Dendritic morphology observed in the solid-state precipitation in binary alloys

The precipitation of gamma(2) phase in Cu-Al beta-phase alloys has been obs erved to occur in the dendritic morphology. Such morphology is rarely obser ved in the solid-state transformations. Earlier it was reported that the ga mma precipitates were formed in the dendritic shape when Cu-Zn beta-phase a lloys were cooled from high temperature. The characteristics of these two a lloy systems have been examined to find the factors promoting the dendritic morphology in the solid-state transformations. Rapid bulk diffusion and fa st interfacial reaction kinetics would promote such morphology. The kinetic s of atom attachment to the growing interface is expected to be fast when c rystallographic similarities exist between the parent phase and the precipi tate. We have predicted the dendritic morphology in the solid-state precipi tation in many binary alloy systems simply based on such crystallographic s imilarities. These alloys include, in addition to Cu-Al and Cu-Zn, the beta -phase alloys in Ag-Li, Ag-Zn, Cu-Ga, Au-Zn, and Ni-Zn systems, gamma-phase alloys in Cu-Sn and Ag-Cd systems, and delta-phase alloys in Au-Cd system. Of these, the alloys in Ag-Zn, Ni-Zn, Ag-Cd, and Cu-Sn systems were prepar ed and it was indeed found that the precipitates formed in the dendritic sh ape.