Containerless rapid solidification of undercooled Cu-Co

摘要: Droplets of Co-16%Cu and Co-71 .6%Cu peritectic alloys were solidified during containerless processing in a 3-m drop tube. The microstructures Co-16% Cu alloy droplets characterized by dendritic or equiaxed a-Co phase with small amount Cu-rich solid solution distributed on a- Co boundaries. Two thresholds droplet diameter observed for at which "equiaxed-dendritic-equiaxed" morphological transitions occur to primary phase. This conspicuous refinement grains results from the fragmentation dendrites caused recalescence effect. For Co-71.6% alloy, forms as coarse columnar large droplets. Theoretical calculations indicate that Marangoni migration contributes more growth disperse Co-rich spheres stimulating collision coalescence than Stokes motion residual gravity falling