Phase transformation in Ni_50.3Ti_49.7-xHf_x (x = 0-25 at. %) high temperature shape memory alloys

The Ni-rich NiTiHf High Temperature Shape Memory Alloys (HTSMAs) exhibit unique capability of recovering apparent deformation under the action of external stimuli such as temperature and stress. These HTSMAs undergo first-order martensitic transformation from a high temperature phase known as Austenite to a low temperature phase known as Martensite at well-defined temperatures which are function of the alloy composition. Their vast utilization in wide range of technologies including aerospace and aircraft industries has led to the development of high strength materials with tuneable phase transformation temperatures and low thermal hysteresis. In this work, we focus on the role of Hf substitution to binary NiTi alloys by investigating the MT characteristics viz. phase transformation temperatures, thermal hysteresis, crystal structure and yield strength of the Ni_50.3Ti_49.7-xHf_x (x = 0-25 at.%) alloys