Orientation Relationship in Fcc–Bcc Phase Transformation Kinetics of Iron: a Molecular Dynamics Study

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The kinetics of the (110)bcc//(111)fcc heterointerface of iron during the fcc–bcc phase transformation has been investigated by molecular dynamics simulation. The various orientation relationships (ORs) between Nishiyama–Wasserman (N–W) and Kurdjumow–Sachs (K–S) ORs, which are experimentally observed, were examined. The planar propagation of the fcc–bcc heterointerface was observed in the case of the N–W and near N–W ORs, whereas a fast needlelike growth after initial planar growth was observed in the case of the K–S and near K–S ORs. The transformation started from the matching area of the fcc and bcc lattice and followed the Bain transformation path. It was confirmed that the difference in the matching area of the fcc and bcc lattices at the interface between the N–W and K–S ORs causes the two different propagation behaviors. In addition, the distribution of the atomic stress in the system during phase transformation was examined. The residual atomic stress was distributed toward the [01̄0]bcc direction after the transformation in the case of the N–W OR. The change in the direction of the Bain deformation path during phase transformation caused a fast needlelike growth after the initial planar propagation in the case of the K–S OR.