than in the Mg-Zn alloy despite their similar grain sizes, increased the damping capacity through grain boundary relaxation by grain boundary sliding. Compared to the Mg-Zn alloy, the existence of the quasicrystal phase particles, which had the coherent interface with low interface energy, was likely to have suppressed and delayed the grain boundary sliding in the Mg-Zn alloy. (C) 2011 Elsevier By. All rights reserved.ELSEVIER SCIENCE BV, Nov. 2011, MATERIALS LETTERS, 65(21-22) (21-22), 3251 - 3253, English[Refereed]Scientific journal
- A process to obtain high strength in a Mg-Zn-Y alloy containing quasicrystalline phase is described. The process involves solutionizing at a high temperature, precipitation of the quasicrystal phase during extrusion, followed by ageing. Tensile yield strengths of over 350 MPa are obtained with grain sizes of 14-20 mu m. (C) 2011 Elsevier B.V. All rights reserved.ELSEVIER SCIENCE SA, Aug. 2011, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 528(21) (21), 6647 - 6651, English[Refereed]Scientific journal
- The deformation mechanism in the crack-tip region of a fine-grained Mg-2.4 at. pct Zn binary alloy was investigated by focused ion beam (FIB) and transmission electron microscopy (TEM) observation and finite element analysis (FEA) at the beginning of the fracture toughness test. The deformed microstructure observations showed the formation of subgrains instead of deformation twins in the fracture toughness tested sample, which was performed at a conventional crosshead speed of 1 mm/min. By preventing the formation of deformation twins at the beginning of the test, the crack tip of the fine-grained magnesium alloys became blunted, and thus, the alloys obtained high fracture toughness. Finite element results showed that the temperature increased 50 to 110 K, and the strain rate became two orders of magnitude higher; however, this temperature increment was not sufficient to form high-angle grain boundaries, i.e., a complete occurrence of dynamic recrystallization. On the other hand, the deformed microstructure observations in the sample, which was tested at a crosshead speed of 50 mm/min, showed the formation of nano-order {10-12} deformation twins and subgrains. The formation of deformation twins was caused, in part, by the severe strain from the operation of a high strain rate in the crack-tip region.SPRINGER, Aug. 2011, METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 42A(8) (8), 2475 - 2480, English[Refereed]Scientific journal
- Four kinds of Mg-x mass%Zn-y mass%Al (x = 6, 8, 10, 12 and y = 3, 4, 5, 6) alloys, each with a grain size of 2 similar to 3 gm and containing quasicrystal phase particles, were successfully produced by casting and extrusion. These rare-earth free wrought processed magnesium alloys showed a reduction in mechanical asymmetry and a weak basal texture. Although the yield strength improved, the elongation decreased with increasing volume fraction of quasicrystal phase particle. The decrease in ductility was related to the existence of coarse quasicrystal phase particles. The strength was affected by the interface strength mechanism; however, the coherency strain in the quasicrystal phase was smaller than that in the conventional phase, due to the strong matching between the matrix and the quasicrystal phase. [doi: 10.2320/matertrans.MC201014]JAPAN INST METALS, Jun. 2011, MATERIALS TRANSACTIONS, 52(6) (6), 1111 - 1115, English[Refereed]Scientific journal
- Very fine grain sizes up to similar to 1 mu m with yield strengths up to about 400 MPa in tension and compression, with elongations ranging from 12% to 18%, have been achieved by chill casting and direct extrusion of Mg(93)Zn(6)Y alloy containing a quasicrystalline phase. These alloys respond to ageing at 150 degrees C, showing two peaks. The hardness stabilizes at the level of the second peak. The effect of precipitation on the yield strength, ductility and yield asymmetry has been studied. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Apr. 2011, SCRIPTA MATERIALIA, 64(7) (7), 661 - 664, English[Refereed]Scientific journal
- The orthorhombic phi-Al5Mg11Zn4 phase is known to be related to quasicrystalline phases, but the exact relationship has not been shown yet. In this study, the relationship of this phase to the icosahedral quasicrystalline phase is explored through analysis of the electron diffraction patterns. It is shown that icosahedral coordinations in three orientations occur in the unit cell - one with three mutually perpendicular twofold axes along (100) of the unit cell, and two with a twofold axis along [100] and a fivefold along [001]. In this, this phase is similar to aluminum and zinc based hexagonal phases which are related to quasicrystals. (C) 2011 Elsevier B.V. All rights reserved.ELSEVIER SCIENCE SA, Apr. 2011, JOURNAL OF ALLOYS AND COMPOUNDS, 509(14) (14), 4676 - 4681, English[Refereed]Scientific journal
- STRENGTHENING MG-AL-ZN ALLOY BY REPETITIVE OBLIQUE SHEAR STRAINGrain refinement is one of the possible ways to enhance the strength of magnesium without losing the ductility and/or toughness. In this study, severe plastic working by caliber rolling has been demonstrated to refine the grain structure of a commercial AZ31 Mg-Al-Zn alloy at a commercial processing speed. As a result, ultra-fine-grain structure with sub-grains in a sub-micro-meter scale was obtained. A simultaneous operation of oblique shear strain weakened the basal texture compared to that of the initial as-extruded alloy, and resulted in tensile ductility comparable to that of the commercially extruded alloy, and showed a higher asymmetry ratio of yield stress in compression/tension than that of the as-extruded alloy.JOHN WILEY & SONS, 2011, MAGNESIUM TECHNOLOGY 2011, 211 - 214, English[Refereed]International conference proceedings
- Intermetallic precipitates formed in heat-treated and aged Mg-Zn and Mg-Zn-Y alloys have been investigated via electron microscopy. Coarse spheroidal precipitates formed on deformation twin boundaries contained domains belonging to either the MgZn2 hexagonal Laves phase or the monoclinic Mg4Zn7 phase. Both phases are structurally related to the quasi-crystalline phase formed in Mg-Zn-Y alloys, containing icosahedrally coordinated zinc atoms arranged as a series of broad rhombohedral units. This rhombohedral arrangement was also visible in intragranular precipitates where local regions with the structures of hexagonal MgZn2 and Mg4Zn7 were found. The orientation adopted by the MgZn2 and Mg4Zn7 phases in twin-boundary and intragranular precipitates was such that the icosahedral clusters were aligned similarly. These results highlight the close structural similarities between the precipitates of the Mg-Zn-Y alloy system.TAYLOR & FRANCIS LTD, 2011, PHILOSOPHICAL MAGAZINE, 91(19-21) (19-21), 2634 - 2644, English[Refereed]Scientific journal
- IMPROVED PROCESSING OF Mg-Zn-Y ALLOYS CONTAINING QUASICRYSTAL PHASE FOR ISOTROPIC HIGH STRENGTH AND DUCTILITYThe stable quasicrystal phase in Mg-Zn-Y alloys has been proved to be beneficial for strength and ductility and has also been shown to impart high fracture toughness. However, the strength of these alloys has been limited to 300MPa with an average grain size of about 1 mu m. We show here a simple procedure in which a Mg93Zn6Y alloy was chilled cast and then extruded. Yield strengths of up to 400 MPa in tension and compression, accompanied by ductility of similar to 14% were obtained with grain of size of about 1 mu m. Compression to tension yield anisotropy ratios were in the narrow range of 0.95 to 1.03. These alloys also showed ageing response with two peaks. The effect of precipitation ageing on the mechanical properties has been studied.JOHN WILEY & SONS, 2011, MAGNESIUM TECHNOLOGY 2011, pp.239-244., 239 - 244, English[Refereed]International conference proceedings
- FRACTURE MECHANISM AND TOUGHNESS IN FINE- AND COARSE-GRAINED MAGNESIUM ALLOYSThe fracture mechanisms in the extruded magnesium alloys with two different grain sizes, 2 and 50 mu m, were investigated by SEM, TEM and EBSD microstructural observations. The coarse-grained alloy showed that the {10-12} type deformation twins formed at the beginning of test, and the crack was propagated into the boundaries between twins and matrix. On the other hand, the fine-grained alloy showed that the sub-grain boundaries formed instead of the deformation twins. No formation of twins at the early deformation stage causes a crack-tip blunting, and thus, the fracture toughness has a high value.JOHN WILEY & SONS, 2011, MAGNESIUM TECHNOLOGY 2011, pp.25-28., 25 - 28, English[Refereed]International conference proceedings
- The texture and tensile properties at room temperature of a fine-grained Mg-Al-Zn alloy rod processed by extrusion were examined before and after superplastic deformation. The tensile properties at room temperature were influenced by the high-temperature deformation conditions. The specimen after being exposed to superplastic deformation under tension tend to show higher ductility and lower strength at room temperature as the strain rate during high-temperature deformation decreased or as deformation temperature increased. The pre-existing basal texture of the rod slightly weakened after superplastic deformation. However, the texture weakening in the rod was not significant compared with that observed in the counterpart alloy in sheet-form probably because the initial distribution of basal planes differs between them. It is suggested that the rotation of crystallographic orientation induced by slip accommodation for grain boundary sliding plays an important role in texture randomization in superplastic magnesium alloys. (C) 2010 Elsevier B.V. All rights reserved.ELSEVIER SCIENCE SA, Sep. 2010, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 527(23) (23), 6350 - 6358, English[Refereed]Scientific journal
- The effect of the low angle grain boundary structure on the mechanical properties and deformation behavior was investigated using Mg-Al-Zn alloys, which were produced by caliber rolling. The {10-12} deformation twins were formed at the head of the crack-tip during fracture toughness even in the fine-grained structures; however, the present caliber rolled alloys showed high strength and fracture toughness balance that resulted from the high fraction of low-angle grain boundaries, which did not become the origin of the micro-void formation.WILEY-BLACKWELL, Sep. 2010, ADVANCED ENGINEERING MATERIALS, 12(9) (9), 837 - 842, English[Refereed]Scientific journal
- The effects of microstructural factors, i.e., grain size and texture, on the deformation behavior near the crack-tip region during the fracture toughness test were investigated using wrought Mg-3 wt.%Al-1 wt.%Zn alloys, which were produced by extrusion or equal-channel-angular extrusion (ECAE). The stress distributions related to deformation twins were predicted by finite element analysis (FEA), and the microstructural evolutions were confirmed by experiment. Deformation twins were formed at the beginning of the fracture toughness test due to the creation of a large stress field near the crack-tip region. The formation region of deformation twins became small with grain refinement due to the changes in the dominant plastic deformation mechanisms. The results from microstructure observations showed similarities to the stress distribution, which used simple stress-strain relations that assumed a mechanical asymmetry following the Hill's potential function. The texture, i.e., basal plane distribution, also affected the formation of deformation twins. The formation region of deformation twins in the ECAE-ed alloy was predicted to be smaller than that in the extruded alloy by FEA, and this tendency was very similar to that in the microstructural observations of the deformed samples. These results can be used to predict the macroscopic deformation features near the crack-tip, and could be helpful for developing magnesium alloys with high performance mechanical properties. (C) 2009 Elsevier B.V. All rights reserved.ELSEVIER SCIENCE SA, Mar. 2010, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 527(7-8) (7-8), 1761 - 1768, English[Refereed]Scientific journal
- Feb. 2010, Zairyo/Journal of the Society of Materials Science, Japan, 59(2) (2), 98 - 103, Japanese[Refereed]Scientific journal
- Nanoindentation creep tests were performed at the grain boundary and grain interior in pure magnesium. The grain boundary showed a high strain rate sensitivity exponent and was dominated by grain boundary sliding due to the high diffusion rate at the grain boundary. The grain boundary affected the deformation behavior of the area at a distance of 2 mu m into the grain interior. On the other hand, the grain interior had a low strain rate sensitivity exponent, because its matrix was too large to be influenced by the grain boundary. The deformation mechanism in the grain interior was determined to be dislocation slip.TAYLOR & FRANCIS LTD, 2010, PHILOSOPHICAL MAGAZINE LETTERS, 90(12) (12), 883 - 890, English[Refereed]Scientific journal
- Superplastic behavior was investigated using an extruded Mg-Zn-Y alloy with the dispersion of the quasicrystal phase particle in fine-grained matrix. Tensile tests showed that the low temperature superplasticity was behaved at a temperature of 473 K and maximum elongation was 462 % at 573 K in 1 x 10(-5) s(-1). The deformed microstructure observation showed that the dominant deformation process was grain boundary sliding. The present alloy also demonstrated a high possibility for secondary forming, such as superplastic forge forming. Furthermore, the forged alloy had a homogeneous microstructures, no mechanical anisotropy and uniform micro-hardness properties in any portion of a forged product.TRANS TECH PUBLICATIONS LTD, 2010, SUPERPLASTICITY IN ADVANCED MATERIALS, 433, 291 - 295, English[Refereed]International conference proceedings
- Structural relationships between monoclinic and Laves phase precipitates in Mg-Zn-Y alloys.Heat-treated Mg-Zn and Mg-Zn-Y alloys form two binary phase intermediate precipitates; a monoclinic structure based on Mg(4)Zn(7) and a hexagonal Laves phase based on MgZn(2). Both phases precipitate along deformation twin boundaries in aged Mg-Zn-Y alloys. High resolution TEM studies determined that the two phases frequently co-exist within individual precipitates. Particles were comprised of distinct domains of a specifically-oriented region of either phase. The interface region between monoclinic and Laves phase also had a monoclinic structure similar to that of Mg(4)Zn(7) but with an enlarged unit cell. This region retains the acute rhomboidal (AR) arrangement of pentagonally co-ordinated zinc atoms common to both Mg(4)Zn(7) and MgZn(2) structures.MINERALS, METALS & MATERIALS SOC, 2010, MAGNESIUM TECHNOLOGY 2010, 347 - 351, English[Refereed]International conference proceedings
- Structure of beta(1)' precipitates in Mg-Zn based alloys: Co-existence of MgZn(2) and Mg(4)Zn(7) phasesAlthough the the rod-like beta(1)' precipitate is among the most important in magnesium alloys, its crystal structure is not yet clear. Its structure has been believed to be based on the Lave's phase MgZn(2), but recently reported to be of monoclinic Mg(4)Zn(7) phase. We have studied the structure of these precipitates by high resolution TEM in a Mg-Zn-Y alloy. It was found that domains of Mg(4)Zn(7) phase coexist with Laves phase MgZn(2) within the precipitates. Structural units of the Mg(4)Zn(7) phase characterized by icosahedral coordination rearrange to form the MgZn(2) structure with the orientation relationship with the matrix reported earlier. The crystallographic relationship between the phases is described. Axially, these phases are related to each other and the matrix as [1 (2) over bar 10](Mgzn2) parallel to [010](Mg4Zn7) parallel to [0001](Mg).MINERALS, METALS & MATERIALS SOC, 2010, MAGNESIUM TECHNOLOGY 2010, 323 - 327, English[Refereed]International conference proceedings
- The ductile fracture mechanism in a fine-grained magnesium alloy has been investigated by transmission electron microscopy-focused ion beam techniques. In coarse-grained or conventional magnesium alloys, twins form at the very beginning of the deformation process, and crack propagation occurs through the twin boundaries. However, in the alloy used in this study, subgrain structures were found instead of twins at the crack tip. Nanoscale twins formed subsequently owing to large stress in the crack propagation route. The fine-grained alloys showed high fracture toughness resulting from resistance to the twins at the beginning of the deformation.TAYLOR & FRANCIS LTD, 2010, PHILOSOPHICAL MAGAZINE LETTERS, 90(11) (11), 831 - 839, English[Refereed]Scientific journal
- It is shown here by high-resolution electron microscopy that the structure of rod-like beta(1)' precipitates perpendicular to the basal planes of the magnesium matrix in Mg-Zn-Y alloys consist of complex domains at nanoscale. These domains can be recognized to be those of monoclinic Mg4Zn7 phase and hexagonal Laves phase MgZn2 with axial orientations [1(2)over-bar10](MgZn2)parallel to[010](Mg4Zn7)parallel to[0001](Mg). Due to disorder, often complete unit cells of the Mg4Zn7 structure cannot be recognized. Inside a domain of Mg4Zn7, the structure may locally transform to that of MgZn2. The structure of both the phases are composed of similar units of icosahedral coordinations. Maintaining the above axial orientation, the Mg4Zn7 can exhibit two orientation relationships with the matrix, (802)(Mg4Zn7)parallel to{10(1)over-bar0}(Mg) or (603)(Mg4Zn7)parallel to{10(1)over-bar0}(Mg). The hexagonal MgZn2 forms in the monoclinic Mg4Zn7 in two different orientations, related to rhombic units (with angle similar to 72 degrees) in the Mg4Zn7 unit cell. With the common axial relationship given above, these two orientation relationships can be given as (0001)(MgZn2)parallel to(120(1)over-bar)(Mg4Zn7) or (0001)(MgZn2)parallel to(206)(Mg4Zn7). One of these two variants forms a known orientation relationship [11(2)over-bar0](MgZn2)parallel to[0001](Mg), (0001)(MgZn2)parallel to{11(2)over-bar0}(Mg) with the matrix. The structure of the MgZn2 was found to be modified by the ordering of zinc layers perpendicular to the hexagonal axis.TAYLOR & FRANCIS LTD, 2010, PHILOSOPHICAL MAGAZINE LETTERS, 90(9) (9), 641 - 651, English[Refereed]Scientific journal
- Isothermal ageing of plastically deformed Mg-Zn-Y alloys resulted in precipitation along [image omitted] twin boundaries. The bulky precipitates so formed had structures similar to those recently reported for the rod-like [image omitted] precipitates, but afforded a more detailed study by high-resolution TEM due to their larger size. The core of the precipitates often had the structure of the monoclinic Mg4Zn7 phase, and had the orientation [image omitted]; [image omitted] with either the matrix or the twin. On this Mg4Zn7 phase, the hexagonal MgZn2 phase grew in two orientations, both with [image omitted]. One of these orientations formed a known orientation relationship [image omitted]; [image omitted] with the matrix. The part of the precipitate with the MgZn2 structure was usually in direct contact with the twin boundary. Both the Mg4Zn7 and MgZn2 phases have layered structures that can be described with similar building blocks of icosahedrally coordinated atoms. The atomic positions of zinc atoms comprise the vertices of these icosahedra and form 'thick' rhombic tiles. The orientations of these rhombuses remain unchanged across the interfaces between the two phases. Near the interface with MgZn2, transition structures formed in the Mg4Zn7 phase, with the Zn:Mg atom ratio between those of the Mg4Zn7 and MgZn2 phases. In these transition structures, the unit cell of the Mg4Zn7 phase is extended along [100] or [001] by half a unit cell length by continuation of the rhombic tiling. Structures of these extended unit cells are proposed.TAYLOR & FRANCIS LTD, 2010, PHILOSOPHICAL MAGAZINE, 90(24) (24), 3355 - 3374, English[Refereed]Scientific journal
- Grain refinement of an Mg-3Al-1Zn-0.2Mn (wt.%) alloy was conducted by severe plastic working with caliber rolling. The alloy's yield strength was increased to more than 400 MPa, which is twice that of an initially extruded alloy, and its yield asymmetry in compression against tension was reduced by the weakened basal texture caused by the shear deformation. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Jan. 2010, SCRIPTA MATERIALIA, 62(2) (2), 113 - 116, English, International magazine[Refereed]Scientific journal
- The microstructure evolutions and texture changes during the compression test were investigated using an extruded magnesium alloy with average grain sizes of 11.4 and 49.6 mu m. The deformation twins were formed in all the samples; however, a comparison of the fraction of deformation twins on the effect of grain size and initial texture, i.e., the cutting position (normal or parallel to the extrusion), showed that the fine-grained alloy and/or the sample with the normal-cut to the extrusion had a lower fraction of deformation twins. On the other hand, the texture change showed different tendencies depending on the grain size and/or the initial texture. In the coarse-grained alloy, since the dominant deformation mechanism was the deformation twins, the lattice was rotated without relation to the initial texture. However, in the fine-grained alloy, even the applied strain of 0.20, the intensity peaks existed at < 1010 > and the basal texture remained in the sample with the parallel- and normal-cut to the extrusion, respectively. This resulted from the difference in the fraction of deformation twins and the occurrence of partial grain boundary sliding. (c) 2009 Elsevier B.V. All rights reserved.ELSEVIER SCIENCE SA, Dec. 2009, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 527(1-2) (1-2), 370 - 375, English[Refereed]Scientific journal
- 日本バイオマテリアル学会, Nov. 2009, 日本バイオマテリアル学会大会予稿集, 31回, 125 - 125, Japanese生体吸収性マグネシウム合金の生体内分解挙動観察
- The texture and tensile properties of a fine-grained Mg-Al-Zn alloy sheet at room temperature prior to and following superplastic deformation were examined. The pre-existing basal texture of the sheet drastically weakened after superplastic deformation, and thus the geometric conditions for basal slip, characterized by the Schmid factor distributions, became more favorable. Consequently, relatively high ductility was maintained after superplastic deformation in spite of cavity formation. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Nov. 2009, SCRIPTA MATERIALIA, 61(9) (9), 883 - 886, English[Refereed]Scientific journal
- The compressive constitutive behavior of a closed-cell aluminum foam (ALPORAS) manufactured by Shinko Wire Co. in Japan was evaluated under static and dynamic loading conditions as a function of temperature. High-strain-rate tests (1000-2000 s(-1)) were conducted using a split-Hopkinson pressure bar (SHPB). Quasi-static and intermediate-strain-rate tests were conducted on a hydraulic load frame. A small but discernable change in the flow stress behavior as a function of strain rate was measured. The deformation behavior of the Al-foam was however found to be strongly temperature dependent under both quasi-static and dynamic loading. Localized deformation and stress state instability during testing of metal foams is discussed in detail since the mechanical behavior over the entire range of strain rates indicates non-uniform deformation. Additionally, investigation of the effect of residual stresses created during manufacturing on the mechanical behavior was investigated. (C) 2009 Published by Elsevier B.V.ELSEVIER SCIENCE SA, Nov. 2009, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 525(1-2) (1-2), 1 - 6, English[Refereed]Scientific journal
- WILEY-V C H VERLAG GMBH, Oct. 2009, ADVANCED ENGINEERING MATERIALS, 11(10) (10), 782 - 787, English[Refereed]Scientific journal
- Quasicrystal and related phase particles were successfully dispersed in wrought-processed Mg-7.6 wt.% Zn-3.9 wt.% Al alloy with homogeneous and fine-grained structures. This rare-earth-free alloy showed high strength and ductility balance, which was superior to that of the well-known quasicrystal phase dispersed in Mg-Zn-RE alloys, with a weak texture and a reduction of mechanical asymmetry in yield strength. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Oct. 2009, SCRIPTA MATERIALIA, 61(7) (7), 705 - 708, English, International magazine[Refereed]Scientific journal
- WILEY-V C H VERLAG GMBH, Aug. 2009, ADVANCED ENGINEERING MATERIALS, 11(8) (8), 654 - 658, English[Refereed]Scientific journal
- Nanoindentation creep and uniaxial tension were conducted on pure Mg with a grain size of about 2 mu m at room temperature and the data were directly compared. Despite the differences in stress state, the two sets of data were found to match remarkably well with each other. An apparent stress exponent value of 4 was obtained and the deformation mechanism was discussed in light of dislocation slips and twinning in anisotropic Mg.MATERIALS RESEARCH SOC, May 2009, JOURNAL OF MATERIALS RESEARCH, 24(5) (5), 1615 - 1618, English[Refereed]Scientific journal
- The microstructure evolution of Mg 2.4 at.% Zn binary alloy was examined during extrusion at low temperature. Fine-grained structure were formed near the grain boundary due to dynamic recrystallization. Rod-shaped precipitates were also formed before the extrusion and were elongated and/or torn off by the strain; the precipitate morphology changed from rods to spherical. The spherical precipitates pin the dislocations they are the nucleation site for new grains and promote recrystallization. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Mar. 2009, SCRIPTA MATERIALIA, 60(6) (6), 411 - 414, English, International magazineScientific journal
- A fine-grained microstructure average grain size of which is around 2 pin was developed in ZK60A magnesium alloy subjected to a FSW process. Material flow arose mainly from basal slips and was governed by simple shear deformations caused by the tool rotation. The development of the fine-grained structure was a complex process driven by severe plastic deformations, formation of deformation bands, grain splitting, twinning and dynamic and/or static recrystallizations. It appears also that the microstructural evolution depended on morphology of fine dispersoids. [doi:10.2320/matertrans.MRA2008192]JAPAN INST METALS, Mar. 2009, MATERIALS TRANSACTIONS, 50(3) (3), 610 - 617, English, International magazine[Refereed]Scientific journal
- Applications of ARB to magnesium alloys were limited due to low deformability. The authors recently found that the rollability of the alloys is significantly improved in highspeed rolling. It is supposed that the severe plastic deformation of magnesium alloy sheets is feasible if rolling in ARB processes is conducted at high speed. In this study, AZ31B and ZK60A sheets are processed by ARB up to five cycles at 423K with a speed of 1000m/min. Vickers hardness increases with increasing number of ARB cycles, while the tensile strength shows the maximum after the second cycle. The grain size is reduced significantly at the first cycle and decreases gradually from the second cycle. The mean grain sizes after five cycles are 1.6μm for AZ31B and 1.8μm for ZK60A. It is concluded that ARB using high-speed rolling is effective for grain refinement of magnesium alloys. © 2009 IOP Publishing Ltd.Institute of Physics Publishing, 2009, Journal of Physics: Conference Series, 165, English[Refereed]International conference proceedings
- Directionally controlled precipitation on twin-boundaries in Mg-Zn-Y alloys.Precipitation strengthening in Mg-Zn-Y alloys occurs via the formation of a fine dispersion of beta(1)' (Mg(4)Zn(7)) rods aligned parallel to the hexagonal axis. In this study, texture and controlled deformation have been used to control the directionality and morphology of the precipitates and their effect on the ageing response. The resulting precipitates were studied via conventional and high-resolution transmission electron microscopy. Texture was developed through extrusion at 300 degrees C, followed by controlled room-temperature deformation to generate microstructures where yield occurred either with, or without, twinning. The ageing response was monitored using hardness testing. Both compressive and tensile deformation accelerated the ageing response. Compression parallel to the extrusion axis generated a high volume fraction of twins. Precipitates on the twin boundaries assumed a low aspect-ratio morphology different from the usual high-aspect ratio rods.MINERALS, METALS & MATERIALS SOC, 2009, MAGNESIUM TECHNOLOGY 2009, 445 - 450, English[Refereed]International conference proceedings
- The atomic structure of shear hands in Pd40Ni40P20 bulk metallic glass has been compared to all undeformed matrix phase using pair distribution functions (PDFs) derived from energy filtered nanobeam electron diffraction. Shear bands do not show any characteristic contrast in transmission electron microscopy (TEM) images when specimens are prepared with uniform thickness. PDFs from a shear hand exhibit a slight decrease in the first peak, indicating a slight difference in packing density and short range order compared to the undeformed matrix.CAMBRIDGE UNIV PRESS, Jan. 2009, JOURNAL OF MATERIALS RESEARCH, 24(1) (1), 1 - 9, English, International magazine[Refereed]Scientific journal
- The fracture mechanism during fracture toughness testing has been investigated on a coarse-grained magnesium alloy, with an average grain size of 50 m, and a low fracture toughness. The results show that {1012}-type deformation twins are formed at the crack tip and many dislocations pile up on these boundaries. The accumulated strains at these boundaries become the origin of fracture; i.e. cracks propagate along these boundaries between the deformation twins and the matrix.TAYLOR & FRANCIS LTD, 2009, PHILOSOPHICAL MAGAZINE LETTERS, 89(1) (1), 2 - 10, English[Refereed]Scientific journal
- The compressive deformation behavior of BMG matrix composites processed by controlled annealing in supercooled liquid region was investigated. The compressive strength decreased with increasing of volume fraction of crystalline phase. From the results of the compressive deformation and microstructure observation in annealed samples in different volume fraction of crystalline phase, the ductile-brittle fracture transition is related to the formation of grain boundary between crystalline particles. It is considered the brittle transition in BMG matrix composites with increasing of volume fraction of crystalline phase is attributed to the fracture originated in the grain boundary and interface between amorphous phase and crystalline phase.Dec. 2008, Progress of Composites 2008 in Asia and Australasia - Proceedings of the 6th Asian-Australasian Conference on Composite Materials, ACCM 2008, 213 - 214
- The influence of pH and flow on the polarisation and impedance behaviour of pure Mg was investigated in 0.6 wt% NaCl borate buffer solutions at pH 6.7, 7.6, and 9.3 using a rotating electrode. The existence of flow prevented the accumulation of the corrosion product and promoted uniform corrosion, leading to an increase of the anodic current density and a decrease of the impedance regardless of the pH of the bulk solution. The influence of the pH did not obviously appear under the static condition, whereas, under the dynamic condition, the anodic current density at pH 6.7 and 7.6 was higher than that at pH 9.3. This result suggests that pH near the surface can be buffered at the pH of bulk solution by borate buffer with the acceleration of ion diffusion. (C) 2008 Elsevier Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Dec. 2008, CORROSION SCIENCE, 50(12) (12), 3561 - 3568, English[Refereed]Scientific journal
- Calcium phosphate precipitated on pure magnesium from artificial plasma (modified Hanks' solution) was varied by anodization and autoclaving, aiming the control of corrosion rate of bioabsorbable magnesium. Rough and smooth anodized film was formed depending on anodizing voltage in 1 N NaOH. The amount of calcium phosphate precipitated on the porous film was 2-3 times larger than that on the smooth film. The Ca/P ratio on the porous film was slightly higher than that on the smooth film. The autoclaving did not significantly influence the morphology of anodized film; however, the precipitation of calcium phosphate was restricted. No significant local corrosion occurred after the immersion in modified Hanks' solution. It is demonstrated that the precipitation of calcium phosphate on magnesium can be controlled by anodization and autoclaving. (c) 2008 Elsevier Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Oct. 2008, CORROSION SCIENCE, 50(10) (10), 2906 - 2913, English, International magazine[Refereed]Scientific journal
- The parametric dependencies of threshold stress for superplastic flow were characterized over a wide range of temperatures using a fine-grained magnesium alloy with various grain sizes. The threshold stress was proportional to the reciprocal of the square root of the grain size at 473 K, whereas it was independent of the grain size at 598 K. The threshold stress decreased with increasing deformation temperature more quickly than the shear modulus did. It was suggested that the temperature dependence of the threshold stress is associated with the interaction between the solute atoms and dislocations. The origin of the threshold stress probably resulted from the dislocations breaking away from the solute atmospheres formed in the grain boundaries and in the lattice at low temperatures and at high temperatures, respectively.SPRINGER, Oct. 2008, METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 39A(10) (10), 2351 - 2362, English[Refereed]Scientific journal
- (一社)歯科基礎医学会, Sep. 2008, Journal of Oral Biosciences, 50(Suppl.) (Suppl.), 125 - 125, English生体吸収性マグネシウム合金の生体内動態に関する研究
- Six kinds of Mg-2.5 at%Zn-0.5 at%RE (RE: rare earth element, Y, Gd, Tb, Dy, Ho and Er) alloys with grain size of 1 similar to 2 mu m and containing a quasicrystalline icosahedral phase were prepared by casting and extrusion. These alloys had high strength and high fracture toughness balances, due to the synergetic effect of grain refinement and the dispersion of quasicrystalline phase particles. Microstructural observations showed a ductile fracture pattern. and that the origin of void nucleation was not the quasicrystalline phase particles but the conventional precipitates and the W-phase particles, because of the difference in the interface structure between the matrix and the particles. [doi: 10.2320/matertrans.MAW200804]JAPAN INST METALS, Sep. 2008, MATERIALS TRANSACTIONS, 49(9) (9), 1947 - 1952, English, Domestic magazine[Refereed]Scientific journal
- Ultrasonic vibration was introduced into the solidification of the AZ91 magnesium alloy. The coarse dendrite microstructure solidified in the AZ91 alloy without any ultrasonic vibration. However, the microstructure with fine uniform non-dendrite grains was achieved with ultrasonic vibration. According to the analysis of refinement mechanism, it indicated that due to the acoustic cavitation and flows induced by ultrasonic vibration, the most of insoluble impurity particles become active as nucleation centers and the temperature gradient near the solidification front increases, which led to the fine uniform microstructure. Besides, the AZ91 alloy produced with ultrasonic vibration exhibited the improved mechanical properties at room temperature, such as compressive yield strength (94 MPa), ultimate compressive strength (376 MPa) and fracture strain (22.0%). (C) 2007 Elsevier B.V. All rights reserved.ELSEVIER SCIENCE SA, Jul. 2008, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 487(1-2) (1-2), 120 - 123, English[Refereed]Scientific journal
- Magnesium and its alloys are potential candidates for bioabsorbable stents. The degradation rate of an indwelled magnesium stent is expected to be controlled under a blood flow. The influence of the controlled flow on the polarization and impedance behavior of pure Mg was thus investigated in a 0.6 mass% NaCl solution using a rotating electrode. The existence of a flow caused an increase in the anodic current density as well as a decrease in the impedance for a few hours of immersion, indicating the acceleration of Mg dissolution and the retardation of the growth of the surface hydroxide film. Interestingly, the existence of a flow retarded the breakdown of the surface film. After the surface film was broken down, the impedance did not depend on the rotation speed. To precisely evaluate the degradation rate of magnesium and its alloys for use in stents, the flow rate of the test solution should be controlled.JAPAN INST METALS, Jun. 2008, MATERIALS TRANSACTIONS, 49(6) (6), 1456 - 1461, English[Refereed]Scientific journal
- Ultrasonic vibration was introduced into the solidification of AZ91 alloy. Various microstructures were produced in this alloy using ultrasonic vibrations at different temperatures of the melt. The coarse dendrite microstructures were obtained with ultrasonic vibrations at temperatures below the liquidus temperature. The fine uniform grains were achieved under ultrasonic vibrations during the nucleation stage, which was mainly attributed to the cavitation and the acoustic flow induced by the ultrasonic vibration. (C) 2008 Elsevier B.V. All rights reserved.ELSEVIER SCIENCE BV, Jun. 2008, MATERIALS LETTERS, 62(17-18) (17-18), 2872 - 2875, English[Refereed]Scientific journal
- Nanocrystalline iron synthesized by mechanical alloying and spark plasma sintering exhibited high yield and ultimate compressive strengths of 2.59 and 3.08 GPa, respectively, with a total true strain of 0.05. Partial recrystallization led to a true strain of 0.4 with a lower strength of 2.25 GPa. A bimodal grain size distribution consisting of average fine grains of 2.5 mu m and nanograins of 85 run is attributed to the combined high strength and large plastic strain. (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, May 2008, SCRIPTA MATERIALIA, 58(9) (9), 759 - 762, English, International magazine[Refereed]Scientific journal
- An AZ91 alloy pretreated by ultrasonic vibration (UV) was subjected to extrusion to refine the microstructure. The results indicated that the UV pretreatment had a strong influence on the microstructure evolution and mechanical properties of the extruded AZ91 alloy. With UV pretreatment, a fine and uniform microstructure with an average grain size of 13.5 mu m was obtained, and the fraction of the fiber-like, partially-recrystallized, structure was markedly reduced. In addition to the superior mechanical properties such as a yield strength of 256 MPa, an ultimate tensile strength of 320 MPa and a fracture elongation of 9.7% were achieved in the extruded AZ91 alloy with UV pretreatment.JAPAN INST METALS, May 2008, MATERIALS TRANSACTIONS, 49(5) (5), 972 - 975, English[Refereed]Scientific journal
- Due to its light weight and abundance as a resource, the utilization of magnesium is increasing. AZ91 alloy is the most common cast magnesium alloy and is widely used as die-casting material. AZ91 is also used for sand mold casting. In sand mold casting, reaction with mold sand is expected because magnesium is a very reactive element. This study investigated the surface condition of AZ91 castings using sand mold. Higher pouring temperature promoted the reaction with silica sand, and the surface of castings became rough. Reacting with mold sand, Mg2Si and Mg and Al complex oxides were precipitated near the casting surface.JAPAN INST METALS, May 2008, MATERIALS TRANSACTIONS, 49(5) (5), 1089 - 1092, English[Refereed]Scientific journal
- Four kinds of extruded Mg-X at.% Zn binary alloys (X = 1.9, 2.4, 3.0, and 3.4) were used to examine the effect of precipitate volume fraction on fracture toughness. All the alloys had fine grain sizes of 1-3 mu m and fine sphere-shaped precipitates of 50-60 nm. The volume fraction of precipitates increased with additional zinc content. The results of mechanical property tests showed that the extruded Mg-2.4 at.% Zn alloy exhibited the best balance of strength and fracture toughness. One of the reasons was the different volume fraction of precipitates at the grain boundaries, which was the source of void formation. According to the fracture surface observations and ductile fracture model analysis, the volume fraction of precipitates of 2%-4% was shown to be enough to improve the fracture toughness for the fine-grained magnesium alloys; i.e., higher contents of zinc atoms were not needed to enhance the mechanical properties.MATERIALS RESEARCH SOC, Apr. 2008, JOURNAL OF MATERIALS RESEARCH, 23(4) (4), 1128 - 1135, English, International magazine[Refereed]Scientific journal
- Tensile, compression and fatigue tests were carried out on a commercially extruded Mg-Al-Zn alloy having an average grain size of about 15 pm. The tensile and compression tests at room temperature showed that the yield strength in tension was much higher than that in compression. The lower yield strength in compression resulted from its texture. The effects of the mechanical anisotropy on the fatigue behavior and its deformed microstructure were also investigated under a stress ratio of R = 0.1 and -1. The fatigue strength, stress amplitude, at N = 10(7) cycles under R = -1 and 0.1 was about 120 and 90 MPa, respectively. The mechanical properties and the deformed microstructure observations indicated that the formation of deformation twins was related to the between maximum stress and the yield strength in tension and compression: the deformation twins were formed in the sample (maximum stress is higher than the yield strength) and showed no deformation twins in the sample (maximum stress is lower than the yield strength).JAPAN INST METALS, Mar. 2008, MATERIALS TRANSACTIONS, 49(3) (3), 681 - 684, English[Refereed]Scientific journal
- Fracture toughness in magnesium alloys by dispersion of quasicrystalline phaseThe fracture toughness and its fracture mechanism were investigated by the extruded Mg-2.6at.%Zn-0.4at.%Y and Mg-2.6at.%Zn-0.4at.%Ho alloys. The both alloys had an average grain size of similar to 1 mu m and two kinds of particles, such as M-Zn delta-phase and quasicrystal line phase, in the matrix. The mechanical tests exhibited good balance of strength and fracture toughness. The fracture surface observations showed that the origin of dimple formation was not the quasicrystal line phase but the delta-phase. This was resulted from the specific structures: coherent interface between the matrix and quasicrystal phase.MINERALS, METALS & MATERIALS SOC, 2008, MAGNESIUM TECHNOLOGY 2008, 317 - +, English[Refereed]International conference proceedings
- Cavities were formed in the random boundaries of superplastic magnesium alloys due to higher boundary energy. The cavity growth rate of the fine-grained alloy (dominant diffusion process: grain boundary diffusion) was lower than that of the coarse-grained alloy (lattice diffusion) during superplastic flow. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Dec. 2007, SCRIPTA MATERIALIA, 57(11) (11), 1008 - 1011, English[Refereed]Scientific journal
- Very high plastic strains exceeding 20% in uniaxial compression tests, which show an inflection in the stress-strain curves of Zr-based bulk metallic glasses, are shown to be a spurious effect due to mechanical interlocking of cracks with shear bands. This type of stress-strain behaviour is misinterpreted as an actual deformation in the literature. The effect of mechanical interlocking is explained by fractographic analysis.TAYLOR & FRANCIS LTD, Sep. 2007, PHILOSOPHICAL MAGAZINE LETTERS, 87(9) (9), 625 - 635, English, International magazine[Refereed]Scientific journal
- Fracture toughness and its deformed structures were investigated on a Mg-3AI-lZn (AZ31) alloy processed by direct extrusion. The average grain sizes of the alloy after extrusion at temperatures of 473 and 573 K were 4.0 and 14.5 mu m, respectively (i.e., fine-grained and coarse-grained alloys). The plane-strain fracture toughness, K-IC, as determined by stretched zone analysis in fine-grained and coarse-grained alloys was estimated to be 24.9 and 22.7 MPam(1/2), respectively. Microstructural observations of the fine-grained alloy after fracture toughness testing showed that non-basal slip and grain-boundary sliding was activated even at room temperature. In addition, the {10-12} deforrilation twins were observed despite the fine-grained Structures. However, the fraction of deformation twins was reduced with grain refinement. which related to the enhancement of fracture toughness with grain refinement.MATERIALS RESEARCH SOCIETY, Sep. 2007, JOURNAL OF MATERIALS RESEARCH, 22(9) (9), 2598 - 2607, English, International magazine[Refereed]Scientific journal
- A bulk nanocrystalline Al-5 at.% Fe alloy was synthesized by mechanical alloying and spark plasma sintering. The alloy exhibited a very high compressive yield strength of 1 GPa with a plastic strain of 0.3. The alloy consists of coarse alpha-Al grains that form from powder boundaries and nanocrystalline regions composed of alpha-Al and Al6Fe phases. The combination of the coarse and nanoscale grains are considered to be the reason for the large plastic strain in such a high-strength material. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Aug. 2007, SCRIPTA MATERIALIA, 57(3) (3), 189 - 192, English, International magazine[Refereed]Scientific journal
- A small variation in the composition of (Zr50Cu50)(100-x)Al-x bulk metallic glasses (BMGs) results in a markedly different mechanical behavior. In contrary to the previous reports, no chemical or structural inhomogeneities were observed in the sample that exhibits a large plastic strain, indicating that the plasticity of Zr-Cu-Al BMGs is not inherently related to their microstructural features. The shear bands in plastic Zr47.5Cu47.5Al5 show localized nanocrystallization whereas the macroscopically brittle Zr45Cu45Al10 shows no indications of nanocrystallization during deformation. (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Jul. 2007, SCRIPTA MATERIALIA, 57(2) (2), 173 - 176, English, International magazine[Refereed]Scientific journal
- Fracture toughness was examined on a commercial M--Zn-Zr alloy, ZK60. The commercial alloy was extruded at a temperature of 493 K to obtain fine grain structures having fine spherical shaped precipitates. The microstructures consisted of equi-axed grains. The average grain size and the precipitate diameter were about 3 mu m and 25 similar to 50 mn, respectively. The yield strength and elongation-to-failure were 287 MPa and 26.7%, respectively. The plane-strain fracture toughness, K-IC, was estimated to be 34.8MPam(1/2) by the stretched zone analysis. These mechanical properties were superior to that of conventional wrought magnesium and magnesium alloys. The deformed microstructure observations showed i) the activation of non-basal dislocations even at room temperature and ii) the pinning of dislocations by the spherical shaped precipitates during the fracture toughness test. Thus, a combination of grain refinement and dispersion of fine spherical shaped precipitates were found to be effective methods for improving the fracture toughness of magnesium alloys.JAPAN INST METALS, Jun. 2007, MATERIALS TRANSACTIONS, 48(6) (6), 1422 - 1426, English, Domestic magazine[Refereed]Scientific journal
- The mechanical properties were investigated by Mg-0.3 at.% Ca-1.8 at.% Zn alloy, which was produced by hot extrusion, having an average grain size of about 1 mu m and spherical precipitates in the matrix. The extruded alloy showed a good balance of the yield strength (sigma(ys) = 291 MPa) and plane-strain fracture toughness (K-IC = 28.3 MPa m(1/2)), obtained by the stretched zone analysis, which were higher than those of conventional wrought magnesium alloys. The microstructure control of both the grain refinement and the dispersion of precipitates in the matrix was a possible method for improvement of the mechanical properties in magnesium alloys. (C) 2007 Elsevier B.V. All rights reserved.ELSEVIER SCIENCE SA, Jun. 2007, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 459(1-2) (1-2), 366 - 370, English, International magazine[Refereed]Scientific journal
- The fracture toughness of an extruded Mg-2.6 at.% Zn-0.4 at.% Y alloy with a grain size of 1 mu m and containing quasicrystalline icosahedral phase was determined to be 32.5 MPa m(1/2), which is much higher than conventional wrought magnesium alloys. Microstructural observations showed that the quasicrystalline phase pinned many dislocation movements and prevented void nucleation because of its coherent interface with the matrix. (c) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Jun. 2007, SCRIPTA MATERIALIA, 56(12) (12), 1091 - 1094, English, International magazine[Refereed]Scientific journal
- Quinary Zr-based alloy compositions with improved glass forming criteria have been sought and the glass forming ability (GFA), thermal stability and mechanical properties of these alloys have been investigated. Monolithic amorphous structure has been confirmed for all compositions in 5 mm rods prepared by a Cu-mold casting method. They also show large plastic strain maximum of about 12% under uniaxial compression test with yield stress of about 2000 MPa. The compressive plasticity of the cast rods was found to be influenced by the casting temperature to a great extent.JAPAN INST METALS, Jun. 2007, MATERIALS TRANSACTIONS, 48(6) (6), 1322 - 1326, English, Domestic magazine[Refereed]Scientific journal
- Two alloys, Mg96.9Zn2.7Ho0.4 and Mg93Zn6Ho, containing a quasicrystal phase were extruded at various temperatures to produce different grain sizes and tested at room temperature in tension and compression. For larger grains the strength of the Mg93Zn6Ho alloy was almost twice that of the Mg96.9Zn2.7Ho0.4 alloy. Yield stresses approached 300 MPa as the grain sizes decreased to 1 mu m. In the case of the Mg93Zn6Ho alloy, at grain sizes less than about 2 mu m, yield stresses in compression become higher than in tension. (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Jun. 2007, SCRIPTA MATERIALIA, 56(11) (11), 935 - 938, English, International magazine[Refereed]Scientific journal
- We have investigated the compression stress-strain behaviors of Ti40Zr25Cu12Ni3Be20 bulk metallic glasses prepared by Cu mold casting from various melt temperatures. Plastic strain was found to vary sensitively on the temperature of melts and subsequent annealing conditions. To understand the origin of the plasticity change, the microstructures were characterized using transmission electron microscopy and a laser-assisted three-dimensional atom probe. The fully amorphous sample cast from 1273 K showed 0.6% plastic strain, and it was enhanced to 1.3% after isothermal annealing at 573 K. The sample cast from 1423 K showed 3.0% plastic strain, from which the presence of nanocrystals with a volume fraction of about 12% was confirmed. The sample cast from a higher temperature (1573 K) contained a larger fraction of crystals, which showed limited plastic strain. The effect of the volume fraction of the nanocrystals on the plasticity of bulk metallic glasses is discussed based on the experimental results.MATERIALS RESEARCH SOCIETY, May 2007, JOURNAL OF MATERIALS RESEARCH, 22(5) (5), 1406 - 1413, English, International magazine[Refereed]Scientific journal
- A commercial Mg-6 wt% Zn-0.5 wt% Zr (ZK60) alloy was used to investigate the effect of precipitate shapes on fracture toughness. The ZK60 alloy was extruded at a temperature of 653 K (extruded alloy). The extruded alloy was annealed at 633 K for 86.4 ks (annealed alloy), and then the annealed alloy was aged at 448 K for 100 ks (aged alloy). The average grain size in all the conditions was about the same, 13.5 +/- 1.0 mu m. The extruded and aged alloys had different shaped precipitates: spherical and rod shaped precipitates, respectively. The plane-strain fracture toughness K-IC of the extruded, annealed, and aged alloys were estimated to be 22.4, 20.2, and 21.0 MPam(1/2), respectively, by the stretched zone analysis. Transmission electron microscopy (TEM) observations showed that the deformation during the fracture toughness test was dominated by a dislocations on the basal slip planes in all the conditions. Such dislocations are commonly activated in magnesium alloys during the tensile and compression tests. The spherical shaped precipitates were found to be more effective than the rod shaped precipitates for improving the fracture toughness in the magnesium alloy.MATERIALS RESEARCH SOCIETY, Apr. 2007, JOURNAL OF MATERIALS RESEARCH, 22(4) (4), 965 - 973, English, International magazine[Refereed]Scientific journal
- Magnesium alloys have great potential for use as structural materials since they are the lightest of all structural alloys in use. In order to use magnesium alloys in structural applications, it is important to ensure that their mechanical properties satisfy both reliability and safety requirements. One of the methods of ensuring that is to investigate the fracture toughness. However, the value of fracture toughness in magnesium alloys has been generally reported to be much lower than that in aluminum alloys. In this study, commercial Mg-Al-Zn alloys having different grain sizes, which were produced by hot extrusion, were used to examine the fracture toughness and deformed microstructures, i.e., after fracture toughness tested samples. The lower fracture toughness of magnesium alloy was related to the formation of deformation twins during fracture toughness tests.The Japan Society of Mechanical Engineers, 2007, The proceedings of the JSME annual meeting, 2007, 325 - 326, Japanese
- High strain rate deformation behavior of Mg-Al-Zn alloys at elevated temperaturesHigh temperature deformation behavior of AZ31 and AZ91 magnesium alloys was examined by compression tests over a wide strain rate range from 10(-3) to 10(3) s(-1) with emphasis on the behavior at high strain rates. The dominant deformation mechanism in the low strain rate range below 10(-1) s(-1) was suggested to be climb-controlled dislocation creep. On the other hand, experimental results indicated that the deformation at a high strain rate of similar to 10(3) s(-1) proceeds by conventional plastic flow of dislocation glide and twinning even at elevated temperatures. The solid-solution strengthening was operative for high temperature deformation at similar to 10(3) s(-1).TRANS TECH PUBLICATIONS LTD, 2007, ENGINEERING PLASTICITY AND ITS APPLICATIONS FROM NANOSCALE TO MACROSCALE, PTS 1 AND 2, 340-341, 107 - +, English[Refereed]International conference proceedings
- The fracture toughness in extruded Mg-Zn binary alloys with the same grain size and texture increased with higher solute concentration and was proportional to the one-third power of the concentration of zinc. This toughening was related to solid-solution strengthening. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Oct. 2006, SCRIPTA MATERIALIA, 55(7) (7), 593 - 596, English, International magazine[Refereed]Scientific journal
- The effect of texture on fracture toughness was investigated for a wrought AZ31 magnesium alloy, which was a commercial rolled plate having strong basal texture. The value of plane-strain fracture toughness, K-IC = 17.6-20.7 MPam(1/2), was obtained from the stretched zone (SZ) analysis. The value of K-IC varied with the distribution of basal texture; the sample having a pre-crack normal to rolled direction was the highest value of K-IC in all present samples. The crack-tip having parallel to the rolled direction was easily able to propagate and/or proceed with applied load. (c) 2005 Elsevier B.V. All rights reserved.ELSEVIER SCIENCE SA, Jun. 2006, JOURNAL OF ALLOYS AND COMPOUNDS, 417(1-2) (1-2), 209 - 213, English[Refereed]Scientific journal
- 生体吸収性金属材料の疑似体液中での耐食性評価の試みステントなどのデバイスは、周辺組織が修復された後には速やかに除去されるもしくは消失することが望ましい。そこで、生体内で分解・吸収される生体吸収性金属材料の開発が求められている。われわれの研究グループでは、低濃度の元素を添加した生体吸収性マグネシウム合金の開発を行っている。一方、生体内での金属材料の分解・吸収速度や安全性の評価法は確立されていない。そこで、生体外での簡便な分解速度の評価法として分極試験の適用を目指している。本研究では、これまでに開発した低濃度のAl、Y、Dyなどを含むマグネシウム二元合金を用い、溶液組成が合金の分極挙動に及ぼす影響について検討した。May 2006, 材料と環境2006講演集, 291 - 294, JapaneseInternational conference proceedings
- May 2006, Scripta Materialia, 54(10) (10), 1827 - 1828, English[Refereed]Scientific journal
- Examination of fracture toughness has been performed a commercial Mg-Zn-Zr alloy, ZK60, with fine strengthening particles. The commercial alloy was extruded at 633 K, and then heat treated at specific conditions. The microstructures were equi-axed grains. and average grain size and precipitate size were 11.6 mu m and 50-150 urn, respectively. The yield strength and elongation-to-failure were 225 MPa and 17.0%. The plane-strain fracture toughness, K-IC, was estimated to be 20.6 MPam(1/2) in stretched zone analysis. From ductile fracture model. all the finer particles did not affect the void formation. The precipitates having a large diameter, more than 100 urn, were supposed to be the origin of void formation.JAPAN INST METALS, Apr. 2006, MATERIALS TRANSACTIONS, 47(4) (4), 995 - 998, English, Domestic magazine[Refereed]Scientific journal
- Fracture toughness and deformation structures have been investigated using an AZ31 magnesium alloy processed by equal-channel-angular extrusion (ECAE). The ECAE-processed alloy (as-ECAE) was annealed at 573 K for 24 h ( annealed-ECAE). The average grain sizes of as-ECAE and annealed-ECAE alloys were 4.0 and 16.3 mu m, respectively. The plane-strain fracture toughness K-IC, obtained by stretched-zone analysis in as-ECAE and annealed-ECAE, were estimated to be 27.3 and 23.5 MPa/m(1/2), respectively. From optical microstructural observations in samples after the fracture-toughness tests, deformation twins were observed in annealed-ECAE. No deformation twins were observed in as-ECAE. In addition, dislocations on basal planes, as well as on non-basal planes, were activated in as-ECAE. It is concluded that the enhancement of the fracture toughness in the fine-grain structure was related to a reduction of deformation twins and dislocation movement in non-basal planes.TAYLOR & FRANCIS LTD, Mar. 2006, PHILOSOPHICAL MAGAZINE LETTERS, 86(3) (3), 195 - 204, English, International magazine[Refereed]Scientific journal
- The fracture toughness in Mg-Al-Zn alloy was improved by the equal-channel-angular extrusion process. The improvement was the result of it large plastic zone size, which was sensitive to elongation-to-failure and,I high strain hardening exponent, created ahead of the fracture pre-crack, because of the modified distribution of the basal texture. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Feb. 2006, SCRIPTA MATERIALIA, 54(4) (4), 633 - 638, English, International magazine[Refereed]Scientific journal
- Compressive behavior of a closed-cell aluminium has been investigated at high strain rates, utilizing AZ31 magnesium alloy bars as compared to maraging steel bars, to estimate the validity of the mechanical response of the foam. Apparent strain rate sensitivity of plateau stress has been observed and strain hardening occurred during compression at the dynamic strain rate. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Feb. 2006, SCRIPTA MATERIALIA, 54(4) (4), 533 - 537, English[Refereed]Scientific journal
- Differential speed rolling (DSR) was applied to the AZ31 magnesium alloy, intended to modify the texture and thus to enhance the room temperature ductility. Especially, effect of DSR temperature on resulting room temperature tensile properties and texture was investigated at a fixed rolling speed ratio of 1.1. The strength was not affected by the rolling temperature: the yield strength and the ultimate tensile strength for all materials processed by DSR were approximately 240 and 290 MPa, respectively. On the other hand, elongation-to-failure increased from 13.6 to 18.5% with decreasing rolling temperature from 573 to 473 K. In addition, the material processed by DSR exhibited approximately 1.5 times larger ductility than that by conventional symmetric rolling at a rolling temperature of 473 K. The DSR at 523 and 473 K resulted in the basal plane orientation at the position inclined by similar to 5 and 8 degrees from the normal direction toward the rolling direction, respectively. It was suggested that the higher ductility of the material processed at lower temperatures is attributed to the slight change in the basal plane orientation and/or reduction in grain size. (c) 2006 Elsevier B.V. All rights reserved.ELSEVIER SCIENCE SA, Feb. 2006, JOURNAL OF MATERIALS PROCESSING TECHNOLOGY, 182(1-3) (1-3), 644 - 647, English[Refereed]Scientific journal
- Effect of grain size and texture on fracute toughness in magnesim and magnesium-aluminum-zinc (AZ31) alloyThe effect of texture and grain size on fracture toughness was investigated by using magnesium alloy (Mg-3Al-1Zn) and pure magnesium. The materials were produced by hot extrusion to obtain (i) strong basal texture and (ii) different grain structure. Tensile strength and ductility were increased with grain refinement. Fracture toughness was higher for samples which were cut parallel to the extrusion direction than those cut normal to the extrusion direction due to different surface energy on basal and non-basal planes. In addition, the fracture toughness was enhanced with grain refinement without relation to materials. Controlling texture and/or grain refinement were show to be effective methods to improve the fracture toughness in magnesium and magnesium alloy.MINERALS, METALS & MATERIALS SOC, 2006, MAGNESIUM TECHNOLOGY 2006, PROCEEDINGS, 395 - +, English[Refereed]International conference proceedings
- Fracture toughness in ultra fine-grained magnesium alloyThe fracture toughness was investigated using in an extruded AZ31 magnesium alloy with an initial grain size of 1.0 mu m. Since the small scale yielding condition was not satisfied with the present thin thickness, the value of plane-strain fracture toughness, K-IC = 27.9 MPam(1/2), was measured from Stretched Zone analysis. The values of K-IC in AZ31 magnesium alloys were dependent on the grain size. The grain refinement was found to be one of the improvement methods for fracture toughness in magnesium alloy.TRANS TECH PUBLICATIONS LTD, 2006, NANOMATERIALS BY SEVERE PLASTIC DEFORMATION, 503-504, 155 - 160, English[Refereed]Scientific journal
- The fracture toughness of extruded pure magnesium increased with grain refinement due to the effect of the plastic zone, which is a sensitive factor related to the mechanical properties of yield strength, elongation-to-failure and strain hardening exponent. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Nov. 2005, SCRIPTA MATERIALIA, 53(9) (9), 1059 - 1064, English, International magazine[Refereed]Scientific journal
- Oct. 2005, Proc. of the 1st Asian Symposium on Magnesium Alloys, 85 - 88, English, International magazineEnhancement of Fracture toughness in AZ31 magnesium alloy through controlling grain structureInternational conference proceedings
- Fully dense bulk nanocrystalline Fe-0.8wt.%C alloy was synthesized by spark plasma sintering of mechanically milled Fe-C nanocrystalline powder. The sample sintered at 600 degrees C was composed of 150 nm ferrite grains with nanocrystalline cementite dispersoids, whose compression yield strength, fracture strength, and plastic strain were 1900 MPa, 3500 MPa, and 40% respectively. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Oct. 2005, SCRIPTA MATERIALIA, 53(7) (7), 863 - 868, English, International magazine[Refereed]Scientific journal
- The precipitation process of an Mg-0.3Ca-0.3Zn (in at.%) alloy has been investigated by transmission electron microscopy and the chemical compositions of the precipitates have been characterized by a three-dimensional atom probe. The reason for the pronounced precipitation hardening in the alloy compared to the Mg-0.3Ca alloy is discussed. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Sep. 2005, SCRIPTA MATERIALIA, 53(6) (6), 675 - 679, English, International magazine[Refereed]Scientific journal
- For a commercially extruded AZ31 alloy, the basal plane in most grains was distributed parallel to the extruded direction. The sample having a pre-crack normal to the basal plane had a higher value of plane-strain fracture toughness than that having a pre-crack parallel to the basal plane. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Sep. 2005, SCRIPTA MATERIALIA, 53(5) (5), 541 - 545, English[Refereed]Scientific journal
- Jun. 2005, Porous Metals and Mtal Foaming Technology, 539 - 542, English, International magazineEnergy Absorption of Cellular Aluminum Allys at High Strain RatesInternational conference proceedings
- A new computational mechanics model is proposed to describe the compression response of two-dimensional cellular materials with consideration of microstructural development. In this modeling, processing conditions to fabricate cellular materials Lire taken into account as a cell-growth mechanism. Representative volume elements (RVE) are generated by the phase-field model. Numerical simulations of compressive deformation are performed by finite element analysis for the selected RVE. The cell size distribution especially affects on the limit stress and the densification process.JAPAN INST METALS, Jun. 2005, MATERIALS TRANSACTIONS, 46(6) (6), 1221 - 1229, English[Refereed]Scientific journal
- The microstructures of Cu60Zr30Ti10 metallic glass prepared by injection casting and melt -spinning have been investigated by transmission electron microscopy (TEM), and three dimensional atom probe ODAP). The as-cast 2 nun diameter rod sample contained Cu rich nanocrystals in the amorphous matrix. while the melt-spun ribbon was fully amorphous, The composition of the Cu-rich nanocrystals was around Cu70Zr10Ti5 with the fee structure (lattice parameter = 0.37 run). which is a metastable Cu phase supersaturated with Zr and Ti. Annealing the as-east rod at 713 K (T-g) for 10 min led to a decrease in compressive plastic strain from 1.8 to 0.6 accompanied by an increase in the volume freaction of the Cu-rich crystal.JAPAN INST METALS, Jun. 2005, MATERIALS TRANSACTIONS, 46(6) (6), 1264 - 1270, English, International magazine[Refereed]Scientific journal
- High-temperature compressive properties at a high strain rate of 10(3) s(-1) were examined in solution treated AZ91 magnesium alloy. Analysis of the flow behavior and microstructural observations indicated that the deformation at high strain rates of similar to 10(3) s(-1) proceeds by 14 conventional plastic flow of dislocation glide and twinning even at elevated temperatures. (c) 2005 Elsevier B.V. All rights reserved.ELSEVIER SCIENCE BV, May 2005, MATERIALS LETTERS, 59(12) (12), 1511 - 1515, English[Refereed]Scientific journal
- Symmetric and asymmetric deformation behavior is theoretically analyzed for regularly cell-structured materials. On the basis of the elasto-plastic formulation by the finite element method, the computational model is constructed in order to understand the effect of various parameters on the deformation mode transition. Symmetric deformation changes itself to asymmetric deformation when increasing the nominal compressive strain. Effects of the relative density, the contact length, and the adhesive bonding on this mode transition are investigated under quasi-static in-plane compression. Besides the relative density, the contact length to thickness ratio (r(c)/t) plays an important role on the symmetric-asymmetric deformation transition. The intercell stress transfer also has an influence on the stability of the cell-structure during crushing. The theoretical prediction is compared with the experimental results in (Part 1) to quantitatively discuss the compressive deformation of regularly cell-structured materials. (C) 2004 Elsevier Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Apr. 2005, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, 42(8) (8), 2211 - 2224, English[Refereed]Scientific journal
- Quasi-static compressive response of regularly cell-structured materials is experimentally studied for various relative density, cell contact length and intercell bonding state. Each cell in this specimen is aligned in a hexagonal closed-pack array. The contact length as well as cell wall thickness of regularly cell-structured materials, plays an important role on the deformation mode transition. The deformation changes itself from symmetric to asymmetric pattern when increasing the contact length to cell-wall thickness ratio. Higher level of collapsing stress is observed in symmetric deformation due to the nearly uniform stress transfer during compression. Work hardening behavior is promoted with increasing the relative density or decreasing the contact length. Asymmetric deformation is associated with a nearly constant collapsing stress. The plateau collapsing stress state is caused by the localized deformation of cell-row in a narrow band of specimen. Liquid epoxy resin between cell walls also influences on the deformation mode of cell-structured materials. In the present study, the experimental observation is presented first (Part 1), followed by the theoretical analysis and comparison between experimental and analytical results in (Part 2). (C) 2004 Elsevier Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Apr. 2005, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, 42(8) (8), 2199 - 2210, English[Refereed]Scientific journal
- High temperature compressive properties in AZ31 magnesium alloy were examined over a wide strain rate range from 10(-3) to 10(3) s(-1). It was suggested that the dominant deformation mechanism in the low strain rate range below 10(-1) s(-1) was dislocation creep controlled by pipe diffusion at low temperatures, and by lattice diffusion at high temperatures. On the other hand, analysis of the flow behavior and microstructural observations indicated that the deformation at high strain rates of similar to 10(3) s(-1) proceeds by conventional plastic flow of dislocation glide and twinning even at elevated temperatures. (C) 2005 Springer Science + Business Media, Inc.SPRINGER, Apr. 2005, JOURNAL OF MATERIALS SCIENCE, 40(7) (7), 1577 - 1582, English[Refereed]Scientific journal
- Dislocation creep behavior of AZ31 magnesium alloy with different texture and grain sizes was examined. At a strain rate of around 10(-3) s(-1). it is suggested that the flow stress is dominated by the texture softening and softening, due to grain boundary sliding at 523 and 673 K. respectively. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Mar. 2005, SCRIPTA MATERIALIA, 52(6) (6), 449 - 454, English[Refereed]Scientific journal
- The present paper is aiming to examine the tribological properties of Mg-Al-Zn alloy, AZ91. Especially, effect of precipitate morphology on tribological properties, such as wear rate and coefficient of friction, was systematically investigated for cast material. Accelerated aging treatment was carried out at temperatures ranging from 150°C to 300°C for 100 hours after solution-treatment at 413°C for 48 hours. A pin-on-disc wear testing machine was used to evaluate tribological properties at room temperature under dry condition, in which an SUJ2 steel disc was used as the counterface. Vickers hardness after the accelerated aging treatment of AZ91 alloy was about HV80 to HV90. Since the hardness of AZ91 was approximately eight times smaller than that of SUJ2, the dominant wear mechanism was assumed to be abrasive wear. However, the composition of wear debris, rise in temperature during wear tests, change in hardness near the wear surface and macroscopic flow of specimens indicated that the adhesive wear also contributed to the wear properties when the size of precipitates were small or the spacing between precipitates were large. It was suggested that the contribution of adhesive wear increased the wear rate and the coefficient of friction. It was concluded that the wear resistance of AZ91 alloy under dry condition would be improved by densely dispersing the precipitates with sufficiently large size, e.g., precipitates with its length of about 1mm that were observed in materials aged at 200°C.Society of Materials Science Japan, 2005, Zairyo/Journal of the Society of Materials Science, Japan, 54(1) (1), 90 - 96, Japanese[Refereed]Scientific journal
- The present paper is aiming to examine the tribological properties of Mg-Al-Zn alloy, AZ91. Especially, effect of precipitate morphology on tribological properties, such as wear rate and coefficient of friction, was systematically investigated for cast material. Accelerated aging treatment was carried out at temperatures ranging from 150°C to 300°C for 100 hours after solution-treatment at 413°C for 48 hours. A pin-on-disc wear testing machine was used to evaluate tribological properties at room temperature under dry condition, in which an SUJ2 steel disc was used as the counterface. Vickers hardness after the accelerated aging treatment of AZ91 alloy was about HV80 to HV90. Since the hardness of AZ91 was approximately eight times smaller than that of SUJ2, the dominant wear mechanism was assumed to be abrasive wear. However, the composition of wear debris, rise in temperature during wear tests, change in hardness near the wear surface and macroscopic flow of specimens indicated that the adhesive wear also contributed to the wear properties when the size of precipitates were small or the spacing between precipitates were large. It was suggested that the contribution of adhesive wear increased the wear rate and the coefficient of friction. It was concluded that the wear resistance of AZ91 alloy under dry condition would be improved by densely dispersing the precipitates with sufficiently large size, e.g., precipitates with its length of about 1mm that were observed in materials aged at 200°C.Society of Materials Science Japan, 2005, Zairyo/Journal of the Society of Materials Science, Japan, 54(1) (1), 90 - 96, Japanese, Domestic magazine[Refereed]Scientific journal
- The applicability of high-strain-rate superplasticity for forming magnesium parts, especially structural component with a boss on a plate designed with the aim of producing mobile electric appliances, was examined. The required microstructure and grain refinement process for target forming was examined prior to the forming trials. Following the examination of the processing design, the high-strain-rate superplastic AZ91 magnesium alloy with a required grain size less than 3.2 mum was produced by hot extrusion under the condition that the Zener-Hollomon parameter was 3 x 10(12) s(-1). It was experimentally confirmed that a boss with a height greater than 5 mm, which is a requirement for electric appliances, could be formed within 10 s even at a low temperature of 523 K using this high-strain-rate superplastic magnesium alloy. Basic knowledge related to the formation of three-dimensionally shaped magnesium parts by utilizing high-strain-rate superplasticity was obtained.JAPAN INST METALS, Aug. 2004, MATERIALS TRANSACTIONS, 45(8) (8), 2531 - 2536, English[Refereed]Scientific journal
- Dynamic elastic properties and damping properties from room temperature to 673 K were examined in AZ31 magnesium alloy. It was suggested that these properties at elevated temperatures were influenced by the occurrence of grain boundary sliding, which is dependent on the grain size and alloy additions. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Aug. 2004, SCRIPTA MATERIALIA, 51(4) (4), 291 - 295, English[Refereed]Scientific journal
- The superplastic behavior of fine-grained metals is well described by the deformation model in which grain boundary sliding (GBS) is accommodated by slip. This slip accommodation process involves the sequential steps of glide and climb, with climb assumed to be the rate-controlling process. The climb distance during GBS is often considered to be on the order of grain size in the conventional theoretical models. However, these models have not been able to predict quantitatively the strain rates actually observed in fine-grained superplastic materials. Therefore, the deformation model was reviewed by comparing the theoretical and phenomenological equations in order to accurately understand the mechanism of the accommodation process. The analyses revealed that the climb process is governed by the effective diffusivity. The climb distance through the grain boundary is of the order of the grain size, and that through the lattice close to the dislocation core size was quantitatively in agreement with the phenomenological relation.JAPAN INST METALS, Aug. 2004, MATERIALS TRANSACTIONS, 45(8) (8), 2497 - 2502, English[Refereed]Scientific journal
- Plastic formability in the secondary processing of an AZ31 magnesium alloy was investigated using fine-grained and relatively coarse-grained materials. respectively. To produce components for mobile electric appliances, boss formability was examined at a relatively low temperature of 523 K. The boss with a height of 14mm was successfully formed in fine-grained material under a nominal forming pressure of 582 MPa in 5 s. Analysis of the boss forming revealed that the forming occurred under the high-strain-rate superplastic condition. The grain size in the boss region was slightly coarsened, probably as a result of strain-induced grain growth, which is a widespread property of superplastic flow. On the other hand, even in the coarse-grained material, a relatively high boss height of 5 mm was obtained under the same forming condition. After the boss forming. grain refinement was observed in the coarse-grained material. It was suggested that the coarse-grained materials exhibited relatively high formability because of dynamic recrystallization. It was concluded that plastic forming concomitant with grain growth was more effective than that concomitant with grain refinement in AZ31 magnesium alloy. An empirical equation to perform plastic forming under the condition concomitant with grain growth was developed.JAPAN INST METALS, Jul. 2004, MATERIALS TRANSACTIONS, 45(7) (7), 2377 - 2382, English[Refereed]Scientific journal
- KLUWER ACADEMIC PUBL, Feb. 2004, JOURNAL OF MATERIALS SCIENCE, 39(4) (4), 1477 - 1480, English[Refereed]Scientific journal
- 大阪工研協会, 2004, 科学と工業, 78(9) (9), 475 - 480, JapaneseAZ31マグネシウム合金の高温圧縮特性[Refereed]Scientific journal
- Experimental prediction of deformation mechanism after continuous dynamic recrystallization in superplastic P/M7475The deformation mechanism in high-strain-rate superplastic P/M7475 before and after continuous dynamic recrystallization (CDRX) was investigated. The recrystallization process in P/M7475 differed from that in conventional superplastic material, I/M7475. In I/M7475, the fine-grained microstructure was obtained by static recrystallization before deformation. On the other hand, the substructure in P/M7475 evolved into fine grains during deformation by CDRX. The percentage of high-angle and random boundaries was low at an initial stage of deformation. However, it increased with strain in P/M7475. The microstructural change in P/M7475 influenced a deformation mechanism and affected grain boundary sliding (GBS). The ratio of contribution of GBS to total elongation was low at an early stage of deformation in P/M7475. However, it increased with deformation progressed. It is suggested that the deformation behavior in P/M7475 changed from dislocation creep to superplasticity as the dominant deformation mechanism changed to GBS. The activation energy for superplastic flow in P/M7475 was close to that for lattice self-diffusion in pure aluminum. It is therefore concluded that the dominant deformation mechanism after CDRX in P/M7475 is GBS accommodated by dislocation movement controlled by lattice self-diffusion, similar to that in I/M7475. (C) 2003 Kluwer Academic Publishers.KLUWER ACADEMIC PUBL, Oct. 2003, JOURNAL OF MATERIALS SCIENCE, 38(19) (19), 3925 - 3932, English[Refereed]Scientific journal
- Three different aluminum-iron alloys were produced by electron-beam deposition with the iron content in the range 1.15-1.71 at.%. These alloys did not contain any identifiable iron-bearing particles, and exhibited full density with high-angle grain boundaries in the micrometer range, and a sub-grain size typically smaller than 100 nm. The tensile deformation characteristics of the alloys were examined at a dynamic strain rate of 1.1 x 10(3) s(-1) and a quasi-static strain rate of I X 10(-3) s(-1) at room temperature. The alloy containing 1.7% Fe exhibited an abnormally high tensile strength of about 950 MPa with a ductility of up to 6%. Detailed atomic resolution imaging of the structure of the alloys has been performed along with an examination of their fracture surface features. The fracture surfaces of the alloys showed ductile dimples which typically spanned five to 10 times the sub-grain diameter. It is postulated that the nano-scale sub-grains of the alloy impart high strength, while the structure associated with high-angle boundaries provides reasonable ductility. Possible mechanisms responsible for the high strength in the present Al-Fe alloys are explored. The present results are also examined in conjunction with a comprehensive survey of available results on the strain-rate sensitivity of tensile yield strength and ductility in microcrystalline, sub-microcrystalline and nanocrystalline metals and alloys, and on the solid-solution strengthening of aluminum alloys. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Aug. 2003, Acta Materialia, 51(14) (14), 4197 - 4208, English, International magazine[Refereed]Scientific journal
- Jul. 2003, Material Science Forum, 465-466, 13 - 20, English, International magazineDynamic deformation of regularly Cell-Structured MaterialsInternational conference proceedings
- Jul. 2003, 426-432, 605 - 610, English, International magazineThe effect of temperature and flow stress for climb-controlled dislocation creep in magnesium alloyInternational conference proceedings
- Diffusion bonding behavior of fine-grained magnesium alloy with the average grain size of 8.5 mum, that was processed by hot rolling, was examined. The material behaved in a superplastic manner at. temperatures of 523 and 573 K, and successfully diffusion bonded at these temperatures. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, May 2003, SCRIPTA MATERIALIA, 48(9) (9), 1249 - 1254, English[Refereed]Scientific journal
- Fine-grained alloys of Mg-3Al-1Zn-0.2Mn in wt.% (AZ31B) were obtained by an equal-channel angular extrusion technique and subsequent annealing at elevated temperatures. Tensile tests were performed at room temperature at a strain rate of 1x10(-3) s(-1). The alloys exhibited an apparent steady-state deformation region and a large tensile elongation of 47%. The deformed microstructure at an elongation of 2% indicated substantial cross-slip to non-basal planes induced by plastic compatibility stress associated with grain boundaries. The non-basal segment of dislocations was found to consist of 40% of the total dislocation density at a yield anisotropy factor of only 1.1 instead of an expected value of 100 obtained from single-crystal experiments. The deformed microstructure at an elongation of 16% indicated recovered regions within twins as well as untwinned matrices. These results indicate that dynamic recovery can occur in Mg alloys at room temperature. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Apr. 2003, ACTA MATERIALIA, 51(7) (7), 2055 - 2065, English[Refereed]Scientific journal
- Fine-grained WZ73 magnesium alloy with the grain size of 1.6mum was produced by Equal-Channel-Angular Extrusion. The material exhibited tensile yield strength of 293 MPa, tensile strength of 350 MPa. and relatively large elongation of 18% at room temperature. The yield strength was almost unchanged up to 473 K. In addition, large superplastic elongation of over 300% was obtained at a temperature of 673 K.JAPAN INST METALS, Apr. 2003, MATERIALS TRANSACTIONS, 44(4) (4), 463 - 467, English[Refereed]Scientific journal
- The materials processing, consisted of a four step process of solution treatment, pre-strain, overaging and hot working, was developed for attaining structural stability at high temperatures in a commercial Mg-Zn-Zr alloy, ZK60. The grain size of the material processed by this schedule was refined to 2.5 mum, and the material behaved in a superplastic manner at 548 K and at a strain rate of 1 x 10(-2) s(-1) owing to the grain size stability at this temperature. From the analysis of the chemical composition of precipitates, it was suggested that the phase Mg-7(Zn,Zr)(3), which was not observed in material without pre-strain, was effective in pinning the grain boundaries at high temperatures.JAPAN INST METALS, Apr. 2003, MATERIALS TRANSACTIONS, 44(4) (4), 775 - 781, English[Refereed]Scientific journal
- High strain rate superplasticity in aluminum alloys and review of its current commercial applicationsSuperplasticity is a viable technique to fabricate a hard-to-form material into a complex shape. The details have been investigated in the past two decades. The limitation for application to commercial mass-production is the low optimum forming speed and/or the material cost. One of the innovations in superplasticity is especially noted to establish the high strain rate superplasticity (HSRS) in early 1990s. Detailed study of the phenomenological aspects in HSRS revealed its deformation mechanism and pointed out the importance of the presence of accommodation helpers such as discontinuous liquid phase with grain boundary sliding. Recently, HSRS has been applied for net-shape forging of engine piston with rapidly solidified At-Si system alloy powders. Another commercial application of HSRS is gas-pressure forming of Al-Mg system alloys to produce large-scale components such as a hard-top roof of an automobile. In this study, we discuss the phenomenological deformation mechanism of HSRS in aluminum alloys and review the current applications in Japan.MINERALS, METALS & MATERIALS SOC, 2003, HOT DEFORMATION OF ALUMINUM ALLOYS III, 199 - 210, English[Refereed]International conference proceedings
- Anomalous activity of nonbasal dislocations in AZ31 Mg alloys at room temperatureAZ31 Mg alloy samples were extruded by an equal channel angular extrusion (ECAE) process and subsequently annealed to obtain fine-grained material with a low dislocation density. Tensile tests at room temperature exhibited an apparent steady-state deformation region and a large tensile elongation of 47%. The deformed microstructure at an elongation of 2% indicated a substantial cross-slip to nonbasal planes possibly induced by grain-boundary compatibility effects. The nonbasal segments of dislocations were found to consist of 40% of the total dislocation density at a yield anisotropy factor of only 1.1 instead of an expected value of 100 from single-crystal experiments.TRANS TECH PUBLICATIONS LTD, 2003, MAGNESIUM ALLOYS 2003, PTS 1 AND 2, 419-4, 231 - 236, English[Refereed]Scientific journal
- Superplastic behavior of an ECAE processed ZK60 magnesium alloySuperplastic behavior of ECAE processed ZK60 was examined at a temperature of 473 K. The grains were equiaxed with a fine grain size of 1.4 mum at the tensile testing temperature. It was found that this material exhibited superplasticity even at a low temperature of 473 K. The maximum elongation of 1083 % was obtained at 1x10(-5) s(-1). The apparent strain rate sensitivity value exhibited about 0.5 in the low strain rate range and remained unchanged during deformation, indicative of no change in grain boundary structure. The normalized plot indicated that the present material behaved almost identically to those with equilibrium grain boundaries. It was suggested that the present ECAE processed ZK60 alloy have the equilibrium grain boundaries at the superplastic temperature in contrast to typical materials processed by severe plastic deformation.TRANS TECH PUBLICATIONS LTD, 2003, MAGNESIUM ALLOYS 2003, PTS 1 AND 2, 419-4, 557 - 562, English[Refereed]Scientific journal
- Diffusion bonding on superplastic-aluminum and -magnesium alloysThe superplastic characteristics and diffusion bonding behaviors were investigated in commercial 7475 aluminum alloy and AZ31 magnesium alloy sheets. In this study, the presently used materials behaved in a superplastic manner at similar to773 K (7475Al) and similar to523 K (AZ31). Then, by the theoretical relationship between pressure and time, these materials were successfully diffusion bonded at the superplastic temperatures. The bonding strength was more than 65 MPa. The experimental bonding conditions in high quality joining, times and pressures, were good agreed with prediction analysis.TRANS TECH PUBLICATIONS LTD, 2003, SUPERPLASTICITY IN ADVANCED MATERIALS, 447-4, 527 - 532, English[Refereed]Scientific journal
- Guide for enhancement of room temperature ductility in Mg alloys at high strain ratesPolycrystalline magnesium are generally fractured intergranularly under dynamic loading, and exhibits limited ductility owing to its HCP structure. In this study, improvement of tensile mechanical properties under dynamic loading has been demonstrated for two commercial magnesium alloys, ZK60 and AZ31. It was found that the strength and ductility of magnesium alloys were enhanced by refining the grain structure. Further enhancement of ductility can be achieved by a simple shear through equal-channel-angular-extrusion (ECAE) process. A commercial AZ31 alloy was subjected to ECAE followed by annealing to develop a different texture compared with the directly-extruded alloy. During the dynamic tensile test, elongation-to-failure was more than twice higher than that of the directly-extruded alloy. It has been demonstrated that, for commercial magnesium alloys, the improvement of strength-ductility balance can be achieved by controlling the grain structure.TRANS TECH PUBLICATIONS LTD, 2003, MAGNESIUM ALLOYS 2003, PTS 1 AND 2, 419-4, 171 - 176, English[Refereed]Scientific journal
- Constitutive equation for superplastic flow in light metallic materialsTwo problems in fine-grained superplasticity, whose details are indispensable to understand the nature of superplastic flow, are discussed using light metallic materials. First, the effect of temperature and grain size on superplastic flow was investigated for the inclusive understanding of the dominant diffusion process. The effective diffusion coefficient for superplastic flow involving the lattice diffusion coefficient and the grain boundary diffusion coefficient were precisely determined. It was found that the superplastic flow in pseudo-single phase aluminum and magnesium alloys is best described by a single constitutive equation using the effective diffusion coefficient. Second, the effect of intergranular and intragranular particles was examined. Two critical strain rates for the elimination of the effect of these particles were developed respectively by considering the suitable deformation models. The constitutive equation for superplastic flow under the influence of intragranular particles was proposed.TRANS TECH PUBLICATIONS LTD, 2003, SUPERPLASTICITY IN ADVANCED MATERIALS, 447-4, 91 - 96, English[Refereed]Scientific journal
- In this study, dry wear tests were carried out to investigate the friction and wear properties of magnesium alloys by using a pin-on-disk wear testing machine at room temperature. Mg-Al-Zn (AZ31, AZ61 and AZ91) alloys were used as test specimens. Mg-Al-Zn alloys fabricated by extrusion method of processing were tested. Furthermore, two kinds of specimens were prepared by heat treatment : one is solution-treated at 413°C for 48 hours and the other is aging-treated at 150°C for 100 hours after solution treatment. SUJ2 was used as a disk material. Wear rates and coefficients of friction were investigated under constant conditions. The main results obtained were as follows. (1) The coefficient of friction decreased with the increment of aluminum content. In addition, it decreased with aging treatment. (2) The wear resistance of solution-treated Mg-Al-Zn alloys was independent of aluminum content. (3) The wear resistance of an aging-treated AZ61 alloy was same compared with a solution-treated one. On the other hand, the wear resistance of an aging-treated AZ91 alloy deteriorated compared with a solution-treated one. Consequently, the wear resistance of aging-treated Mg-Al-Zn alloys was dependent on aluminum content. It was confirmed that precipitated particles had an influence upon the wear resistance of aging-treated Mg-Al-Zn alloys.Society of Materials Science Japan, 2003, Zairyo/Journal of the Society of Materials Science, Japan, 52(6) (6), 702 - 708, Japanese[Refereed]Scientific journal
- The influence of grain structure on the formability of an AZ31 magnesium alloy rolled sheet was examined by deep drawing for five materials. Each sheet was formed at a drawing speed of 60 mm/min into a cup, which had a square bottom of 50 × 50 mm2, and a maximum depth of 18 mm. It was found that the materials with grain sizes of ≤ 10 μm could be formed to the maximum depth without cracking, even at the lowest temperature investigated (423 K). Tensile mechanical testing of the rolled sheets revealed that these materials with high drawability also had a high Lankford value at the forming temperature. In addition, the surface roughness at the corners of the deep drawn cup was somewhat reduced in the fine - grained materials. The present results suggest that a magnesium alloy sheet with a fine-grain structure has the potential for deep drawing at relatively low temperatures.Japan Institute of Light Metals, 2003, Keikinzoku/Journal of Japan Institute of Light Metals, 53(2) (2), 50 - 54, Japanese[Refereed]Scientific journal
- Mechanical deformation of Pd40Ni40P20 was characterized in compression over a wide strain rate range (3.3 x 10(-5) to 2 x 10(3) s(-1)) at room temperature. The compression sample fractured with a shear plane inclined similar to42 degree with respect to the loading axis, in contrast to similar to56 degree for the case of tension. This suggests the yielding of the material deviates from the classical von Mises yield criterion, but follows the Mohr-Coulomb yield criterion. Fracture stress as well as strain was found to decrease with increasing applied strain rate. The compressive stress (similar to1.74 GPa) was also found to be higher than the tensile fracture stress at a quasi-static strain rate. Close examination of the stress-strain curves revealed that localized shear might have occurred at a compressive stress of about similar to1.4 GPa, much lower than the "apparent" yield stress of 1.74 GPa. However, the stress of 1.4 GPa for shear band initiation is almost the same as the fracture stress measured at a dynamic strain rate of 5 x 10(2) s(-1). These results suggested that the fracture of a bulk metallic glass is sensitive to the applied loading rate. (C) 2002 Elsevier Science Ltd. All rights reserved.ELSEVIER SCI LTD, Nov. 2002, INTERMETALLICS, 10(11-12) (11-12), 1071 - 1077, English, International magazine[Refereed]Scientific journal
- In the present paper, open-celled AA6101-T6 aluminum foams, Duocel, with virtually the same relative density of 0.09 were tested at both a dynamic strain rate of 1.2 x 10(3) s(-1) and quasi-static strain rate of 1 x 10(-3) s(-1) in compression at room temperature. These Duocel foams have different cell sizes (10, 20, and 40 ppi) but similar cell morphology and microstructure. The mechanical strength and energy absorption of these foams were characterized as a function of strain rate and cell morphology. Experimental results indicated that the mechanical responses of Duocel foams were independent of the cell size and strain rate. Similar tests were also conducted with fully dense AA6101-T6 aluminum alloy and the results were compared with those obtained from the foam materials.JAPAN INST METALS, Oct. 2002, MATERIALS TRANSACTIONS, 43(10) (10), 2548 - 2553, English[Refereed]Scientific journal
- Cellular metallic foams have interesting potential for impact energy absorption. In this study, modification of solid in a closed-cell Al-Ca-Ti foam was carried out, adding the strengthening elements of Zn and Mg for enhancement of energy absorption. Samples with dimensions of 100 x 100 x 100 mm(3) were examined at a dynamic strain rate corresponding to the crashing speed of automobiles. The compression deformation behavior of the Al-7Zn-0.5Mg-1.5Ca-1.5Ti (by mass%) foam was found to be different from that of the original Al-1.5Ca-1.5Ti (by mass%) foam. Plateau stress could be effectively enhanced with the combined effect of strengthening solid alloy and increasing the aspect ratio of cell wall thickness against cell edge length. Plateau stress of the modified foam was independent of strain rate, while the stress in Al-Ca-Ti foam exhibited a certain strain rate sensitivity. Plateau strain, designated as the strain where the compressive stress reached 1.5 times higher value than the yield stress, was also enhanced by the present modification. As a result, absorption energy was also effectively enhanced but was independent of strain rate as a result of the present modification.JAPAN INST METALS, Jul. 2002, MATERIALS TRANSACTIONS, 43(7) (7), 1778 - 1781, English[Refereed]Scientific journal
- Fine-grained ZK60 magnesium alloy with the grain size of 1.4 mum was processed by equal-channel-angular extrusion. The material exhibited low temperature superplasticity. The normalized plot suggested that the present material had equilibrium grain boundaries at the superplastic temperature in contrast to typical materials processed by severe plastic deformation. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Jun. 2002, SCRIPTA MATERIALIA, 46(12) (12), 851 - 856, English[Refereed]Scientific journal
- Feb. 2002, Magnesium Technology 2002, 137 - 140, English, International magazineIMPROVEMENT OF STRENGTH-DUCTILITY BALANCE IN COMMERCIAL MAGNESIUM ALLOYS UNDER DYNAMIC LOADINGInternational conference proceedings
- Study on the superplastic deformation mechanism using magnesium-based materialsInvestigations to develop correct models for understanding the superplastic flow mechanism are very much in order. In the present paper, two problems in the fine-grained superplasticity, whose details are indispensable to understand the nature of superplastic flow, were discussed using magnesium-based materials. First, the effect of temperature and grain size on superplastic flow was investigated for the inclusive understanding of the dominant diffusion process. We precisely determined the effective diffusion coefficient for superplastic flow involving lattice diffusion coefficient and grain boundary diffusion coefficient. A phenomenological constitutive equation for superplastic flow using the effective diffusion coefficient was developed. Second, the effect of intergranular and intragranular particles was examined. Two critical strain rates for the elimination of the effect of these particles were developed respectively by considering the suitable deformation models. In addition, constitutive equation for superplastic flow under the influence of intragranular particle was proposed.MINERALS, METALS & MATERIALS SOC, 2002, CREEP DEFORMATION: FUNDAMENTALS AND APPLICATIONS, 147 - 155, English[Refereed]International conference proceedings
- Grain refinement and superplasticity in magnesium alloysUltrafine-grained (UFG) material can be processed by powder metallurgy (PM) route using rapidly solidified powder or severe plastic deformation in magnesium alloys. In the present paper, the authors paid attention to the low-temperature superplasticity of these fine-grained materials in order to shed light on the mechanism of superplastic flow. Especially, the effect of particle and grain boundary structure on superplastic flow, which is indispensable to understand the nature of superplasticity, was discussed. The critical strain rates for the elimination of the effect of intergranular and intragranular particles could be developed using fine-grained PM magnesium alloy. Severe plastic deformation is also the promising route to attain UFG materials. However, the materials often have non-equilibrium grain boundary. It has been pointed out that the non-equilibrium grain boundary structure hampers the dislocation motion for accommodation process of grain boundary sliding, and hence retards the superplastic strain rate. Therefore, it is necessary to investigate the processing route to obtain UFG material with equilibrium grain boundary.MINERALS, METALS & MATERIALS SOC, 2002, ULTRAFINE GRAINED MATERIALS II, 469 - 478, English[Refereed]International conference proceedings
- In this study, the influences of the grain sizes on the magnesium alloy are investigated to evaluate the friction and wear properties under a dry condition by using a pin-on-disk test machine. Four kinds of ZK60 magnesium alloys with different grain sizes from 6mm to 100mm were used as test specimens and SUJ2 was used for counter materials. It was shown that the wear rate on the small grain size's specimen was increased by the larger plastic deformation near to the worn surface. And, it was also made clear that the coefficient of friction increased due to the influence of adhesive wear in the case of small grain sizes. On the other hand, in the case of large grain size's specimen, the wear-resistance properties increased as compared with the small grain size's specimen because the wear type was an abrasive wear without a plastic deformation. It is appeared that the average coefficient of friction on ZK60 magnesium alloy was about 0.3 in this test condition.Society of Materials Science Japan, 2002, Zairyo/Journal of the Society of Materials Science, Japan, 51(10) (10), 1154 - 1159, Japanese[Refereed]Scientific journal
- High-strain-rate superplastic magnesium alloy, AZ91, was processed through the ingot metallurgy route, The relationship between working temperature and resulting grain size indicated that the grain size tends to decrease with decreasing working temperature in AZ91. Based on this preliminary result, the ingot was hot extruded at a relatively low temperature of 523 K with a reduction ratio of 44. A very fine grain size of 1.7 mu-m was attained only by hot extrusion. The fine-grained structure as stable blow 573 K. Owing to the fine grain size, high-strain-rate superplasticity was observed at temperatures of similar to 548 K.JAPAN INST METALS, Jan. 2002, MATERIALS TRANSACTIONS, 43(1) (1), 78 - 80, English[Refereed]Scientific journal
- Tensile behavior of a bulk metallic glass Pd40Ni40P20 was characterized under both quasi-static and dynamic strain rate conditions. No major difference was observed. Multiple shear bands formed in samples tested at the dynamic strain rate. However, shear band interaction appears to have an insignificant effect on the plasticity of the alloy. (C) 2002 Acta aterialia Inc. Published by Elsevier Science Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Jan. 2002, Scripta Mateialia, 46(1) (1), 43 - 47, English, International magazine[Refereed]Scientific journal
- Polycrystalline magnesium generally fractures intergranuarly under dynamic loading, and exhibits limited ductility owing to its HCP structure, In this study, improvement of tensile mechanical properties under dynamic loading has been demonstrated for a commercial magnesium alloy of AZ31. A commercial AZ31 alloy was subjected to simple shear processing through ECAE (equal-channel-angular-extrusion) followed by annealing to develop a texture that differs from directly-extruded alloy. During the dynamic tensile test, elongation-to-failure was more than twice as high than that of the directly-extruded alloy. Inspection of the fracture surface on the dynamically deformed sample revealed that the ECAE processed alloy followed by annealing fractured with the development of ductile dimples and few macro cracks, which is often observed on the fracture surface of magnesium alloys.JAPAN INST METALS, Dec. 2001, MATERIALS TRANSACTIONS, 42(12) (12), 2652 - 2654, English[Refereed]Scientific journal
- It is very important to understand the strain rate dependence of the plateau stress or the impact energy for the applications to a suitable design of automotive components. Limited data are, however, available for the mechanical response of metallic foams under dynamic loading in comparison with polymer foams. In this study, the mechanical response and absorbed energy of an open-celled SG91A aluminum foam with the low relative density of 0.03-0.065 is evaluated at a dynamic strain rate in similar to 10(3) s(-1) order in compression by the split Hopkinson pressure bar apparatus. In order to investigate the effect of microstructure in the solid material, solution treatment and aging are performed and then examined at the same dynamic strain rate. As a result, mechanical strength and absorption energy for as-received and heat treated SG91A aluminum foams showed the strain rate dependence. This dependency was clearly decreased by the heat treatment. This mechanical response directly affects the energy absorption: the strain rate dependence of absorption energy is weakened with enhancing the ductility in solid materials by the heat treatment. Therefore, it is possible to control the absorption energy of the metallic foam by the modification of its microstructure, which affects the ductility in the solid material.JAPAN INST METALS, Oct. 2001, MATERIALS TRANSACTIONS, 42(10) (10), 2087 - 2092, English[Refereed]Scientific journal
- There is a great demand for more weight reduction in aluminum foams for fuel economy in the automotive and aerospace fields. The enhancement of compressive strength in a close-celled aluminum can be achieved by the selection of matrix material or modification of the cellular structure without increasing relative density. A commercial closed-cell aluminum (ALPORAS (R)) is made by adding foaming agent into a molten alloy. In this study, the matrix aluminum was strengthened by adding 5%Zn and 1%Mg without an increase in weight. The compressive strength of the present foam is found to be approximately twice as high as that of the conventional foam (ALPOPAS (R)).JAPAN INST METALS, Oct. 2001, MATERIALS TRANSACTIONS, 42(10) (10), 2118 - 2123, English[Refereed]Scientific journal
- An examination of consolidation conditions by hot extrusion of AZ31 magnesium alloy machined chips was conducted to enhance the bonding of individual chips, in order to improve the mechanical properties. Hot extrusions were carried out in the superplastic and non-superplastic region. Microstructural observations revealed that grain refinement was attained by extruding machined chips, and the grain sizes of the chip-extruded materials were smaller than 5 mum. The interfaces of individual chips of extruded materials were not identified when the chips were extruded in the superplastic region. The ultimate tensile strength was about 300 MPa and elongation-to-failure was about 10% for chip-extruded materials that were extruded in the superplastic region. These materials were comparable with the as-received alloy with respect to the room temperature strength, although the ductility was reduced to half. It was confirmed that chip consolidation utilizing superplastic flow is useful to enhance the bonding of individual grains. (C) 2001 Kluwer Academic Publishers.KLUWER ACADEMIC PUBL, Oct. 2001, JOURNAL OF MATERIALS SCIENCE, 36(20) (20), 5007 - 5011, English[Refereed]Scientific journal
- Dynamic recrystallization (DRX) behavior was systematically examined in two commercial Mg-Al-Zn alloys in order to clarify the relationship between deformation conditions and the resulting microstructure. The materials were deformed by upset forging at temperatures ranging from 473 to 673 K at an initial strain rate of 3.3 x 10(-2) s(-1). Grain refinement was observed during deformation. It was found that the dynamically recrystallized grain size decreases with an increasing Zener-Hollomon parameter and/or a decreasing initial grain size. A phenomenological constitutive equation was developed in order to provide a guideline for the control of the grain size of hot deformed AZ61 alloy.JAPAN INST METALS, Jul. 2001, MATERIALS TRANSACTIONS, 42(7) (7), 1200 - 1205, English[Refereed]Scientific journal
- Magnesium alloys are generally brittle owing to their HCP structure. In this study, improvement of tensile mechanical properties under dynamic loading has been demonstrated for a pure magnesium and a ZK60 magnesium alloy. The solution-treated ZK60 alloy exhibits yielding at a dynamic strain rate of 1.8 x 10(3) s(-1), which was not observed in a pure magnesium. The yield stress of the ZK60 alloy increases at the dynamic strain rate with a similar slope of Hall-Petch relation at a quasi-static strain rate. Enhancement of ductility can be also achieved by refining grain structures for the ZK60 alloy. The high ductility of the fine-grained alloy is due to the absence of macroscopic cracking at mechanical twin boundaries. It is found that the absorption energy per weight in the fine-grained ZK60 is twice higher than that of high strength aluminum alloys.JAPAN INST METALS, Jul. 2001, MATERIALS TRANSACTIONS, 42(7) (7), 1177 - 1181, English[Refereed]Scientific journal
- PERGAMON-ELSEVIER SCIENCE LTD, Jul. 2001, SCRIPTA MATERIALIA, 45(1) (1), 89 - 94, English[Refereed]Scientific journal
- The parametric dependencies for superplastic flow in powder metallurgy (PM) magnesium alloys and composites were characterized so as to elucidate the deformation mechanism. The mechanism was proposed to be slip accommodated grain boundary sliding. However, the PM alloys and composites were strengthened at low temperatures below similar to 550K. This was different from the case in ingot metallurgy (IM) magnesium alloys, that behaved identically over a wide range of temperatures. The critical strain rate, below which the effect of intragranular particle is lost, was developed by considering the dislocation-particle interaction during slip accommodation process. It was suggested that the diffusional relaxation around the intragranular oxide particles was not completed during the slip accommodation process at low temperatures, and this caused the dislocation pile-up at the intragranular particles. II was expected that the dislocation pile-up at the intragranular particles would contribute to the strengthening at low temperatures in PM alloys and PM composites. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Lid. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Jun. 2001, ACTA MATERIALIA, 49(11) (11), 2027 - 2037, English[Refereed]Scientific journal
- Possibility of combination of high-strain-rate superplasticity and low-temperature superplasticity was experimentally confirmed using extremely fine-grained magnesium alloy. In order to achieve such a superior superplastic behavior, the required grain size and the suitable processing was considered. It was suggested that the required grain size of less than or equal to approximate to 0.4 mum can be obtained through the processing from powder metallurgy route, using rapidly solidified powder. Therefore, superplastic behavior was examined using powder metallurgy processed Mg-Zn-Zr alloy (ZK61). Tensile tests revealed that high-strain-rate superplasticity was obtained even at low temperatures of approximate to 473 K, which is corresponding to half the absolute melting point of the material. This was attributed to the fine grain size of 0.65 mum. (C) 2001 Elsevier Science B.V. All rights reserved.ELSEVIER SCIENCE SA, Jun. 2001, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 307(1-2) (1-2), 119 - 128, English[Refereed]Scientific journal
- Metallic foams are expected to be used as the impact energy absorber material because of their unique deformation characteristics, which almost constant compressive stress appears in a wide range of strain. This phenomenon is well known as the regime of collapse plateau. It is very important to know strain rate dependence of the plateau stress, and the impact energy for suitable design of automotive components. Only limited amount of mechanical response data of metallic foams under dynamic loading are, however, available comparing with those of polymeric foams. In this study, the absorbed energy of an open-celled magnesium foams with a relative density of 0.03-0.06 is evaluated at a dynamic strain rate of similar to 10(3) s(-1) in compression by using the split Hopkinson pressure bar apparatus. In order to investigate the effect of microstructure in the solid material, solution treatment and aging are performed to all the specimens and then examined for the same strain rates. Peak stress and plateau stress per (relative density)(3/2) for as-received and heat treated AZ91 foams showed the strain rate dependence, which decreased by the heat treatment. Therefore, it is possible to control the absorption energy of the AZ91 metallic foam by means of microstructural improvement, which controls the ductility in the solid material. (C) 2001 Published by Elsevier Science B.V.ELSEVIER SCIENCE SA, Jun. 2001, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 308(1-2) (1-2), 283 - 287, English[Refereed]Scientific journal
- PERGAMON-ELSEVIER SCIENCE LTD, May 2001, SCRIPTA MATERIALIA, 44(8-9) (8-9), 1493 - 1496, English[Refereed]Scientific journal
- Effect of microstructural factors on superplastic behavior in magnesium-based composites was reviewed in order to obtain insights on ways to enhance the superplastic properties, such as high-strain-rate superplasticity, low-temperature superplasticity, and high ductility. The review shows that the reduction in grain size of the matrix directly increases the strain rate and/or decreases the temperature for optimum superplastic flow. The effect of reinforcement addition is shown to reduce the superplastic elongation, but enhance the superplastic strain rate, presumably owing to grain size stability of composites at high temperatures. Ductility enhancement is not necessarily attained by refining initial grain size. It is suggested that it is necessary to disperse the reinforcement uniformly in order to obtain higher ductility.MINERALS METALS MATERIALS SOC, Apr. 2001, METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 32(4) (4), 923 - 929, English[Refereed]Scientific journal
- Improvement of tensile mechanical properties under dynamic loading is demonstrated for a commercial magnesium alloy. Ductility in magnesium is enhanced by the addition of alloying elements. Further enhancement of ductility can be achieved by the refining grain structures for the commercial magnesium alloy. The high ductility of the fine-grained alloy is owing to the absence of macroscopic cracking at mechanical twin boundaries, while the coarse-grained alloy fractured at a smaller strain owing to the stress concentration at twin boundaries. It should be expected that the fine-grained alloy exhibits the high speed impact performance during foreign object damage.The Japan Society of Mechanical Engineers, 2001, The proceedings of the JSME annual meeting, 1, 353 - 354, Japanese
- Recently, semi-solid forming has been mainly utilized for automotive components such as the brake cylider. Semi-solid forming is a metal processing technique, which is becoming of large interest owing to many inherent advantages from a view point of saving energy, comparing with conventional forging (solid state) and casting (liquid state). In spite of the feasibility of semi-solid forming, its industrial application is limited. The faster forming speed tends to be required with complicating the figuration of compacts to attain the stable formability. It is noted that the applied uniaxial strain rate to materials is 10^2〜10^3 s^<-1> during forming. Very few data are, however, available concerning with the compressive behavior of semi-solid materials at a commercial forming rate. A classical Split Hopkinson Pressure Bar was used to estimate the dynamic mechanical properties of semi-solid aluminum alloy.The Japan Society of Mechanical Engineers, 2001, The proceedings of the JSME annual meeting, 1, 365 - 366, Japanese
- Grain refinement of a commercial magnesium alloy for superplastic formingSuperplastic forming was performed at a high strain rate of 10(-2) s(-1) for a commercial ZK60 magnesium. The relatively high forming temperature of 673 K was decided from the superplastic characteristics owing to its grain size similar to 5 mum. In order to prevent the grain growth during the high temperature superplasticity, the possibility of low temperature superplasticity(LTSP) in magnesium was derived. The required gain size for high strain rate superplasticity(HSRS) at the low homologous temperature was estimated, and the fabrication techniques to develop the fine-grained structure were discussed.TRANS TECH PUBLICATIONS LTD, 2001, SUPERPLASTICITY IN ADVANCED MATERIALS, ICSAM-2000, 357-3, 459 - 464, English[Refereed]Scientific journal
- Superplasticity of a particle-strengthened WE43 magnesium alloySuperplastic behavior was examined in fine-grained (similar to2 mum) WE43 magnesium alloy. that contained, within its grains, spherical precipitates with a diameter of similar to 200 nm. The material exhibited superplasticity with an elongation-to-failure of over 1000% at a temperature of 673 K and a strain rate of 1 x 10(-4) s(-1). Large elongations were obtained in spite of the existence of particles. The dominant deformation mechanism was suggested to be grain boundary sliding accommodated by slip controlled by grain boundary diffusion. Data analysis based on the constitutive equation for superplastic how revealed that the normalized strain rats for particle-strengthened WE43 alloy was about fifty times lower than that for conventional superplastic magnesium alloys. It was suggested that the existence of intragranular particles affects the superplastic flow.JAPAN INST METALS, Jan. 2001, MATERIALS TRANSACTIONS JIM, 42(1) (1), 157 - 162, English[Refereed]Scientific journal
- Compressive mechanical properties of aluminum alloy in the semi-solid state at dynamic strain rateRecently, semi-solid forming has been mainly utilized for automotive components (e.g., brake cylinder, automotive wheel). Semi-solid forming has many inherent advantages comparing with the conventional forging and casting; (1) reduction of solidification shrinkage and extension of the die life comparing with the casting in the fully liquid state, (2) reduction of the force during forging operations and enhancement of the size accuracy, comparing with the forging in the fully solid state. Very few data are, however, available concerning with the compressive behavior of semi-solid materials (SSM) at a dynamic forming rate for the commercial process. Therefore, establishment of the constitutive equation and modeling for semi-solid forming under dynamic loading isn t sufficiently achieved. In this study, compressive properties of SSM have been investigated at a dynamic strain rate (similar to1.0x10(3) s(-1)) are corresponding to the actual forming speed. A classical Split Hopkinson Pressure Bar was used to estimate the dynamic mechanical properties.JAPAN INST METALS, 2001, PRICM 4: FORTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, VOLS I AND II, 2599 - 2602, English[Refereed]International conference proceedings
- Ductility enhancement of commercial magnesium alloys by controlling grain structuresMagnesium alloys are generally brittle owing to their HCP structure. In this study, improvement of tensile mechanical properties has been demonstrated for a commercial AZ31 magnesium alloy. The effect of the modification for (a) the grain size and (b) texture have been investigated on the mechanical properties. Tensile mechanical properties have been compared for an ingot, an extruded and an annealed AZ31 followed equal-channel-angular-extrusion(ECAE) process. As a result, enhancement of ductility can be achieved by refining grain structures through the conventional extrusion, further enhancement with controlling the texture for a commercial AZ31 magnesium alloy.JAPAN INST METALS, 2001, PRICM 4: FORTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, VOLS I AND II, 1183 - 1186, English[Refereed]International conference proceedings
- Superplastic behavior in ingot metallurgy WE43 magnesium alloySuperplastic behavior of a particle-strengthened WE43 magnesium alloy was examined to clarify the effect of intragranular particles. The material had a fine grain size of similar to 2 mum and contained spherical precipitates of similar to 0.2 mum. The precipitates were observed to reside in both the grain boundaries and the grain interiors. The material exhibited superplasticity with an elongation-to-failure of over 1000% at a temperature of 673 K and a strain rate of 1 x 10(-4) s(-1). Large elongations were obtained in spite of the existence of particles. It appears that grain boundary sliding is accommodated by slip controlled by grain boundary diffusion in the WE43 alloy. The data analysis revealed that the normalized strain rate compensated by effective diffusion coefficient for WE43 was about fifty times of magnitude lower than that for the conventional superplastic magnesium alloys. It was suggested that the superplastic flow is influenced by the existence of intragranular particles.JAPAN INST METALS, 2001, PRICM 4: FORTH PACIFIC RIM INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS AND PROCESSING, VOLS I AND II, 2043 - 2046, English[Refereed]International conference proceedings
- Effective diffusivity for superplastic flow in magnesium alloysEffective diffusivity for superplastic flow was investigated using a relatively coarse-grained (17 and 30 mum) Mg-Al-Zn alloy. Tensile tests revealed that the strain rate was inversely proportional to the square of the grain size and to the second power of stress. The activation energy was close to that for grain boundary diffusion at low temperatures, and was close to that for lattice diffusion at high temperatures. From the analysis of stress exponent, grain size exponent and activation energy, it was suggested that the dominant diffusion process was influenced by temperature and grain size. It was demonstrated that the notion of effective diffusivity explained the dominant diffusion process.TRANS TECH PUBLICATIONS LTD, 2001, SUPERPLASTICITY IN ADVANCED MATERIALS, ICSAM-2000, 357-3, 147 - 152, English[Refereed]Scientific journal
- Japan Institute of Light Metals, 2001, Keikinzoku/Journal of Japan Institute of Light Metals, 51(10) (10), 503 - 508, Japanese[Refereed]
- Experimental study of structural magnesium alloys with high absorption energy under dynamic loadingImprovement of tensile mechanical properties under dynamic loading is demonstrated for two commercial magnesium alloys. Ductility in magnesium is enhanced by the addition of alloying elements. Further enhancement of ductility can be achieved by the refining grain structures for two commercial magnesium alloys, ZK60 and AZ31. The high ductility of the fine-grained alloy is owing to the absence of macroscopic cracking at mechanical twin boundaries, while the coarse-grained alloy fractured at a smaller strain owing to the stress concentration at twin boundaries. It is noted that the absorption energy per weight in the fine-grained magnesium is twice higher than those of high strength aluminum alloys. It should be expected that the fine-grained alloy exhibits the high speed impact performance during foreign object damage.ELSEVIER SCIENCE BV, 2001, FUNDAMENTAL ISSUES AND APPLICATIONS OF SHOCK-WAVE AND HIGH-STRAIN-RATE PHENOMENA, PROCEEDINGS, 37 - 42, English, International magazineInternational conference proceedings
- Mechanical properties in structural magnesium alloys under dynamic tensile loadingRecently, it has been demonstrated that pure Mg exhibits low ductility under dynamic loading at room temperature owing to its HCP structure. Very limited data are currently available for magnesium alloys under dynamic loading. In order to be used for structural components, it is important to know the mechanical properties of magnesium alloys at a dynamic strain rate. It has been reported for some structural magnesium alloys at a quasi-static strain rate that the enhancement of ductility can be achieved by the refining their microstructures. Thus refining microstructure enables to raise the possibility for the development of a structural magnesium alloy with high ductility at a dynamic strain rate. In this study, the tensile mechanical properties of some magnesium alloys are investigated. As a result, it was found that the structural magnesium alloys consisting of fine-grained microstructure exhibited sufficient ductility under dynamic loading. The high ductility of the extruded alloy was owing to the transition in the fracture mechanisms with grain refinement. It should be expected that the alloy exhibits the high speed impact performance during foreign object damage.ELSEVIER SCIENCE BV, 2001, IMPACT ENGINEERING AND APPLICATION, VOLS I AND II, 547 - 552, English, International magazineInternational conference proceedings
- Influence of strain rate on the tensile mechanical behavior in Pd40Ni40P20 bulk metallic glassUnderstanding of the dynamic failure mechanism in bulk metallic glass is important for the application of this class of materials to a variety of engineering problems. Limited data are, however, currently available for the dynamic mechanical properties. The purpose of this study is to clarify the influence of strain rate on the tensile strength and fracture behavior. The tensile mechanical behavior of a bulk metallic glass, Pd40Ni40P20, was investigated over a wide strain rate range (1x10(-3) similar to 2.8x10(3) s(-1)). As a result, it was found that the tensile fracture stress of the material was very high (1600 MPa) and was virtually independent of strain rate. Inspection of the specimen fractured at a dynamic strain rate revealed that the present material has a huge amount of the local melt at the fracture surface. Comparing to a simple shear-off surface observed at the strain rate of 1x10(-3) s(-1), the fracture surface at the dynamic strain rate of 2.8x10(3) s(-1) was rough. The rough surface is caused by a simultaneous operation of multiple shear bands. Shear band interaction has limited effect on the plasticity of a bulk metallic glass, but it can improve the fracture toughness.ELSEVIER SCIENCE BV, 2001, IMPACT ENGINEERING AND APPLICATION, VOLS I AND II, 577 - 582, English, International magazineInternational conference proceedings
- Impact energy absorption affected by the cell size in a closed-cell aluminum foamMetallic foams also have a potential for absorbing impact energy and enhancement of the absorption energy can be achieved by the extent of plateau strain and an increase in the plateau stress. In this study, modification of the structure in a closed-cell aluminum foam was performed for the crashworthiness. The edge length of the modified foam is obviously reduced from that of the conventional aluminum foam, while the aspect ratio of the wall thickness against the edge length increases by the present modification. A novel Split Hopkinson Pressure Bar was used to estimate the dynamic compressive properties. As a result of the compression tests at a dynamic strain rate (similar to1 x 10(3) s(-1)), the plateau stress of the modified foam was found to exhibit a remarkable increase as compared to that of a conventional foam without increasing the relative density. It was found that the absorption energy per unit volume (W) of the modified foam was similar to30% higher than that of the conventional foam.ELSEVIER SCIENCE BV, 2001, IMPACT ENGINEERING AND APPLICATION, VOLS I AND II, 237 - 242, English, International magazineInternational conference proceedings
- Impact energy absorption of metal foam with the controlled microstructure under dynamic loadingMetallic foams are expected to use for the impact energy absorber because of their deformation characteristics where almost constant compressive stress appears in a wide range of strain, well-known as the plateau regime. It is very important to know the strain rate dependence of the plateau stress or the impact energy for applications to a suitable design of automotive components. Limited data are, however, available for the mechanical response of metallic foams under dynamic loading comparing with polymer foams. In this study, the absorbed energy of open-celled aluminum and magnesium foams with the relative density of 0.03 similar to 0.065 is evaluated at a dynamic strain rate similar to 10(3) s(-1) in compression by using the split Hopkinson pressure bar apparatus. In order to investigate the effect of microstructure in the solid metals, solution treatment and aging are performed to all the specimens and then examined for the same strain rates. As a result, plateau stress of all the as-cast metallic foams showed the strain rate dependence in comparison with that at a quasi-static strain rate of 1x10(-3) s(-1), while those of solution treated and aged foams are independent of strain rate. Therefore, it is possible to control the mechanical response of the metallic foams owing to the ductility of base metals as the factor of energy absorption.ELSEVIER SCIENCE BV, 2001, FUNDAMENTAL ISSUES AND APPLICATIONS OF SHOCK-WAVE AND HIGH-STRAIN-RATE PHENOMENA, PROCEEDINGS, 361 - 365, English, International magazineInternational conference proceedings
- 2001, Porc. Materials Week 2000, (2001), CD, EnglishEffects of cell characteristics on the mechanical properties of metal foams[Refereed]International conference proceedings
- 2001, Porc. Materials Week 2000, (2001), CD, EnglishDynamic loading simulation of open cellular materials[Refereed]International conference proceedings
- 2001, J. Mater. Processing Tech., 117, (2001), CD, JapaneseOpen-cellular magnesium alloy foams – Their production and mechanical proeprties[Refereed]
- Superplastic behavior was examined in fine-grained (∼2 μm) WE43 magnesium alloy, that contained, within its grains, spherical precipitates with a diameter of ∼200 nm. The material exhibited superplasticity with an elongation-to-failure of over 1000% at a temperature of 673 K and a strain rate of 1 × 10-4 s-1. Large elongations were obtained in spite of the existence of particles. The dominant deformation mechanism was suggested to be grain boundary sliding accommodated by slip controlled by grain boundary diffusion. Data analysis based on the constitutive equation for superplastic flow revealed that the normalized strain rate for particle-strengthened WE43 alloy was about fifty times lower than that for conventional superplastic magnesium alloys. It was suggested that the existence of intragranular particles affects the superplastic flow.Japan Institute of Metals (JIM), 2001, Materials Transactions, 42(1) (1), 157 - 162, English[Refereed]Scientific journal
- Deformation behavior of a coarse-grained AZ31 magnesium alloy was investigated at elevated temperatures using commercial rolled sheet. The as-received material had equiaxed grains with an average grain size of 130 mum. The tensile tests revealed that the material exhibited high ductility of 196% at 648 K and 3x10(-5) s(-1). Stress exponent, grain size exponent and activation energy were characterized to clarify the deformation mechanism. It was suggested from the data analysis that the high ductility was attributed to the deformation mechanism of glide-controlled dislocation creep. In addition, constitutive equation was developed for the present alloy. (C) 2001 Elsevier Science Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, 2001, INTERNATIONAL JOURNAL OF PLASTICITY, 17(3) (3), 387 - 397, English[Refereed]Scientific journal
- Superplasticity-Current Status and Future Potential, Dec. 2000, Proc. of MRS Fall Meeting, 601, 291 - 302, English, International magazineRoutes to Develop Fine-Grained Magnesium Alloys and Composites for High Strain Rate SuperplasticityInternational conference proceedings
- Nov. 2000, Proc. of 2000 Powder Metallurgy World Congress, Powder Society of Powder Metallurgy, 1100 - 1103, English, International magazineThe Development of Cavitation in P/M Al-Zn-Mg AlloyInternational conference proceedings
- Nov. 2000, Proc. of 2000 Powder Metallurgy World Congress, Powder Society of Powder Metallurgy, 1073 - 1076, English, International magazineSuperplasticity in a Powder Metallurgy Magnesium AlloyInternational conference proceedings
- Application of superplasticity in commercial magnesium alloy for fabrication of structural componentsAn investigation of the superplastic characteristics of magnesium alloys with several grain sizes revealed that grain boundary sliding took place more easily with grain refinement. The required grain size for high strain rate superplastic forming was estimated to be similar to2 mum. The required grain structure could be obtained by several procedures, hot extrusion with a high extrusion ratio, severe plastic deformation via equal channel angular extrusion, consolidation of machined chip, and/or powder metallurgy processing of rapidly solidified powders, on a laboratory scale. The processing route of hot extrusion was selected in this study. An experimental study of superplastic press forming was conducted for a commercially extruded ZK60 alloy, The fabricated product did not essentially contain macroscopic defects, i,e, cracks or cavities, From an examination of tensile characteristics, it was found that the post-formed alloy exhibited higher strength and higher ductility compared with some conventional cast magnesium alloys, aluminium alloys, and steels, The experimental results support the possibility of using superplastically formed magnesium to produce structural components. MST/4781.I O M COMMUNICATIONS LTD INST MATERIALS, Nov. 2000, MATERIALS SCIENCE AND TECHNOLOGY, 16(11-12) (11-12), 1314 - 1319, English[Refereed]Scientific journal
- Processing of cellular magnesium materialsEspecially cellular aluminum materials have been extensively developed and investigated in the recent years But also magnesium is suitable metal for cellular metals due to its low density. By a special casting method open-cellular magnesium with a very low density of 0.05 g/cm(3) is fabricated that shows high potential for usage as energy absorbers.WILEY-V C H VERLAG GMBH, Apr. 2000, ADVANCED ENGINEERING MATERIALS, 2(4) (4), 184 - 187, English[Refereed]Scientific journal
- The mechanical properties of open-cellular epoxies with a cubic prism structure have been investigated by compressive tests with angles between the beam and the load direction of 0 degrees (90 degrees) and 45 degrees. When the angle was 45 degrees, the stress fluctuated in a plateau region about a roughly constant flow up to a strain of 77%. However, when the angle was 0 degrees (90 degrees), the flow stress changed significantly with the strain passing through a series of peaks. The absorption energy per unit volume was found to be essentially independent of the angle between the beam and the load direction.TAYLOR & FRANCIS LTD, Apr. 2000, PHILOSOPHICAL MAGAZINE LETTERS, 80(4) (4), 215 - 220, English[Refereed]Scientific journal
- Effects of heat treatment on compressive properties of AZ91 Mg and SG91A Al foams with open-cell structureCompressive properties were investigated for the as-cast and T6 heat-treated AZ91 Mg and SG91A Al foams with open-cell structure. The foams showed an elastic region at an initial stage, then a plateau region with a nearly constant flow stress to a large strain of about 60%, and finally a densification region where the stress increased rapidly. The relative stress of the as-cast foams was higher than that of the T6 foams, taking into consideration the influence of the relative density. (C) 2000 Elsevier Science S.A. All rights reserved.ELSEVIER SCIENCE SA, Mar. 2000, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 280(1) (1), 225 - 228, English[Refereed]Scientific journal
- Dynamic compression of an ultra-low density aluminium foamThe dynamic compressive behavior of an ultra-low density, open-celled SG91A aluminium foam fabricated by casting technique was investigated at a dynamic strain rate of 1.4 x 10(3) s(-1). It was found that the plateau stress of the SG91A foam exhibited strain rate dependence, in a manner similar to other metallic foams such as AZ91 foam and ALPORAS. In the present study, efforts were made to correlate the plateau stress with the density of different foams, and it was further compared with existing models. II is of interest to note that the absorption energy normalized by the relative density at the dynamic strain rate is similar to 60% higher than that at quasi-static strain rates (similar to 1 x 10(-3) s(-1)). Published by Elsevier Science S.A.ELSEVIER SCIENCE SA, Mar. 2000, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 280(2) (2), 349 - 353, English[Refereed]Scientific journal
- Superplastic behavior in commercial wrought magnesium alloysSuperplastic behavior of five commercial wrought magnesium alloys in as-received condition were examined to grasp the ability of superplastic forming. The materials used in the present study was an AZ31 rolled sheet, an AZ31 extruded rod, an AZ61 rolled sheet, an AZ61 extruded sheet and a ZK60 extruded rod. All the materials have been tested at different temperature and strain rate ranges where their respective superplastic behavior could be obtained. The tensile tests revealed that all the materials exhibited high ductility at about 673 K with elongations-to-failure of over 200%. The results indicated that the commercial wrought magnesium alloys have a potential for superplastic forming. However, strain rate for the maximum elongation was in the range of 10(-4) to 10(-5) s(-1) except ZK60 extruded rod, that exhibited the maximum elongation at a relatively high strain rate of 10(-3) s(-1). Further grain refinement is required to perform high-strain-rate superplastic forming using commercial wrought alloys.TRANS TECH PUBLICATIONS LTD, 2000, MAGNESIUM ALLOYS 2000, 350-3, 171 - 176, English[Refereed]Scientific journal
- PERGAMON-ELSEVIER SCIENCE LTD, Jan. 2000, SCRIPTA MATERIALIA, 42(3) (3), 249 - 255, English[Refereed]Scientific journal
- Grain refinement of commercial magnesium alloys for high-strain-rate-superplastic formingSuperplasticity usually occurs when grain size is small, typically less than similar to 10 mum In this study, the deformation mechanisms at elevated temperatures in magnesium alloy with different grain sizes are discussed. From the discussion, the grain requirement for high strain rate superplasticity (10(-2) similar to 10(0) s(-1)) is derived. The strain rate range is chosen because it corresponds to the forming rate in commercial mass-production. Four different processing routes for grain refinement are presented and the developed grain structures are compared. Finally, a fine-grained magnesium alloy fabricated by commercial extrusion route is selected to demonstrate the proposed high strain rate superplastic forming at a strain rate of similar to 10(-2) s(-1).TRANS TECH PUBLICATIONS LTD, 2000, MAGNESIUM ALLOYS 2000, 350-3, 159 - 170, English[Refereed]Scientific journal
- Ductility enhancement in magnesium alloys under dynamic loadingImprovement of tensile mechanical properties under dynamic loading is demonstrated for two commercial magnesium alloys. Ductility in magnesium is enhanced by the addition of alloying elements. Further enhancement of ductility can be achieved by the refining grain structures for two commercial magnesium alloys, AZ31 and WE43. The high ductility of the extruded alloy is owing to the transition in the fracture mechanisms from intergranular fracture to transgranular one with grain refinement. It is especially noted that the absorption energy per weight in the fine-grained magnesium is twice higher than that of high strength aluminum alloys. It should be expected that the alloy exhibits the high speed impact performance during foreign object damage.TRANS TECH PUBLICATIONS LTD, 2000, MAGNESIUM ALLOYS 2000, 350-3, 97 - 102, English[Refereed]Scientific journal
- Compressive deformation behavior of Al2O3 foamDeformation behavior of an Al2O3 foam with an open-cellular structure was investigated by compressive tests. The variation in flow stress with strain was significantly large and there was no densification region. Breakage of the columns is responsible for the large variation in flow stress with strain and no densification region. The relative stress of the Al2O3 foam was lower than the value predicted by Gibson and Ashby. This is probably because of the high degree of cracking in the columns and the presence of partial closed-faces. (C) 2000 Elsevier Science S.A. All rights reserved.ELSEVIER SCIENCE SA, Jan. 2000, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 277(1-2) (1-2), 213 - 217, English[Refereed]Scientific journal
- Compressive properties of open-cellular SG91A Al and AZ91 MgMechanical properties of open-cellular SG91A Al and AZ91 Mg have been investigated by compressive tests. The strain to densification of the cellular AZ91 Mg was almost the same as that of the cellular SG91A Al, though the AZ91 Mg solid with the relative density of 100% showed much lower ductility than the SG91A Al solid. By compensation with the yield stress of the solid and the relative density, the stress-strain relation of the cellular AZ91 Mg was in agreement with that of the cellular SG91A Al. (C) 1999 Published by Elsevier Science S.A. All rights reserved.ELSEVIER SCIENCE SA, Nov. 1999, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 272(2) (2), 455 - 458, English[Refereed]Scientific journal
- Oct. 1999, Material Science Forum (Proc. of CFEMS-8) Key Engineering Materials, 171-174, 337 - 342, English, International magazineExperimental Study of the Mechanical Properties at Elevated Temperatures in Commercial Mg-Al-Zn Alloys for Superplastic FormingInternational conference proceedings
- Oct. 1999, Proc. 6th Japan International SAMPE Symposium, 444 - 447, English, International magazineHigh-Strain-Rate-Superplasticity and Fracture Mechanism in a Magnesium-Based CompositeInternational conference proceedings
- Superplasticity at Low Temperatures in a ZK61 Magnesium Alloy Produced by Powder MetallurgySuperplastic behavior of a fine-grained magnesium alloy, ZK61, was investigated at about half the absolute melting point The material was produced by powder metallurgy. The tensile test revealed that the material exhibited superplasticity. The maximum elongation of 659% was obtained at 473 K and 1 x 10(-3) s(-1). Furthermore, it was noted that a large elongation of 283% was attained at a high strain rare of 1 x 10(-2) s(-1). The optimum superplastic strain rate in the present alloy was faster than that in some conventional magnesium alloys, that were shown to exhibit superplasticity at low temperatures. It was suggested that the small grain size increased the optimum superplastic flow in the present alloy.TRANSTEC PUBLICATIONS LTD, Oct. 1999, Material Science Forum(Proc. of CFEMS-8) Key Engineering Materials, 171-174, 363 - 368, English, International magazineInternational conference proceedings
- PERGAMON-ELSEVIER SCIENCE LTD, Oct. 1999, SCRIPTA MATERIALIA, 41(10) (10), 1055 - 1060, English[Refereed]Scientific journal
- The effect of temperature and grain size on superplastic flow was investigated using a relatively coarse-grained (similar to 20 mu m) Mg-AI-Zn alloy for the inclusive understanding of the dominant diffusion process. Tensile tests revealed that the strain rate was inversely proportional to the square of the grain size and to the second power of stress. The activation energy was close to that for grain boundary diffusion at 523-573 K, and was close to that for lattice diffusion at 598-673 K. From the analysis of the stress exponent, the grain size exponent and activation energy, it was suggested that the dominant diffusion process was influenced by temperature and grain size. It was demonstrated that the notion of effective diffusivity explained the experimental results. (C) 1999 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Oct. 1999, ACTA MATERIALIA, 47(14) (14), 3753 - 3758, English[Refereed]Scientific journal
- Superplastic behavior of a commercial magnesium alloy, AZ61, has been investigated. Tensile tests were carried out at temperatures ranging from 573 to 673 K and strain rates ranging from 10(-5) to 10(-3) s(-1). Superplastic behavior was observed in the low strain rate range and, especially, a maximum elongation-to-failure of 461% was obtained at 648 K at a strain rate of 3 x 10(-5) s(-1). The alloy showed a high strain rate sensitivity exponent of 0.5. Inspection of the specimen surface after deformation revealed direct evidence for grain boundary sliding (GBS). In addition, the distribution of misorientation angles was essentially unchanged during superplastic flow. From these results, it was concluded that the dominant deformation mechanism was GBS.JAPAN INST METALS, Sep. 1999, MATERIALS TRANSACTIONS JIM, 40(9) (9), 931 - 934, English[Refereed]Scientific journal
- KLUWER ACADEMIC PUBL, Sep. 1999, JOURNAL OF MATERIALS SCIENCE LETTERS, 18(18) (18), 1477 - 1480, English[Refereed]Scientific journal
- Low temperature superplastic behavior of a magnesium alloy, ZK60, was investigated at about half the absolute melting point. The grains were equiaxed with an average size of 6.5 mu m. The tensile tests revealed that the material exhibited low temperature superplasticity (LTSP) with elongation-to-failure of over 400%. Microstructural observations suggested that grain boundary sliding (GBS) made a substantial contribution to the total strain. The stress exponent, grain size exponent and activation energy for superplastic flow were also characterized. The strain rate was inversely proportional to the cube of the grain size and to the second power of stress. The activation energy was close to that for grain boundary diffusion in magnesium. It is suggested that the deformation mechanism for LTSP is GBS accommodated by dislocation movement controlled by grain boundary diffusion.JAPAN INST METALS, Aug. 1999, MATERIALS TRANSACTIONS JIM, 40(8) (8), 809 - 814, English[Refereed]Scientific journal
- PERGAMON-ELSEVIER SCIENCE LTD, Jul. 1999, SCRIPTA MATERIALIA, 41(4) (4), 365 - 371, English[Refereed]Scientific journal
- Jun. 1999, Metal Foams and Porous Metal Structure, 147 - 152, English, International magazineProcessing of Cellular Magnesium MaterialsInternational conference proceedings
- Jun. 1999, Metal Foams and Porous Metal Structure, 353 - 358, English, International magazineEnergy Absorption of Light-Weight Metallic Foams under Dynamic LoadingInternational conference proceedings
- PERGAMON-ELSEVIER SCIENCE LTD, Jun. 1999, SCRIPTA MATERIALIA, 41(2) (2), 209 - 213, English[Refereed]Scientific journal
- May 1999, Proc. of the International Conference on Solid-Solid Phase Transformations '99 (JIMIC-3), 289 - 292, English, International magazineEvolution in Microstructure and Superplastic Flow at High-Strain-Rate in Dynamically Recrystallized Aluminum AlloyInternational conference proceedings
- PERGAMON-ELSEVIER SCIENCE LTD, Apr. 1999, Scripta Mateialia, 40(9) (9), 1021 - 1027, English, International magazine[Refereed]Scientific journal
- PERGAMON-ELSEVIER SCIENCE LTD, Mar. 1999, SCRIPTA MATERIALIA, 40(8) (8), 921 - 927, English[Refereed]Scientific journal
- Superplastic deformation and viscous flow in an Zr-based metallic glass at 410 degrees CThe thermal properties of an amorphous alloy (composition in at.%: Zr-10Al-5Ti-17.9Cu-14.6Ni), and particularly the glass transition and crystallization temperature as a function of heating rate, were characterized using Differential Scanning Calorimetry (DSC). X-ray diffraction analyses and Transmission Electron Microscopy were also conducted on samples heat-treated at different temperatures for comparison with the DSC results. Superplasticity in the alloy was studied at 410 degrees C, a temperature within the supercooled liquid region. Both single strain rate and strain rate cycling tests in tension were carried out to investigate the deformation behavior of the alloy in the supercooled liquid region. The experimental results indicated that the alloy did not behave like a Newtonian fluid.MATERIALS RESEARCH SOCIETY, 1999, BULK METALLIC GLASSES, 554, 379 - 384, English[Refereed]International conference proceedings
- Low temperature superplastic behavior in ZK60 magnesium alloyLow temperature superplastic behavior of a magnesium alloy, ZK60, was investigated at about half the absolute melting point. The grains were equiaxed and the average size was 6.5 mu m. The tensile tests revealed that the material exhibited low temperature superplasticity (LTSP) with elongation-to-failure of over 400%. While the experimental variables in the constitutive equation for superplasticity, stress exponent and activation energy, were characterized. The strain rate was proportional to the second power of stress. The activation energy was close to that for grain boundary diffusion in magnesium. It is suggested that the deformation mechanism for LTSP is grain boundary sliding controlled by grain boundary diffusion as well as high temperature superplasticity (HTSP).TRANSTEC PUBLICATIONS LTD, 1999, TOWARDS INNOVATION IN SUPERPLASTICITY II, 304-3, 303 - 308, English[Refereed]Scientific journal
- Observation of high-strain-rate superplasticity in ZK60 and SiCp/ZK60 compositeSuperplastic properties of a 17vol% SIC particulate-reinforced ZK60 magnesium composite was investigated and compared with those of the unreinforced alloy. It was found that the composite, because of its microstructure, exhibited superplasticity (elongation-to-failure > 400%) at high strain rates (similar to 0.1 s(-1)). In addition, the material showed a high strain rate sensitivity of 0.5 and an activation energy of 81kJ/mol in the superplastic region. The unreinforced alloy also exhibited similar results. Direct comparison of the modulus-compensated stress as a function of diffusion- and grain size-compensated strain rate for two materials revealed that the normalized stress of the composite is similar to that of the unreinforced alloy. Based on these results, it was proposed that the dominant deformation mechanisms of both materials are grain boundary sliding accommodated by a grain boundary diffusion process.TRANSTEC PUBLICATIONS LTD, 1999, TOWARDS INNOVATION IN SUPERPLASTICITY II, 304-3, 297 - 302, English[Refereed]Scientific journal
- Microstructural dynamics during high-strain-rate superplastic flow in PM 7475 alloyA 7475 aluminum alloy processed by powder metallurgically (P/M7475) has shown superplastic elongation more than 1000 % at a temperature of 788 K. The maximum elongation of P/M 7475 was recorded near a strain rate of 1x10(-1) s(-1), which is 3 orders magnitude faster than that of ingot metallurgically processed 7475 (I/M7475). This excellent superplastic performance at a higher strain rate is owing to a fine grain size of about 1 mu m developed by dynamic recrystallization at an early stage of superplastic flow. Morphology of grain boundary sliding with straining was inspected by the scanning electronmicroscopy. The contribution of grain boundary sliding was found to be low at an early stage of deformation, but was increasing with deformation. It was found that this trend was corresponding to an increase of misorientation angle by dynamic recrystallization with straining.TRANSTEC PUBLICATIONS LTD, 1999, TOWARDS INNOVATION IN SUPERPLASTICITY II, 304-3, 333 - 338, English[Refereed]Scientific journal
- Jan. 1999, Proc. of Plasticity '99 The Seventh International Symposium on Plasticity and its Current Applications, 1049 - 1052, English, International magazineLow Temperature Superplastic Deformation Characteristics and The Constitutive Equation in ZK60 Magnesium AlloyInternational conference proceedings
- Jan. 1999, Proc. of Plasticity '99 The Seventh International Symposium on Plasticity and its Current Applications, 1029 - 1036, English, International magazineGrain Boundary Characteristics in Superplastic Al-Zn-Mg AlloyInternational conference proceedings
- PERGAMON-ELSEVIER SCIENCE LTD, Jan. 1999, SCRIPTA MATERIALIA, 40(4) (4), 477 - 484, English[Refereed]Scientific journal
- Microstructure and superplastic properties in an ECAE Al-4Mg-0.5Sc alloy processed at elevated temperaturesEqual-channel-angular-extrusion(ECAE) was conducted to an Al-4Mg-0.5Sc alloy at two elevated temperatures of 473 and 673 K. The effect of processing temperature during heavily straining was investigated. Microstructural examinations revealed the formation of fine-grained(similar to 0.5 mu m) structure at a low operating temperature of 473K, whereas: a coarse-grain(similar to 25 mu m) was formed at 673 K. The material processed at 473 K exhibited the lon er flow stress with higher ductility and high strain rate sensitivity of 0.5 indicating the dominant deformation mechanism was grain boundary sliding. Finer grain structure exhibited the high-strain-rate superplasticity can be obtained at the lon:er processing temperature. The results indicate that the operating temperature has highly influenced the ECAE process.TRANS TECH PUBLICATIONS LTD, 1999, TOWARDS INNOVATION IN SUPERPLASTICITY II, 304-3, 109 - 114, English[Refereed]Scientific journal
- Deformation characteristics at elevated temperatures were examined in an AZ31 magnesium alloy. The as-received bar was extruded for refineing its microstructure. The extruded alloy had equiaxed grains with an average grain size of approx. 5 μm. Tensile test revealed that the material exhibited superplasticity. The maximum elongation of 608% was obtained at a temperature of 598 K and at a strain rate of 1 × 10-4 s-1. Microstructural observations indicated that the dominant deformation process was grain boundary sliding. The strain rate sensitivity exponent in the superplastic region was 0.5 and the activation energy was close to that for grain boundary diffusion in magnesium. Experimental results suggested that the dominant deformation mechanism in AZ31 was grain boundary sliding accommodated by dislocation glide controlled by grain boundary diffusion.Japan Inst of Light Metals, 1999, Keikinzoku/Journal of Japan Institute of Light Metals, 49(8) (8), 401 - 404, Japanese[Refereed]Scientific journal
- PERGAMON-ELSEVIER SCIENCE LTD, Oct. 1998, SCRIPTA MATERIALIA, 39(9) (9), 1249 - 1253, English[Refereed]Scientific journal
- Sep. 1998, Magnesium Alloy and Their Applications, DGM, 395 - 400, English, International magazineSuperplastic Behavior in ZK60 Alloy and its CompositeInternational conference proceedings
- Aug. 1998, Proc. of The Third Pacific Rim International Conference on Advanced Materials and Processing, 1891 - 1896, English, International magazineSuperplastic Behavior of Doubly-Extruded ZK60/SiC/17p Magnesium-Based Composite Over a Wide Range of TemperatureInternational conference proceedings
- Aug. 1998, Proc. of The Third Pacific Rim International Conference on Advanced Materials and Processing, 1765 - 1770, English, International magazineContribution of Grain Boundary Sliding in Superplastic 7475 Alloys Processed by Powder Metallurgy and Ingot MetallurgyInternational conference proceedings
- Aug. 1998, Proc. of The Third Pacific Rim International Conference on Advanced Materials and Processing, 2091 - 2096, English, International magazineMechanical Properties in Al94Cr1Mn3Cu2 Alloy Strengthened by Nano-Quasicrystalline ParticlesInternational conference proceedings
- Plastic deformation, microstructure and deformation substructure in an A1-14 wt% Ni-14 wt% Mm (misch metal) alloy produced from amorphous powders were examined focusing on the effects of the initial average grain size d(0), the grain boundary sliding and the motion of dislocations on the superplasticity. The as-received and annealed specimens with d(0)=0.8, 1.6 and 2.5 mu m deformed at 573 K at an initial strain rate of 1/s. The specimen with d(0)=0.8 mu m showed high-strain-rate superplasticity accompanied by low flow stress and 350% elongation, while the flow stress increased and elongation decreased with greater grain size. Grain refinement occurred and the frequency of small angle boundaries showed a complicated change during superplastic deformation. On the other hand, in the specimen with d(0)=1.6 mu m, the grains coarsened rapidly. A large number of;dislocations were observed in grains even in the superplastically deformed specimen. The high-strain-rate superplasticity of A1-14 wt% Ni-14 wt% Mm alloy is controlled by the grain boundary sliding but the motion of dislocations also plays an important role in accommodating the highly strained region near triple junctions of the grain boundaries. (C) 1998 Acta Metallurgica Inc.. Published by Elsevier Science Ltd. All rights reserved.PERGAMON-ELSEVIER SCIENCE LTD, Aug. 1998, ACTA MATERIALIA, 46(13) (13), 4469 - 4478, English[Refereed]Scientific journal
- Microstructure of AA5056 Al-Mg alloy is refined drastically to nano-scale by the equal-channel-angular-extrusion(ECAE) process. Dynamic mechanical properties at room temperature in the ECAE processed 5056 Al-Mg alloy (5056-ECAE) are characterized by a modified Hopkinson-bar method. Yield stress (YS) in 5056-ECAE exhibits remarkably higher value than that of a fully annealed 5056 alloy(5056-O). Hall-Petch(H-P) relation of 5056 alloy is compared with those of a binary Al-Mg alloy and Aluminum. The slope of the H-P relation in the granular 5056 alloy is almost equal to that of a binary Al-Mg alloy with a similar content of magnesium, and larger than that of Aluminum. On the other hand, the slope of the sub-grained alloy exhibits lower value than that of the granular alloy. The result indicates that grains effectively refined by the ECAE process, however, the grain boundary strength of the sub-grained alloy is relatively lower than that of the granular alloy. The elongation-to-failure of 5056-ECAE exhibits a larger value than those of some fine-grained bulk aluminum alloys such as a mechanically alloyed aluminum. Fractography of 5056-ECAE revealed that this alloy was fractured with ductile dimples. The result supports the possibility that this alloy exhibits the high speed impact performance and capability for high-rate forming. (C) 1998 Acta Metallurgica Inc.PERGAMON-ELSEVIER SCIENCE LTD, Jul. 1998, NANOSTRUCTURED MATERIALS, 10(5) (5), 755 - 765, English[Refereed]Scientific journal
- Jun. 1998, The Joint Commitee for Advanced Materials Research, 466 - 469, English, International magazineMicrostructural Dynamics in High-strain-rate Superplastic 7475 AlloyInternational conference proceedings
- Jun. 1998, Proc. of The Special Symposium on Advanced Materials, 458 - 461, English, International magazineGrain-Size Dependence of Low Temperature Superplastic Behavior in ZK60 Magnesium AlloyInternational conference proceedings
- Jun. 1998, Proc. of The Special Symposium on Advanced Materials, 450 - 453, English, International magazineDynamic Mechanical Properties of Fine-Grained Bulk Aluminum AlloysInternational conference proceedings
- Strain-rate dependence of mechanical properties in AA5056 Al-Mg alloy processed by equal-channel-angular-extrusionMicrostructure of AA5056 Al-Mg alloy is refined dramatically by the equal-channel-angular-extrusion (ECAE) process. Tensile properties at room temperature in the ECAE-processed 5056 Al-Mg alloy (5056-ECAE) are characterized as a function of strain rate. Total elongation of 5056-ECAE increases with strain rate in the same way as some fully annealed Al-Mg alloys, and the result supports the possibility of using the alloy for high-rate forming. Yield stress (YS) and ultimate tensile strength (UTS) in 5056-ECAE exhibit remarkably higher values than those of the fully annealed 5056 alloy (5056-O). UTS of 5056-ECAE is almost independent of strain rate below the strain rate of 6.5 x 10(2) s(-1); compared.with 5056-O. Change in the strain rate sensitivity of UTS may be caused by the difference in the interaction between solute atoms and dislocations. (C) 1998 Elsevier Science S.A. All rights reserved.ELSEVIER SCIENCE SA, Jun. 1998, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, A247(1-2) (1-2), 270 - 274, English[Refereed]Scientific journal
- Feb. 1998, Superplasticity and Superplastic Forming, 313 - 319, English, International magazineDuctility and Cavitation at Elevated Temperatures in a Superplastic ZK60-Based CompositeInternational conference proceedings
- Feb. 1998, Superplasticity and Superplastic Forming, 179 - 186, English, International magazineLow Temperature Superplastic-Like Behavior of ZK60 Magnesium AlloyInternational conference proceedings
- 1998, Proc. The First Asian-Australasian Conference on Comosites Materials (ACCM-1), (1998), 529/1-4, EnglishSize-effect of reinforcement on the dynamic tensile properties in aluminum-based composite[Refereed]International conference proceedings
- Superplasticity in a doubly extruded magnesium based composite, ZK60 reinforced with 17 vol-%SiC particles, was investigated. The influences of strain rate on the flow stress and elongation in the composite were characterised. It was found that the composite exhibited superplasticity (elongation > 400%) at high strain sates (similar to 0.1 s(-1)). In addition, the material showed a high strain rate sensitivity of 0.5 and an activation energy of 81 kJ mol(-1) in the superplastic region. Based upon these results, it was proposed that the dominant deformation mechanism is gain boundary sliding accommodated by a grain boundary diffusion process. A comparison of the superplastic behaviour was also made between the doubly extruded and singly extruded composites. (C) 1998 The Institute of Materials.INST MATERIALS, Jan. 1998, MATERIALS SCIENCE AND TECHNOLOGY, 14(1) (1), 32 - 35, English[Refereed]Scientific journal
- Mechanical alloying (MA) of solid solution strengthened Al-Mg-Li alloys can add additional strengthening via oxide and carbide dispersoids with 5 similar to 30 nanometer in size, and produce fine grains with sub-micron size. In this process, a large amount of non-equilibrium structural defects are introduced, which can significantly affect the mechanical properties of fine grained materials. For example, these materials have been shown to exhibit superplasticity at very high strain rates at moderate temperatures. Very limited data are available for the effect of grain size in MA materials. Therefore, mechanically-allayed Al-Mg-Li alloy with a grain size of 1.9 mu m was prepared by superplastic extrusion, and its strength compared with fine-grained material with grain size of 0.4 mu m. As a result, at an elevated temperature of 823 K, the strength of the fine grained alloy is lower than that of a coarse-grained one, and its ductility is higher. This result is expected owing to the occurrence of grain boundary sliding in the fine grained alloy. (C) 1998 Acta Metallurgica Inc.PERGAMON-ELSEVIER SCIENCE LTD, Dec. 1997, NANOSTRUCTURED MATERIALS, 8(8) (8), 1067 - 1075, English[Refereed]Scientific journal
- Oct. 1997, Proc. of The 8th International Conference on Adoptive Structures and Technology, 84 - 90, English, International magazineHigh Strain Rate Superplasticity and its ApplicationsInternational conference proceedings
- Sep. 1997, Mater. Sic. Forum, 233/234, 261 - 268, EnglishDuctility Enhancement at Elevated Temperatures in a ZK60-based Composite[Refereed]Scientific journal
- PERGAMON-ELSEVIER SCIENCE LTD, Sep. 1997, SCRIPTA MATERIALIA, 37(5) (5), 673 - 678, English[Refereed]Scientific journal
- Aug. 1997, Proc. of IMSP '97, 141 - 148, English, International magazineSuperplastic Behavior of ZK60 Magnesium Alloy in a Wide Range of TemperatureInternational conference proceedings
- May 1997, Rex'96 the third International Conference on Recrystallization and Related Phenomena, 529 - 536, English, International magazinePost Deformed Mechanical Properties and Microstructures in a Superplastically-Extruded in 905XL AlloyInternational conference proceedings
- Elsevier Ltd, Mar. 1997, Scripta Materialia, 36(6) (6), 699 - 705, English[Refereed]Scientific journal
- Superplastic characteristics in a doubly-extruded ZK60/SiC/17p magnesium-based compositeA fine-grained (similar to 1.7 mu m) magnesium-based composite, ZK60/SiC/17p, is shown to behave superplastically in a wide range of temperature. The influences of strain rate on the flow stress and elongation in the composite were characterized. It was found that the composite exhibited superplasticity (elongation > 300%) in a wide range of temperature (463 similar to 773 K). In addition, the material showed a high strain rate sensitivity of 0.5 and an activation energy of 81 kJ/mol at high strain rates (similar to 0.1 s(-1)) and at relatively high temperatures. Based upon these results, it was proposed that the dominant deformation mechanism is grain-boundary sliding accommodated by a grain-boundary diffusion process at high temperatures. Datum at a low temperature of 463 K (=0.5 Tm), however, does not fall on the liner function of the Arrhenius plot for the high temperature region. This indicates that the deformation mechanism at low temperatures is provably different form that at high temperatures.TRANS TECH PUBLICATIONS LTD, 1997, SUPERPLASTICITY IN ADVANCED MATERIALS - ICSAM-97, 243-2, 321 - 326, English[Refereed]Scientific journal
- Observation of superplasticity in a magnesium-based ZK60/SiC/17p composite at a low temperatureSuperplasticity was normally observed at relatively low strain rates (< 10(-3) s(-1)) and at temperatures above 0.5T(m),, where T-m, is the melting point of the material. Recent advances in material processing have resulted in the development of superplasticity at high strain rates (greater than or equal to 0.1 s(-1)) and low temperatures in materials with submicron-sized grains. Low temperature superplasticity, although often occurs at low strain rates, has many advantages over superplasticity at high temperatures. Recently, a fine-grained (similar to 1.7 mu m) magnesium-based composite (ZK60/SiC/17p) produced by PIM methods was shown to exhibit high strain rate superplasticity at about 623K, which corresponds to 0.67T(m), where T-m is the absolute melting point. In the present paper, we demonstrate that ZK60/SiC/17p composite also behaves in a superplastic manner at a low temperature (less than or equal to 0.5T(m)). The strain rate sensitivity, m, is measured to be 0.38. The examination of fractured specimens, however, indicates the occurrence of grain boundary sliding. A possible deformation mechanism at 463K is discussed.MINERALS, METALS & MATERIALS SOC, 1997, THERMEC '97 - INTERNATIONAL CONFERENCE ON THERMOMECHANICAL PROCESSING OF STEELS AND OTHER MATERIALS, VOLS I-II, 1847 - 1852, English, International magazineInternational conference proceedings
- Microstructure evolution during high-strain-rate superplastic flow in Al-Ni-misch metal alloy produced from amorphous powdersChanges in microstructure and deformation substructure in Al-14mass%Ni-14mass%misch metal alloy produced from amorphous powders were investigated during superplastic deformation at a high-strain-rate of 1s(-1) at 873K. Grain refinement occurred and the frequency of small angle boundaries increased in superplastically deformed specimens. Dynamic recovery and recrystallization occurred. Dislocations were observed in grains and were annihilated at grain boundaries during superplastic deformation. High-strain-rate superplasticity was mainly controlled by grain boundary sliding. Dislocations played an important role in the accommodation of residual stress induced by the grain boundary sliding. Small precipitates of Al(3)Mm and Al3Ni effectivaly suppressed the grain growth during annealing and acted as nucleation and/or annihilation sites of dislocations.MINERALS, METALS & MATERIALS SOC, 1997, THERMEC '97 - INTERNATIONAL CONFERENCE ON THERMOMECHANICAL PROCESSING OF STEELS AND OTHER MATERIALS, VOLS I-II, 1983 - 1989, English, International magazineInternational conference proceedings
- Feb. 1996, Mater. Sci. Forum, 204-206, 479 - 484, EnglishGrain Size Dependence on the Dynamic Characteristics in a Mechanically Alloyed IN905XL Alloy[Refereed]Scientific journal
- The deformation mechanisms of a fine grained Al-14 mass%Ni-14 mass%Mm [Mm=misch metal] crystalline alloy consolidated from its amorphous powders have been discussed from the mechanical data examined previously at strain-rates between 10(-3) and 100 s(-1) at temperatures from 773 to 898 K. This alloy exhibits superplasticity at unusually high strain rates of nearly 1 s(-1) in the temperature range from 848 to 885 K, which is close to the measured melting point. By incorporation of the temperature dependence of grain size, threshold stress and shear modulus into the constitutive equation, the activation energy is found to be 158 kJ mol(-1) at temperatures below the melting point. In the temperature range above the melting point, however, the activation energy is very large at more than 350 kJ mol(-1). This activation energy in the temperature range below the melting point is similar to that for lattice self-diffusion of aluminum, and all mechanical data in these temperatures ranges can be represented by a single equation. It is postulated that superplastic flow in the Al-Ni-Mm crystalline alloy is controlled by a grain boundary sliding mechanism accommodated by dislocation climb controlled by lattice self-diffusion at the solid state, and in the temperature range higher than the melting point is accommodated by the liquid phase at grain boundaries and/or interfaces. The further deformation mechanisms in high strain rate superplasticity should take the phase state of liquid and solid into account.JAPAN INST METALS, Dec. 1995, MATERIALS TRANSACTIONS JIM, 36(12) (12), 1467 - 1475, English[Refereed]Scientific journal
- Fine-grained IN905XL aluminum alloys with five grain sizes between 0.8 and 8.1 mu m have been developed by a combination of mechanical alloying and conventional extrusion in order to investigate the influence of the strain rate on the mechanical properties. Negative strain rate sensitivity of how stress is observed up to 10 s(-1) for all samples. Above the strain rate of 1 x 10(3) s(-1), however, all samples show the positive strain rate sensitivity of strength. Total elongation at high strain rates is generally larger than that at low strain rates. Flow stresses increase with decreasing grain size for ail strain rates. The measured values of strength of the coarse grained IN905XL with sizes above 4.3 mu m agree with the values estimated from a cooperation of the strengthening by the grain size refinement, magnesium solute atoms and oxides and carbides dispersion. In the Hall-Fetch relations at high strain rates, the gradient of the curve increases with increasing reciprocal square root of the grain size. For fine-grained samples, therefore, an additional strengthening mechanism should be considered such as the difference in the characteristics of the boundary.ELSEVIER SCIENCE SA LAUSANNE, Dec. 1995, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, A204(1-2) (1-2), 12 - 18, English[Refereed]Scientific journal
- Nov. 1995, Net Shape Processing of Powder Materials, AMD, ASME, 216, 99 - 107, English, International magazineStrength and Formability in Aluminum Alloys Produced by Mechanical AlloyingInternational conference proceedings
- Three IN905XL aluminum alloys with fine grain (1 mu m), intermediate grain (3 mu m), and coarse grain (5 mu m) have been developed by a combination of mechanical alloying (MA) and conventional extrusion in order to investigate their mechanical properties at dynamic strain rates of 1 X 10(3) and 2 X 10(3) s(-1) and a quasi-static strain rate of 10(-3) s(-1). Flow stresses are found to increase with decreasing grain size for all the strain rates tested. Negative strain-rate sensitivity of flow stress is observed up to 1 X 10(3) s(-1) in both intermediate- and coarse-grained IN905XL. At the highest strain rate of 2 x 10(3) s(-1), however, all samples showed a positive strain-rate sensitivity of strength. Total elongation at high strain rates is generally larger than that at low strain rates. Total elongation also decreases with grain size for all the strain rates. This decrease in elongation results from an initiation of microcracks at interfaces between the matrix and pal-tides finely dispersed near grain boundary regions, introduced during MA processing; then, this initiation leads elongation of alloys to small limited values.SPRINGER, Oct. 1995, METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 26A(10) (10), 2521 - 2526, English[Refereed]Scientific journal
- Aug. 1995, Proceedings of the Tenth International Conference Composite Materials, ICCM-10, vol. II: Metal Matrix Composites, 799 - 806, English, International magazineDeformation Behavior at Very High Strain Rates in a 17 vol% SiC/ZK60 CompositeInternational conference proceedings
- Jul. 1995, Proceedings of the 1995 International Conference on Metallurgical and Materials Applications of Shock-Wave and High-Strain-Rate Phenomena (EXPLOMET'95), 885 - 891, English, International magazineInfluence of Strain Rate on the Mechanical Properties in a Magnesium-base CompositeInternational conference proceedings
- MINERALS, METALS & MATERIALS SOC, Feb. 1995, Light Weight Alloys for Aerospace Applications III, 483 - 492, English, International magazineDynamic Deformation Characteristics in Mg-Li Binary alloysInternational conference proceedings
- Very high strain rate (also known as positive exponent) superplasticity in three mechanically alloyed IN9021, IN9052 and IN905XL aluminum alloys has been characterized over a wide range of strain rates between 10(-3) to 300 s(-1) in air at temperatures from 698 to 873 K. The temperature dependence of how stress, elongation and strain rate sensitivity exponent (m value) reveals that optimum superplasticity might occur at temperatures close to or above the melting point of each alloy. The presence of a liquid phase, resulting from the low melting point regions, as a result of solute segregation by mechanical alloying, is responsible for the observed positive exponent superplasticity. It is proposed that superplastic how at high strain rates is controlled by a grain boundary sliding mechanism accommodated with relaxing the stress concentration by isolated liquid phases at grain boundaries. Mechanically alloyed processing is a powerful method to produce the desired microstructures with not only fine grain size but also optimizing segregation in solute along boundaries, required for positive exponent superplasticity in aluminum alloys.JAPAN INST METALS, Feb. 1995, MATERIALS TRANSACTIONS JIM, 36(2) (2), 317 - 322, English[Refereed]Scientific journal
- The compressive behaviors at strain rates from 4×10-6 to 1×10-2 s-1 at temperatures from 1373 to 1448 K were characterized to investigate the influence of grain size for powder metallurgically processed TiAl intermetallics with fine grained structures of about 18 μm in size and ingot metallurgically processed TiAl with coarse grained structures of about 380 μm. For coarse and fine grained intermetallics of TiAl at higher stresses, stress exponent of about 4 is found and the rate controlling deformation may be a diffusion controlled dislocation process. At intermediate stresses for the fine grained TiAl, a stress exponent of about 2 is found, and the rate controlling deformation is proposed to be grain boundary sliding. In two different grained intermetallics, furthermore, the measured activation energy from 343 to 370 kJ/mol is obtained. © 1995, Japan Society of Powder and Powder Metallurgy. All rights reserved.1995, Journal of the Japan Society of Powder and Powder Metallurgy, 42(2) (2), 259 - 263, English[Refereed]Scientific journal
- Fine grained IN905XL aluminum alloys with five grain sizes between 0.8 and 8.1 μm have been developed by a combination of the mechanical alloying method and a conventional extrusion process in order to investigate the tensile properties at a dynamic strain rate of 2×103 s-1 and a quasi-static strain rate of 1×10-3 s-1. Total elongation at dynamic strain rates is generally larger than that at quasi-static strain rate. Total elongation also decreases with grain size for both strain rates. From an observation with scanning electron microscope (SEM), this trend is due to an initiation of micro-crack at the interface between the matrix and particles finely dispersed near grain boundary region, introduced during mechanically alloying processing, then leads elongation of alloys to small limited values. © 1995, Japan Society of Powder and Powder Metallurgy. All rights reserved.1995, Journal of the Japan Society of Powder and Powder Metallurgy, 42(2) (2), 180 - 184, English[Refereed]Scientific journal
- The Al-14wt.%Ni-14wt.%Mm (Mm = misch metal) alloy and the Al-14.8wt.%Ni-6.6wt%Mn-2.3wt.%Zr alloy have been produced by a high pressure gas atomization technique and a powder metallurgy method. Both alloys have a finely mixed structure consisting of aluminium phase and intermetallic compounds homogeneously embedded in the ultrafine-grained aluminium matrix. At room temperature, both alloys exhibit high tensile strength exceeding 800 MPa and at high temperature, nearly 873 K, high strain rate superplasticity is observed. In particular, a maximum elongation of 600% is obtained at a high temperature of 873 K at a constant strain rate of 1 s-1 in Al-Ni-Mm-Zr alloy. This strain rate is many orders of magnitude higher than those for typical commercial superplastic alloys. Both the grain size refinement of the aluminium matrix and the dispersion of intermetallic compounds are interpreted as contributing to the achievement of the ultrahigh tensile strength at room temperature and high strain rate superplasticity at high temperatures near 873 K.ELSEVIER SCIENCE SA, May 1994, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 181, 1068 - 1071, English[Refereed]Scientific journal
- The tensile behaviours of an Al-14wt.%Ni-14wt.%Mm (Mm = misch metal) crystalline alloy consolidated from its amorphous powders was characterized at strain rates between 10(-3) and 100 s-1 at temperatures from 773 to 898 K. This alloy exhibited superplasticity at unusually high strain rates of nearly 1 s-1 in a temperature range from 848 to 885 K. A maximum elongation of about 650% was obtained at a constant strain rate of 1 s-1 at a very high temperature of 885 K, which was close to or lower than the melting point. The microstructure of the Al-Ni-Mm crystalline alloy annealed in the optimum superplastic temperature range consists of grains with a mean size of about 1-2 mum and fine particulates a size of about 1.2 mum and a high volume fraction of about 40%. By incorporation of the temperature dependence of grain size and shear modulus into the constitutive equation, the stress exponent and the activation energy were found to be 2 and 421 kJ mol-1 respectively. It is postulated that superplastic flow in the Al-Ni-Mn crystalline alloy is controlled by a grain boundary sliding mechanism, but the accommodation process remained unclear.ELSEVIER SCIENCE SA, May 1994, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 181, 1064 - 1067, English[Refereed]Scientific journal
- INFLUENCE OF THE MAGNESIUM CONCENTRATION ON THE RELATIONSHIP BETWEEN FRACTURE MECHANISM AND STRAIN RATE IN HIGH PURITY AL-MG ALLOYSIn order to clarify the influence of magnesium atomic concentration in the solute on interaction with dislocations, Al-Mg binary alloys with various magnesium contents from 1.8 wt.% to 8.4 wt.% and aluminium in high purity were prepared. Furthermore, the influence of magnesium concentration on the fracture mechanism of these alloys has been investigated in the wide strain rate range from 1 x 10(-4) to 2 x 10(3) s(-1) at room temperature. Total elongations of prepared materials are larger at high strain rates. We suggest models of void nucleations, which are valuable for strain rates and concentrations of magnesium. Fractographs obtained by scanning electron microscopy observation revealed that the voids are very close together in alloys with high magnesium content, while void growth occurs to give a large ductile dimple failure in alloys with low magnesium content as the failure progresses. Large total elongations at high strain rates are caused by the change in the mode of void growth.ELSEVIER SCIENCE SA LAUSANNE, Mar. 1994, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, A176(1-2) (1-2), 181 - 189, English[Refereed]Scientific journal
- Certain microstructural characteristics, such as second-phase particles, solute atoms, gain size and grain orientation, affect the impact strength of aluminum alloys. In this paper, we discuss the influence of solute magnesium atoms on impact strength and ductility. In order to investigate the influence of solute magnesium atoms, five kinds of binary Al-Mg alloys with 2∼8 wt.% magnesium concentration and high-purity aluminum were used. Dynamic tensile tests (1.5×103s-1) were performed using a Hopkinson pressure bar system, and static tests (1×10-4, 2×10-3s-1) were performed with an Instron machine for reference. The values of flow stress at certain strain can be described as a linear function of magnesium concentration beyond 2.7 wt.%. Total elongation increases with increasing strain rate and decreases with increasing magnesium concentration.The Japan Society of Mechanical Engineers, Oct. 1993, 日本機械学会論文集(A編), 59(566) (566), 2356 - 2361, Japanese, Domestic magazine[Refereed]Scientific journal
- There are certain kinds of microstructural characteristics such as second-phase particles, solute atoms, grain size and grain orientation, which affect the impact strength of aluminum alloys. In this paper we discuss the influence of distribution of second-phase particles in various commericial Al-Mg-Si system alloys. Test alloys were prepared with five kinds of heat treatment : T4, under aging, T6, over aging and O temper. The deformation behavior of these alloys was investigated using a compression test at room temperature. Dynamic tests (4×102∼2×103s-1) were performed using a Hopkinson pressure bar system, and static tests (1×10-3∼1×10-ls-1) were performed with an Instron machine for reference. It has been revealed that strain rate sensitivity of flow stress varies with the interaction between second-phase particles and dislocations.The Japan Society of Mechanical Engineers, Oct. 1993, 日本機械学会論文集(A編), 59(566) (566), 2350 - 2355, Japanese, Domestic magazine[Refereed]Scientific journal
- The deformation behavior of aluminum single crystals (99.998% purity) was investigated using a compression test at room temperature. Static tests (1×10-5∼1×10-1 s-1) were performed with an Instron machine, and dynamic tests were performed using a Hopkinson pressure bar system. The flow stress of a crystal properly oriented for double slip increases with increasing strain rate in the range of 1×10-5 to 1×10-1 s-1, while that of crystals properly oriented for single slip is independent of strain rate in the same range. Flow stress increases rapidly with increasing strain rate beyond 4×102 s-1 for all crystals. From observation with a scanning electron microscope, it is revealed that as the strain increase, the density of slip bands increases and the contrast of slip bands is weakened.The Japan Society of Mechanical Engineers, May 1993, Transactions of the Japan Society of Mechanical Engineers Series B, 59(561) (561), 1208 - 1212, Japanese, Domestic magazine[Refereed]Scientific journal
- A new aluminium-based crystalline alloy, Al-14wt.%Ni-14wt.%Mm (Mm, misch metal), was prepared by warm consolidation of its amorphous powders. The as-extruded Al-Ni-Mm crystalline alloy had both an ultra fine-grained (70 nm) structure and a uniform distribution of very fine particulates (Al3Mm and Al3Ni) of size 70 nm. This alloy, without requiring any subsequent thermomechanical treatment, was found to behave in a superplastic manner at very high strain rates of about 1 s-1 at test temperatures of about 873 K.ELSEVIER SCIENCE SA LAUSANNE, Mar. 1993, JOURNAL OF ALLOYS AND COMPOUNDS, 193(1-2) (1-2), 29 - 32, English[Refereed]Scientific journal
- 1993, 軽金属, 43(5) (5), 252 - 257, Japanese実用アルミニウム合金の引張変形挙動に及ぼすひずみ速度の影響Scientific journal
- Mechanical properties at high strain rates were investigated by considering the specific strengthening mechanisms involving the effects of grain size, solid solution and second phase particles. Aluminum and its alloys were tested in tension or compression at strain-rates between 10-5 and 2000 S-1 at room temperature. The conclusions were as follows: (1) Aluminum tested at high strain rates could not exhibit strengthening due to grain size refinement according to the well known Hall-petch equation. (2) Solutes such as magnesium were able to increase the yield stress of aluminum at high strain rates. The yield stresses at high strain rates for Al-Mg alleys increased with magnesium addition, but the variation in strengthening rate with an additional content of magnesium was almost similar to that at low strain rates. (3) The treatment of strengthening by the second phase particles was clearly valid to improve the yield stress of Al-Mg-Si alloys at high strain rates. Basically, a decrease in the mean spacing between the second phase particles led the yield stress at high strain rates to be high, It was suggested that an optimum control in distribution of second phase particles was the most valid way for an improvement of the yield stress at high strain rates comparing with oher strengthening methods. © 1993, The Society of Materials Science, Japan. All rights reserved.1993, Journal of the Society of Materials Science, Japan, 42(483) (483), 1414 - 1419, English, Domestic magazine[Refereed]Scientific journal
- The stress and ductility of some commercial aluminum alloys (1050, 3003, 3004 and 5182) have been investigated as a function of strain rate over the range from 1-301 to 1-304 at room temperature. The nominal stresses at a strain of ε=0.105 for both 1050 and 3003 alloys increase with increasing strain rate, but the nominal stresses for both 3004and 5182 alloys decrease with increasing strain rate in the low and intermediate ranges from 1-10-3 to 1-201s. The alloys showing the above negative strain rate sensitivity of stress in this strain rate range contain magnesium atoms insolute. Therefore, this behavior of stress in these alloys is possibly related to the interaction between magnesium atomsin solute and dislocations. Uniform elongations of alloys except a 1050 alloy show the maximum values in an intermediate strain rate range. Total elongations increase with increasing strain rate for all alloys investigated. © 1993, The Japan Institute of Light Metals. All rights reserved.1993, journal of japan institute of light metals, 43(5) (5), 252 - 257, English, Domestic magazine[Refereed]Scientific journal
- High strain-rate superplasticity was obtained in the mechanically alloyed aluminum IN905XL alloy. Introducing a threshold stress into the rate equation, the true values of n and Q established. It is postulated that superplastic flow in the IN905XL alloy is controlled by a grain boundary sliding mechanism accommodated by dislocation climb or glide controlled by grain boundary diffusion. © 1993, Japan Society of Powder and Powder Metallurgy. All rights reserved.1993, Journal of the Japan Society of Powder and Powder Metallurgy, 40(3) (3), 337 - 340, English[Refereed]Scientific journal
- A mechanically alloyed IN9052 aluminum alloy with an ultra-fine grained structure is characterized at three temperatures of 773, 848 and 863 K and over a strain rate range from 1 X 10(-3) to 100 s-1. The maximum elongation of 330% was obtained at an extremely high strain rate of 10 s-1 at 863 K. In the high strain rate range, where superplasticity was found, a relatively high strain rate sensitivity of more than 0.3 (n = 3) was obtained.ELSEVIER SCIENCE SA LAUSANNE, Dec. 1992, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 159(1) (1), L1 - L4, English[Refereed]
- Nov. 1992, International Symposium on Impact Engineering, 1, 115 - 120, English, International magazineHIGH TEMPERATURE PROPERTIES AT HIGH STRAIN-RATES IN NEAR-NANO SCALE MATERIALSInternational conference proceedings
- Jun. 1992, Proc. of Aluminum-Lithium, 1111 - 1116, English, International magazineHigh Temperature Deformation Characteristics of Extruded 2090 Aluminum-Lithium Alloys in a Wide Range of Strain-RateInternational conference proceedings
- Jun. 1992, Proc. of Aluminum-Lithium, 1081 - 1086, English, International magazinePositive Exponent Strain-Rate Superplasticity in Mechanically Alloyed Aluminum IN905XLInternational conference proceedings
- Jun. 1992, The 8th International Congress on Heat Treatment of Materials, Heat & Surface '92, 231 - 234, English, International magazineMicrostructure Control for High Strain-rate Superplasticity in Aluminum-based AlloysInternational conference proceedings
- PERGAMON-ELSEVIER SCIENCE LTD, Mar. 1992, SCRIPTA METALLURGICA ET MATERIALIA, 26(5) (5), 761 - 766, English[Refereed]Scientific journal
- PERGAMON-ELSEVIER SCIENCE LTD, Jan. 1992, SCRIPTA METALLURGICA ET MATERIALIA, 26(2) (2), 185 - 190, English[Refereed]Scientific journal
- PERGAMON-ELSEVIER SCIENCE LTD, Jan. 1992, SCRIPTA METALLURGICA ET MATERIALIA, 26(2) (2), 191 - 196, English[Refereed]Scientific journal
- PERGAMON-ELSEVIER SCIENCE LTD, Sep. 1991, SCRIPTA METALLURGICA ET MATERIALIA, 25(9) (9), 2053 - 2057, English[Refereed]Scientific journal
- Jul. 1991, Proc. of ICM 6, Kyoto, 307 - 312, English, International magazineInfluence of temperature on stability of high strain rate deformation in some commercial aluminum alloysInternational conference proceedings
- Jun. 1991, Superplasticity in Advanced Materials, 569 - 574, English, International magazinePOSITIVE EXPONENT STRAIN-RATE SUPERPLASTICITY IN MECHANICALLY ALLOYED ALUMINUMInternational conference proceedings
- Jan. 1991, Journal de physique, IV, Colloque C3, Suppl. au Journal de Physique III, 1(C3) (C3), 347 - 352, English, International magazineTHE MICROSTRUCTURAL EVOLUTION DURING DEFORMATION UNDER SEVERAL STRAIN RATES IN A COMMERCIAL 5182 ALUMINUM ALLOY[Refereed]Scientific journal
- Jan. 1991, Journal de physique, IV, Colloque C3, Suppl. au Journal de Physique III, 1(C3) (C3), 341 - 346, English, International magazineSTRAIN RATE DEPENDENCE ON MECHANICAL PROPERTIES IN SOME COMMERCIAL ALUMINUM ALLOYS[Refereed]Scientific journal
- Dec. 1990, 材料, 39(447) (447), 1619 - 1624, Japanese, Domestic magazine実用アルミニウム合金の高速変形特性[Refereed]Scientific journal
- High strain-rate deformation characteristics in some commercial aluminium alloys, or 1050, 3003, 3004, 5182 and 7N01 alloys, have been investigated at high strain rate over 103S-1. The main conclusions are summarized as follows (1) The strain-rate sensitivity of flow stress in all commercial aluminium alloys has been observed in the high strain rate range. (2) Three types in typical change of ductility with strain rate have been observed in the high strain rate range the first is that little change in ductility over strain rate as both 1050 and 7N01 alloys, the second is that ductility increases with strain rate as both 3003 and 3004 alloys, and the last is that ductility decreases with strain rate as 5182 alloy. (3) The alloys, that show larger ductility in the high strain rate range than that in the low strain rate range, are both 3003 and 3004 alloys, but both alloys of 5182 and 7N01 show lower ductility in the high strain rate range than in the low strain rate range, and 1050 alloy shows no change in ductility. (4) In commercial aluminium alloys, it is clear that one of the requirements to obtain larger ductility in the high strain rate range is an increasing value of strain rate sensitivity exponent m with strain. © 1990, The Society of Materials Science, Japan. All rights reserved.1990, Journal of the Society of Materials Science, Japan, 39(447) (447), 1619 - 1624, English[Refereed]Scientific journal
- Jul. 1989, ADVANCES IN PLASTICITY, 421 - 424, English, International magazineInfluence of Strain Rate and Temperature on the Flow Stress and Ductility of Some Commercial Aluminum AlloysInternational conference proceedings
- Jul. 1989, ADVANCES IN PLASTICITY, 425 - 428, English, International magazineDynamic Flow Stress at Low Temperatures of 304N and 316L Stainless SteelsInternational conference proceedings
- 2021, スマートプロセス学会誌, 10(4) (4)Control of Microstructure in Ti-6Al-4V Porous Structure Fabricated by Electron Beam Powder Bed Fusion
- 2020, 軽金属学会大会講演概要, 138thEffect of aluminum and third element addition on enhancing dynamic fracture toughness in magnesium
- 2019, 軽金属学会大会講演概要, 136thマグネシウムの高速変形特性に及ぼすマンガンの影響
- 2019, 軽金属学会大会講演概要, 137th第一原理計算によるマグネシウムの衝撃靭性向上に向けた亜鉛添加効果の解明
- 2018, 軽金属学会大会講演概要, 135th超高速衝撃荷重下におけるマグネシウム合金の変形挙動に及ぼす溶質イットリウムの影響
- 2018, 日本金属学会講演概要(CD-ROM), 163rd超高速衝突変形によるマグネシウムの内部組織変化
- 2018, 軽金属学会大会講演概要, 134thマグネシウムの生体内分解性に与える溶質カルシウム元素の影響
- 2018, 軽金属学会大会講演概要, 134thマグネシウムの衝撃変形挙動に及ぼす亜鉛濃度の影響
- 2018, 軽金属学会大会講演概要, 135thマグネシウムの生体内分解性に及ぼす溶質元素添加の影響
- 2018, 日本金属学会講演概要(CD-ROM), 163rdマグネシウムの粒界強度および塑性異方性に対するマンガンの添加効果
- 2018, 日本金属学会講演概要(CD-ROM), 162ndマグネシウム合金の粒界強度および塑性異方性に対する溶質元素添加の効果
- 2017, 日本金属学会講演概要(CD-ROM), 161st生体内分解性Mg-Ca合金の異方性改善に対する第三元素の添加効果
- 2017, 日本金属学会講演概要(CD-ROM), 160thマグネシウム合金の衝撃破壊靭性に対する溶質元素添加の効果
- 2017, 日本金属学会講演概要(CD-ROM), 161st亜鉛の生体内分解性に及ぼす元素添加効果
- 2015, 軽金属学会大会講演概要, 128thMg-Ca合金の転位すべりおよび粒界強化効果に及ぼす第三元素の影響
- 2015, 日本金属学会講演概要(CD-ROM), 157thMg-Ca合金の衝撃靭性改善に寄与する第三元素添加効果
- 2015, 日本金属学会講演概要(CD-ROM), 157th微細結晶粒マグネシウムの常温延性に及ぼすイットリウムの添加効果
- The Japan Society of Mechanical Engineers, 18 Mar. 2014, 関西支部講演会講演論文集, 2014(89) (89), "3 - 21", Japanese312 Fracture Behavior of AZ31 Magnesium Alloy under Dynamic Loading
- The Japan Society of Mechanical Engineers, 18 Mar. 2014, 関西支部講演会講演論文集, 2014(89) (89), "3 - 22", Japanese313 Plastic Deformation Behavior of Dilute Mg-Y alloys
- The Japan Society of Mechanical Engineers, 18 Mar. 2014, 関西支部講演会講演論文集, 2014(89) (89), "3 - 28", Japanese319 Strengthening of Mg-Ca binary alloy by grain refinement
- The Japan Society of Mechanical Engineers, 18 Mar. 2014, 関西支部講演会講演論文集, 2014(89) (89), "3 - 23", Japanese314 Effect of Yttrium Addition on Ductility of Magnesium under dynamic loading
- The Japan Society of Mechanical Engineers, 10 Jan. 2014, バイオエンジニアリング講演会講演論文集, 2014(26) (26), 99 - 100, Japanese1C42 Fabrication of biodegradable Mg-0.3at.%Ca alloy with high strength
- 2014, 日本金属学会講演概要(CD-ROM), 155thマグネシウムの粒界すべりに及ぼす溶質原子の影響
- Fabrication of Porous Titanium Based Alloy for Medical Implantチタン製インプラントの創製を目指し、新規積層造形法を利用したポーラス材料の開発および力学機能制御因子の解明を試みた。大阪工研協会, Dec. 2013, 科学と工業, 87(12) (12), 428 - 432, JapaneseIntroduction scientific journal
- 日本材料学会, 27 Nov. 2013, 腐食防食部門委員会資料, 52(295) (295), 6 - 12, Japaneseマグネシウム合金の構造材への応用の現状と課題 (第295回例会 構造材料へのマグネシウム合金の適用の現状と腐食課題)
- 高圧ガス保安協会, 2013, 高圧ガス, 50(8) (8), 514 - 519, Japanese二次加工性に富み，等方変形可能な高強度希土類元素フリーマグネシウム合金[Refereed]Introduction scientific journal
- The Japan Society of Mechanical Engineers, 30 Nov. 2012, Materials and processing conference, 2012(20) (20), "437 - 1"-"437-3", Japanese437 Experimental study of penetrating artificial bone by high-strength Mg nail
- The Japan Society of Mechanical Engineers, 30 Nov. 2012, Materials and processing conference, 2012(20) (20), "610 - 1"-"610-3", Japanese610 Influence of strain rate and temperature on compression behavior of pure magnesium
- OS0304 Deformation behavior near crack-tip in magnesiumThe effect of microstructural factor, such as grain size, on the deformation behavior near the crack tip region during the fracture toughness test was investigated using wrought Mg-Al-Zn alloy. The stress distributions related to {10-12} twinning was predicted by FEA, and the microstructural evolutions were confirmed through experiments. This type of twinning was formed at the beginning of the fracture toughness test due to the creation of a large stress field near the crack-tip region. The formation region of twinning became small with grain refinement because of the changes in the dominant plastic deformations. The results from microstructure observations showed similarities to the stress distribution from FEA. These results can be used to predict the macroscopic deformation features near the crack-tip.The Japan Society of Mechanical Engineers, 22 Sep. 2012, M&M材料力学カンファレンス, 2012, "OS0304 - 1"-"OS0304-2", Japanese
- J041015 Effect of grain boundary structure on grain boundary migration in magnesiumThe grain boundary plasticity was investigated using [1-100] symmetric tilt boundaries in magnesium through MD simulation. Grain boundary migrations occurred without any influences on grain boundary structures due to the reduction in the internal energy. On the other hands, the grain boundary structures affected the distance of grain boundary movement; the grain boundaries with high energies enhanced the grain boundary migration. The grain boundary migration was also influenced by the addition of solute atoms; the solute atoms provided stability to the grain boundary structures in magnesium, and thus, suppressing the grain boundary migration.The Japan Society of Mechanical Engineers, 09 Sep. 2012, Mechanical Engineering Congress, Japan, 2012, "J041015 - 1"-"J041015-2", Japanese
- 日本材料学会, 2012, 学術講演会講演論文集, 61, 5 - 6, Japanese103 Effect of grain size on deformation mechanism near crack-tip region in magnesium alloys
- The Japan Society of Mechanical Engineers, 19 Sep. 2011, Abstracts of ATEM : International Conference on Advanced Technology in Experimental Mechanics : Asian Conference on Experimental Mechanics, 2011(10) (10), "OS19 - 3-4-1", EnglishOS19-3-4 Strengthening Mg-Al-Zn Alloys by Severe Plastic Rolling
- 日刊工業出版プロダクション, 2011, 工業材料, 59巻,pp.62-65(7) (7), 62 - 66, Japanese構造用途に向けたマグネシウム合金の適用課題 ~ねばり強くするために~Introduction scientific journal
- The development of a degrading biomaterial is highly desired for use in new treatment modalities. In the search for degradable materials, a new category of biomaterials made from corroding metals was noticed. Magnesium and its alloys are biodegradable metals and exhibit improved mechanical properties and corrosion resistance compared to pure magnesium and industrial magnesium alloys. Previous research has demonstrated that magnesium alloys have acceptable biocompatibility as new biodegradable biomaterials.SPRINGER-VERLAG TOKYO, 2010, INTERFACE ORAL HEALTH SCIENCE 2009, 318 - +, English
- The Japan Society of Mechanical Engineers, 16 Mar. 2009, 関西支部講演会講演論文集, 2009(84) (84), "3 - 23", Japanese323 Influence of Morphology of Dispersed Quasi-crystalline Phase in Mg-Zn-Y Alloys on Their Wear Property
- 日本鋳造工学会, 25 Feb. 2009, Journal of Japan Foundry Engineering Society, 81(2) (2), 70 - 76, JapaneseSurface and Interior Microstructure Changes of Aluminum Cast Iron by High Temperature Oxidation
- 日刊工業新聞社, Jul. 2008, 工業材料, 56(7) (7), 50 - 53, Japaneseジュラルミンに匹敵する高強度・高靱性マグネシウム合金創製の試み[Invited]Introduction scientific journal
- アグネ技術センター, Apr. 2008, Materials science & technology, 78(4) (4), 359 - 362, JapaneseHigh strength and fracture toughness of magnesium alloys by dispersion of icosahedral phase particles[Invited]Introduction scientific journal
- 日本材料学会, 2008, 学術講演会講演論文集, 57, 61 - 62, Japanese307 Prediction for deformation twins formation by FEM simulation and fracture toughness in wrought magnesium alloys
- 10 Oct. 2007, 大会講演概要, 113, 307 - 308, JapaneseCavitation behavior in superplastic Mg-Al-Zn alloys
- 11 Apr. 2007, 大会講演概要, 112, 377 - 378, JapaneseEffect of microstructural characteristics on fracture toughness in magnesium alloys
- 11 Apr. 2007, 大会講演概要, 112, 25 - 26, JapaneseFracture toughness of extruded Mg-Zn-Y alloy containing quasicrystal phase
- 11 Apr. 2007, 大会講演概要, 112, 31 - 32, JapanesePossible improvement of the strength-ductility balance in Al and Mg alloys by grain refinement
- 11 Apr. 2007, 大会講演概要, 112, 33 - 34, JapaneseSynthesis of high-strength Al-Fe alloy by mechanical milling and spark plasma sintering
- 日本材料学会, 2007, 学術講演会講演論文集, 56, 95 - 96, Japanese425 Investigations of fracture toughness in magnesium alloys produced by severe plastic deformation
- 13 Apr. 2006, 大会講演概要, 110, 163 - 164, EnglishMicrostructural evolution of Mg-Al binary alloys during extrusion process
- 13 Apr. 2006, 大会講演概要, 110, 187 - 188, JapaneseFracture toughness in extruded Mg-Zn alloys
- 13 Apr. 2006, 大会講演概要, 110, 189 - 190, EnglishThe effect of grain size and particle distribution on strength of Mg-Zn-Ho alloys containing quasicrystalline phase
- 日本材料学会, 2006, 学術講演会講演論文集, 55, 101 - 102, Japanese407 Effect of grain size on fracture toughness and deformed microstructure in magnesium alloys
- 日本材料学会, 2005, 学術講演会講演論文集, 54, 457 - 458, Japanese721 The Effect of Microstructure on Fracture Toughness in an AZ31 Magnesium alloy
- Ductility Enhancement of Magnesium under Dynamic LoadingImprovement of tensile mechanical properties under dynamic loading has been demonstrated for a commercial magnesium alloy of AZ31. A commercial AZ31 alloy was subjected to simple shear processing through ECAE(equal-channel-angular-extrusion) followed by annealing to develop a different texture compared with the directly-extruded alloy. During the dynamic tensile test, elongation-to-failure was more than twice higher than that of the directly-extruded alloy. Inspection of the fracture surface on the dynamically deformed sample revealed that the ECAE processed alloy followed by annealing fractured with the development of ductile dimples and few macro cracks, which is often observed on the fracture surface of magnesium alloys.The Japan Society of Mechanical Engineers, 05 Nov. 2004, Materials and processing conference, 2004(12) (12), 209 - 210, Japanese
- 01 Nov. 2004, 大会講演概要, 107, 151 - 152, JapaneseConstitutive equation and the deformation mechanism for superplastic flow in aluminum and magnesium alloys
- Oct. 2004, まてりあ, 43, 810 - 814, Japanese軽量化のための材料技術～マグネシウム合金の可能性～[Invited]Introduction scientific journal
- Aug. 2004, 工業材料, 52, 31 - 35, Japaneseマグネシウム合金の自動車部材への適用の期待と課題[Invited]Introduction scientific journal
- The Effect of Accelerated Aging Temperature on Friction and Wear Properties of AZ91 AlloyIn this study, casting material of AZ91 alloys have used as test specimens. Four kinds of test specimens aging-treated at 150℃, 175℃, 225℃ and 300℃ for 100 hours were used. The effect of temperature on accelerated aging on their friction and wear properties were evaluated by a pin-on-disk tester under dry condition at room temperature. As a result, it became clear that the coefficient of friction and the wear-resistance were affected by the accelerated aging temperature.The Japan Society of Mechanical Engineers, 17 Oct. 2003, Materials and processing conference, 2003(11) (11), 239 - 240, Japanese
- 20 Apr. 2003, 大会講演概要, 104, 253 - 254, JapaneseRole of Grain Boundary on the Deformation Behavior of Pure Magnesium at Room Temperature
- 社団法人日本材料学会, 15 Apr. 2003, 材料, 52(4) (4), 442 - 442, Japanese米国ローレンス・リバモア国立研究所に滞在して
- 日本塑性加工学会, 25 Jan. 2003, 塑性と加工, 44(504) (504), 10 - 14, JapaneseSuperplastic Forming of Magnesium Alloys
- Influence of Temperature and Strain Rate on Compressive Flow Stress in an AZ31 Mganesium AlloyA commercial AZ31 cast magnesium alloy was tested in compression in the temperature range from 296 K to 723 K and at strain rates of (10)^<-3>S^<-1>, (10)^<-2>S^<-1>, (10)^<-1>S^<-1> and (10)^<-3>S^<-1>. Based on the data obtained at the strain rate range from (10)^<-3>S^<-1> to 10^<-1>S^<-1>, the influence of the elevated temperature and the strain rates on the flow stress at a plastic strain of 0.1 was analyzed using the Zener-Hollomon parameter Z. The measured value of the strain rate sensitivity m varied from 0.11 at 523 K to 0.20 at 723 K. The measured value of the apparent activation energy was 144 kJ/mol.The Japan Society of Mechanical Engineers, 2003, 関西支部講演会講演論文集, 2003(78) (78), "10 - 9"-"10-10", Japanese
- 大阪工研協会, Dec. 2002, 科学と工業, 76(12) (12), 625 - 628, Japanese解説 マグネシウム板材作製装置 (機器特集)
- Dec. 2002, 鋳造工学, 74(12) (12), 828 - 834, Japanese軽金属セル構造体の衝撃エネルギー吸収特性[Invited]Introduction scientific journal
- 16 Oct. 2002, 大会講演概要, 103, 31 - 32, JapaneseBenefits and Tasks in Superplastic Forming of Magnesium Alloys
- 16 Oct. 2002, 大会講演概要, 103, 23 - 24, JapaneseLow temperature superplasticity in a ZK60 magnesium alloy processed by ECAE
- 日本材料学会, 2002, 学術講演会講演論文集, 51, 347 - 348, Japanese432 AZ91 マグネシウム合金の圧縮特性に及ぼす温度およびひずみ速度の影響
- Oct. 2001, 軽金属, 51, 503 - 508, Japaneseマグネシウム超塑性の研究[Invited]Introduction scientific journal
- 大阪工研協会, Sep. 2001, 科学と工業, 75(9) (9), 468 - 475, JapaneseAZ31マグネシウム合金切粉押出材の機械的性質に及ぼすひずみ速度の影響
- Jun. 2001, 金属, 71, 502 - 508, Japaneseマグネシウム合金の超塑性[Invited]Introduction scientific journal
- 25 Apr. 2001, 鋳物 : 講演大会講演概要集, 138, 26 - 26, Japanese実成形速度域における半溶融アルミニウム合金の圧縮変形挙動
- Lead, Feb. 2001, 塑性と加工, 42, 99 - 105, Japanese最近のマグネシウム合金板材加工技術[Invited]Introduction scientific journal
- 316 Enhancement of Dynamic Tensile Ductility in a Magnesium-based Composite through Controlling Its MicrostructureMechanical properties and microstructure have been investigated on a 17 vol% SiC paniculate-reinforced ZK60 magnesium-based composite (ASTM designation: ZK60/SiC/17p). The composite exhibits a high specific strength as well as a maraging steel, and limited ductility < 1%. In order to enhance the ductility under dynamic loading, additional extrusion was performed to homogenize the morphology in distributed reinforcements. It has been revealed that a homogeneous distribution of reinforcements is effective to enhance the ductility under dynamic loading.The Japan Society of Mechanical Engineers, 24 Nov. 2000, Materials and processing conference, 2000(8) (8), 119 - 120, Japanese
- 510 Effects of the Grain Size on Friction and Wear Properties of ZK60 Magnesium AlloyIn this research, wear and friction properties of a magnesium alloy have been studied in pin-on-disk under dry condition at room temperature. Used specimens are ZK60 magnesium alloys that have different grain sizes, and they are examined to investigate the influence of grain size exerted on friction and wear properties. As a result, it was proved that wear-resistance improved with increasing grain size. The coefficient of friction was about 0.3 for the coarse-grained alloy, and decreased with refining the grain structure.The Japan Society of Mechanical Engineers, 24 Nov. 2000, Materials and processing conference, 2000(8) (8), 173 - 174, Japanese
- アグネ技術センター, Nov. 2000, 金属, 70(11) (11), 979 - 985, Japanese, Domestic magazineECAEプロセスによる軽量金属材料の結晶粒微細化と機械的性質の改善Introduction scientific journal
- 25 Sep. 2000, 鋳物 : 講演大会講演概要集, 137, 62 - 62, Japanese軽量金属基セル構造体の衝撃エネルギー吸収能
- 大阪工研協会, May 2000, 科学と工業, 74(5) (5), 227 - 233, Japanese解説 マグネシウム材料の超塑性を利用した塑性加工
- 15 Apr. 2000, 大会講演概要, 98, 323 - 324, JapaneseMechanical Properties under Dynamic Loading in Fine-Grained Magnesium Alloys
- Apr. 2000, まてりあ, 39, 347 - 354, Japanese, Domestic magazineマグネシウム合金およびその複合材料における超塑性のための材料作製プロセスと変形挙動Introduction scientific journal
- 20 Mar. 2000, まてりあ : 日本金属学会会報, 39(3) (3), 299 - 299, Japanese大阪市立工業研究所
- 413 Study of improving wear resistance on magnesium alloy compositeThis paper was investigated in wear properties on ZK60 magnesium alloy, and 17vol.% SiC particle reinforced ZK60 magnesium alloy composite. And effect of SiC particle for wear resistance and wear mechanism was considered. Moreover effect of grain size was examined to improve wear resistance. The result shows that wear loss on SiC particle reinforced ZK60 magnesium alloy composite is increased due to falling of SiC particle and abrasive wear by fallen particle. It is important to enlarging grain size to improve wear resistance of magnesium alloy.The Japan Society of Mechanical Engineers, 16 Mar. 2000, 関西支部講演会講演論文集, 2000(75) (75), "4 - 19"-"4-20", Japanese
- 日本材料学会, 2000, 学術講演会講演論文集, 49, 223 - 224, Japanese217 軽量金属基セル構造体の衝撃エネルギ吸収利用
- May 1999, 大会講演概要, 96, 91 - 92, JapaneseFabrication of open-cellular AZ91 Mg-Aloy by casting
- May 1999, 大会講演概要, 96, 93 - 94, JapaneseEvaluation of Absorption Energy under Dynamic Loading in a Magnesium-based Cellular Structure
- 大阪工研協会, Mar. 1999, 科学と工業, 73(3) (3), 103 - 107, Japanese熱間押出ししたAZ31マグネシウム合金の超塑性挙動
- 30 Jan. 1999, 軽金属, 49(1) (1), 48 - 49, JapaneseTowards Innovation in Superplasticity
- Jan. 1999, 複合材料シンポジウム講演要旨集, 24, 53 - 54, JapaneseSuperplastic Behavior in Magnesium-Based Composite
- 09 Nov. 1998, 大会講演概要, 95, 233 - 234, JapaneseImprovement of Mechanical Properties under Dynamic Loading in AZ31 Alloy by Thermomechanical Treatment
- 01 May 1998, 大会講演概要, 94, 259 - 260, JapaneseInfluence of Strain Rate on the Mechanical Properties in Mg-Li Binary Alloys
- 大阪工研協会, Feb. 1998, Sci. Ind., 72(2) (2), 75 - 82, JapaneseSuperplasticity and Its Application in Metallic Materials
- 日本材料学会, 1998, 学術講演会講演論文集, 47, 165 - 166, Japanese507 マグネシウム合金基複合材料の強化粒子均一分散化による超塑性伸びの向上
- 日本材料学会, 1998, 学術講演会講演論文集, 47, 251 - 252, Japanese237 高速超塑性アルミニウム合金 P/M7475 における粒界すべりの粒界性格依存性
- 20 Oct. 1997, 大会講演概要, 93, 111 - 112, JapaneseInfluence of Strain Rate on the Mechanical Properties in 6061 Al-Based Composite Reinforced by Si_3N_4 Particles
- 大阪工研協会, Dec. 1996, 科学と工業, 70(12) (12), 501 - 504, Japanese200tf定速度押出機
- Nov. 1996, 大会講演概要, 91, 363 - 364, JapaneseDuctility at Elevated Temperatures in a ZK60 Magnesium-based Composite
- 日本材料学会, 1996, 学術講演会講演論文集, 45, 91 - 92, Japanese313 マグネシウム合金 ZK60 の超塑性に及ぼす結晶粒径の影響
- Nov. 1995, 大会講演概要, 89, 139 - 140, JapaneseDynamic Deformation Behavior in Aluminum Alloys Strengthening by Second Phase Particles
- 社団法人日本材料学会, 15 Jul. 1995, 材料, 44(502) (502), 984 - 984, Japanese第3回宇宙航空機用軽量合金に関するシンポジウム参加報告
- 14 Apr. 1995, 大会講演概要, 88, 75 - 76, JapaneseDeformation Behavior under Dynamic Strain Rate in Solid-Solution Hardening Aluminum Alloys
- 日本材料学会, 1993, 学術講演会前刷, 42, 231 - 233, Japanese228 Al-Ni-Mm-Zr合金の超塑性特性に及ぼす結晶粒径の影響(組織と変形I)
- 日本材料学会, 1989, 学術講演会前刷, 38, 320 - 322, Japanese323 実用アルミニウム合金の高速変形挙動(破壊と変形)
- Joint work, NTS, Feb. 2012, Japanese破壊力学大系-壊れない製品設計へ向けて-Scholarly book
- Contributor, マグネシウム合金, テクノシステム, 2010最新 フラクトグラフィ －各種材料の破面解析とその事例
- Contributor, マグネシウム合金, 丸善, 2007エコマテリアルハンドブック
- 日本金属学会2018年春期講演大会, Mar. 2018, Japanese, Domestic conferenceマグネシウム合金の粒界強度および塑性異方性に対する溶質元素添加の効果Poster presentation
- 平成29年度宇宙科学に関する室内実験シンポジウム, Feb. 2018, Japanese, Domestic conference等軸結晶粒からなる純マグネシウムの超高速衝撃荷重下における組織変化Poster presentation
- 軽金属学会関西支部 若手研究者・院生による研究発表会, Dec. 2017, Japanese, Domestic conference超高速衝撃下における純マグネシウムの組織変化Poster presentation
- 軽金属学会関西支部 若手研究者・院生による研究発表会, Dec. 2017, Japanese, Domestic conference生体内分解性マグネシウム合金の機械的性質に対する添加元素の役割解明Poster presentation
- 軽金属学会関西支部 若手研究者・院生による研究発表会, Dec. 2017, Japanese, Domestic conference高温高速せん断変形させたAl-Mg合金の組織変化に及ぼすシリコン添加の影響Oral presentation
- 軽金属学会関西支部 若手研究者・院生による研究発表会, Dec. 2017, Japanese, Domestic conference軽量フットペダル創製に向けたマグネシウム合金のマクロ/ミクロ構造設計Poster presentation
- 軽金属学会関西支部 若手研究者・院生による研究発表会, Dec. 2017, Japanese, Domestic conference亜鉛の生体内分解性に及ぼす結晶配向および元素添加の影響Poster presentation
- 軽金属学会関西支部 若手研究者・院生による研究発表会, Dec. 2017, Japanese, Domestic conferenceマグネシウム合金の衝撃破壊特性に及ぼすカルシウムおよび亜鉛添加の影響Poster presentation
- 軽金属学会関西支部 若手研究者・院生による研究発表会, Dec. 2017, Japanese, Domestic conferenceマグネシウム基コンポジットの機械的性質評価Poster presentation
- 軽金属学会関西支部 若手研究者・院生による研究発表会, Dec. 2017, Japanese, Domestic conferenceマグネシウムの生体内分解性に及ぼすカルシウム添加の影響Poster presentation
- 軽金属学会第133回秋期大会, Nov. 2017, Japanese, Domestic conference衝撃荷重下におけるMg-4%Al-1%Ca合金の変形挙動Oral presentation
- 軽金属学会第133回秋期大会, Nov. 2017, Japanese, Domestic conference高温高速せん断変形させたAl-4%Mg合金の組織変化におよぼすシリコン添加の影響Oral presentation
- 軽金属学会第133回秋期大会, Nov. 2017, Japanese, Domestic conferenceマグネシウム基アパタイト複合材料の機械的性質評価Poster presentation
- 第12回材料の衝撃問題シンポジウム, Oct. 2017, Japanese, Domestic conference衝撃圧縮荷重下におけるMg-Ca合金の変形応答に及ぼすCa添加の影響Poster presentation
- 第12回材料の衝撃問題シンポジウム, Oct. 2017, Japanese, Domestic conference純マグネシウムの超高速衝撃荷重下における変形応答Poster presentation
- 第12回材料の衝撃問題シンポジウム, Oct. 2017, Japanese, Domestic conference強ひずみ加工によるMg-3Al-1Zn合金の高靱性化Poster presentation
- 日本金属学会2017年秋期講演大会, Sep. 2017, Japanese, Domestic conference超高速衝撃荷重が作用した純マグネシウムの変形応答Oral presentation
- 日本金属学会2017年秋期講演大会, Sep. 2017, Japanese, Domestic conference生体内分解性Mg-Ca合金の異方性改善に対する第三元素の添加効果Poster presentation
- 日本金属学会2017 年秋期講演大会, Sep. 2017, Japanese, Domestic conference水酸アパタイト分散マグネシウム合金基複合材料の組織と 機械的特性Oral presentation
- 日本金属学会2017年秋期講演大会, Sep. 2017, Japanese, Domestic conference純亜鉛の圧縮変形に伴う組織変化Poster presentation
- 日本金属学会2017年秋期講演大会, Sep. 2017, Japanese, Domestic conference高温衝撃せん断ひずみ付与にともなうAl-Mg-Si合金の組織変化Poster presentation
- 日本金属学会2017年秋期講演大会, Sep. 2017, Japanese, Domestic conference亜鉛の生体内分解性に及ぼす結晶配向の影響Poster presentation
- 日本金属学会2017年秋期講演大会, Sep. 2017, Japanese, Domestic conferenceマグネシウム-亜鉛合金の分解性に及ぼす集合組織の影響Poster presentation
- 日本金属学会2017年秋期講演大会, Sep. 2017, Japanese, Domestic conferenceマグネシウムの衝撃破壊特性に及ぼすカルシウムおよび亜鉛の添加効果Poster presentation
- 日本金属学会2017年秋期講演大会, Sep. 2017, Japanese, Domestic conferenceCoCrFeMnNi系高エントロピー合金の室温変形メカニズムに関する基礎研究Poster presentation
- 日本バイオマテリアル学会関西ブロック第12回若手研究発表会, Aug. 2017, Japanese, Domestic conference亜鉛の生体内分解性に及ぼす元素添加効果Poster presentation
- The 7th Asian Symposium on Magnesium Alloys (ASMA7), Jun. 2017, English, International conferenceEffect of solute atoms on dynamic fracture toughness in magnesium alloysPoster presentation
- The 7th Asian Symposium on Magnesium Alloys (ASMA7), Jun. 2017, English, International conferenceEffect of calcium on compressive deformation response of Mg-Ca alloyPoster presentation
- 軽金属学会第132回春期大会, May 2017, Japanese, Domestic conference高温高速せん断ひずみ付与にともなうAl-Mg-Si合金の組織変化Poster presentation
- 軽金属学会第132回春期大会, May 2017, Japanese, Domestic conferenceマグネシウムの高速圧縮変形挙動に及ぼすカルシウムの添加効果Poster presentation
- 日本金属学会 2017 年春期講演大会（第160回）, Mar. 2017, Japanese, Domestic conferenceマルチパス溝ロール圧延による Mg-3Al-1Zn 合金の結晶組織制御Poster presentation
- 日本金属学会 2017 年春期講演大会（第160回）, Mar. 2017, Japanese, Domestic conferenceマグネシウム合金の衝撃破壊靭性に対する溶質元素添加の効果Poster presentation
- 日本金属学会 2017 年春期講演大会（第160回）, Mar. 2017, Japanese, Domestic conferenceマグネシウムのin vitro疲労特性に与えるカルシウム添加の影響Oral presentation
- 軽金属学会 第 131 回秋期大会, Nov. 2016, Japanese, Domestic conference生体内分解性マグネシウム合金の疲労特性に及ぼすZn添加の影響Poster presentation
- 軽金属学会 第 131 回秋期大会, Nov. 2016, Japanese, Domestic conference衝撃荷重下におけるAl-Mg二元合金の変形挙動Oral presentation
- 軽金属学会 第 131 回秋期大会, Nov. 2016, Japanese, Domestic conference高強度マグネシウム合金の骨組織への貫入応答評価Oral presentation
- 軽金属学会 第 131 回秋期大会, Nov. 2016, Japanese, Domestic conference高温衝撃圧縮荷重の作用によるAlMg-Si合金の組織変化Poster presentation
- 軽金属学会 第 131 回秋期大会, Nov. 2016, Japanese, Domestic conference強度および生体内分解速度の最適化に向けたMg-Zn合金のミクロ組織制御Oral presentation
- 軽金属学会 第 131 回秋期大会, Nov. 2016, Japanese, Domestic conference強ひずみ圧延加工によるMg-3Al-1Zn合金の衝撃破壊靱性改善Poster presentation
- 日本金属学会 2016 年秋期講演大会（第159回）, Sep. 2016, Japanese, Domestic conference高温・衝撃荷重下における純マグネシウムの圧縮変形応答Poster presentation
- 日本金属学会 2016 年秋期講演大会（第159回）, Sep. 2016, Japanese, Domestic conferenceマグネシウム合金の疲労特性に及ぼす Ca および Zn の添加効果Poster presentation
- 軽金属学会 第 130 回春期大会, May 2016, Japanese, Domestic conferenceAl-Mg二元合金の粒界強度に及ぼす溶質マグネシウム濃度の影響Oral presentation
- 日本金属学会 2016 年春期講演大会（第 158 回）, Mar. 2016, Japanese, Domestic conference有限要素解析を利用した生体内分解性マグネシウム合金製ステントの創製Oral presentation
- 日本金属学会 2016 年春期講演大会（第 158 回）, Mar. 2016, Japanese, Domestic conference生体内分解性 Mg-Zn 合金の高強度化および分解性評価Poster presentation
- 日本金属学会 2016 年春期講演大会（第 158 回）, Mar. 2016, Japanese, Domestic conference衝撃荷重下における純マグネシウムの一軸圧縮変形応答Poster presentation
- 日本金属学会 2016 年春期講演大会（第 158 回）, Mar. 2016, Japanese, Domestic conference高速変形による CoCrFeMnNi 系 HEA の変形帯形成Poster presentation
- TMS Annual meeting, Mar. 2016, English, International conferenceLattice Ordering and Microstructure of Ultra-High Strength Mg-Ca-Zn AlloysOral presentation
- Twenty-Fourth International Symposium on Processing and Fabrication of Advanced Materials (PFAM XXIV) 2015, Dec. 2015, English, International conferenceThe mechanical performance of biodegradability magnesium alloy stentInvited oral presentation
- Twenty-Fourth International Symposium on Processing and Fabrication of Advanced Materials (PFAM XXIV) 2015, Dec. 2015, English, International conferenceInfluence of calcium concentration on superplastic behavior in Mg-Ca binary alloysOral presentation
- Twenty-Fourth International Symposium on Processing and Fabrication of Advanced Materials (PFAM XXIV) 2015, Dec. 2015, English, International conferenceEvaluation of in vitro fatigue of the biodegradable Mg-Ca alloy in simulated body fluidInvited oral presentation
- Twenty-Fourth International Symposium on Processing and Fabrication of Advanced Materials (PFAM XXIV) 2015, Dec. 2015, English, International conferenceEffect of calcium solute addition on improving mechanical properties of magnesium alloysOral presentation
- ICSAM 2015, Sep. 2015, English, International conferenceSuperplastic Deformation Behavior in Dual-Phase Mg-Ca AlloyOral presentation
- Mg 2015, Sep. 2015, English, International conferenceEffect of Zinc and Calcium Solute Additions on Deformation Behavior of Mg Estimated by First Principles CalculationOral presentation
- Biomaterials International 2015, Jun. 2015, English, International conferenceStrength ening and Degradation Behavior of Magnesium-Cal cium Binary AlloyOral presentation
- Biomaterials International 2015, Jun. 2015, English, International conferenceExperimental Study of Enhancing strength and ductility in Mg-Zn-Ca alloy for bio-absorbable stent applicationOral presentation
- Biomaterials International 2015, Jun. 2015, English, International conferenceEnhancement of ductility in Mg-Zn-Ca alloy for fastening soft tissueOral presentation
- 日本機械学会関西支部 平成26年度関西学生会学生員卒業研究発表講演会, Mar. 2015, Japanese, Domestic conference第三元素の添加による Mg-Ca 合金の粒界強化効果Oral presentation
- 日本金属学会第156回 春期講演大会, Mar. 2015, Japanese, Domestic conference双晶を導入した純マグネシウムの減衰能Oral presentation
- 日本機械学会関西支部 平成26年度関西学生会学生員卒業研究発表講演会, Mar. 2015, Japanese, Domestic conference生体内分解性 Mg-Zn 合金の強度－分解性バランスOral presentation
- 日本機械学会関西支部 平成26年度関西学生会学生員卒業研究発表講演会, Mar. 2015, Japanese, Domestic conference強ひずみ加工による CoCrFeMnNi 合金の高強度化Oral presentation
- 日本機械学会関西支部 平成26年度関西学生会学生員卒業研究発表講演会, Mar. 2015, Japanese, Domestic conference強ひずみ加工による Al-Mg 合金の高強度化Oral presentation
- 日本機械学会関西支部 平成26年度関西学生会学生員卒業研究発表講演会, Mar. 2015, Japanese, Domestic conference亜鉛添加による生体内分解性マグネシウム合金の高強度化Oral presentation
- 日本機械学会関西支部 平成26年度関西学生会学生員卒業研究発表講演会, Mar. 2015, Japanese, Domestic conferenceマグネシウム合金の加工硬化挙動に及ぼすイットリウム添加の影響Oral presentation
- TMS2015 144th Annual Meeting & Exhibition, Mar. 2015, English, Orlando, USA, International conferenceRole of Yttrium Solute on Compression Behavior of Mg-Y AlloyOral presentation
- TMS2015 144th Annual Meeting & Exhibition, Mar. 2015, English, Orlando, USA, International conferenceEffect of Alloy Composition on Microstructure and Strength of Fine Grained Extruded Mg-Zn-Y alloys Containing Quasicrystal PhaseOral presentation
- 日本機械学会関西支部 平成26年度関西学生会学生員卒業研究発表講演会, Mar. 2015, Japanese, Domestic conferenceECAE 加工を施した Mg-Ca 合金の機械的特性Oral presentation
- TMS2015 144th Annual Meeting & Exhibition, Mar. 2015, English, Orlando, USA, International conferenceDeformation Response of Mg-Y Alloys under Dynamic LoadingOral presentation
- TMS2015 144th Annual Meeting & Exhibition, Mar. 2015, English, Orlando, USA, International conferenceDeformation Behavior of Binary Magnesium Alloys Under Dynamic LoadingInvited oral presentation
- 日本軽金属学会第127回秋期大会, Nov. 2014, Japanese, Domestic conference生体分解性デバイス向けたマグネシウム合金の 高延性化Oral presentation
- 日本軽金属学会第127回秋期大会, Nov. 2014, Japanese, Domestic conference生体内分解性Mg-Ca合金の擬似体液環境に おける疲労特性Oral presentation
- 日本軽金属学会第127回秋期大会, Nov. 2014, Japanese, Domestic conferenceMg-Ca系二相合金の高温変形特性Poster presentation
- 日本金属学会第155回 秋期講演大会, Sep. 2014, Japanese, Domestic conference生体用マグネシウム合金の機械的性質に与えるカルシウム濃度の影響Oral presentation
- 日本金属学会第155回 秋期講演大会, Sep. 2014, Japanese, Domestic conference生体軟組織固定に向けたマグネシウム合金の高延性化Poster presentation
- 日本金属学会第155回 秋期講演大会, Sep. 2014, Japanese, Domestic conference生体内分解性を有するマグネシウム・ステント創製に向け た材料およびモデルの検討Poster presentation
- 日本金属学会第155回 秋期講演大会, Sep. 2014, Japanese, Domestic conference純マグネシウムにおける一軸変形応答と減衰能の対比Oral presentation
- 日本金属学会第155回 秋期講演大会, Sep. 2014, Japanese, Domestic conferenceマグネシウムの粒界すべりに及ぼす溶質原子の影響Poster presentation
- 日本金属学会春期（154回）大会, Mar. 2014, Japanese, Domestic conference人工骨に対するマグネシウム合金製ネイルの貫入性能評価Oral presentation
- 日本機械学会 第26回バイオエンジニアリング講演会, Jan. 2014, Japanese, Domestic conference高強度を有する生体内分解性 Mg-0.3at.%Ca 合金の開発Oral presentation
- International Symposium on EcoTopia Science 2014, Dec. 2013, English, International conferenceStrength and in vitro degradation behavior of fine-grained Mg-Ca alloysPoster presentation
- International Symposium on EcoTopia Science 2013, Dec. 2013, English, International conferenceMechanical Response of Mg-Ca Alloy Nails Penetrating the Bone Tissue and Their in vitro Degradation BehaviorPoster presentation
- International Symposium on EcoTopia Science 2015, Dec. 2013, English, International conferenceEnhancement of Damping Capacity in Magnesium for Biomedical Implant ApplicationPoster presentation
- 日本軽金属学会秋期（124回）大会, Nov. 2013, Japanese, Domestic conferenceMg-Ca合金の生体内分解性および力学特性に及ぼすカルシウム濃度の影響Poster presentation
- 日本軽金属学会秋期（124回）大会, Nov. 2013, Japanese, Domestic conferenceAZ31マグネシウム合金の衝撃破壊靭性に及ぼす結晶組織の影響Poster presentation
- The 4th Symposium of Indian Scientists Association in JAPAN(ISAJ)．India-Japan Symposium on Emerging Materials for Health, Environment and Safety, Oct. 2013, English, International conferenceGrain refinement of magnesium alloys for improving mechanical performance[Invited]Invited oral presentation
- The 4th Symposium of Indian Scientists Association in JAPAN(ISAJ)．India-Japan Symposium on Emerging Materials for Health, Environment and Safety, Oct. 2013, English, International conferenceDeformation response of pure magnesium under dynamic compression loadingPoster presentation
- 日本金属学会秋期（153回）大会, Sep. 2013, Japanese, Domestic conferenceカルシウム添加したマグネシウム合金の擬似体液中における分解挙動Oral presentation
- The 8th International Symposium on Impact Engineering (ISIE-2013), Sep. 2013, English, International conferenceEvaluation of impact fracture toughness of AZ31 magnesium alloyPoster presentation
- The 8th International Symposium on Impact Engineering (ISIE-2013), Sep. 2013, English, International conferenceDeformation behavior of porous materials characterized with high speed imagingOral presentation
- The 8th International Symposium on Impact Engineering (ISIE-2013), Sep. 2013, English, International conferenceDeformation behavior of Mg-Y alloy under dynamic compression loadingPoster presentation
- PRICM 8, Aug. 2013, English, Hawaii, International conferenceDegradation behavior and mechanical properties of Mg-Ca alloy after immersion in simulated body fluidOral presentation
- 軽金属学会第124回春期大会(2013), May 2013, Japanese, Domestic conferenceAZ31マグネシウム合金の衝撃破壊靱性評価Poster presentation
- 日本機械学会 関西学生会平成24年度学生員卒業研究発表講演会, Mar. 2013, Japanese, Domestic conference純マグネシウムの変形挙動に及ぼすひずみ速度の影響Poster presentation
- 日本機械学会 関西学生会平成24年度学生員卒業研究発表講演会, Mar. 2013, Japanese, Domestic conferenceβ型Mg-Li系合金の高温変形特性Oral presentation
- 日本機械学会 関西学生会平成24年度学生員卒業研究発表講演会, Mar. 2013, Japanese, Domestic conferenceマグネシウム円管の衝撃エネルギー吸収能評価Oral presentation
- 日本金属学会春期（152回）大会, Mar. 2013, Japanese, Domestic conferenceカルシウム添加によるマグネシウム合金の高強度化と生体内分解性評価Oral presentation
- 日本金属学会2013年春期(第152回)講演大会, Mar. 2013, Japanese, Domestic conferenceカルシウム添加によるマグネシウム合金の高強度化と生体内分解性評価Oral presentation
- 日本金属学会2013年春期(第152回)講演大会, Mar. 2013, Japanese, Domestic conferenceイットリウム添加によるマグネシウム合金の延性改善効果Oral presentation
- 日本金属学会2013年春期(第152回)講演大会, Mar. 2013, Japanese, Domestic conferenceYを微量添加したマグネシウム合金の塑性変形応答Oral presentation
- 日本金属学会2013年春期(第152回)講演大会, Mar. 2013, Japanese, Domestic conferenceYを極微量添加したMg合金の室温圧縮変形による再結晶組織形成過程の観察Oral presentation
- TMS2013 142nd Annual Meeting & Exhibition, Mar. 2013, English, International conferenceMicrostructure Design of Ultra-Fine-Grained Mg-Al Alloy for Bioabsorbable Implant ApplicationsOral presentation
- 日本機械学会 関西学生会平成24年度学生員卒業研究発表講演会, Mar. 2013, Japanese, Domestic conferenceMg-Ca合金のin vitro分解性および力学的特性評価Oral presentation
- 日本機械学会 関西学生会平成24年度学生員卒業研究発表講演会, Mar. 2013, Japanese, Domestic conferenceMg-Al-Zn系合金の衝撃破壊靭性評価Poster presentation
- TMS2013 142nd Annual Meeting & Exhibition, Mar. 2013, English, International conferenceIncreasing Volume Fraction of Precipitates and Strength of a Mg-Zn-Y Alloy by Pre-Aging DeformationOral presentation
- TMS2013 142nd Annual Meeting & Exhibition, Mar. 2013, English, International conferenceEvolution of Microstructure during Caliber Rolling of AZ31 AlloyOral presentation
- TMS2013 142nd Annual Meeting & Exhibition, Mar. 2013, English, International conferenceEffect of Microstructural Factors on Damping Capacity in Pure MagnesiumOral presentation
- 東北大学金属材料研究所共同研究ワークショップ・第35回日本バイオマテリアル学会東北地域講演会, 2013, Japanese, Domestic conference生体内分解性マグネシウム合金の強度・分解性制御[Invited]Invited oral presentation
- TMS2013 142nd Annual Meeting & Exhibition, 2013, English, International conferenceIncreasing Volume Fraction of Precipitates and Strength of a Mg-Zn-Y Alloy by Pre-Aging DeformationOral presentation
- International Union of Materials Research Society - International Conference in Asia (IUMRS-ICA) 2013, 2013, English, International conferenceGrain Refinement and Textue Modification of Magnesium Alloys for improving Mechanical Performance[Invited]Invited oral presentation
- TMS2013 142nd Annual Meeting & Exhibition, 2013, English, International conferenceEvolution of Microstructure during Caliber Rolling of AZ31 AlloyOral presentation
- TMS2013 142nd Annual Meeting & Exhibition, 2013, English, International conferenceEffect of Microstructural Factors on Damping Capacity in Pure MagnesiumOral presentation
- 日本機械学会第20回機械材料・材料加工技術講演会(M&P2012), Dec. 2012, Japanese, Domestic conference純マグネシウムの圧縮変形応答に及ぼすひずみ速度及び温度の影響Oral presentation
- 日本機械学会第20回機械材料・材料加工技術講演会(M&P2012), Dec. 2012, Japanese, Domestic conference高強度マグネシウム合金製ネイルの人工骨への貫入に関する研究Oral presentation
- 軽金属学会第123回秋期大会(2012), Nov. 2012, Japanese, Domestic conference結晶粒微細化による生体内分解性Mg-Ca合金の高強度化Poster presentation
- 軽金属学会第123回秋期大会(2012), Nov. 2012, Japanese, Domestic conferenceMg-Y二元合金の衝撃延性Poster presentation
- 日本金属学会2012年秋期(第151回)講演大会, Sep. 2012, Japanese, Domestic conference純Mg のダンピング特性に及ぼす双晶及び底面配向の影響Oral presentation
- 日本金属学会2012年秋期(第151回)講演大会, Sep. 2012, English, Domestic conferenceFormation of twin related nano-domains during fracture of a fine grained magnesium alloyOral presentation
- IUMRS-ICA(International Union of Materials Research Societies International Conference in Asia 2012), Aug. 2012, English, International conferenceTexture Change due to Tensile Superplastic Deformation in Fine-Grained Magnesium AlloysOral presentation
- IUMRS-ICA(International Union of Materials Research Societies International Conference in Asia 2012), Aug. 2012, English, International conferenceAchieving Very High Isotropic Strength with Ductility by Simple Processing of Mg-Zn-Y Alloys Containing Quasicrystal PhaseOral presentation
- NIMS Conference 2012, Jun. 2012, English, つくば国際会議場, International conferenceFormation of nano-scale twins and double twins during fracture of fine grained magnesium alloysOral presentation
- 日本材料学会 第61期学術講演会, May 2012, Japanese, 岡山大学, Domestic conferenceき裂先端部の変形メカニズムに及ぼす結晶粒径の影響Oral presentation
- 日本金属学会2012年春期大会, Mar. 2012, Japanese, 横浜国立大学, Domestic conference純マグネシウムのホール・ペッチ則に及ぼすひずみ速度の影響Poster presentation
- 日本金属学会2012年春期大会, Mar. 2012, Japanese, 横浜国立大学, Domestic conference骨への貫入性能を有するマグネシウム合金創製に向けた基礎研究Poster presentation
- 日本金属学会2012年春期大会, Mar. 2012, Japanese, 横浜国立大学, Domestic conferenceカルシウム添加による生体内分解性マグネシウム合金の高強度化Poster presentation
- 日本金属学会2012年春期大会, Mar. 2012, Japanese, 横浜国立大学, Domestic conferenceMg-Y二元合金の高速変形応答Poster presentation
- 日本金属学会2012年春期(第150回)講演大会, Mar. 2012, Japanese, Domestic conferenceMg-Y 合金の潤滑下トライボロジー特性と摩擦に伴う内部組織の変形挙動Poster presentation
- 日本金属学会2012年春期大会, Mar. 2012, Japanese, 横浜国立大学, Domestic conferenceMg-Y合金の潤滑下トライボロジー特性とそれに伴う内部組織の変形挙動Poster presentation
- TMS 2012 Annual Meeting, Magnesium Technology 2012, Mar. 2012, English, Orlando Convention Center, International conferenceFORMATION OF NANO-SCALE TWINS AND LOW ANGLE GRAIN BOUNDARIES DURING FRACTURE OF A FINE GRAINED MAGNESIUM ALLOYSOral presentation
- TMS 2012 Annual Meeting, Magnesium Technology 2012, Mar. 2012, English, International conferenceEvaluating the effect of pre-ageing deformation on beta-prime precipitate size and distribution in Mg-Zn(-Y) AlloysOral presentation
- TMS 2012 Annual Meeting, Magnesium Technology 2012, Mar. 2012, English, Orlando Convention Center, International conferenceDevelopment of High Strength and Toughness Magnesium Alloy by Grain Boundary ControlOral presentation
- 日本金属学会2011年秋期大会, Nov. 2011, Japanese, 沖縄コンベンションセンター, Domestic conference添加剤を含む潤滑油下における純マグネシウムの摩擦摩耗特性の評価Poster presentation
- 日本金属学会2011年秋期大会, Nov. 2011, Japanese, 沖縄コンベンションセンター, Domestic conference超微細結晶粒Mg-Zn-Ca 合金の超塑性Poster presentation
- 日本金属学会2011年秋期大会, Nov. 2011, Japanese, 沖縄コンベンションセンター, Domestic conference純マグネシウムのダンピング特性に及ぼす結晶粒組織の影響Poster presentation
- 日本金属学会2011年秋期大会, Nov. 2011, Japanese, 沖縄コンベンションセンター, Domestic conferenceナノインデンテーションを用いたマグネシウムの粒界・粒内クリープの評価Poster presentation
- 日本金属学会2011年秋期(第149回)講演大会, Nov. 2011, English, Domestic conferenceThe effect of β1′Precipitate refinement on the strength and ductility of Mg-Zn(-Y) alloysPoster presentation
- ASMA-4, Oct. 2011, English, International conferencePossibility for development of high strength and toughness magnesium alloysInvited oral presentation
- ATEM’11, JEME-MMD, Sep. 2011, English, 神戸国際会議場, International conferenceStrengthening Mg-Al-Zn Alloys by Severe Plastic RollingOral presentation
- ATEM’11, JEME-MMD, Sep. 2011, English, 神戸国際会議場, International conferenceProduction of Ultrafine Grain Size by Direct Extrusion of a Chill Cast Mg-Zn-Y Alloy Containing Quasicrystal Phase with A Very High Isotropic StrengthOral presentation
- ATEM’11, JEME-MMD, Sep. 2011, English, 神戸国際会議場, International conferenceDevelopment of High Strength and Toughness Magnesium Alloys by Microstructural ControlsOral presentation
- 第 146 回超塑性研究会 「先進マグネシウム合金の展開」, Jun. 2011, Japanese, 千葉工業大学津田沼キャンパ, Domestic conference構造用途に向けたマグネシウム合金の結晶粒微細化Invited oral presentation
- TMS 2011 Annual Meeting/Magnesium Technology 2011, Mar. 2011, English, TMS, San Diego, International conferenceImproved Processing of Mg-Zn-Y Alloys Containing Quasicrystal Phase for Isotropic High Strength and DuctilityOral presentation
- TMS 2011 Annual Meeting/Magnesium Technology 2011, Mar. 2011, English, TMS, San Diego, International conferenceFracture Mechanism and Toughness in Fine- and Coarse-Grained Magnesium Alloys[Invited]Invited oral presentation
- TMS 2011 Annual Meeting, Mar. 2010, English, TMS, San Diego, USA, International conferenceStrengthening Mg-Al-Zn Alloy by Repetitive Oblique Shear StrainOral presentation
- International Magnesium Symposium for Advanced Industry Trends, Dec. 2007, English, International conferenceProgress in Wrought Mg Alloy Development and Improvement of Mechanical Properties[Invited]Invited oral presentation
- 2nd Asian Symposium on Magnesium Alloys (ASMA-Ⅱ), Oct. 2007, English, International conferenceDesign of high-strength, high Ductility and High Toughness Magnesium Alloys by Dispersion of Nano-sized lcosahedral Phase Particles[Invited]Invited oral presentation
- 2nd Asian Symposium on Magnesium Alloys (ASMA-Ⅱ), Oct. 2007, English, International conferenceEffect of Texture and Grain Size on the Strengthening of Mg Alloys with Ductility[Invited]Invited oral presentation
- The 17th Iketani Conference: The Doyama Symposium on Advanced Materials, Sep. 2007, English, International conferenceMicrostructure design of high-strength Mg alloy with ductility and toughness[Invited]Invited oral presentation
- International Magnesium Workshop, May 2007, English, International conferenceDuctility Enhancement in Mg Alloys at High Strain Rate[Invited]Invited oral presentation
- 4th International conference on materials processing for properties and performance, 2005, English, International conferenceImprovement of strength and ductility balance in Mg alloys by modification of grain structure[Invited]Invited oral presentation
- Hot Deformation of Aluminum III, 2003 TMS Annual Meeting, Mar. 2003, English, The Minerals, Metals & Materials Society, International conferenceHigh Strain Rate Superplasticity in Aluminum Alloys and Review of Its Current Commercial Applications[Invited]Invited oral presentation
- Platform Science and Technology in Advanced Magnesium 2003, Jan. 2003, English, International conferenceGuide for enhancement of room temperature ductility in Mg alloys at high strain rates[Invited]Invited oral presentation
- 2002 TMS Annual Meeting, Feb. 2002, English, Seattle, United States, International conferenceGrain Refinement and Superplasticity in Magnesium Alloys[Invited]Invited oral presentation
- 2002 TMS Annual Meeting, Feb. 2002, English, Seattle, United States, International conferenceStudy on the Superplastic Deformation Mechanism using Magnesium-Based Materials[Invited]Invited oral presentation
- Platform Science and Technology in Advanced Magnesium 2000, Jul. 2000, English, International conferenceDuctility Enhancement in Magnesium Alloys under Dynamic Loading[Invited]Invited oral presentation
- Platform Science and Technology in Advanced Magnesium 2000, Jul. 2000, English, International conferenceGrain Refinement of Commercial Magnesium Alloys for High-strain-rate-superplastic Forming[Invited]Invited oral presentation
- 1999 MRS Fall Meeting, Superplasticity-Current Status and Future Potential, Dec. 1999, English, Boston, United States, International conferenceSUPERPLASTICITY IN MAGNESIUM ALLOYS AND ITS COMPOSITES[Invited]Invited oral presentation
■ Research Themes
- 日本学術振興会, 科学研究費助成事業, 基盤研究(C), 東北大学, 01 Apr. 2022 - 31 Mar. 2025骨形成能を有する生体吸収性マグネシウム合金の可能性－分解挙動と生体反応の評価－
- Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (C), Osaka Research Institute of Industrial Science and Technology, 01 Apr. 2021 - 31 Mar. 2024Development of magnesium biomaterials as a mineral reservoir本研究では、マグネシウム生体材料に対して、適正な力学特性や分解性に加えて、カルシウムとリンの貯蔵と供給源としての役割（貯蔵機能）も付与することにより骨組織修復の促進を図った貯蔵機能型マグネシウム生体材料を創製することを目的としている。マグネシウム生体材料中のカルシウムやリンの存在形態の影響を解明するため、カルシウムとリンの形態が化合物の場合についての検討から着手した。カルシウムとリンを含む化合物としてリン酸三カルシウムを選択した。リン酸三カルシウムは生体吸収性（体内で徐々に分解吸収されて骨に置き換わる性質）をもったセラミックであるためカルシウムとリンの貯蔵と供給源として適切な化合物であると考えた。 リン酸三カルシウムの粒子がマグネシウム合金中に分散した複合材料を作製した。この作製にあたってはリン酸三カルシウムとマグネシウム合金の粉末を混合し、押出し加工によって固化した。この結果、マクロ的な欠陥のない良好な複合材料を作製することができた。得られた複合材料の材料学的な評価を進めた。押出し加工にともなって化学変化（化合物の分解など）がないことをエックス線回折によって確認した。また、リン酸三カルシウムの粒子の分散も顕著な凝集を起こすことなく均一に分散していることを走査電子顕微鏡観察によって確認した。複合材料の材料強度を圧縮試験によって評価した結果、0.2%耐力が約300MPaで十分に高い強度に達していることがわかった。材料学的な観点からは非常に良好な複合材料を作製することができた。 並行して、既存の実験サンプルを用いて小動物を用いた効率的な動物実験に関する検討を行い、動物の利用の仕方に関して確認した。
- Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (C), 01 Apr. 2020 - 31 Mar. 2023Development of novel bioabsorbable metal alloy for urinary tract surgery
従来は生体に非吸収性のチタンが用いられてきた自動縫合器に応用するための新規可溶性合金を開発し、自動縫合器を用いた腸管利用新膀胱造設術に応用するために、まずは計算シミュレーションに基づく亜鉛合金の組成を検討し、モデル合金を試作した。 その後、試作材について、成形性や強度、溶解性を評価するこ とにより最適な合金の組成を選定した。続いて、この合金をステープル型に成形し、小型動物(ラット)の膀胱内に全身麻酔下に手術で埋植し、飼育後に膀胱を 摘出し、尿路内でのステープルの溶解性、強度を評価するとともに、合金の埋植が生体に及ぼす影響につき検討した。 引き続き、大型動物(ブタ)の膀胱内に全身麻酔下に手術で新規可溶性合金ステープルを埋植し、3カ月間飼育した後に安楽死させ、埋植部の組織結合性、縫合部周囲の炎症、結石形成性を評価すること により、尿路に使用した場合の安全性と有用性につき検討した。 - 科学研究費補助金／基盤研究(A), Apr. 2017 - Mar. 2021, Principal investigatorCompetitive research funding
- Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (C), Tohoku University, 01 Apr. 2017 - 31 Mar. 2020Development of new osteosynthetic system with biodegradable Mg alloy for craniofacial surgeriesThe purpose of this research is to develop a new osteosynthetic system for facial bones, which is made of metal with sufficient strength and exhibits bioabsorbability, using magnesium alloy. In the present study, we carried out an implantation of implants with magnesium alloy to pigs that were large enough to simulate the application to humans. As a result, biosafety, complete resorption one year after implantation, and fracture healing were confirmed, but bone resorption occurred due to the effect of gas generated during resorption, which did not occur in our previous studies using small animals. And, it was revealed that the screws would fall off, and it was confirmed again that the gas needs to be suppressed. The adverse effects of gas were not solved by devising the shape of the screw, then we tried to add surface treatment with brushite on the magnesium implants. Our results suggested that surface treatment with brushy is useful to suppress and control gas generation.
- Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (C), Tohoku University, 01 Apr. 2015 - 31 Mar. 2018Development of a next generation type reconstruction method using biogradable magnesium alloy meshTo solve the problems concerning residues in the body and strength of the biomaterials, we performed a research of a next generation reconstruction method using biogradable magnesium alloy mesh and got the next results. 1. The living body safety was confirmed by in vitro cell toxicological test of a containing element and in vivo rat back subcutaneous transplantation. But the hydrogen gassing was confirmed by the absorption process. 2. Development of a bone transplantation fixed way by a biodegradablility magnesium alloy pin: A magnesium alloy pin of transplantation bone fixing (Mg pin) has been developed. It was possible to fix a bone fragment for 24 weeks by a Mg pin by an experiment of rabbit.No complications were observed in a follow up period for 6 months postoeprtively, and the healing process was excellent. Control of hydrogen gas which occurs in an absorption early stage of a Mg pin and consideration of surface design of the Mg pin seemed to be necessary.
- 学術研究助成基金助成金／基盤研究(C), Apr. 2015 - Mar. 2018Competitive research funding
- Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (C), Tohoku University, 01 Apr. 2014 - 31 Mar. 2017The examination about the osteoinductive activity of the biodegradable magnesium alloyThe aim of this study was to clarify the influence of the physiological environment surrounding Mg alloys on their corrosion behaviour. A Mg-1.0Al alloy with a fine-grained structure was formed into plates using titanium (Ti) as a control. These plates were implanted into the subperiosteum in the head, subcutaneous tissue of the back, and in the muscle of the femur of rats for 1, 2 and 4 weeks. The Mg alloy was corroded fastest in the head, at an intermediate level in the back, and slowest in the femur. The insoluble salt deposition at the Mg alloy surface had no influence on the volume loss. Gas cavities formed around the Mg alloy at all implantation sites and decreased after 4 weeks. Histopathological examination revealed that the Mg alloy exhibited good biocompatibility, as was seen with Ti. In addition, vascularized fibrous capsules formed around the plates and became mature with time. The volume loss in the different anatomical locations correlated with capsule thickness.
- 官署支出官 近畿経済産業局長, 中小企業経営支援等対策費補助金, 2017, Principal investigator【サポイン】生体内分解性ステープルの量産技術開発Competitive research funding
- 科学研究費補助金／基盤研究(A), Apr. 2013 - Mar. 2016, Principal investigatorCompetitive research funding
- Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (C), Osaka Municipal Technical Research Institute, 01 Apr. 2012 - 31 Mar. 2015Achieving high strength and high damping capacity in biodegradable magnesiumThe purpose of this study was to achieve both high strength and high damping capacity through thermomechanical processing in biodegradable magnesium, which is applicable to orthopedic implants. To begin with, the effect of microstructural factors including grain size, texture and the existence of twins on damping capacity was clarified in pure magnesium. By controlling the microstructure of Mg-Ca alloys through thermomechanical processing, the alloy showed higher strength and damping capacity.
- Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (B), Tohoku University, 01 Apr. 2011 - 31 Mar. 2014Development of degradation controlled alloy with long-term release of bioactive metallic ionBiodegradaion mechanism and effect of new bone formation of magnesium alloys were examined by animal implant experiments. In subcutaneous implant model, Two magnesium alloys of different composition showed different degradation rate. Magnesium alloy of slow rate degradation revealed rapid organization of surrounded tissue. In intraosseous implant model, magnesium alloys showed similar degradation behavior to subcutaneous implant model. New bone was formed around magnesium alloys. New bone formation showed gradual increase in magnesium alloy with high rate degradation. In magnesium alloy with slow rate degradation, bone showed initial increase and afterwords gradual decrease. Magnesium alloys showed high contact rate with bone. Magnesium alloy were demonstrated the high compatibility to bone tissue.
- 科学研究費補助金／萌芽研究, Apr. 2012 - Mar. 2014, Principal investigatorCompetitive research funding
- 研究成果最適展開支援プログラム シーズ育成タイプ, 2013, Principal investigatorA-STEP「生体内分解性金属材料の骨固定用デバイスへの展開」Competitive research funding
- Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (B), National Institute for Materials Science, 2009 - 2012Understanding and control of biodegradability of bioabsorbable Mg alloysDegradation properties of Mg alloys depend on the kind of alloys, which relates to the amount of gas cavity formed in the soft tissue surrounding the implant site. Extraordinary inflammation was not observed even for the Mg alloy having rapid degradation rate. The local pH increase due to the OH- release accompanying the degradation may suppress cell growth when it goes over the acceptable range of cells. Coating of pure Mg with bioabsorbable medical polymers is effective to reduce initial degradation rate of pure Mg and successfully improves cytocompatibility.
- 研究成果最適展開支援プログラム シーズ育成タイプ, 2012, Principal investigatorA-STEP「生体内分解性金属材料の骨固定用デバイスへの展開」Competitive research funding
- 科学研究費補助金／基盤研究(B), 2009 - 2011, Principal investigatorCompetitive research funding
- 研究成果最適展開支援プログラム シーズ育成タイプ, 2011, Principal investigatorA-STEP「生体内分解性金属材料の骨固定用デバイスへの展開」Competitive research funding
- Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (B), Tohoku University, 2008 - 2010The development and application of composite functional medical device using new biodegradable magnesium alloyTo apply biodegradable magnesium alloy for medical device, its biocompatibility and absorption velocity were examined in vitro and in vivo. In vitro, elevated activity of alkaline phosphatase was confirmed in osteoblast by magnesium ion addition. Magnesium alloy revealed the relationship between the degradation velocity and amount of gas formation. There was no pathological change in skin and bone tissue around magnesium alloy. The newly bone formation around magnesium alloy implant was seen in vivo examination. The biocompatibility and bone formation of magnesium alloy were confirmed by these results.
- Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (B), National Institute for Materials Science, 2007 - 2009Development of a High Performance Alloy-Recycling Process with Scrap Materials Including ImpuritiesWe have manufactured a small prototype casting machine for continuous casting experiments with scrap aluminum which includes impurities. We have experimented using this machine to collect basic data for establishing an ultrasonic vibration continuous casting process with Al-Si alloys, which are representative casting alloys. The techniques for controlling the solidification structures of continuous casting ingots are incomplete, and thus we further have investigated the melting temperature, cooling rate, and the shape of the molds. Moreover, by additional application of ultrasound vibration to melts flowing down on an inclined cooling horn as they pass through the liquidus line where the primary crystals appear, we have succeeded in the creation of materials with ultrafine-grained structures. It is difficult to powder aluminum alloy scraps which include a large amount of impurities such as iron, because there are problems concerning the viscosity of the melts and the degree of superheat. However, by changing the design of the nozzle which supplies the melts into an atomized gas jet, we have succeeded in the creation of powders with a mean diameter of 50μm.
- Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research, Grant-in-Aid for Scientific Research (B), National Institute for Materials Science, 2006 - 2008Enhanced age hardening response and microstructure of Mg alloys by the addition of alloying elements時効硬化型マグネシウム合金の組織解析および時効硬化性に及ぼす合金元素添加の影響に関する研究を行った。さらに、優れた時効硬化性を示す合金について、熱間押出しにより棒材を作製し、その機械的特性を測定し展伸材としての可能性を調べた。Mg-Zn(-Zr)合金にAgとCaを微量かつ同時添加、Mg-Sn(-Al)合金にZnを微量添加することにより、析出物が微細化され時効硬化性が著しく向上することを発見した。その上、それらの合金の押出材を製造し室温引張特性を調べたところ、300MPaを超える0.2%耐力(降伏強度)を示すことがわかった。
- 日本学術振興会, 科学研究費助成事業, 特定領域研究, 独立行政法人物質・材料研究機構, 2006 - 2007バルク金属ガラスの高速変形応答解析と変形誘起組織変化の相関解明バルク金属ガラスにおける不均一変形はせん断帯の形成による局所変形であるため、せん断帯の形成およびその進展を制御することが、室温付近での見かけ上の延性増加のためのポイントとなる。本研究ではバルク金属ガラスのせん断帯形成に及ぼすひずみ速度の影響について調査し、強度と延性のひずみ速度依存性を明確にするとともに、変形応答解析および内部組織解析の結果を基に、バルク金属ガラスの変形誘起組織変化の有無を検討した。 PdNip系金属ガラスの圧縮変形応答を調べたところ、PdおよびPの濃度分布が不均一であるほど、せん断帯形成に由来する応力振動の起こる頻度が高くなり、見かけ上の圧縮ひずみが増加することがわかった。また、せん断帯付近の組織を高分解能透過電子顕微鏡により観察した結果、せん断帯はナノ結晶を含まないアモルファス構造であったことから、過冷却液体温度域の比較的広い金属ガラスの局所せん断変形はアモルファス構造を維持したまま進行することがわかった。 他方、変形誘起による結晶化の有無と圧縮変形応答の相関性を明らかにするため、共晶組成と亜共晶組成からなるZrCuAl系合金について、ひずみ速度依存性を調査した。亜共晶組成合金の応力振幅間隔は、共晶組成合金の場合と比較して狭くなっていることから、せん断帯の形成と相互作用が起こる頻度は亜共晶組成である方が高くなることがわかった。変形組織観察の結果、亜共晶組成合金のせん断帯部位では、ナノ結晶が生成していることが確認され、組織構造が不均一である合金ほど、せん断帯が形成され易いことがわかった。また、亜共晶組成合金の高速圧縮変形時における応力低下速度は、共晶組成合金の場合と比較して、緩やかであったことから、せん断帯における局所粘性流動応力はナノ結晶生成に起因する粘性増加の影響を受けることが示唆される結果を得た。
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