ON THE FORMATION OF THE BANDED STRUCTURE IN RAPID SOLIDIFICATION

Rapid solidification experiments on metallic alloys over the last deca de have provided widespread observations of a novel banded structure. We present the results of numerical and analytical studies of the non- linear dynamics of the solidifying interface which provide insights in to the mechanism of formation of this structure. These studies are bas ed on a model of directional solidification which includes non-equilib rium effects and consists of a one-dimensional boundary integral equat ion for the temperature field combined with a boundary-layer approxima tion for the solute field. Three main ingredients of the banding mecha nism emerge from these studies: the presence of non-linear oscillation s of the solidification rate driven by solute trapping, the dramatic e ffect of latent heat diffusion on the character of these oscillations, and the propagation of ''optical growth fronts'' connecting collision -controlled and diffusion-controlled interfacial regions.