Eutectic growth in bulk undercooled melts

Abstract

Kinetic effect of the atom-attachment at the solid–liquid interface and thermal undercooling are incorporated into the analysis of the eutectic growth in bulk undercooled melts. When crystallization products contain intermetallic compounds or other topologically complex phases, the kinetic effect will significantly alter the eutectic growth behaviors, and maintain the coupled eutectic growth to higher undercoolings. Such phenomena are exhibited more notably in alloy systems where the eutectic phases have a narrow crystallization temperature range at the eutectic composition. The growing interface is essentially unstable in the undercooled melt owing to the existence of a negative temperature gradient in the liquid along the growth direction, and tends to break down into dendritic morphology. Considering that the thermal diffusion length is much larger than the eutectic lamellar spacing, the eutectic dendrite is treated as a thermal dendrite. It is found that the thermal undercooling at the eutectic dendrite tip increases with the increasing growth velocity, but its proportion of the total undercooling is higher at the lower undercoolings. In other words, the effect of the thermal diffusion on the eutectic growth is more significant at the low growth velocities.