Rapid eutectic growth under containerless condition

Rapid eutectic growth in a highly undercooled liquid was accomplished by containerlessly processing Co-Mo eutectic alloy in a drop tube. The containerless state during free fall produces substantial undercoolings up to 391 K (0.24T(E)) in falling droplets before crystallization. The eutectic growth mechanism is found to transform from lamellar eutectic to anomalous eutectic if the droplet undercooling exceeds a critical value of about 56 K, which coincides well with the lower boundary of the calculated eutectic coupled zone. Although the reduced gravity level of 10(-2)-10(-3) g has little influence on this eutectic growth mechanism transition, it frequently results in the formation of spherical anomalous eutectic grains owing to the symmetrical temperature field and concentration field surrounding solid/liquid interface. Both theoretical analyses and experimental observations indicate that the independent nucleation and cooperative branched growth of two eutectic phases are responsible for the eutectic growth mechanism transition. The three-dimensional structural model of anomalous eutectic grain is a two-phase composite dendrite. (C) 2002 American Institute of Physics.