NONEQUILIBRIUM INTERFACE KINETICS DURING RAPID SOLIDIFICATION

During rapid solidification crystals can grow at rates of up to 250 m s-1 and non-equilibrium attachment kinetics of atoms at the solid-liquid interface become readily apparent. Kinetically suppressed impurity partitioning results in supersaturated solid solutions. Interface temperatures are well below their equilibrium values. Equilibrium partition coefficients can be exceeded by factors of 10(3) and equilibrium solubilities can be exceeded by factors of 10(5) in this manner. Models for this process are aimed at the attainment of predictive capabilities for solidification processing, and for other growth processes in general. Models that predict the interfacial undercooling and partition coefficient as functions of the interface velocity and the composition of the liquid at the interface are reviewed. High-speed measurements of the temperature and the compositions at the rapidly moving solid-liquid interface during pulsed laser melting have been taken to test these models and the results are presented. The consequences for the cellular, dendritic, or oscillatory breakdown of a rapidly moving interface are discussed.