High undercooling and rapid dendritic growth of Cu-Sb alloy in drop tube

Droplets of Cu-20%Sb hypoeutectic alloy has been rapidly solidified in drop tube within the containerless condition. With the decrease of droplet diameter, undercooling increases and the microstructures of primary copper dendrite refines. Undercooling up to 207 K (0.17 T_L) is obtained in experiment. Theoretic analysis indicated that, because of the broad temperature range of solidification, the rapid growth of primary copper dendrite is controlled by the solutal diffusion. Judging from the calculation of T ₀ curve in the phase diagram, it is shown that the critical undercooling of segregationless solidification is ΔT₀ = 474 K. At the maximum undercooling of 207 K, the growth velocity of primary copper phase exceeds to 37 mm/s, and the distinct solute trapping occurs.