Peritectic solidification of highly undercooled Cu-Co alloy

Peritectic solidification has been investigated on Cu _91.7 Co _8.3 alloy by containerless processing in a 3m drop tube. Droplets ranging from 100 to 900μm in diameter have been obtained. The microstructure of the droplets larger than 150μm is characterized by primary α-Co dendrites embedded in Cu-rich matrix, and the completion of peritectic transformation is facilitated as droplet size decreases. It is also found that α-Co dendrites and peritectic cells are conspicuously refined with the decrease of droplet diameter due to the fragmentation of α-Co dendrites by remelting during recalescence. In those droplets finer than 150μm, the precipitation of α-Co dendrites and the peritectic transformation have been suppressed completely, and a coarse metastable supersaturated Cu-rich dendritic microstructure is formed directly from the undercooled melt. In addition, the dendritic growth of primary α-Co phase has been calculated on the basis of the modified LKT/BCT model.