Thermodynamic description and growth kinetics of stoichiometric precipitates in the phase-field approach

In theoretical analyses and computational simulations chemical free energies of stoichiometric compounds and solid solution phases are often approximated by parabolic functions. In the present work, we focus on examining the effect of different approximations of chemical free energies on predicted precipitate growth kinetics with phase-field modelling. As an example, we studied the precipitation of plate-like θ^′ (Al₂ Cu) in Al-4 wt%Cu Alloys. Using six sets of chemical free energies for θ^′ and Al-Cu solid solution, growth kinetics of θ^′ precipitates were simulated by assuming either constant diffusivity or constant atomic mobility. It is demonstrated that the parabolic function provides a good description for the chemical free energy of a stoichiometric compound while the growth kinetics is sensitive to the approximation of chemical free energy for the solution phase.