Shape memory and martensite deformation response of Ni₂MnGa

The purpose of this paper is twofold: to establish the magnitude of detwinning stress levels of non-modulated martensite in Ni₅₃Mn ₂₅Ga₂₂ as a function of heat treatments utilizing single crystals, and to study the shape memory strains from constant-load temperature cycling experiments for aged and unaged conditions. The maximum transformation strains of 5.2% are consistent with the theoretical predictions based on energy minimization theory. The results exhibit a remarkable narrowing of the thermal hysteresis (as low as 2 °C) with increasing applied stress and a considerable two-way shape memory effect. Using microscopy, it is shown that aging produces a finer martensitic plate structure with an accompanying increase in detwinning stress compared to the unaged case.