The role of disconnections in phase transformations

The topological model of phase transformations is described in terms of disconnections. Disconnection motion is shown to produce a variety of phase transformations with accompanying plastic strain. These strains, together with elastic strains associated with equilibrium arrays of interface defects, define expected habit planes and orientation relationships. Non-equilbrium defect arrays resulting from kinetic constraints are discussed. Example applications of the topological model are presented for several types of martensitic transformations and several examples of diffusional transformations.