Formation of microstructure in the Cd-In-Sn ternary eutectic

Abstract

Specimens of the Cd-In-Sn ternary eutectic were solidified unidirectionally at very low speeds and quenched during freezing to form a representative solid/liquid interface for subsequent study. The microstructure was observed to consist of two broken lamellar phases, Cd and λ-Sn, in a matrix of In3Sn. The Cd phase tended to become fibrous at the highest growth rates used. Many different relative orientations of the Cd and λ-Sn lamellae were observed, indicating that these phases grow independently of one another, with no preferred growth orientation. From the observed microstructure, it was concluded that the Cd and λ-Sn phases are hexagonal faceting phases in this alloy, while the In3Sn phase is non-faceting. The Cd-Cd and λ-Sn-λ-Sn phase spacings were found to follow the usual law, λ2 R = constant, where λ. is the phase spacing and R is the growth rate. The Cd-Cd phase spacing was always smaller than the λ-Sn-λ-Sn phase spacing. The observation that this ternary eutectic forms, on freezing, an intimate mixture of the three solid phases confirms the earlier prediction of Smith that, for this to occur, at least one of the phases must not form continuous lamellae.