Thermal Cycling and Deformation Effects in Ni-Ti-Co Shape Memory Alloys

Abstract

The Ni-Ti-based alloys with compositions around 50%Ni – 50%Ti (atomic %) constitute the lightest and most important group, from the point of view of industrial applications, of the so-called Shape Memory Alloys (SMA). The SMA exhibit some unusual thermomechanical behaviours, like the shape memory effect and pseudoelasticity, which are related to a thermoelastic martensitic transformation. The forming of Ni-Ti alloys is rather complicated and needs some thermomechanical processes, like hot and cold rolling and subsequent thermal treatments. The martensitic transformation is sensitive to the alloy processing [1] and also to the thermal cycling (repetition of the temperature induced transformation) [2–5]. In this evolution, the presence of dislocations plays an important role.