ON THE KINETICS OF INTERFACE-DIFFUSION-CONTROLLED PERITECTOID REACTIONS

We consider the peritectoid reaction alpha + beta --> omega as it occu rs at previously existing planar alpha/beta interfaces, and at suffici ently low temperatures that volume diffusion is negligible and interph ase boundary diffusion is rate-controlling. With the further assumptio n that the participating phases have fixed compositions and that the i nterfacial diffusion process is driven by gradients in interfacial cur vature, we obtain a unique solution for the growth of the product omeg a layer along the alpha/beta interface. Both the layer thickness and t he steady lengthening velocity are predicted. The layer thickness is o f the same order as the capillary length; it would be difficult to det ect by conventional means, but could be revealed for example by T.E.M. The layer growth is determined entirely by the undercooling, the inte rfacial energies and the relevant kinetic quantities. The presence of such thin layers at parent phase interfaces is expected to exert a pro found influence on microstructurally determined properties. (C) 1998 A cta Metallurgica Inc.