Transformation Behavior of TiNiPt Thin Films Fabricated Using Melt Spinning Technique
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Transformation Behavior of TiNiPt Thin Films Fabricated Using Melt Spinning Technique Tomonari Inamura, Yohei Takahashi*, Hideki Hosoda, Kenji Wakashima, Takeshi Nagase1, Takayoshi Nakano1, Yukichi Umakoshi1 and Shuichi Miyazaki2. Precision and Intelligence Laboratory, Tokyo Institute of Technology, Yokohama, Kanagawa 226-8503, Japan. (*Graduate student, Tokyo Institute of Technology) 1 Department of Materials Science & Engineering, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan. 2 Institute of Materials Science, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan. ABSTRACT Martensitic transformation behavior of Ti50Ni40Pt10 (TiNiPt) melt-spun ribbons were investigated where the heat treatment temperature was systematically changed from 473K to 773K. A hot-forged bulk TiNiPt material with the similar chemical composition was also tested as a comparison. θ-2θ X-ray diffraction analysis and transmission electron microscopy observation revealed that the as-spun ribbons were fully crystallized. The apparent phases of as-spun ribbons at room temperature are both B19 martensite and B2 parent phase instead of B2 single phase for the hot-forged bulk material. No precipitates were found in as-spun and heat-treated ribbons. It was revealed by differential scanning calorimetry that all the specimens exhibit one-step transformation. The martensitic transformation temperatures of the TiNiPt as-spun ribbons are 100K higher than those of the hot-forged bulk material, and the martensitic transformation temperature decreases with increasing heat treatment temperature. INTRODUCTION Ti-Ni alloy has a thermoelastic martensitic transformation from B2-structure (parent) to B19'-structure (martensite) and exhibits shape memory effect (SME) and superelasticity (SE) [1]. Actuation temperature of shape memory alloys (SMAs) is determined by the martensitic transformation temperature (Ms) of the alloys. Ms of Ti-Ni binary alloy is at most around 400K [1] and therefore the SME of Ti-Ni alloy cannot be used at high above 400K. In order to expand the applications related with SMAs, development of Ti-Ni based SMAs with high Ms compared to the Ti-Ni binary alloy has been strongly required. Effects of ternary addition on Ms of Ti-Ni have been extensively investigated and most of additional elements such as Co, Fe, Mn, Cr and V are known to decrease Ms of Ti-Ni. However, it has been known that some ternary additions such as Hf, Nb, Zr, Pd, Au and Pt raise Ms of Ti-Ni [2-4]. Our group has systematically investigated Ms and SME of Ti-Ni alloys containing platinum group metals in the pseudobinary systems of TiNi-TiRh, TiNi-TiIr and TiNi-TiPt [4-7]. It is known that microstructure, transformation behavior and mechanical properties of rapidly solidified Ti-Ni based SMAs are different from those of bulk material [8]. However, there is no report concerning phase constitution, transformation behavior and mechanical properties of rapidly solidified Ti-Ni alloy containing Pt. In this paper, phase constitution, crysta
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