Geometry of triple junctions during grain boundary premelting

TL;DR

This paper investigates the microscopic structure of triple junctions during grain boundary premelting, revealing how atomistic physics regularizes these junctions and affects their equilibrium and dynamics.

Contribution

It introduces a disjoining potential approach to define and analyze triple junctions at the atomistic scale, supported by multi-phase field simulations.

Findings

Atomistic physics regularizes triple junctions during premelting.

A well-defined microscopic contact angle exists at the triple junction.

Results provide insights into grain boundary phase transitions and liquid metal embrittlement.

Abstract

Grain Boundaries (GB) whose energy is larger than twice the energy of the solid/liquid interface exhibit the premelting phenomenon, for which an atomically thin liquid layer develops at temperatures slightly below the bulk melting temperature. Premelting can have a severe impact on the structural integrity of a polycrystalline material and on the mechanical high temperature properties, also in the context of crack formation during the very last stages of solidification. The triple junction between a dry GB and the two solid/liquid interfaces of a liquid layer propagating along the GB cannot be defined from macroscopic continuum properties and surface tension equilibria in terms of Young's law. We show how incorporating atomistic scale physics using a disjoining potential regularizes the state of the triple junction and yields an equilibrium with a well-defined microscopic contact angle. We support this finding by dynamical simulations using a multi-phase field model with obstacle potential for both purely kinetic and diffusive conditions. Generally, our results should provide insights on the dynamics of GB phase transitions, of which the complex phenomena associated with liquid metal embrittlement are an example.