Crystallography and migration mechanisms of planar interphase boundaries

A general and yet simple theory is developed to predict the orientation relationship, orientation, structure and migration mechanisms of planar interphase boundaries in phase transformations. In contrast to existing theories that are based essentially on matching of atoms or lattice sites within two parallel, closely-packed planes in the two lattices, the present theory involves consideration of matching of edges of closely-packed lattice planes. In terms of the present theory, planar interphase boundaries are defined by the Moire plane resulting from the intersection between at least two sets of closely-packed lattice planes, and that such boundaries migrate in their normal directions by successive nucleation and lateral gliding, within the macroscopic interphase planes, of interfacial defects of Moire ledges that have unique heights and displacement vectors. A brief comparison is provided between the present theory and approaches of phenomenological theory of martensite crystallography, invariant line, structural ledges and disconnections.