Ni24.7Ti50.3Pd25.0 high temperature shape memory alloy with narrow thermal hysteresis and high thermal stability

High temperature shape memory alloys with operating temperatures above 100 deg C are in demand for use as solid-state thermal actuators in aerospace, automobile and other engineering applications. The present study deals with transformation behaviour and thermal stability of Ni24.7Ti50.3Pd25.0 (at.%) high temperature shape memory alloy, in cast and homogenized condition. The martensite finish temperature and transformation hysteresis of the alloy were determined to be 181.0 deg C and ~8.5 deg C respectively. The alloy showed high stability upon stress-free thermal cycling, variation in transformation temperatures being ±1 deg C. The narrow thermal hysteresis and high thermal stability of the alloy upon transformation cycling has been discussed and correlated with its microstructural features, activation energy and elastic strain energy of thermoelastic martensitic transformation. The alloy exhibited modulus of ~82 GPa and hardness of ~4.7 GPa in martensite phase