Construction of Gallium-Tin Nonequilibrium State Diagram and Its Analysis

Overcooling of gallium-tin alloys under normal conditions has been studied by thermal analysis. The following samples have been analyzed: Ga (I); two hypoeutectic alloys: 95% Ga + 5% Sn (II), 90% Ga + 10% Sn (III); eutectic alloy: 96.3% Ga + 13.7% Sn (IV); and five hypereutectic alloys with Sn content of 20% (V), 35% (VI), 50% (VII), 80% (VIII), and pure tin (IX). A nonequilibrium state diagram of this system is constructed. Herewith, the eutectic composition does not vary and the eutectic temperature decreases to 5.5 degrees C, that is, 26 degrees C below that of three-phase eutectic equilibrium. The eutectic temperature does not actually vary upon a variation of cooling rates of eutectic alloy from 0.06 to 60 degrees C/min. It has been detected that a slight decrease in overcooling is expected in the hypoeutectic region, whereas in the hypereutectic region overcooling increases while the alloy composition approaches eutectic. Activities and activity coefficients of components on the lines of equilibrium and nonequilibrium liquidus have been calculated. It is demonstrated that the activities on the lines of both equilibrium and nonequilibrium liquidus decrease in a predictable manner, and the activity coefficients increase while the composition approaches eutectic. Concentration paths of equilibrium and nonequilibrium crystallization are shown in the state diagrams.