Primary dendrite arm spacing during unidirectional solidification of Pb-Bi peritectic alloys

摘要

The primary dendrite arm spacing (X) of the leading primary phase is significant to microstructures during unidirectional solidification of peritectic alloys. In Pb-Bi peritectic alloys, the relationship between solidification processing parameters (growth velocity, V) and primary dendrite arm spacing [lambda) of primary a phase has been investigated based on the experimental results and theoretical analysis. Alloys with compositions of 26,28,30 and 34 wt percent Bi have been directionally solidified at the growth velocities ranging from 5 to 500 mu m/s and a constant temperature gradient of 20 K/mm. The dendrites of primary alpha phase grew in a complex matrix of peritectic beta phase over the range of growth velocities. The average primary dendrite arm spacing X, as function of growth velocity, can be given as X = 39.25 V~(-0.35883), lambda = 60.62 V~(-0.22567), lambda = 75.28V~(-0.17649) and lambda = 36.3 V~(-0.39085) for Pb-26wt percent Bi, Pb-28wt percent Bi, Pb-30wt percent Bi and Pb-34wt percent Bi peritectic alloys, respectively. A parametric agreement is found with the Hunt and Trivedi's models.