Solidification behavior and microstructure of Ag-Cu eutectic alloy at different sub-rapid cooling rates

The microstructures of rapidly solidified Ag-39.9 at. % Cu eutectic alloys have been widely studied, while the research between microstructures and sub-rapid cooling rates is still lacking. Ag-39.9 at. % Cu eutectic alloy was solidified in quartz crucibles under different conditions. The alloy that was melted and in-situ cooled in a quartz crucible to room temperature solidified into eutectic dendrites composed of regular lamellae. The alloy that was melted and injection cast into a quartz crucible solidified into equiaxed eutectic colonies with primary alpha-Ag phase embedded. If the quartz crucible was further immersed in a gallium-indium liquid, a new spherical eutectic colony structure was found, with anomalous eutectic or primary alpha-Ag phase at the central part and a "ring" of coarse lamellar eutectic structure separating the eutectic colony into two parts. It is demonstrated that the cooling rate influences not only the primary phase selection and eutectic lamellar spacing, but also the eutectic nucleation and growth mode.