Phase Constituent and Reverse Martensitic Transformation Temperature of PtTi-CoTi Diffusion Couple Heat-Treated at 1373K
- PDF / 724,922 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 15 Downloads / 191 Views
Phase Constituent and Reverse Martensitic Transformation Temperature of PtTi-CoTi Diffusion Couple Heat-Treated at 1373K Hideki Hosoda1, Satoshi Tsutsumi1+, Masaki Tahara1, Tomonari Inamura1, Kenji Goto2, Hiroyasu Kanetaka3, Yoko Yamabe-Mitarai4 1 Precision and Intelligence Laboratory, Tokyo Institute of Technology, Yokohama, Kanagawa, Japan. (+ Graduate student, now with JFE Steel Corporation, Kawasaki, Japan) 2 Tanaka Kikinzoku Kogyo K.K., Hiratsuka, Kanagawa, Japan. 3 Liaison Center for Innovative Dentistry, Graduate School of Dentistry, Tohoku University, Sendai, Miyagi, Japan. 4 High Temperature Materials Unit, Functional Structure Materials Group, National Institute of Materials Science, Tsukuba, Ibaraki, Japan. ABSTRACT The reverse martensitic (austenite) transformation temperatures (As) were investigated using a diffusion couple of PtTi and CoTi with a continuous compositional gradient. It was found that PtTi and CoTi form a complete solid solution of (Pt, Co)Ti at 1373K. Surface relief was formed by heating due to the austenite transformation. Judging from the formation of the surface patterns and the corresponding chemical compositions, As monotonously decreases with increasing Co content at a rate of -70K/at%Co, and As is estimated to be close to room temperature (RT) when the Co concentration is 15at%Co. Besides, micro Vickers hardness values measured at RT are minimized around 15at%Co. INTRODUCTION Since shape memory alloys (SMAs) possess several unique properties such as shape recovery by heating over austenite transformation temperature, low apparent elastic modulus and constant deformation stress during stress-induced martensitic transformation, new applications are being developed. Especially, novel practical high-temperature shape memory alloys (HTSMAs) are desired for high temperature uses. A fascinated candidate is PtTi because the phase transformation is quite high around 1300K from B2 parent phase to B19 martensite phase [1]. The phase transformation is the martensite type [2]. The martensitic transformation temperature changes with the deviation from stoichiometry; martensitic transformation start temperature Ms reported in Ref.[1] is 1308K at 45at.%Pt-Ti, 1343K at 50at%Pt-Ti, and 1273K at 52.5at%Pt-Ti. The high temperature shape memory effect of PtTi has been confirmed by deformation at 1123K followed by heating at 1523K, in addition to pseudoelasticity appeared during heating on a temperature range below Ms [3]. Then, PtTi is a promising HTSMA. However, the actuation temperature range is relatively narrow (
Data Loading...
