Anisotropic elastic properties and phase stability of B2 and B19 CuZr structures under hydrostatic pressure

Abstract

B2 CuZr exhibits a stress-induced martensitic transformation from a B2 to a B19 structure during tensile deformation, and that is believed to be the reason for the pronounced ductility and work hardening of CuZr-based bulk metallic glass (BMG) composites. In order to gain a better insight into the structural transformation of CuZr precipitates, the phase stabilities as well as the anisotropic elastic and thermodynamic properties of both B2 cubic (CsCl-type) CuZr and B19 (β-AuCd-type) CuZr structures under hydrostatic pressures up to 30 GPa are investigated by first principles calculations. Moreover, the effects of the hybridization between the electronic orbitals of the constituent atoms on the variation of the elastic properties of the B2 CuZr structure are discussed. The results show that the Young's modulus (E), bulk modulus (B) and shear modulus (G) increase significantly with increasing pressure. Noticeably, for pressures up to 30 GPa, the B2 CuZr structure shows a stronger anisotropy along the (1 1 0) plane than for the (1 0 0) plane. Under high pressure, the stability of both B2 CuZr and B19 CuZr phases decrease while the Helmholtz free energy (F) and the formation enthalpy (H) of B2 CuZr increase monotonically. However, the different stability decreasing trajectories of both B2 and B19 CuZr phases result in a high propensity of martensitic transformation from the B2 to B19 structure. Our results may have implications for better understanding the phase stability of B2 and B19 CuZr structures under high pressure and can shed light on the structure-property relationships of BMG composites reinforced with shape-memory crystals.