Nucleation and growth of βCu₃Sb intermetallic compound in undercooled Cu-31% Sb eutectic alloy

A Cu-31% Sb eutectic alloy has been rapidly solidified during containerless processing in a drop tube. The microstructures are characterized by βCu₃Sb grains plus a small amount of αCu solid solution formed at the grain boundaries, instead of cooperative growth into a eutectic like other binary eutectic alloys. With the decrease of droplet size, βCu₃Sb grain is refined and equiaxed grain of αCu solid solution forms in droplets. Melt undercoolings up to 225 K (0.245T_E) are estimated by a heat transfer model of droplet solidification. Both experimental and calculated results indicate that, as undercooling rises, the nucleation rate of βCu₃Sb intermetallic compound increases. The growth velocities of eutectic structure and dendrites of βCu₃Sb and αCu increase with rising undercooling. The growth of βCu ₃Sb phase is dominant when undercooling is lower than 53 K. When undercooling exceeds 53 K, the growth dominance of the βCu₃Sb phase will be replaced by the αCu phase. In contrast, the growth of lamellar eutectic can never become dominant in undercooled melt. This is just the reason why a eutectic microstructure cannot be formed in Cu-31% Sb eutectic alloy during rapid solidification. Microstructural evolution of βCu ₃Sb grain dominates the microstructure of Cu-31% Sb eutectic alloy.