Rapid Hypoeutectic Growth Within a Highly Undercooled Liquid Under Containerless Condition

Rapid hypoeutectic growth from a highly undercooled liquid was accomplished by containerless processing Ni-32%Sb hypoeutectic alloy in a 3m drop tube. The containerless state during the free fall of the droplet produces substantial undercooling up to 350K (0.24TL). The growth mechanism is found to transform from primary α-Ni dendrite plus lamellar eutectic to lamellar eutectic and finally to anomalous eutectic if droplet undercooling exceeds the two thresholds of 112K and 242K, respectively. Based on the current eutectic and dendritic growth models, the eutectic coupled zone is calculated and used to explain the growth mechanism transition. Calculations also indicate that the growth of α-Ni primary dendrite was mainly controlled by solute diffusion.