Rapid solidification of hypereutectic silver-copper alloy in drop tube

The Ag-50wt%Cu hypereutectic alloy was solidified and investigated in a 3 m drop tube, and its nucleation and microstructure characteristics were explored also. The results showed that (1) with the decrease of droplet size, the structural morphology transforms from the dendrites with long trunk and thin short secondary arms to fine dendritic structures; (2) the dendritic growth is mainly controlled by solute diffusion within the whole undercooling regime, while the influence of thermal diffusion-controlled growth becomes stronger above a critical undercooling about 268 K; (3) the refinement of dendritic structure is caused by large amounts of nuclei within droplet; (4) when droplet diameter is smaller than 300 micron, the undercooling and growth velocity were estimated to be greater than 268 K and 290 mm/s respectively, while the solute trapping effect may occur.