Ternary eutectic growth in microgravity environment

Rapid growth of Ag_38.5 Cu_33.4 Ge_28.1 ternary eutectic alloy was accomplished in a 3m drop tube and its phase selection and growth mechanism were investigated. The experimental results revealed that the semiconductor phase (Ge) was the primary nucleating phase during solidification, which agrees with the calculated results of nucleation rate. The solid solution phase (Ag) and intermetallic compound phase η(Cu₅ Ge₂) grew cooperatively and lamellar structures similar to binary eutectic formed. Moreover, with the decreasing of droplet size, the growth morphology of primary (Ge) phase transformed from plate-like to granular shape and a kind of anomalous ternary eutectic formed. The microgravity environment has a significant effect on the crystal growth process, which makes the (Ge) phase distribute homogeneously and the anomalous eutectic grains show good geometrical symmetry. The calculation of cooling rate versus droplet diameter showed that it was the high cooling rate and large undercooling that brought about the eutectic growth morphology transition.