Burst character of thermoelastic shape memory deformation in ferromagnetic Ni–Fe–Ga–Co alloy

The shape memory deformation in single crystals of Ni$_{49}$Fe$_{27}$Ga$_{18}$Co$_6$ alloy under uniaxial compression conditions has been studied. It was found that samples in the martensite state deformed in the [110] and [100] directions exhibit strongly anisotropic properties. Despite virtually equal residual strain and the work of deformation in the two cases, the subsequent behavior of samples during shape recovery on heating at a constant rate is principally different. In the former case, the shape memory deformation exhibits a burst character and takes place at a temperature that is significantly higher than the martensite transformation temperature in the initial (undeformed) crystal. In contrast, the shape recovery in the latter case proceeds smoothly at a temperature that is only slightly higher than the martensite transformation temperature in the initial crystal. Due to the burst character of shape memory deformation, the crystal standing on a solid base acquires a velocity above 20 m/s. The results are quantitatively analyzed in terms of the theory of diffuse phase transitions.