Self accommodating microstructure of the B19 martensites in Ni-Ti-Cu alloys

The microstructure of shape memory alloys is characterized by the self accommodating arrangement of martensite variants. While the self accommodating microstructures of the B19’ martensite in Ni-Ti alloys has been established to be the <111>_C 3-variant plate group, there is insufficient information regarding that of the orthorhombic B19 martensite found in Ni-Ti-Cu alloys. In this study, we investigated the martensitic microstructures in the Ni₄₁Ti₅₀Cu₉ alloy using transmission electron microscopy (TEM) and observed that the self accommodating arrangement consists of stacks of 3-variant plate groups. This paper examines the driving force for the formation of such unusual self accommodating plate groups on the basis of the crystallographic information provided by TEM.