THEORIES AND OBSERVATIONS OF CHEMICALLY-INDUCED INTERFACE MIGRATION

The diffusional coherency strain theory and its implications for chemi cally induced mig ration of liquid films and grain boundaries are revi ewed and critically examined. The critical experiments in metals and o xides show the validity of this theory. The observed characteristics o f this phenomenon: misfit dislocations at the initial boundary locatio n; migration direction; faceting; dependence on grain boundary structu re, on boundary curvature, and on temperature are also consistent with the coherency strain theory. Other theories are also described, but a re mostly inconsistent with the observations, and there is very little experimental evidence for the validity of any of them. There was expe rimental evidence that the coherency strain theory is also valid for d iscontinuous precipitation. The significance of lattice diffusion at s mall distances in the order of the lattice spacing is examined. The re lated phenomena of diffusion induced recrystallisation and surface cor rugation are also described. Finally, some examples of these phenomena in the practical materials are presented. (C) 1995 The Institute of M aterials and ASM International.