Role of interface morphology on the martensitic transformation in pure Fe

Using classical molecular dynamics simulations, we study austenite to ferrite phase transformation in iron, focusing on the role of interface morphology. We compare two different morphologies; a flat interface in which the two phases are joined according to Nishiyama-Wasserman orientation relationship vs. a ledged one, having steps similar to the vicinal surface. We identify the atomic displacements along a misfit dislocation network at the interface leading to the phase transformation. In the case of the ledged interface, stacking faults are nucleated at the steps, which hinder the interface motion, leading to lower mobility of the inter-phase boundary, than that of a flat interface. Interestingly, we also find the temperature dependence of the interface mobility to show opposite trends in the case of flat vs. ledged boundary. We believe that our study is going to present a unified and comprehensive view of martensitic transformation in iron with different interface morphologies, which is lacking at present, as flat and ledged interfaces are treated separately in the existing literature.