Microstructure of one of the ternary eutectic alloys in the Bi-In-Sn system

Abstract

Two ternary eutectic alloys are known to exist in the Bi-In-Sn ternary system. Experiments were conducted to determine the phases present, the structure, and the volume fraction of each phase in one of the two eutectics. The eutectic investigated melted at 332 K and had a composition of 31.6 wt pct Bi, 48.8 wt pct In, and 19.6 wt pct Sn. The phases present are the major phase BiIn2, the β phase of the In-Sn system, and the γ phase of the In-Sn system. The structure consists of the major phase in which are embedded fibers of the two minor phases. The measured volume fractions of the phases are approximately 56 pct BiIn2, 24 pct β, and 20 pct γ. The volume fraction of the two minor phases (44 pct) in the eutectic is well above the percentage of fibrous phase usually found in binary eutectics.