Phase field modeling of channel dislocation activity and γ′ rafting in single crystal Ni–Al

Dislocation-precipitate interaction and directional coarsening (rafting) of γ′ precipitates in single crystal Ni–Al alloys under external load are investigated by three-dimensional computer simulations. The simulation technique is based on an integrated phase field model that characterizes simultaneously the spatiotemporal evolution of both precipitate microstructure and dislocations. The initial configurations consisting of cuboidal γ′ particles and dislocations in γ channels are constructed according to experimental observations and phase field simulations of the dislocation filling process in the γ channels. For a given state (sign and magnitude) of the lattice misfit and external load commensurate with experimental values, the predicted morphologies of the rafted γ′ precipitates and the rafting kinetics agree well with experimental observations. This indicates that plasticity plays a dominant role in the rafting process as compared to elastic modulus mismatch between γ and γ′ phases, which has been ignored in the present simulations. The spatial variation of chemical potential of solute atoms caused by the coupling between channel dislocations and misfit stress is evaluated from concentration and stress distributions, from which diffusion fluxes in the γ channels are analyzed.