Modeling of rapid solidification during splat quenching

In thermal spray deposition, splats are formed by the impact of molten droplets on a solid substrate or a pre-deposited layer. This paper presents an integrated heat transfer and rapid solidification model for microstructure formation in a single splat. Heat and mass diffusion equations are solved with a moving dendrite tip/melt interface. A unified dendrite growth theory is introduced at the interface that employs the marginal stability criterion to determine the tip operating conditions of dendrites, and is applicable to both free dendrite growth in an undercooled melt and constrained dendrite growth under a positive temperature gradient. The theory can predict the transition of solidification morphology, e.g., from dendritic to planar growth and therefore, the microstructure formation in the splat. The model is used to investigate the microstructure development of Al-Cu alloy splats on a copper substrate. A microstructure map is developed based on the melt undercooling and thermal contact conditions between the splat and the substrate.