Kinetic Pathways of Ordering and Phase Separation Transformations Using Steepest-Entropy-Ascent Quantum Thermodynamics Modeling

Abstract

The kinetics of ordering and concurrent ordering and phase separation are analyzed with an equation of motion initially developed to account for dissipative processes in quantum systems. A simplified energy eigenstructure, or pseudo-eigenstructure, is constructed from a static concentration wave method to describe the configuration-dependent energy in a binary alloy. This pseudo-eigenstructure is used in conjunction with an equation of motion that follows steepest entropy ascent to calculate the kinetic path that leads to ordering and phase separation in a series of hypothetical alloys. By adjusting the thermodynamic solution parameters, it is demonstrated that the model can predict: (a) the stable equilibrium state, (b) the unique thermodynamic path and kinetics of continuous or discontinuous ordering, and (c) the kinetics of concurrent processes involving simultaneous ordering and phase separation.

Keywords: steepest entropy ascent, non-equilibrium, phase transformation kinetics, atomic ordering, phase separation