SOLIDIFICATION OF SILVER GERMANIUM ALLOYS IN AN AMORPHOUS MATRIX ABOARD THE SPACE STATION MIR

A first step in an experiment series aimed at establishing the underco oling properties of eutectic alloys embedded in an inert matrix under microgravity conditions was performed aboard the Mir orbital laborator y. Here metallic samples of the Ag-Ge eutectic system were embedded in a boron trioxide matrix and processed in the CSK-1 space furnace. The results demonstrated a performance of the sample containment and furn ace operation as expected. The undercooled melt droplets solidified sp ontaneously without contacting container walls and with no indication of sedimentation. Microgravity effects are apparent from the microstru cture of polished cross sections. The structure of the primary silver or germanium precipitates is significantly finer and shows a more even distribution for the space processed samples as compared to ground co ntrol samples. The germanium concentration in the silver precipitates is larger in space samples. Both these observations point to a larger undercooling in the microgravity processed samples, which however coul d not be measured directly in this preliminary test. In addition, an u nexpected occurrence of a grouping of germanium crystallites in a 5-fo ld symmetry was observed in the flight samples only.