MODELING OF NONEQUILIBRIUM CRYSTALLIZATION AND TRANSFORMATION DIAGRAMS

The exact treatment of the kinetics of crystallization under isotherma l or continuous cooling conditions is presented based on models of nuc leation and crystal growth. From the explicit time or cooling rate dep endence of the crystallization temperature at a fixed value of the cry stallized function, the reduced time-temperature transformation (T-T-T ) and reduced temperature-cooling rate transformation (T-CR-T) curves are constructed. The coordinates of such representations are the reduc ed temperature T/T(m), T(m) being the melting temperature, and the red uced time or cooling rate, which are defined and related to specific s ystem properties. Other reduced quantities are introduced such as the reduced nucleation frequency and reduced crystal growth rate, which ar e shown to be useful to compare the crystallization behaviour of diffe rent systems. The usefulness of the method to describe the non-equilib rium crystallization of a supercooled melt is illustrated by consideri ng three model systems: SiO2, Se61.5Ge15.4Sb23.1 and Nd13Fe79B8.