Thermal effects associated with stress-induced martensitic transformation in a TiNi alloy

Abstract

Stress-induced martensitic transformation in a polycrystalline TiNi alloy (Ti-50.1 at.%Ni) has been investigated by following the instantaneous temperature change during deformation, the effects of strain rate on the kinetics of transformation and the calorimetric effects associated with the thermally induced transformation. Two separate stages of transformation strain and temperature increment are observed during stress-induced martensitic transformation in this alloy. Differential scanning calorimetry results show two exothermic peaks during cooling. The sum of the enthalpy changes for these two events is exactly equal to the single enthalpy change during martensite-to-parent transformation. It is proposed that the two stages of transformation strain and temperature rise during stress-induced transformation are related to the two calorimetric events in thermally induced transformation. It is shown that the stress-strain hysteresis loop as well as the two stages of temperature rise are influenced by the strain rate.