Microstructural characteristics and mechanical properties of peritectic Cu-Sn alloy solidified within ultrasonic field

The dynamic solidification of peritectic Cu-70%Sn alloy was accomplished within a 20kHz ultrasonic field under the power range up to 440W. The ultrasound promotes the nucleation of primary ε(Cu₃Sn) phase and prevents the bulk undercooling of liquid alloy. As sound power increases, the ultrasonic field brings about a striking size refinement effect to the primary ε intermetallic compound by more than one order of magnitude. Meanwhile, it facilitates or even completes the usual peritectic transformation (L+ε→η) which occurs only to a very limited extent during static solidification. This is mainly because the refinement of primary ε phase induced by ultrasound greatly reduces the characteristic length of peritectic microstructure, which increases solid state Fourier number by more than one order of magnitude. The dramatic increase in the volume fraction of peritectic phase and the prominent grain refinement effect due to ultrasound lead to the remarkable improvement of mechanical properties for Cu-70%Sn alloy, whose compressive strength and microhardness are increased by factors of 4.8 and 1.45, respectively.