Deformation-induced phase transformation and twinning in Fe and Fe-C alloys

The phase transformations and twinning in a nano-sized face-centred cubic (FCC) crystal of iron with different carbon contents are studied by molecular dynamic (MD) simulations. The simulation cells are stretched uniaxially along the [100](FCC) direction. It is found that the FCC matrix transforms into the body-centred cubic (BCC) phase following the Nishiyama-Wassermann orientation relationship (OR). Then, the 'BCC <-> hexagonal close-packed (HCP)' and 'BCC <-> FCC' transformations occur following different variants of the Burgers OR and the Pitsch OR, respectively. The {112}(BCC) twins form between two neighbouring BCC grains. Additionally, the carbon atoms can destabilise the BCC phase, inhibit the phase transformation and pin phase interfaces, leading to tiny BCC twins.