Papers by Author: Kenji Wakashima

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Authors: Tomonari Inamura, Hideki Hosoda, Kenji Wakashima, Shuichi Miyazaki
Abstract: Anisotropy in elastic properties of Ti-24mol%Nb-3mol%Al (TiNbAl), a new biomedical shape memory alloy developed by our group, was characterized in a temperature range from 133K to 413K. A well developed <110>{112}-type recrystallization texture is formed by an annealing at 1273K for 1.8ks after a severe cold-rolling. Young’s modulus of the -phase exhibited a strong anisotropy depending on the loading direction. Young’s modulus along of -phase of TiNbAl around room temperature was estimated to be , with assuming that the texture is perfectly developed.
Authors: Hideki Hosoda, Yosuke Horiuchi, Tomonari Inamura, Kenji Wakashima, H.Y. Kim, Shuichi Miyazaki
Abstract: In order to increase critical stress for slip in Ti-Nb base shape memory alloys, strengthening by carbon additions (0.2 and 0.5mass%C) to Ti-27mol%Nb was investigated. It was found that all the alloys were  (bcc) phase at room temperature, and TiC existed in C-added alloys. The grain size was decreased with carbon content due to grain boundary pinning. Texture measurement revealed that strong {112}<110> recrystallization texture was formed in C-free alloy and that weak {001}<110> texture in C-added alloys. Tensile tests revealed that clear superelasticity appeared in C-free alloy but that stress-induced martensitic transformation seems to be suppressed by TiC in C-added alloys. The critical stress for slip was linearly increased by carbon content. Then, carbon addition affects the shape memory properties of TiNb alloys, and is effective to enhance the critical stress for slip.
Authors: Kenji Wakashima, T. Shimoyamada, H. Noma, Tomonari Inamura, Hideki Hosoda
Abstract: In this paper, we describe our recent work on metal matrix composites (MMCs) with submicron-size TiB2 and Al2O3 particulates that are synthesized in situ from Al-rich Al-Ti-B and Al-TiO2- B powder reactants by reactive sintering. Reaction sequences examined in the two different reactant systems are summarized, and some experimental results on elevated-temperature properties, i.e. thermal expansion, temperature dependence of dynamic tensile modulus and creep behavior, are shown and discussed from micromechanics-based viewpoints.
Authors: Hideki Hosoda, Ryosuke Tachi, Tomonari Inamura, Kenji Wakashima, Shuichi Miyazaki
Abstract: Martensitic transformation temperatures were measured and transformation strains were evaluated in a promising high temperature shape memory alloy TiAu with a compositional range from 46 to 53mol%Au. It was found by differential scanning calorimetry that martensitic transformation start temperature (Ms) is kept almost constant value of 880K in the Au-rich side of the stoichiometric composition. On the other hand, Ms decreases monotonically with decreasing Au content in the Au-poor side. X-ray diffraction analysis revealed that apparent phase of all the alloys at room temperature is B19 martensite phase. Under an assumption that the atomic volume is constant during martensitic transformation, the lattice parameters of B2 parent phase and maximum transformation strain were calculated. It was found that the maximum transformation strain depends on chemical composition and that it reaches 10.75% for Ti-53mol%Au alloy. The value is comparable to that of Ti-Ni.
Authors: Hideki Hosoda, Y. Fukui, Tomonari Inamura, Kenji Wakashima, Shuichi Miyazaki, Kanryu Inoue
Authors: Hideki Hosoda, Yusuke Fukui, Tomonari Inamura, Kenji Wakashima, Shuichi Miyazaki
Abstract: In order to replace Ti-Ni shape memory alloys, new biomedical shape memory alloys have been developed which are composed of beta titanium and nontoxic elements only. In this paper, experimental results of mechanical and shape memory properties are reported for the Ni-free Ti-18mol%Nb shape memory alloys containing 3mol% of 13-group and 14-group ternary elements in the periodic table. The ternary elements selected are Al, Ga, In, Ge and Sn. It was found that the solution treated alloys exhibit good shape memory effect but almost no pseudoelasticity at room temperature. Ultimate tensile strength and elongation to failure at room temperature are ranged from 250 to 710MPa and from 13 to 21%, respectively, depending on the kind of ternary elements. Effect of solution hardening on strength is discussed.
Authors: Kenji Wakashima, T. Nishida, Tomonari Inamura, Hideki Hosoda
Abstract: A new route to designing smart active composites, which deals with fiber-reinforced in-plane anisotropic piezoelectric lamina and laminates, is proposed and its quantitative procedure formulated. Two examples of design are highlighted: unidirectionally active laminate and twist bimorph. Some progress in experimental work on the latter is briefly described.
Authors: Y. Yamamoto, Tomonari Inamura, Kenji Wakashima, Hee Young Kim, Shuichi Miyazaki, Hideki Hosoda
Abstract: Internal friction of Ti-24mol%Nb-3mol%Al (Ti-24Nb-3Al) shape memory alloy with a well-developed texture was investigated by dynamic mechanical analysis (DMA) in a tensile mode with a frequency of 1Hz and a temperature range of 123~423K. Ti-24Nb-3Al alloy fabricated by Ar arc-melting was cold-rolled with a reduction in thickness of 99% and then heat-treated at 1173K for 3.6ks in vacuum to develop a recrystallization texture. The martensitic transformation temperature and internal friction (tan δ) were evaluated under the stress amplitude of 36MPa. The tensile direction was selected to be the rolling direction (RD) and the transverse direction (TD). The specimen was β-single phase with a well-developed {112}β<110>β texture at room temperature and exhibited high damping during martensitic transformation and in the martensite phase. The relationship between internal friction and the tensile direction is discussed on the view point of the crystallography of the transformation.
Authors: Yasuhiro Kusano, Tomonari Inamura, Hideki Hosoda, Kenji Wakashima, Shuichi Miyazaki
Abstract: Effects of 3d transition metal element additions on phase constitution at room temperature and mechanical properties of Ti-Cr and Ti-Cr-Sn alloys were investigated in this study. Ti-5Cr and Ti-5Cr-3Sn (in mol%) alloys with or without 3mol% of 3d-transition-metals of V, Mn, Fe, Co and Ni were investigated. X-ray diffraction analysis showed that Ti-5Cr binary and Ti-5Cr-3Sn ternary alloys consisted of α' (hcp) and β (bcc) two phases, and the others were β single phase. Then, the additions of the 3d transition metals stabilize  phase. The results were in good agreement with optical microscopy observation. Vickers hardness tests revealed hardening occurred by the additional elements, and the hardening must be mainly due to solid solution hardening. Besides, the hardness was lowered by 3mol%Sn addition. Tensile tests revealed that the additions of Fe, Co and Ni improve strength while V and Mn improve ductility.
Authors: S. Tsutsumi, Hideki Hosoda, Tomonari Inamura, Kenji Wakashima
Abstract: Phase equilibrium and phase constitution of the Au-Cu-Ga-Mn quaternary system at 873 K was studied along the AuMn-Cu2MnGa (=CuMn0.5Ga0.5) both of which are ferromagnetic shape memory alloys. Three alloys were investigated: AuMn, Cu2MnGa and Au0.5Cu0.5Mn0.75Ga0.25 (AuMn:CuMn0.5Ga0.5=1:1). It was found that 1 ordered bct phase with the axis ratio c/a=0.948 was formed in the AuMn alloy due to the Mn reduction by evaporation during melting. The CuMn0.5Mn0.5 alloy was composed of MgZn2-type Laves phase and Cu9Al4-type  phase. Besides, the following three phases existed in the Au0.5Cu0.5M0.75Ga0.25 alloy: Laves,  and 2 ordered bct with c/a=1.041. The c/a value of the ordered bct phase is decreased by Cu and/or Ga substitution in AuMn. The values of electron atom ratio (e/a) calculated based on chemical compositions for the  phases were 1.61 and 1.68, which were close to the ideal value of 1.62 (=21/13). Based on the results, ordered bcc  (transforming into bct at lower temperature), and Laves are judged to be equilibrium phases at 873 K along the AuMn-Cu2MnGa.
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