MODELING OF NONEQUILIBRIUM CRYSTALLIZATION AND TRANSFORMATION DIAGRAMS

The exact treatment of the kinetics of crystallization under isothermal or continuous cooling conditions is presented based on models of nucleation and crystal growth. From the explicit time or cooling rate dependence of the crystallization temperature at a fixed value of the crystallized 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 reduced temperature T/T(m), T(m) being the melting temperature, and the reduced time or cooling rate, which are defined and related to specific system properties. Other reduced quantities are introduced such as the reduced nucleation frequency and reduced crystal growth rate, which are shown to be useful to compare the crystallization behaviour of different systems. The usefulness of the method to describe the non-equilibrium crystallization of a supercooled melt is illustrated by considering three model systems: SiO2, Se61.5Ge15.4Sb23.1 and Nd13Fe79B8.