EFFECT OF A SHARP GRADIENT OF CONCENTRATION ON NUCLEATION OF INTERMETALLICS AT INTERFACES BETWEEN POLYCRYSTALLINE LAYERS

Recent works on reaction kinetics in bimetallic multilayers have demon strated that the unidirectional sharp concentration gradient, which de velops as interdiffusion proceeds at the interface, is able to delay o r to inhibit nucleation of intermetallics. A thermodynamic and kinetic approach is proposed in order to explain such a phenomenon. The exist ence of a critical concentration gradient, beyond which nucleation is suppressed, is found to be strongly dependent on the atomic transport in both intermetallics and metastable solid solution and more specific ally on the activation energy of each phase. Consequently, the tempera ture appears to be the most significant variable controlling the exist ence and the value of a critical concentration gradient. Copyright (C) 1996 Acta Metallurgica Inc.