Nucleation and growth of beta Cu_3Sb intermetallic compound in undercooled Cu-31 percent Sb eutectic alloy

摘要

A Cu-31 percent Sb eutectic alloy has been rapidly solidified during containerless processing in a drop tube. The microstructures are characterized by beta Cu_3Sb grains plus a small amount of alpha Cu 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, beta Cu_3Sb grain is refined and equiaxed grain of alpha Cu 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 beta Cu_3Sb intermetallic compound increases. The growth velocities of eutectic structure and dendrites of beta Cu_3Sb and alpha Cu increase with rising undercooling. The growth of beta Cu_3Sb phase is dominant when undercooling is lower than 53 K. When undercooling exceeds 53 K, the growth dominance of the beta Cu_3Sb phase will be replaced by the alpha Cu 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 percent Sb eutectic alloy during rapid solidification. Microstructural evolution of beta Cu_3Sb grain dominates the microstructure of Cu-31 percent Sb eutectic alloy.