Atomic-scale investigations on the migration mechanism of the P-type FCC/HCP interface under different deformation modes in pure titanium

This work systematically investigated the migration behaviors of the FCC/HCP phase interface that satisfies prismatic-type (P-type) orientation relationship (OR) in pure Ti during plastic deformation using molecular dynamics (MD) simulations. The migration of the P-type phase interface is accomplished with the two-layer growth steps movements. Through topological analysis, these two-layer growth steps are regarded as interface defects, and their dislocation vector and step height are FCC + HCP (or HCP - FCC) and 2. 749 Å (very close to the simulated result of 2. 71 Å) in pure Ti, respectively. Simultaneously, their nucleation and migration also cause the specific phase interfacial structure formation, consisting of the HCP || FCC, HCP || FCC, and HCP || FCC interfaces and resulting in the morphological variation in the FCC lamella. The screw-type dislocations promote the interface migration by interacting with the phase interface to cause local interfacial structural variation or by acting as a source of dislocations to dissociate into step dipole pairs at the interface during the loading process. In addition, the interface migration behavior is significantly affected by the deformation modes. Compared to pure shear loading, the introduction of additional tensile stress can promote the rapid migration of the P-type phase interface by forming the local stress concentrations at the FCC tip to facilitate the massive nucleation of the growth steps. This work could provide an in-depth understanding on the P-type phase interface migration behaviors at atomic-scale, and offer theoretical guidance for governing the growth of the FCC lamellae in Ti alloys.