Rapid growth of Cu-Pb monotectics under containerless condition

Rapid growth of Cu-10%Pb hypermonotectics and Cu-37.4%Pb monotectics have been achieved under containerless condition in drop tube. With the increase of droplet undercooling, the primary (Cu) phase in hypermonotectios shows a morphology transition of coarse dendrite → fragmental dentrite → equiaxed dentrite. The momotectic microstructure transfers from multiple monotectic cell to single monotectic cell. Corresponding to the droplet diameter changing from 1000 to 100 μm, the calculated maximum undercooling for hypermonotectics and monotectics are 269 K (0.2 T_L) and 245 K (0.2 T_M) respectively. The maximum growth velocity of (Cu) dendrite is 2.4 m/s in Cu-10%Pb hypermonotectics. The growth of primary (Cu) phase is always controlled by solute diffusion. The effect of Marangoni migration is more significant than that of Stokes motion, and the Marangoni migration velocity decreases when droplet diameter becomes small.