Dendritic growth and solute trapping in rapidly solidified Cu-based alloys

Rapid solidification of binary Cu-22%Sn peritectic alloys and Cu-5%Sn-5%Ni-5%Ag quaternary alloys was accomplished by glass fluxing, drop tube and melt spinning methods. The undercooled, by glass fluxing method, Cu-22%Sn peritectic alloy was composed of α(Cu) and δ(Cu₄₁Sn ₁₁) phases. If rapidly solidified in a drop tube, the alloy phase constitution changed from α(Cu) and δ(Cu₄₁Sn ₁₁) phases into a single supersaturated (Cu) phase with the reducing of droplet diameter, and the maximum solubility of Sn in (Cu) phase extended to 22%. The Cu-5%Sn-5%Ni-5%Ag quaternary alloy was composed of (Cu) and (Ag) phases under the containerless processing condition in a drop tube, and the solute microsegregation of (Cu) phase was obvious. When the Cu-5%Sn-5%Ni-5%Ag quaternary alloy was solidified by melt spinning method, microsegregation was suppressed and solute trapping occurred. The experimental results show that the microstructures of primary (Cu) phase in the two alloys transfer from coarse dendrites into equiaxed grains with the increase of cooling rate and undercooling, which is accompanied by the grain refinement effect.