Effect of Annealing Conditions on Microstructure Evolution of NiMnFeGa Shape Memory Thin Film

Abstract

The microstructure evolution of sputtered polycrystalline Ni54.75Mn13.25Fe7Ga25 ferromagnetic shape memory thin film annealed under different conditions is studied. Microstructure of different annealed films was studied using Transmission Electron Microscope (TEM) and corresponding selected area electron diffraction (SAED) patterns. The result shows that in the microstructure of as-deposited Ni54.75Mn13.25Fe7Ga25 free-standing film, after annealed at 1073 K for different time, the crystalline grain grows up with the increase of the annealing time. By analysis of the SAED patterns, the structure of the thin films change from face-centered cubic austenite to orthorhombic structure martensite compared between the film annealed at 1073 K for 10 mins, 1hr, 4 hrs, and 24 hrs respectively. It indicated that the heat treatment is an effective method of crystallizing behavior for the thin film.