Study on the Solidus Line in Sn-Rich Region of Sn-In Phase Diagram

Abstract

Binary phase diagrams are important tools for designing desired alloys. In the Sn-rich region of the Sn-In alloy phase diagram, the solidus line appears as a dotted line in current literature plots to indicate uncertainty. The contour of the solidus has now been clarified as a result of the present investigation. Four alloys, Sn₇₀In₃₀, Sn₇₅In₂₅, Sn₈₀In₂₀, and Sn₈₅In₁₅ were melted at 300 °C for 10 h and annealed between 120 and 200 °C in the (L + γ) two-phase region. The morphology and chemical compositions of annealed specimens were analyzed using both field emission scanning electron spectroscopy and energy-dispersive x-ray spectrometry. The results reveal that the liquid phase, initially appearing at the eutectic temperature, invades the solid along grain boundaries with penetration gradually increasing with increasing annealing temperature and a granular structure form. The average compositions in grains of Sn₇₀In₃₀, Sn₇₅In₂₅, Sn₈₀In₂₀, and Sn₈₅In₁₅ specimens correspond to the solidus concentrations, and the solidus line and (β + γ)/γ phase boundary can be determined as a fit to these temperature-composition points.