FREEZE COATING OF A MOVING SUBSTRATE WITH A BINARY ALLOY

Abstract

A theoretical model is presented for the problem of the deposition of a coaling layer on a flat moving substrate. The coating material is a binary alloy. Upon solidification, three distinct regions exist above the substrate: the solid region, the mixed phase region or mushy zone, and the liquid melt region. The model accounts for convection in the melt, conduction in the mixed phase region, conduction in the solid part of the coating, and conduction in the substrate. The convection in the melt is induced by the combined action of the substrate velocity and the coating deposition velocity. The numerical solution of the model determines the effect of the main parameters of the problem on the solid coating thickness and the size of the mushy zone. These parameters are exemplified by the Prandtl number, the inverse Stefan number, the ratio of the melt deposition velocity to the substrate velocity, and the ratios of material properties in the two phases (solid and liquid) and the substrate. The effect of the melt superheat and substrate undercooling on the formation of the coating layer is also considered.