STEPS, DISLOCATIONS AND DISCONNECTIONS AS INTERFACE DEFECTS RELATING TO STRUCTURE AND PHASE-TRANSFORMATIONS

Interfacial defects may exhibit both dislocation and step-like charact er. The Burgers vector of such a defect is an invariant topological qu antity which can be determined mathematically or graphically by circui t mapping. Step character cannot be determined directly by such method s, but a new definition of scalar step heights is presented here in te rms of crystallographic parameters. This partition of a disconnection into dislocation and step portions facilitates the analysis of process es such as phase transformations; the dislocation portion is associate d with the long-range strain field and shape change and the step porti on with divergences in diffusional fluxes associated with growth. Exam ples are given in the h.c.p./f.c.c. case for various types of defect. Copyright (C) 1996 Acta Metallurgica Inc.