Comparative study of deformation-induced martensite stabilisation via martensite reorientation and stress-induced martensitic transformation in NiTi

This paper presents a comparative study of the effects of deformation via stress-induced martensitic transformation and via martensite reorientation on the transformation behaviour of a polycrystalline NiTi alloy. It was found that the two deformation modes had very similar effects on the thermomechanical behaviour of the alloy after the deformation, including the recovery of deformation upon subsequent heating, the development of two-way memory effect, and the stabilisation of the martensite. It was established in this study that the transformation deformation, either stress-induced martensitic transformation or the martensite reorientation, is incomplete at the end of the stress plateau and continues in the homogeneous deformation afterwards. This study also provided a direct comparison of the effects of the two deformation modes on the transformation heat. It was found in both cases the heat effect of the reverse transformation of the oriented martensite, stress-induced or reoriented, decreased with increasing pre-deformation, in agreement with previous study on deformation via stress-induced martensitic transformation but in contradiction to a previous study on deformation via martensite reorientation.