Free energy of grain boundary phases: Atomistic calculations for $\Sigma$5(310)[001] grain boundary in Cu

TL;DR

This study uses atomistic simulations to demonstrate a temperature-induced phase transition between different grain boundary structures in copper, highlighting the role of vibrational entropy in stabilizing high-temperature phases.

Contribution

It introduces a thermodynamic integration method to compute grain boundary free energies, enabling the prediction of phase stability and transitions at low homologous temperatures.

Findings

Identifies a first-order phase transition in Cu grain boundary structure.

Shows vibrational entropy stabilizes high-temperature GB phases.

Provides a method to characterize GB phase diagrams at low temperatures.

Abstract

Atomistic simulations are employed to demonstrate the existence of a well-defined thermodynamic phase transformation between grain boundary (GB) phases with different atomic structures. The free energy of different interface structures for an embedded-atom-method model of the $\Sigma 5 (310) [001]$ symmetric tilt boundary in elemental Cu is computed using the nonequilibrium Frenkel-Ladd thermodynamic integration method through molecular dynamics simulations. It is shown that the free-energy curves predict a temperature-induced first-order interfacial phase transition in the GB structure in agreement with computational studies of the same model system. Moreover, the role of vibrational entropy in the stabilization of the high-temperature GB phase is clarified. The calculated results are able to determine the GB phase stability at homologous temperatures less than $0.5$, a temperature range particularly important given the limitation of the methods available hitherto in modeling GB phase transitions at low temperatures. The calculation of GB free energies complements currently available $0\,\mathrm{K}$ GB structure search methods, making feasible the characterization of GB phase diagrams.