Coherency strain in two dimensions; effects on phase equilibria, diffusion and phase transformations in multicomponent systems

Some recent advances in the description of equilibrium and diffusion in ternary systems are reviewed. The stabilizing effect of coherency strain energy is discussed for the pseudo-ternary system In-P-Ga-As, and the experimental determination of nonlinear coherent diffusion behaviour in this system considered. The general effects of elastic energy on the homogenization kinetics of coherent planar heterostructures are discussed. Under certain circumstances, it is possible that an initially coherent lattice-matched monophase system will become incoherent - and phase separate as a result of interdiffusion and partial homogenization. The dissolution of a thin second-phase coherent film in a semi-infinite matrix may be influenced in two ways by coherency: The strain energy will affect not only the equilibrium condition, but also the rates of diffusion in the matrix phase. In isothermal binary systems under local equilibrium, the interfacial concentrations will remain constant during dissolution. In corresponding ternary systems, and in contrast to the precipitation case, one generally expects a regular and predictable migration of the local equilibrium tie-line as dissolution proceeds.