Microstructural analysis and phase transformation in Ni–Mn–Ga ferromagnetic shapememory alloys

Abstract

The martensitic thermoelastic and magnetic transformations have been investigated for theNi–Mn–Ga ferromagnetic shape memory alloys. The martensitic phase of the shapememory alloy responds to the application of stress and, as a result, the martensite variantsare rearranged to accommodate the applied stress, which results in the macroscopic shapechange. The shape recovery property of Ni–24.7 Mn–24.8 Ga (at.%) alloy with martensitictransformation temperatures has been analysed. The mechanisms of the magneticmicrostructure, which cause the martensite band domains and run diagonally in amicrograph from left to right, have been observed. The micrograph also showsthat the martensitic transformation of Ni–24.7 Mn–24.8 Ga (at.%) alloy not onlydepends on the structural rearrangement but also responds to a magnetic field. It isobserved that upon cooling from the high-temperature austenite parent phase, theferromagnetic shape memory alloys exhibit transition from paramagnetism toferromagnetism. It is studied that the Ni–Mn–Ga alloy is an intrinsically suitable ductilematerial.