Monoclinic angle, shear response, and minimum energy pathways of NiTiCu martensite phases from ab initio calculations

Abstract

Ti50Ni50-xCux alloys are observed to exhibit multiple martensitic transformations from B2 to an orthorhombic B19 and a monoclinic B19′ phase. In addition, DFT calculations have predicted a B19ʺ phase with a higher monoclinic angle as the thermodynamically stable ground state. This study investigated the effects of Cu content and shear stress on the monoclinic angles, phase stabilities of the various martensites, the minimum energy pathways, and the relative total energies among the phases in this pseudo-equiatomic Ti(Ni50-xCux) system. A new monoclinic phase (B19M) with a monoclinic angle lower than that of B19′ was found at above a critical Cu content. This confirms the formation of an inte..