Effect of Pre-Strain on Transformation and Deformation Behavior in Ti–50 at%Ni Shape Memory Alloy

In many cases that shape memory alloys are applied to engineering and medical fields, it is necessary to deform them in martensitic phase and after that, to recover them by heating. However, if a slip-deformation occurs, a shape recovery does not occur completely even if heated up above a reverse transformation finish temperature Af. It is reported that transformation temperatures are changed by pre-deformation and in constrained strain condition. Therefore, it is important to investigate the relationship between the pre-deformation and the deformation and transformation characteristics such as the recovery stress, the transformation temperatures and so on. The purpose of this paper is to clarify the influence of the pre-deformation on the recovery strain, the recovery stress and the transformation temperatures in a Ti–Ni shape memory alloy. The material used in this study is Ti–50 at%Ni alloy annealed at 1103 K for 60 s. The variation of the recovery strain, the recovery stress and the transformation temperatures by the pre-straining are investigated experimentally, and also the variation of the transformation and deformation characteristics by the pre-straining is discussed in relation to the volume fraction of slip-deformed martensite.