Effects of flow on morphological stability during directional solidification

Research involving the interaction of flow with morphological instability during directional solidification of binary alloys is reviewed. In general, flow may arise during the solidification process from thermal and solutal buoyancy, changes in density upon solidification, thermocapillary forces at free boundaries, or external forcing of the system. We focus primarily on the last of these, giving details of the influence of various forced flows on the critical conditions for morphological instability. These flows include the asymptotic suction profile, stagnation-point flow, and periodically driven shear flows. Parallel shear flows are unable to stabilize morphological instabilities in three dimensions but may lead to new long-wave, traveling instabilities. Flow-induced, long-wave instabilities are also encountered in the presence of both steady and modulated stagnation-point flows. Unsteady, nonparallel shear flows may stabilize morphological instability if the flow parameters are adjusted properly.