In situ X-ray monitoring of convection effects on segregation freckle formation

Abstract

Visualizations of the solidification process under the influence of thermo-solutal convection were obtained by means of X-ray radioscopy within a Hele-Shaw cell filled with Ga-25wt%In alloy. The density-driven melt flow causes the formation of vertical segregation channels (chimneys) in the mushy zone. The development of the chimneys and the probability of their surviving depend sensitively on the spatial and temporal properties of the flow field. The second part of this study concerns the case when the natural convection is superimposed by an electromagnetically driven flow perpendicular to the dendrites growth direction. The main effects of forced melt flow are a modification of the dendritic structure and flow-induced redistribution of the solute concentration. © Published under licence by IOP Publishing Ltd.