An atomistic simulation study of the migration of an austenite–ferrite interface in pure Fe

Molecular dynamics (MD) simulations using an embedded atom method potential for pure Fe were performed to determine the atomic mechanisms taking place during the migration of a face-centered-cubic–body-centered-cubic (fcc–bcc) interface. A centro-symmetry parameter (CSP) has been utilized to discriminate between atoms of the fcc and bcc phases. It is shown from both simulation and disconnection theory that the primary structural disconnections formed when creating the fcc–bcc bicrystal do not move laterally across the boundary as the transformation proceeds. However, it is observed that a second set of glissile disconnections forms on the terraces and the interface migrates by the rapid advance of these mobile defects. The rate-limiting step of the interface propagation process is the nucleation of new bcc islands on the terraces and it is shown that the nucleation event is heterogeneous, with the primary disconnections acting as the preferred nucleation sites. The nucleation and growth mechanisms identified here may provide important insights into the mobility of more general incoherent interphase boundaries.