Surface effects on structural phase transformations in nanosized shape memory alloys

We systematically investigated the role of surface on the B2-B19 transformation of free-standing nanoparticles by classical molecular dynamics simulations. It was found that the surface of particles has a shell structure with a thickness of 2 unit cells, suppressing the B2-B19 transformation locally. Below a critical size, this surface shell leads to the reduction of the transformation latent heat and the vanishing of B2-B19 transformation. We propose a Landau-type model based on the core-shell structure of particles, which reproduces well the relation between transformation temperature and particle size. Our results provide a microscopic insight into the origin of surface-induced size effect on the structural phase transformations in nanosized shape memory alloys.