Modeling of precipitation kinetics in multicomponent systems: Application to model superalloys

A new general model dealing with nucleation, growth and coarsening simultaneously has been developed for the simulation of precipitation in non-dilute multicomponent alloys. Nucleation is implemented using the Zeldovich theory that includes regression effects. Growth and coarsening are modeled using the recently developed growth law in multicomponent alloys that accounts for capillarity, mass balance at the interface matrix-precipitate and diffusion-flux couplings. Numerical results are confronted to atom probe tomography (APT) experiments on model NiCrAl superalloys and to rigid lattice kinetics Monte Carlo (LKMC) simulations and are found in very good agreement with both APT experiments and LKMC simulations. We emphasize this work on the evolution of phase concentrations. The temporal evolution of the mean precipitate composition is found to be non-monotonic during the phase transformation, and phase composition does not follow the tie line due to a complex interplay between capillarity and diffusion process. The widespread availability of both thermodynamic and mobility databases makes this new model very suitable for material design.