Kinetic Pathways of Phase Decomposition Using Steepest-Entropy-Ascent Quantum Thermodynamics Modeling. Part I: Continuous and Discontinuous Transformations

TL;DR

This paper introduces a quantum thermodynamics-based model to analyze phase decomposition kinetics in alloys, capable of capturing both continuous and discontinuous transformation pathways in non-equilibrium systems.

Contribution

It develops a novel equation of motion within the steepest-entropy-ascent quantum thermodynamics framework to model phase decomposition processes.

Findings

Predicts conditions for spinodal decomposition and nucleation in alloys.

Provides a method to track non-equilibrium kinetic pathways.

Demonstrates the applicability of quantum thermodynamics to materials science.

Abstract

The decomposition kinetics of a solid-solution into separate phases are analyzed with an equation of motion initially developed to account for dissipative processes in quantum systems. This equation and the steepest-entropy-ascent quantum thermodynamic framework of which it is a part make it possible to track kinetic processes in systems in non-equilibrium, while retaining the framework of classical equilibrium thermodynamics. The general equation of motion is particularized for the case of the decomposition of a binary alloy, and a solution model is used to build an approximate energy eigenstructure, or pseudo-eigenstructure, for the alloy system. This equation is then solved with the pseudo-eigenstructure to obtain a unique reaction path and the decomposition kinetics of the alloy. For a hypothetical solid-solution with a miscibility gap at low temperatures, the conditions under which this framework predicts a continuous transformation path (spinodal decomposition) or a discontinuous one (nucleation and growth) are demonstrated.