Phase-field simulation of microstructure development involving nucleation and crystallographic orientations in alloy solidification

A proper treatment of nucleation in phase-field simulations is developed, in which the calculation of nucleation kinetics in binary melts is taken into account and the free energy change of nucleation is obtained by maximizing it relative to the composition of the nuclei. Using the phase-field model for polycrystalline solidification coupled with the nucleation strategy, the typical solidification microstructures encountered in castings are simulated. The selection of columnar grains and the columnar-to-equiaxed transition (CET) are clearly shown. The results also indicate that the columnar zone length and the equiaxed grain size increase with a decrease in cooling rate, which results from the competition between nucleation and growth.