Determination of the orientation relationship between austenite and 5M modulated martensite in Ni–Mn–Ga alloys

The microstructural and crystallographic characteristics of 5M martensite in an Ni₅₀Mn₂₈Ga₂₂ alloy were investigated by electron backscatter diffraction (EBSD) analysis. The microstructure of 5M martensite observed at room temperature can be characterized by broad plates with alternately distributed fine lamellae (variants). With the accurate EBSD orientation measurements and by application of monoclinic superstructure information, four twin-related variants in one broad plate were identified. On the basis of the correct orientation data of martensite variants acquired from the EBSD measurements, the more favourable orientation relationship between austenite and 5M martensite was revealed to be the Pitsch relation with (101)_A//()_5M and []_A//[]_5M by detailed crystallographic calculation without residual austenite.