Effect of Cold Working Ratio on Function Deterioration Process of Ti-Ni Shape Memory Alloy

Abstract

To investigate the effect of cold working ratio on function deterioration process of Ti-Ni shape memory alloy, repeated loading-unloading tests with constant strain condition were carried out. The chemical composition of specimen is Ti-50.3at%Ni and cold working ratio (CW) is 30.1 % 43.0 % and 51.0 %. Heat-treatment condition is at 673 K for 3.6 ks. The decrement of recovery strain decreases with increasing CW. Moreover, lower CW leads to the decreasing of the number of loading-unloading cycle which decrement of recovery strain slowdown starts. Furthermore, decrement of maximum applied stress decreases with increasing CW. On the other hand, in spite of critical stress for inducing martensite increases with increasing CW, the decrement of critical stress for inducing martensite is almost same regardless of CW. From these results, increasing of CW leads increasing of deterioration resistance. These tendencies are caused by the variation of dislocation density and grain size due to the variation of CW.