Phase-Field Modeling of Precipitation Growth and Ripening During Industrial Heat Treatments in Ni-Base Superalloys

We develop a phase-field model for the simulation of chemical diffusion limited microstructure evolution, with a special focus on precipitation growth and ripening in multicomponent alloys. Further, the model accounts for elastic effects, which result from the lattice-misfit between the precipitate particles and the parent matrix phase. To be able to simulate particle growth and ripening in one dimension, we introduce an extra optional driving-force term, which mimics the effect of curved interfaces in one dimension. As a case study, we consider the one-dimensional (1D) gamma'-precipitation growth and ripening under the influence of a realistic multistep heat treatment in the multicomponent Ni-based superalloy CMSX-4. The required temperature-dependent thermodynamic and kinetic input parameters are obtained from CALPHAD calculations using the commercial software-package ThermoCalc. The required temperature-dependent elastic parameters are measured in-house at the chair of Metals and Alloys, using resonance ultrasound spectroscopy and high-temperature X-ray defraction. Finally, the model is applied to calculate the equilibrium shape of a single gamma'-particle with periodic boundary conditions. Relations to the shapes of gamma'-particles in respect of heat-treated experimental microstructures are discussed.