# Grain boundary triple junction dynamics: a continuum disconnection model

## TL;DR

This paper introduces a continuum disconnection model for grain boundary and triple junction dynamics in polycrystalline materials, capturing the microscopic mechanisms and predicting their evolution under various conditions.

## Contribution

It develops a novel crystallography-respecting continuum model based on disconnection mechanics, incorporating thermally-activated processes and microstructure constraints.

## Key findings

- Model predicts GB and TJ mobilities depend on disconnection properties.
- TJ drag effect influences microstructure evolution.
- Results align with molecular dynamics and experimental data.

## Abstract

The microstructure of polycrystalline materials consists of networks of grain boundaries (GBs) and triple junctions (TJs), along which three GBs meet. The evolution of such microstructures may be driven by surface tension (capillarity), applied stresses, or other means that lead to a jump in chemical potential across the GBs. Here, we develop a model for the concurrent evolution of the GB/TJ network based upon the microscopic mechanism of motion; the motion of line defects (disconnections) in the GB that have both dislocation and step character. The evolution involves thermally-activated disconnection formation/annihilation and migration of multiple disconnections modes/types. We propose this crystallography-respecting continuum model for the disconnection mechanism of GB/TJ dynamics derived with a variational approach based on the principle of maximum energy dissipation. The resultant TJ dynamics is reduced to an optimization problem with constraints that account for local microstructure geometry, conservation of Burgers vectors, and thermal-kinetic limitations on disconnection fluxes. We present analysis of and numerical simulations based upon our model to demonstrate the dependence of the GB and TJ mobilities and the TJ drag effect on the disconnection properties, and compare the predictions with molecular dynamics and experimental observations.