Molecular dynamics simulation of interface dynamics during the fcc-bcc transformation of a martensitic nature

The structural and dynamic properties of the interface during the fcc-bcc transformation in pure iron have been investigated by molecular dynamics simulations. An embedded atom method potential was used for the atomic interactions. Two interfaces, close to the Bain and Kurdjumov-Sachs orientation relations, have been examined during the fcc-to-bcc transformation. In each simulation the system was left to evolve freely at the imposed temperature. In a system with fully periodic boundaries no interface motion has been observed, whereas systems with at least one free boundary do show a mobile interface. After an incubation time, there is a very fast transformation from fcc to bcc, with interface velocities reaching values in the range of 200-700 m/s, depending on the interface orientation and on temperature. The characteristics of the transformation are of a martensitic nature, without this being imposed on the system. During the incubation time a complex interface structure is formed, which appears to be essential for the martensitic transformation. From the atomic displacements during the transformation, the occurrence of slip planes can be identified.