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

The primary dendrite arm spacing (λ) 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 (λ) of primary α phase has been investigated based on the experimental results and theoretical analysis. Alloys with compositions of 26, 28, 30 and 34 wt% Bi have been directionally solidified at the growth velocities ranging from 5 to 500 μm/s and a constant temperature gradient of 20 K/mm. The dendrites of primary α phase grew in a complex matrix of peritectic β phase over the range of growth velocities. The average primary dendrite arm spacing λ, as function of growth velocity, can be given as λ = 39.25V^-0.35883, λ = 60.62V^-0.22567, λ = 75.28V^-0.17649 and λ = 36.3V^-0.39085 for Pb-26 wt% Bi, Pb-28 wt% Bi, Pb-30 wt% Bi and Pb-34 wt% Bi peritectic alloys, respectively. A parametric agreement is found with the Hunt and Trivedi's models.