Almost compatible X-microstructures in CuAlNi shape memory alloy

A systematic study of a specific martensitic microstructure, called the X-microstructure, is carried out with the focus on the CuAlNi shape memory alloy undergoing the cubic-to-orthorhombic transformation. The set of all crystallographically distinct candidate X-microstructures is determined, and it is shown that, according to the crystallographic theory of martensite, none of them is compatible. Almost compatible X-microstructures, which involve elastic strains, are thus examined. These microstructures are searched in the neighborhood of all candidate X-microstructures by minimizing the total elastic strain energy with respect to the microstructure parameters. Several low-energy X-microstructures are found, and it is shown that the total elastic strain energy correlates reasonably well with one of the indicators which characterize incompatibility of the corresponding candidate X-microstructure.