Martensitic transformation and shape memory effect in Ni_54.75Mn_13.25Fe₇Ga₂₅ ferromagnetic shape memory alloy

The martensitic transformation and shape memory effect of Ni_54.75Mn_13.25Fe₇Ga₂₅ (at.%) alloy are studied in the present paper. It is shown that tetragonal martensite with parallel bands substructure transforms to parent phase heated by electron beam. It can be clearly observed that the martensite band becomes smaller and smaller, then transforms to parent phase completely in the end. A large reversible transformation strain, about 1.5%, is obtained in this undeformed polycrystalline alloy due to martensitic transformation and its reverse transformation. This transformation strain is also increased to 1.8% by the external magnetic field. It is believed that the effect of the magnetic field on the preferential orientation of martensitic variants increases the transformation strain.