Phase and microstructure selection in directional solidification of Pb-Bi peritectic alloys

Based on the directional solidification of Pb-Bi peritectic alloys with moderate or high and low growth velocities, the competition between the primary α and peritectic β phases was predicted by using the highest interface growth temperature criterion and the nucleation and constitutional undercooling criterion, respectively. The calculated results show that the critical growth velocities for α→β transition under moderate/high growth velocities are 20, 14, 8.5 and 2 mm/s for Pb-26%Bi, Pb-28%Bi, Pb-30%Bi and Pb-34%Bi (mass fraction) alloys, respectively. For the low growth velocities, the phase selection map is divided into 8 growth zones including the single phase growth zone and the growth zone of two phases mixed. The phase selection and microstructure morphology can be predicted by using the phase selection map combined with solidification rate ratio (G/V) and initial content of the alloy (C ₀).