MORPHOLOGICAL STABILITY OF A BINARY ALLOY DURING DIRECTIONAL SOLIDIFICATION - INITIAL TRANSIENT

We consider directional solidification of a binary alloy during the in itial transient period in which the interface velocity, concentration, and temperature gradients are changing with time. We introduce sinuso idal perturbations of the planar crystal-melt interface and numericall y calculate the time evolution of these perturbations. The results for morphological instability are in good agreement with the Mullins and Sekerka analysis of the time-independent base state if the instantaneo us values of the temperature gradient and solidification velocity are used in the analysis; the agreement increases with decreasing degree o f instability.