Prediction of transformation stresses in NiTi shape memory alloy

Abstract

It is well known that interfaces play an important role in determining the mechanical response of materials. This paper focuses on the transforming shape memory alloy NiTi and is aimed towards a better understanding of austenite-martensite interface structure (steps and dislocation arrays) and the determination of transformation stress corresponding to the translation of this interface. In the present work, we characterize the defect content at the cubic-monoclinic interfaces via the Topological Model. The defect-induced displacement fields are generated within the framework of the Eshelby-Stroh formalism and further improved with Molecular Statics simulations accounting for interactions at the atomic level. The resulting defect core disregistry fields are employed as input to a modified Peierls-Nabarro framework for evaluating the transformation stress. We applied the proposed methodology to the particular case of NiTi alloy single crystals of specific orientations and predicted the transformation stress levels in close agreement with experiments. Moreover, the short-range interactions of dislocation core disregistry fields are shown to be responsible for the experimentally observed non-Schmid behavior of transformation stress levels. Overall, the paper represents an effort to improve our understanding of shape memory materials considering theory, computer simulation and experiment.