The mechanism of hcp-bcc phase transformation in Mg single crystal under high pressure

Abstract

The mechanism of phase transformation from hexagonal close-packed (hcp) to body-centered-cubic (bcc) structure in Mg single crystal under high pressure is studied by molecular dynamics (MD) simulations. The hcp-bcc phase transformation is achieved by a shear-shuffle mechanism, through the formation of bcc nanotwinned structure and the subsequent detwinning. The nanotwinned structure can effectively accommodate the shear caused by the hcp-bcc phase transformation, which facilities the growth of bcc phase under hydrostatic pressure. The detwinning turns the bcc nanotwinned structure into bcc nano-polycrystalline. Two twinning modes with the opposite twinning shear occur during the detwinning, which can accommodate the shear in different directions. The mechanism of hcp-bcc phase transformation revealed in this work brings out a comprehensive understanding of the plastic mechanism under high pressure, which is helpful for the further materials design under high pressure.