Effect of elastic stress on two-phase binary diffusion couples

A front-tracking finite difference approach has been used to examine the Influence of misfit strain and applied stress on interdiffusion in binary, coherent, two-phase planar diffusion couples assuming local thermodynamic equilibrium at the interface. The phases are cubic; possess different lattice parameters, elastic constants, and diffusivities; and can be oriented in either the [001] or [111] direction. Interface compositions, which are time independent in the stress-free case, become time dependent when Stresses are present and are affected by both the elastic state of the system and the relative diffusivities. Interfacial compositions can vary by up to a few atomic percent with time and can be-either greater or less than the stress-free values for the same set of materials parameters, : depending on the volume fraction of the phases. At sufficiently small times, the interfacial position can be approximated as proportional to the square root of time. Interfacial velocities in this regime can differ by up to a factor of 2 from an otherwise equivalent unstressed system. The nonlinear equations resulting from the coupling of stress and composition were linearized in the bulk phases and could be solved either implicitly or explicitly. Equations governing the interface motion and compositions were not linearized and were solved implicitly at each time-step.