(V) CALPHAD Based Cellular Model of Dendrite Growth

A computational model of dendritic growth based on the CALPHAD thermodynamic model was developed in this study. The dendrite growth was simulated using cellular automata (CA) with the equilibrium conditions in interfacial cells. The developed novel model (CACALPHAD) overcomes the current limitation of the published CA models, in which linearized phase diagrams are used, and allows for the investigation of some practical alloys such as stainless steels. To reduce the computational time, the study proposes a lookup table to store the thermodynamic information and an efficient interpolation scheme to retrieve the information during the simulation. The model takes into account the curvature effect of the evolving solid/liquid (S/L) interface by incorporating the capillarity undercooling into the thermodynamic information during the simulation. The developed CA-CALPHAD model can be used to investigate the free growth and constrained growth in response to different solidification parameters. The results of modeling include the dendrite morphology, dendrite size, solute segregation in the dendrite, and the dendrite growth rate. The paper investigates the solidification of a ternary stainless steel alloy (Fe-Cr-C) and demonstrates that a higher cooling rate increases the solute segregation, produces a finer grain, and increases the susceptibility to sensitization.