Double-diffusive convective modes and induced microstructure localisation during solidification of binary alloys

Abstract

We analysed the coupling of convection and solid-liquid interface morphology during upward Bridgman solidification of both transparent and metallic alloys in a cylinder. Localised microstructures are observed for typical alloys but not for lead-30 wt% thallium. This difference is quantitatively explained from phase diagrams and from the more general form of constitutional supercooling criterion, extended for non-dilute alloys. Even if the convection induces a lateral concentration gradient, there is not any lateral gradient on the level of morphological instability and there is not any propagation front of morphological instability for lead-30 wt% thallium alloy. In solidification experiments, convection can be generated by either radial thermal gradient or solute axial gradient. The formation and dynamics of double-diffusive convective pattern is analysed during the transient and different thermal radial gradient conditions.