Segregation-induced phase transformations in grain boundaries

TL;DR

This paper demonstrates atomistic simulations showing that grain boundary phase transformations can occur in binary alloys due to segregation, enabling thermodynamic analysis of these transformations and their critical phenomena.

Contribution

It provides the first evidence of segregation-induced phase transformations in grain boundaries within a binary alloy system and introduces a thermodynamic integration method for free energy calculations.

Findings

Segregation induces phase transformations in grain boundaries.

Thermodynamic integration can calculate free energy differences.

GB phase transformations depend on chemical segregation at fixed temperature.

Abstract

Phase transformations in metallic grain boundaries (GBs) present significant fundamental interest in the context of thermodynamics of low-dimensional physical systems. We report on atomistic computer simulations of the Cu-Ag system that provide direct evidence that GB phase transformations in a single-component GB can continue to exist in a binary alloy. This gives rise to segregation-induced phase transformations with varying chemical composition at a fixed temperature. Furthermore, for such transformations we propose an approach to calculations of free energy differences between different GB phases by thermodynamic integration along a segregation isotherm. This opens the possibility of developing quantitative thermodynamics of GB phases, their transformations to each other, and critical phenomena in the future.