Predicting solid-liquid interfacial characteristics during rapid solidification

A numerical model capable of predicting cellular and dendritic growth at low and high velocities based on Hunt's approach (Hunt, 1990) is proposed to quantify the degree of non-equilibrium at the solid-liquid interface and thus to determine if an additive manufacturing process route exhibits rapid solidification. The developed model accounts for various undercoolings, as well as the variation in the partition coefficient, liquidus slope, and diffusion coefficient at high velocities. The model is used to estimate the range of cellular/dendritic primary spacing during Laser Powder Bed Fusion (LPBF) for a given set of input parameters. The magnitude of various undercooling values, along with the tip Peclet number and spacing Peclet number are then estimated in order to quantify the extent of non-equilibrium at the solid-liquid interface. Good qualitative agreement is achieved between these values and the analytical KGT model. This new model can help to understand how the solid-liquid interface varies with changes in the processing conditions and material system during LPBF, and thus to improve control of microstructure evolution.