Solute distribution during rapid solidification into an undercooled melt

Rapid solidification experiments show that a solute-rich core generally exists in a solid rapidly solidified from an undercooled melt. Several simplified models have been proposed to explain and predict this phenomenon. This paper presents a generalized model that includes mass as well as heat diffusion in both solid and liquid phases and considers nonequilibrium solidification kinetics including solute-trapping to treat the local recalescence. For given local temperature gradients and cooling rates, the model leads to a one-dimensional moving boundary problem with a strongly coupled boundary condition at the solid/liquid interface. The solution is obtained by employing an implicit iterative scheme that uses a coordinate transformation. The model predicts successfully a solute-rich core as observed in the experiments. The results show that both melt undercooling and cooling rates strongly affect the solute distribution in the solidified solid. Selected results for dilute aluminum-copper alloys are presented to illustrate the unique features of solute distribution in rapidly solidified alloys.