An interface-tracking model of moving boundaries in multi-phase systems: application to solidification

A new approach to modelling of phase boundary migration is presented. In particular, a meso-scale model of alloy solidification, which can resolve solid grain boundaries as they grow through the diminishing liquid phase, has been developed. The initial condition is of a superheated, but cooling, liquid alloy in a domain with a mixed thermal boundary condition. After activation via nucleation of solid, the model tracks the phase boundaries as discrete fronts across a fixed computational grid, and the kineticsof motion are derived from theories of dendritic growth. Each interface is formed by interpolation between representative computational markers, and is the boundary between liquid and partial solid with a dendritic morphology. The model simulates the non-equilibrium growth of both a columnar front and equiaxed grains, and can thus be used to predict the final grain structure in metallic alloy castings. The evolution of microstructure and heat are fully coupled in the formulation. The method is illustrated by the example of the simulation of Al-Cu alloy solidification.