EBSD characterization of crystallographic orientations and twin interfaces of modulated martensite in epitaxial NiMnGa thin film

Abstract

The crystal structure and the global texture of 7M modulated martensite in epitaxial Ni50Mn30Ga20 thin films were investigated by X-ray diffraction (XRD), and the local crystallographic orientations correlated with microstructural features were revealed by electron backscatter diffraction (EBSD). The microstructure of 7M martensite can be classified into two distinct constituents. One refers to long straight strips with relatively homogeneous contrast, running parallel to one edge direction of the substrate. The other refers to shorter and bent plates with relatively high relative contrast, being oriented with the plate length direction roughly in 45° with respect to the substrate edges. Each 7M martensite plate is designated as a single orientation variant, and four orientation variants that are twin-related one another constitute one variant group. With the local crystallographic orientations of martensite plates and the orientations of inter-plate interface traces, the Type I, Type II and compound twin interfaces in the low and high relative contrast zones were determined.