Reaction layer growth in a substrate/polycrystalline film system

Two common observations during the growth of a reaction layer between two materials are the generation of large stresses and the formation of pegs, i.e., protrusions of the reaction layer into one or both of the reactant materials. We present a combined kinetics/thermodynamics/mechanics analysis of the growth of a reactant layer between a thin film and a substrate and predict the evolution of both the peg morphology and the growth stresses in the film. Peg formation is favored when the stress-free strain associated with the reaction is large, the reactant/product interface energy is small, and when the grain size in the reactant film is large compared with the film thickness. The mechanics analysis is based upon a dislocation description of the transformation. The resultant predictions of stress and peg evolution are consistent with a wide range of experimental observations.