A COMPARATIVE-STUDY OF THE THEORY OF THE O-LATTICE AND THE PHENOMENOLOGICAL THEORY OF MARTENSITE CRYSTALLOGRAPHY TO PHASE-TRANSFORMATIONS

The approaches of the phenomenological theory of martensite crystallog raphy (PTMC) and the theory of the O-lattice (TOL) to describe the ele ments of a phase transformation are compared for an O-line transformat ion strain. A number of simple relationships between the O-lattice tre atment and the PTMC have been established. The displacement associated with the long range strain component is shown to be identical in both treatments when the planes defined by the path of the O-lines are cor related to the slip plane of the dislocations. A characteristic featur e of the TOL approach is that this displacement is allowed to vary for a fixed habit plane. When the displacement is associated with an inte rfacial step, it is equivalent to a transformation dislocation, whose Burgers vector is explicitly expressed in terms of a D-lattice vector in the TOL formula. This method is extended to consider the tilt or te nt-shaped surface relief effects observed at precipitates in a Ti-Cr a lloy. Good agreement is found between the predictions of this approach and the measurements reported in the literature. (C) 1998 Acta Metall urgica Inc.