Transformation and slip behavior of Ni₂FeGa

Ni₂FeGa is a relatively new shape memory alloy (SMA) and exhibits superior characteristics compared to other SMAs. Its favorable properties include low transformation stress, high reversible strains and small hysteresis. The first stage of stress-induced martensitic transformation is from a cubic to a modulated monoclinic phase. The energy barriers associated with the transformation from L21 (cubic) to modulated martensite (10M-martensite) incorporating shear and shuffle are established via atomistic simulations. In addition, the slip resistance in the [111] direction and the dissociation of full dislocations into partials as well as slip in the [001] direction are studied. The unstable stacking fault energy barriers for slip by far exceeded the transformation transition state barrier permitting transformation to occur with little irreversibility. Experiments at the meso-scale on single crystals and transmission electron microscopy were conducted to provide further proof of the pseudoelastic (reversible) behavior and the presence of anti-phase boundaries. The results have implications for design of new shape memory alloys that possess low energy barriers for transformation coupled with high barriers for dislocation slip.