Surface evolution in two-component system

Mullins' theory of capillary driven shape evolution in solid was extended for two-component systems, taking into account the difference in mobility of the components in the surface layer. A close set of equations describing evolution of both surface profile and surface composition was derived. The developed theory was applied for two problems: (i) grain boundary grooving; (ii) flattening of periodically corrugated surfaces. The main result is the formation of concentration inhomogeneity on the surface and in the bulk beneath the surface during a capillary driven shape change of the surface. The changes in all linear dimensions of groove with time are shown to follow t(1/4) law, where t is annealing time, however, the groove shape differs from Mullins' theory. A region of the surface adjacent to grain boundary is shown to become enriched by the slow component. In general, the flattening kinetics of a periodically corrugated surface in two-component system does not follow exponential law because the redistribution of elements in the surface layer decreases the rate of flattening. (C) 2002 Published by Elsevier Science Ltd on behalf of Acta Materialia Inc.