CAFD model for solidification of multicomponent and multiphase alloys

A combined cellular automaton - finite difference (CAFD) model has been enhanced to predict the formation of secondary eutectic phases during solidification allowing more accurate simulation of the as-cast microstructure of Ni-base superalloys. A CAFD model developed previously allows the prediction of the columnar-equiaxed transition, and defect formation, such as stray grains, or melt-back during the casting of single-crystal turbine blades. However, it is based on binary alloys with constant thermodynamic data. This work proposes a general formalism to extend the model to multicomponent and multiphase systems. The characteristic lamellar spacing of the eutectic structure in the interdendritic regions is in the order of a few microns. Since the code is dedicated to the prediction of mesoscale solidification structures, it is not possible to treat the nucleation and growth of each separate phase within the eutectic. As a consequence, the eutectic phases are treated numerically as a single phase with its own specific nucleation law and a rule-of-mixtures approach is used to calculate the eutectic fraction. The extended model is applied to Ni-based superalloys and the resulting predictions of microsegregation and microstructural formation are presented and discussed.