Kinematic and topological models of martensitic interfaces

A new model of martensitic transformations has been presented recently where the habit plane consists of segments of coherent terraces reticulated by an array of line defects. These defects accommodate any coherency strains present and the transformation is effected by lateral motion of disconnections across the terraces. Provided the terraces and line defects satisfy certain criteria, the mechanism of transformation is conservative. Moreover, the topological parameters of the defects (Burgers vectors and step heights) can be determined rigorously enabling the overall habit plane inclination and orientation relationship to be determined.The objective of the present paper is to compare predictions for the habit planes according to this topological method with those of the classical theories in the case of transformations in ZrO2 and Ti. The two approaches lead to disparate solutions, and the origin and magnitude of the disparities are elucidated. Unlike habit planes in the classical model, which are invariant planes, topological ones are misfit-relieved semi-coherent configurations.