Solidification characteristics of highly undercooled Ag-Ge eutectic alloys

The Ag-Ge eutectic alloy system was intensively investigated with respect to its solidification characteristics at large undercoolings which are obtained by the B₂O₃ glass fluxing technique combined with argon protection. Grain size refinement was found in the Ag-15 wt% Ge hypoeutectic alloy. With increasing undercoolings the feather-like structure disappeared in the Ag-19 wt% Ge eutectic alloy, and even silver slips showed up at sufficient undercoolings. Nevertheless, the fact that germanium has nucleated in preference to silver is indicated by a fine germanium line in the middle of the silver slips. The various morphologies of the germanium phase in the Ag-25 wt% Ge hypereutectic alloy including the five-fold symmetry structure were explained by the joint action of high undercoolings (i.e. growth velocities) and density differences. The coupled zone of this alloy system was qualitatively estimated.