Transition from primary ε phase to peritectic η phase in Cu-75%Sn hyperperitectic alloy under laser rapid solidification

Laser rapid solidification experiments were performed on Cu-75%Sn hyperperitectic alloy to investigate microstructure evolution at scanning velocities ranging from 1 to 100 mm/s. As the scanning velocity is higher than 20 mm/s, peritectic η phase will directly solidify from the liquid instead of by peritectic reaction (ε+L-η), and no primary e phase forms in the solidified microstructures. By considering that primary e and peritectic η phases are both intermetallic compounds in Cu-75%Sn alloy, the competitive growth model proposed by Umeda et al for the growth of peritectic alloys is modified based on the maximum growth temperature criterion. Using this modified model, the calculated solidified critical velocity for primary ε phase transition to η phase is 19.5 mm/s, which approaches the experimental results of 10 to 19.3 mm/s.