Phase morphology of Pb–Sn–Cd ternary eutectic

Abstract

A method for viewing the detailed solid/liquid interface morphology of metallic eutectic systems has been developed. It is based on an apparatus designed to allow the unidirectional solidification of metallic samples having low thermal mass at considerably lower, and more stable, growth rates than have previously been possible with conventional equipment. As a result, high resolution quench interfaces can be produced which in quality rival those of transparent organic analogue systems. Application of this technique to the solid/liquid interface of the Pb–Sn–Cd ternary eutectic has revealed a number of new facts. It was discovered that the Cd phase forms a facet plane coplanar with its basal plane and with the Pb/Cd lamellar habit plane. Qualitative observations of the differing behaviour of the Pb and Sn phases in contact with the Cd facet plane allowed the magnitudes of the three solid/solid interfacial free energies to be compared and a mechanism for the formation and stabilization of the ABCBA lamellar structure to be postulated.

MST/352