A modified microscopic cellular automaton model for the simulation of microstructure evolution during solidification/melting of nickel-based superalloys

A quantitatively modified microscopic cellular automaton model (CA) is established to simulate the microstructure evolution during solidification/melting of IN718 nickel-based superalloys. As compared to the original CA model, the modified CA model has the merits of solute conservation and the inherent incorporation of the melting/solidification algorithms. Inspired by the diffuse interface models, the present model optimizes the diffusion and solute redistribution, and the solute conservation within the computational domain is achieved restrictively. The KGT (Kurz-Giovanola-Trivedi) model was used to calculate the solidification/melting kinetics according to the undercooling values. After testing the grid size independency and grid anisotropy of the modified CA model, it was applied to simulate the growth of multiequiaxed and columnar dendrites of the IN718 alloy under different cooling rates, and the segregation of solute Nb in the liquid phase was quantified. The results reveal that the segregation of Nb was weakened with higher cooling rates during solidification. The simulation of dendritic coarsening during isothermal holding was carried out by the modified CA model in a straightforward manner after the solidified dendrites were obtained. The simulation results effectively mimicked the coarsening behavior driven by the coherent influences of solidification and melting mechanisms, which were uncapable to be reproduced by the original CA model. This study provides a powerful tool with high computation efficiency for better understanding the microstructure evolution mechanisms in nickel-based superalloys during solidification and melting in practical engineering incidents.