Thermomechanical stability of Ni–Mn–Ga single crystal

Abstract

Thermomechanical behavior of Ni–Mn–Ga single crystal was investigated and the experimental results show that the stability of two-way memory effect (TWME) is very sensitive to the heating and cooling rate as well as external load. There were internal stresses accumulated during thermal cycling which affected the martensite variants distribution. Consequently, the strain versus temperature curve became inconsistent with martensite strain changed from contraction to elongation, or vice versa. The internal stress accumulated during thermal cycling was estimated based on the change in M s according to the modified Clausius–Clapeyron equation. Its magnitude is comparable to the critical stress needed to reorient the twinned variants. The irregularity in the strain versus temperature curve was explained as a result of the stress-affected redistribution of twinned variants during the forward transformation.