Crystal structures and textures of hot forged Ni 48 Mn 30 Ga 22 alloy investigated by neutron diffraction technique

Abstract

A ferromagnetic shape memory alloy of Ni₄₈Mn₃₀Ga₂₂ prepared by induction melting was successfully hot forged. Strong textures and a large anisotropy of in plane plastic flow were developed during the hot forging process. The crystal structures, both in austenitic and martensitic states, were investigated by means of neutron powder diffraction technique. The result suggests that Ni₄₈Mn₃₀Ga₂₂ has a cubic L2₁ Heusler structure at room temperature, the same as that in the stoichiometric Ni₂MnGa. When cooled to 243 K, the Ni₄₈Mn₃₀Ga₂₂ alloy changes into a seven layered orthorhombic martensitic structure. No substantial change of the neutron diffraction pattern was observed upon further cooling to 19 K, indicating that there is no intermartensitic transformation in the investigated alloy, which is different from the transformation processes in the Ni–Mn–Ga alloys with higher martensitic transformation temperatures.