Papers by Author: Tomonari Inamura

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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: Abdul Wadood, Tomonari Inamura, Hideki Hosoda, Shuichi Miyazaki
Abstract: In order to develop new nickel-free biomedical Ti-based alloys, effect of silver additions on mechanical properties of Ti-5Cr (mol%) alloy was investigated. Cold workability of Ti-5Cr alloy was 5% in thickness reduction and the cold rolling reduction was improved to be 38% by 2mol% Ag addition and 96% by 4mol%Ag addition. The improvement was due to β phase stabilization. From the XRD results, α’ martensite was the dominant phase in Ti-5Cr-2Ag alloy and β phase was the dominant phase in Ti-5Cr-4Ag alloy. By tensile tests, Ti-5Cr-4Ag alloy showed good strength of 447 MPa in ultimate tensile strength (UTS) and ductility of 13% in fracture strain. Ti-5Cr-4Ag showed higher hardness of HV398 than Ti-5Cr-2Ag with HV288. The hardening by increase of Ag is probably due to the solid solution strengthening. By the cyclic loading-unloading tensile tests with a constant strain increment, Ti-5Cr-4Ag showed pseoudoelastic behavior. Ti-5Cr-4Ag also showed shape memory effect with 57% in shape recovery ratio. It is concluded that Ti-5Cr-4Ag is hopeful as a new non-allergic shape memory material for biomedical applications.
Authors: Takeshi Teramoto, Masaki Tahara, Tomonari Inamura, Hideki Hosoda, Shuichi Miyazaki
Abstract: Composition dependence of the compatibility condition at junction plane (JP) (interface between habit plane variants (HV)) was evaluated by geometrically non-linear theory of martensite in Ti-Nb-Al shape memory alloys that have β (cubic) to α” (C-orthorhombic) martensitic transformation. The kinematic compatibility (KC) condition requires non-zero rotation of HV to form compatible JP; the angle of this rotation is termed θ. This means that the invariant habit plane (HP) and the compatible JP are not formed simultaneously. It turned out that twelve types of θ exist depending on the pair of HV. Composition dependence of each type of θ was systematically investigated. The previous results of transmission electron microscopy observations were also discussed in terms of the present results.
Authors: Motoki Okuno, Tomonari Inamura, Hiroyasu Kanetaka, Hideki Hosoda
Abstract: Deformation behavior and texture development of NiMnGa ferromagnetic shape memory alloy (FSMA) particles embedded polymer composites were investigated by compression tests and X-ray diffraction pole-figure analysis (XRD-PF). Both the NiMnGa/silicone and NiMnGa/epoxy composites exhibited a characteristic three-stage deformation which is often seen in shape memory alloys due to martensite variant reorientation. XRD-PF revealed that (004) texture was developed in the compressed NiMnGa/silicone due to the retention of martensite variant reorientation. On the other hand, significant texture change was not recognized in the compressed NiMnGa/epoxy. Rearranged martensite variants was kept after unloading in silicone matrix having low Young's modulus, but reverse reorientation occurred in epoxy matrix with high Young's modulus. The rearrangement behavior of martensite variants is strongly affected by elastic properties of matrix.
Authors: Tomonari Inamura, Ryutaro Shimizu, Hideki Hosoda, Shuichi Miyazaki
Abstract: The effect of reduction rate on the deformation texture of cold-rolled Ti-26mol%Nb-3mol%Al shape memory alloy was investigated. The alloy is the parent phase (β: bcc) at room temperature (RT) and the martensite start temperature is much lower than RT; no residual martensite was detected after cold-rolling. The reduction rate, r, was varied in the range of 60 ~ 99%. Texture evolution was as following; γ-fiber à {001}<110> à {001}<110> + {112}<110> (α-fiber). The strength of {001}<110> was maximized at about r = 97%. The recrystallization texture is expected to be controlled by the reduction rate; optimization of r is supposed to be promising to obtain the {001}<110> recrystallization texture that is preferred for superelastic deformation.
Authors: Masatoshi Ii, Masaki Tahara, Hideki Hosoda, Shuichi Miyazaki, Tomonari Inamura
Abstract: The preferred morphology of self-accommodation (SA) microstructure in a Ti-Nb-Al shape memory alloy was investigated by the evaluation of the frequency distribution of the habit plane variant (HPV) clusters using in-situ optical microscopy. The observed HPV clusters were classified into two different types; one is the cluster connected by the {111}o type I twin (Type I) and the other is connected by the <211>o type II twin (Type II). The total fractions of the Type I and Type II clusters were 52% and 48%, respectively. The incompatibility at junction planes (JPs) of the two clusters was almost the same among these clusters. However, most of the larger martensite plates (> 50μm) formed Type I cluster at the later stage of the reverse martensitic transformation, i.e., at the early stage of the forward transformation upon cooling. The ratio of the fraction of Type I and II is almost 2:1 at the early stage of the forward transformation.
Authors: Hideki Hosoda, Tomonari Inamura
Abstract: In this paper the recent development of NiMnGa-particles-embedded polymer-matrix magnetodriven composites achieved by our group is described. The NiMnGa single-crystal particles can be easily fabricated by mechanically crushing the polycrystalline ingots due to intrinsic intergranular brittleness. The elastic back stress from the matrix polymer induces the reverse reorientation of martensite variants after removing the magnetic field. However, the actuation strain observed was very small around 10ppm which was 1/1000 times lower than the calculated value. Some possible reasons for the disagreement are that the crystallographic orientation of NiMnGa particles is random distribution, lattice defects introduced during crushing suppress reorientation of martensite variants, and that the elastic restriction from the matrix polymer is higher than expected. Therefore, the martensite variant reorientation behavior of the NiMnGa/silicone composites has been investigated from the viewpoint of (1) volume fraction of matrix polymer, (2) elastic modulus of polymer and (3) direction of magnetic field applied. And also, the internal structures of the composites were directly evaluated by microfocused X-ray computed tomography (µ-CT).
Authors: Abdul Wadood, Tomonari Inamura, Hideki Hosoda, Shuichi Miyazaki
Abstract: The effect of ageing on mechanical, shape memory and pseudoelastic properties of our recently developed Ti-5Cr-4Ag alloy was investigated for biomedical and engineering applications. The results are summarized as follows. (A) Solution-treated alloy exhibited ductile behavior (13% fracture strain), shape memory properties (57% shape recovery) and pseudoelastic response. (B) Ageing at 573K and 973K for 3.6ks has resulted into improvements of UTS and yield stress. However the fracture strain, shape recovery ratio and pseudoelastic response were decreased due to precipitation of α (hcp) phase and stabilization of remaining β (bcc) phase. (C) Ag addition suppressed ω (hexagonal) phase precipitation as ω phase could not be detected for solution-treated and aged conditions. It is concluded that Ti-5Cr-4Ag in solution-treated and 973K aged conditions has potential for biomedical and engineering applications due to good strength-ductility correspondence, shape memory and pseudoelastic properties and suppression of ω phase precipitation.
Authors: Hideki Hosoda, Makoto Taniguchi, Tomonari Inamura, Hiroyasu Kanetaka, Shuichi Miyazaki
Abstract: Effects of single- and multi-step aging on mechanical properties and shape memory properties of Ti-6Mo-8Al (mol%) biomedical shape memory alloy were studied using tensile tests at room temperature (RT). The solution-treated alloy at RT was two phase of bcc β and martensite α". Tensile tests revealed that the solution-treated alloy exhibited good shape memory effect. As for the single-step aging, (1) pseudoelastic shape recovery by unloading was observed after aging at 623K, (2) the alloy became brittle after aging at 773K due to ω embrittlement, and (3) strength was improved with small shape memory effect by aging at 1023K. On the other hand, after a multistep aging at 773K-1023K-1123K, the alloy was strengthened and showed perfect shape recovery. The improvement must be achieved by the formation of fine and uniform hcp α precipitates.
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.
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