Containerless solidification of undercooled Ag-Cu-Sb alloy droplets under microgravity conditions

Containerless solidification of undercooled Ag-Cu-Sb alloy droplets under microgravity conditions was investigated by using a 3m drop tube. It was found that the microstructure of the solidified particles depends strongly on their sizes. In larger particles (>500 μm), a microstructure which consists of a radiating ternary eutectic structure plus an irregular ternary eutectic structure plus strip-like primary Cu₂Sb phase and/or facetted Sb phase was observed. However, the smaller particles (<500 μm) show a wide variety of microstructures. Besides a refined radiating structure, two other ternary eutectic structures have been formed. Moreover, some primary structures were also identified in some particles. By comparing with the previous results under 1 g condition, it was supposed that the microgravity environment in drop tube induce a highly symmetric temperature field in droplets, thus leading to the formation of the above radiating ternary eutectic structure.