Effect of Ti 3 Si on Texture in Ti-Nb Based Shape Memory Alloys
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0980-II05-50
Effect of Ti3Si on Texture in Ti-Nb Based Shape Memory Alloys Ryutaro Shimizu1, Kei Masumoto1, Yusuke Fukui1, Tomonari Inamura2, Kenji Wakashima2, Hideki Hosoda2, and Shuichi Miyazaki3 1 Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, 226-8503, Japan 2 Precision and Intelligence Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midoriku, Yokohama, 226-8503, Japan 3 Institute of Materials Science, University of Tsukuba, Tennodai 1-1-1, Tsukuba, Ibaraki, 3058573, Japan
ABSTRACT Effect of Ti3Si particles on recrystallization texture of Ti-Nb based superelastic alloys has been investigated using X-ray pole figure measurement and electron backscatter diffraction (EBSD) technique. The alloys used were Ti-24mol%Nb-3mol%Al-Xmol%Si (X=0~0.9, termed XSi) and Ti-24mol%Nb-3mol%Si alloy (3Si). The apparent phase at room temperature was βphase (bcc). Besides, (Ti, Nb)3Si particles with PTi3 type crystal structure were formed in the alloys with Si content higher than 0.7mol%. After the cold rolling of 99% reduction in thickness, a rolling texture of the β-phase was formed to be mainly {001}ββ regardless of the presence of the (Ti, Nb)3Si particles. After the solution treatment at 1273K, a recrystallization texture formed to be {112}ββ in all the alloys except for 3Si. The average grain size of the recrystallized alloys was 20~40µm. On the other hand, the solution treated 3Si exhibited the {001}ββ texture and the average grain size of 3µm. It is concluded that the {001}ββ texture with fine grains of the solution treated 3Si is obtained by the suppression of grain boundary migration due to the existence of the (Ti, Nb)3Si particles. INTRODUCTION NiTi is a practical shape memory alloy (SMA) and used for biomedical applications. However, the possibility of the Ni hypersensitivity due to the implantation of NiTi has been pointed out. A new SMA consisted of nontoxic elements only is strongly required. Several β-titanium alloys (bcc) have a martensitic transformation from β to α” (c-centered orthorhombic) [1,2]. Some of these alloys without toxic elements exhibit the shape memory effect (SME) and the superelasticity (SE) [3-8]. In general, titanium alloys have technical achievements as biomaterials. β-titanium alloys with β-α” martensitic transformation are, therefore, regarded as candidate new biomedical SMAs to replace NiTi. Our group has systematically investigated SME, SE and mechanical properties of the TiNb based β-titanium alloys [9-12]. A striking feature of the TiNb based SMAs is that these alloys have a good cold-workability. Cold-rolling with reduction rate of 99% is possible in TiNb based SMAs. Sheet and wire of TiNb based SMAs are easily fabricated by cold-rolling without intermediate annealing. We have confirmed that strong textures appear as a result of the severe cold-working in the TiNb based SMAs [13-14]. The rolling texture is mainly {001}ββ and SE is hardly observed in the as-rolled material due to a large amount of lattice defects [15]. Subscript β indicates β-phase, hereaf
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