Influence of epitaxial stress on spinodal decomposition in binary alloys with large size effects: Application to the Au-Ni system

Within the framework of Cahn's pioneering theory of spinodal decomposition, the effect of the epitaxial stress on the stability of a binary alloy soli d solution against infinitesimal compositional fluctuations is revisited. I t is shown that the elastic energy term due to a coherent lattice mismatch with a substrate modifies the linearised diffusion equation. This term is p articularly high when size effects between the two constituents are strong. It is then necessary to take into account anharmonic terms in the expressi on of the elastic energy. From the modified diffusion equation, a new spino dal curve, called the epitaxial coherent spinodal, may be calculated for di fferent substrate lattice parameters. The results of the model are compared with recent experiments on coherently grown (001) Au-Ni alloys. A modulate d structure has been evidenced upon annealing which is in good agreement wi th our calculations. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.