Quasi-aperiodic grain boundary phases of {\Sigma}5 tilt grain boundaries in refractory metals

TL;DR

This study uncovers new quasi-aperiodic grain boundary phases in refractory metals, revealing complex structures and diffusion behaviors, and challenges prior understanding of GB ground states through advanced structure search and simulations.

Contribution

It introduces the discovery of split kite quasi-aperiodic phases in a5 tilt GBs of BCC refractory metals, expanding knowledge of GB structural complexity.

Findings

Identification of new split kite phases in refractory metals

Better agreement of phase-contrast images with split kite models

Evidence of complex aperiodic phases as a general GB phenomenon

Abstract

We report new ground-state structures and phase transitions in $\Sigma$5[001] tilt grain boundaries (GBs) in body-centered cubic (BCC) refractory metals Nb, Ta, Mo, and W. $\Sigma$5 tilt GBs have been extensively investigated over the past several decades, with their ground-state structure -- composed of kite-shaped structural units -- previously thought to be well understood. By performing a rigorous GB structure search that optimizes the number of atoms in the boundary core, we predict new quasi-aperiodic "split kite" phases analogous to those previously found in GBs in face-centered cubic metals. Our results suggest that complex aperiodic phases of GBs appear to be a general phenomenon, as validated through density functional theory calculations. Moreover, the atoms in the split kite phase demonstrate distinct collective diffusion dynamics. Phase-contrast image simulations of split kites show better agreement with experimental observations, offering an alternative explanation for previous microscopy results and motivating future atomically resolved imaging of the GB structure.