Spinodal decomposition and coarsening of stressed thin films on compliant substrates

The microstructural evolution and long-time coarsening behavior of a thin f ilm attached to a compliant substrate is investigated for a spinodally deco mposing, binary, two-phase alloy using a Cahn-Hilliard type equation. Elast ic fields arise because of composition dependence of the lattice parameter (compositional self-strain) as well as an average misfit between the film a nd substrate. This leads to a local mass flux within the film that depends on the global composition field as well as the thickness and elastic proper ties of the substrate. Three distinct coarsening regimes are observed: a ra pid initial stage of spinodal decomposition into alternating phases, a tran sition region where internal interfaces grow and coalesce, and a final coar sening regime where the outermost layers grow with little change in the int ernal structure. An asymptotic expression for the long-time coarsening rate is derived as a function of the compositional self-strain, the average mis fit strain, the film thickness and the total (film plus substrate) thicknes s. The analytic predictions are in good agreement with numerical simulation s for a variety of film and substrate thicknesses and compositional and ave rage film misfit strains. (C) 2001 Acta Materialia Inc. Published by Elsevi er Science Ltd. All rights reserved.