Plane front solidification of two phase peritectic tin-cadmium alloys: Part 2

Abstract

Banding during plane front solidification of binary peritectic alloys consists of the deposition of alternating layers of the primary (α) and peritectic (β) phases. This phenomenon is considered in relation to the cycle of alternating metastable growth followed by nucleation proposed by Trivedi to account for its formation. The study revealed the following. Nucleation of at least one of the two phases must be caused by a heterogeneous nucleation catalyst foreign to the system, unless large undercooling is generated. Fluctuations in growth conditions are very important in promoting nucleation. Nucleation will be followed by both a short and a long period of transient growth. Solid grown under metastable conditions may be subject to partial remelting on reheating to or above the peritectic temperature. For Cd-Sn peritectic alloys, the following points were found. The primary Sn phase (α) growing metastably below the peritectic temperature, under steady growth conditions, will nucleate the peritectic phase (β) when the Sn content at the solid/liquid interface reaches ∼12 wt-%, corresponding to an interface temperature of ∼206°C. Steady state freezing of the α phase is possible for any Cd content less than ∼, 3 wt-%. The maximum undercooling that can be producedfor nucleation of the α phase during metastable growth of the β phase under steady growth conditions is ∼ 0.5 K.