Compatibility and accommodation in displacive phase transformations

The role of disconnections and lattice-invariant deformation in displacive phase transformations is reviewed, particularly the defect structure of equilibrium habit planes, the mechanism of transformation, and the deformation accompanying growth. This is extended to the 3-D topological modeling of a product embedded in its parent phase. Stress concentrations arise where the interface orientation deviates from the equilibrium habit, such as plate tips and edges. Various mechanisms are discussed for the amelioration and accommodation of these stresses. These include the well established mechanism of self-accommodating assemblies of variants. New mechanisms are proposed relating to the defect structure within individual plates and its interaction with crystal dislocations. Some supporting experimental observations are presented.