ORIGIN OF MICROSTRUCTURE IN THE 332 K EUTECTIC OF THE BI-IN-SN SYSTEM

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 interfac es of all three solidifying phases, BiIn2, gamma-Sn and beta-In, were found to be of the non-faceted type and the resulting eutectic interfa ce was flat and isothermal. At all growth rates used, an intimate mixt ure of the three phases was formed. At low growth rates, the microstru cture was found to approximate a three phase fibrous structure, while at higher growth rates it tended to be lamellar, with lamellae alterna ting in the sequence -gamma Sn-BiIn2-beta-In-BiIn2-gamma-Sn-BiIn2-beta -In-. The phase spacing was found to follow the usual law: lambda(2)R = constant, where lambda is the phase spacing, and R is the growth rat e. The microstructure formed is compared with that of ternary eutectic s that contain faceting phases, studied earlier.