Analysis of Melt Undercooling and Crystallization Kinetics

While melt undercooling is often observed during solidification, the study of nucleation is challenging due to the numerous possible heterogeneous sites present in even high-purity melts. Identification of active nucleation sites requires developing well-planned experimentation. In samples with well-defined and controlled undercooling the identification can be established for the active sites. The successful identification of nucleation sites reveals that there are a number of possible sites and mechanisms that can act to catalyze nucleation. The sites and mechanisms that have been identified involve primary phases developed during cooling of alloy melts, liquid-added particle interfaces being modified (e.g., by adsorption or reaction) creating a particle type-independent nucleation potency, dissolved impurities precipitating out of the melt at high undercoolings to catalyze nucleation, and nucleation sites resulting from residual solid preserved in cavities in inclusions or surface coatings.