Atomistic dynamics of the bcc ↔ fcc phase transition in iron: Competition of homo- and heterogeneous phase growth

Using molecular-dynamics simulation, we study the dependence of the martensitic (cc → bcc) and of the austenitic (bcc → fcc) phase transformation in Fe. By using a bi-phasic crystal containing an fcc-bcc interface, both heterogeneous and homogeneous phase growth can be studied. We focus on the dependence of the phase-growth dynamics on the available volume and show that in large volumes, homogeneous phase nucleation is favored at the cost of heterogeneous growth. In addition, we study the influence of the interface geometry on the phase transformation behavior. We find that, while the interface roughens in both cases, a Kurdjumov-Sachs interface geometry leads to a dendritic interface growth, while the Nishiyama-Wassermann interface geometry remains globally planar.