Phase and microstructure formation in rapidly solidified Cu-Sn and Cu-Sn-Ti alloys

Abstract

In this work, the microstructure and phase formation in binary Cu-Sn and ternary Cu-Sn-Ti alloys under rapid solidification conditions are studied as a function of alloy composition and cooling rate and compared to the results from solidification at low cooling rate in a Differential Scanning Calorimetry furnace. At high cooling rates (103–104 K/s) a metastable Cu5.6Sn phase is observed in all selected binary alloys, which could be explained to have formed via diffusionless martensitic transformation from the parent β phase. An increasing amount of Sn results in the transition of preferential phase formation in the sequence of α, Cu5.6Sn and δ. In the ternary alloys, Ti is observed to form (Cu,Sn)3Ti5 compound at both low and high cooling rates due to the low solubility of Ti in the α phase, and the fraction of (Cu,Sn)3Ti5 and α phases tend to increase with increasing Ti amount but that of Cu5.6Sn decreases. The results are of relevance for the development and optimization of Cu-Sn based alloys for processing techniques involving rapid solidification with varying cooling rates, e.g. laser additive manufacturing.