Origin of microstructure in the 332 K eutectic of the Bi-In-Sn system

Abstract

Specimens of the 332 K eutectic of the Bi-In-Sn system were solidified unidirectionally at low speeds and quenched to form a representative solid/liquid interface for subsequent study. The solid/liquid interfaces of all three solidifying phases, BiIn₂, γ-Sn and β-In, were found to be of the non-faceted type and the resulting eutectic interface was fiat and isothermal. At all growth rates used, an intimate mixture of the three phases was formed. At low growth rates, the microstructure was found to approximate a three phase fibrous structure, while at higher growth rates it tended to be lamellar, with lamellae alternating in the sequence -γ-Sn-BiIn₂-β-In-BiIn₂-γ-Sn-BiIn₂-β-In-. The phase spacing was found to follow the usual law: λ²R =constant, where λ is the phase spacing, and R is the growth rate. The microstructure formed is compared with that of ternary eutectics that contain faceting phases, studied earlier.