Some features of Ni-Fe-Ga shape memory alloys under compression

Three Ni-Fe-Ga ferromagnetic polycrystalline alloys having a martensitic transformation close to room temperature have been produced. Some results on their stress-strain behaviour under compression will be presented in this work. At temperatures below Af (finish of the reverse martensitic transformation), multiple steps in the stress-strain curves indicate the possibility of stress-induced martensite to martensite transformations. In this temperature domain, the critical stress to induce the variant reorientation and intermartensitic transformations is nearly temperature independent. In addition, the alloys show almost perfect strain recovery on unloading, that is the so-called rubber-like effect. As the temperature is increased (T⩾Af) the multiple step stress-strain curves evolve to a single-step transformation corresponding to stress-induced martensite from the parent phase.