Dislocation content of grain boundary phase junctions and its relation to grain boundary excess properties

TL;DR

This paper investigates the dislocation content of grain boundary phase junctions, revealing how their Burgers vectors relate to excess properties and phase transformations, which is crucial for understanding their energetics and interactions.

Contribution

It introduces a general Burgers circuit analysis for GB phase junctions, incorporating non-DSC contributions from excess atoms and properties, advancing the understanding of their dislocation structure.

Findings

Burgers vectors of junctions often include a significant non-DSC component.

Normal Burgers vector component relates to excess volume and atom count differences.

Expressions derived connect GB phase transformations with junction motion and energy.

Abstract

We analyze the dislocation content of grain boundary (GB) phase junctions, i.e., line defects separating two different GB phases coexisting on the same GB plane. While regular GB disconnections have been characterized for a variety of interfaces, GB phase junctions formed by GBs with different structures and different numbers of excess atoms have not been previously studied. We apply a general Burgers circuit analysis to calculate the Burgers vectors b of junctions in two {\Sigma}5 Cu boundaries previously simulated with molecular dynamics. The Burgers vectors of these junctions cannot be described by the displacement shift complete (DSC) lattice alone. We show that, in general, the normal component of b is not equal to the difference in the GB excess volumes, but contains another contribution from the numbers of GB atoms per unit area {\Delta}N required to transform one GB phase into another. In the boundaries studied, the latter component dominates and even changes the sign of b. We derive expressions for the normal and tangential components of b in terms of the DSC lattice vectors and the non-DSC part due to {\Delta}N and additional GB excess properties, including excess volume and shears. These expressions provide a connection between GB phase transformations driven by the GB free energy difference and the motion of GB junctions under applied normal and shear stresses. The proposed analysis quantifies b and therefore makes it possible to calculate the elastic part of the energy of these defects, evaluate their contribution to the nucleation barrier during GB phase transformations, and treat elastic interactions with other defects.