A model of the kinetics of the temperature-induced phase transformation in NiTi alloys and its experimental verification

A model, describing the kinetics of the temperature-induced austenite phase transformation processes in shape memory alloys (SMAs) is presented. The model is formulated for a general stress and temperature state in the solid body and allows the computation of the austenite phase fraction evolution in it, that is, the dependence of the amount of the austenite phase fraction on the values of the temperature and stress. It is shown that the predicted amount of the austenite phase fraction is not dependent on the control volume discretization. The model does not take into account microstructural changes in the material and the existence of different phases in the material (R-phase, twinned martensite). The experimental verification of the model was conducted using SMA nitinol wire that was prestrained (detwinned martensite state) and subjected to a heat load. It was shown that the austenite phase fraction predicted by the model agrees very well with the tabulated (reference) and experimental data.