An enthalpy based model for microstructure evolution during binary alloy solidification

Abstract An enthalpy based solidification model is presented to simulate the evolution of binary alloy microstructure. The model is capable of simulating the nucleation and growth of multiple equiaxed and columnar grains subjected to a given undercooling or cooling rate. Thermal and species transport, forced convection, buoyancy driven convection, shrinkage driven flow and formation of secondary arms are incorporated in the model. The developed model uses a volume averaged enthalpy based solidification solver which is coupled with a pressure based flow solver and a probabilistic nucleation model. Simulations are performed to show the ability of the model in predicting microstructure evolution, flow pattern and microsegregation. Subsequently, the model is used to study the effect of cooling rate on grain size and solute segregation during microstructure evolution, formation of secondary arms and the effect of undercooling on primary arm spacing in columnar grain growth. The effect of natural convection on columnar dendrite growth is also studied. It is found that grain size and solute segregation decreases with increase in cooling rate. Also, it is observed that for columnar growth the primary arm spacing decreases with increase in initial undercooling but remains almost unaffected with change in specified number of nuclei. The developed model is extended to capture three-dimensional dendrite growth with secondary arms.