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Peritectic transformation is one of the main mechanisms during solidification of peritectic alloys, and accompanied with dissolution of primary phase. In the present work, the effect of solidification temperature on the peritectic transformation and dissolution of primary α-dendrite was investigated during directional solidification of Pb–26wt%Bi peritectic alloy. The resulting microstructures of the alloy in consideration of different solidification temperature have been investigated using optical microscopy. The volume fraction of peritectic β-phase and the average size of α-dendrite core were measured using image analyzing software SISC IAS V8.0. These results show that the increment in β-phase volume fraction and decrement in size of α-dendrite core first increase, then decrease with falling solidification temperature. These results can be explained from the viewpoint of a reduced solidification temperature leading to the rate of peritectic transformation first increases to a maximum, and then decreases.

Sn–40.5 wt%Pb–2.6 wt%Sb ternary alloy was directionally solidified with a constant temperature gradient (G = 18 K/mm) and growth rates ranging from 1 μm/s to 30 μm/s. Experimental results indicated that the lamellar structure consisted of Pb-rich and Sn-rich phases. The lamellar spacings (λ) and microhardness (HV) were measured and the HV increased with increasing growth rate (V) or decreased with increasing lamellar spacing. The dependences of λ and HV on V were determined by using a linear regression analysis. The relationships between the λ, V and HV were given as: λ = 3.39 V − 0.51 , H V = 12.65 V 0.11 and H V = 16.42 λ − 0.2 , respectively. The fitted exponent values were in accordance with the previous experimental results obtained from Sn–Pb alloys and In–Bi–Sn ternary 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.