Calphad coupled phase-field model with mechano-chemical contributions and its application to rafting of γ’ in CMSX-4

A novel Calphad coupled mechano-chemical phase-field model is presented which in addition to chemo-elastic contributions to the driving force further includes mechano-chemical effects on diffusion (stress-driven diffusion), equilibrium compositions and driving force. These effects have their origin in the concentration dependency of the eigenstrains and can significantly influence the phase transformation kinetics, especially in Ni-based superalloys where the different dissolved elements have strongly different partial molar volumes. In this paper, all mechano-chemical contributions to diffusion, equilibrium concentrations and driving force are derived starting from a free energy functional. In order to use the model in conjunction with Calphad databases, elastic effects are incorporated in an efficient and consistent way by a posteriori treatment of the chemical quasi-equilibrium data.