Phase Transformation Kinetics: Advanced Modeling Strategies

Abstract

Phase transformations in the solid state are often heterogeneous and can be described by concurring modes of nucleation, growth, and impingement. The classical Johnson–Mehl–Avrami–Kolmogorov-(JMAK-) model, although offering an easy-to-use description of the transformation kinetics, is limited to very specific cases of the transformation modes. Instead, a generalized modular model of phase transformation kinetics can be proposed that provides a flexible formalism adaptable to various modes of nucleation, growth, and impingement. Due to its large versatility, the modular model approach can be easily applied for characterization of phase transformation kinetics beyond the scope of classical JMAK(-type) modeling. Three different strategies recently employed for such advanced modeling are presented: (I) deliberate variation of the nucleation mode upon crystallization of an Fe-Ni-B metallic glass in order to determine separate activation energies for nucleation and growth, (II) incorporation of specific, dedicated modes for nucleation and growth kinetics for the allotropic hcp–fcc transformation in cobalt introducing driving-force-dependent rates of transformation, and (III) implementation of quantitative microstructural data for the description of the precipitation kinetics in a supersaturated CuCo alloy.