Steps, dislocations and disconnections as interface defects relating to structure and phase transformations

Abstract

Interfacial defects may exhibit both dislocation and step-like character. The Burgers vector of such a defect is an invariant topological quantity which can be determined mathematically or graphically by circuit mapping. Step character cannot be determined directly by such methods, but a new definition of scalar step heights is presented here in terms of crystallographic parameters. This partition of a disconnection into dislocation and step portions facilitates the analysis of processes such as phase transformations; the dislocation portion is associated with the long-range strain field and shape change, and the step portion with divergences in diffusional fluxes associated with growth. Examples are given in the h.c.p./f.c.c. case for various types of defect.