Superlubric-Locked Transition of Twist Grain Boundaries in 3D Crystals

TL;DR

This study investigates the tribological behavior of twist grain boundaries in 3D crystals, revealing a load-induced structural transition that causes a superlubric-locked transition with significant friction change, supported by simulations and theoretical modeling.

Contribution

It introduces a novel load-induced structural transition in twist grain boundaries, providing a Landau theory and phase diagram, expanding understanding of tribological properties in 3D crystals.

Findings

Load provokes a first-order structural transformation in TGBs.

Transformation causes a superlubric-locked transition with a large friction jump.

Phenomena are robust across different lattice models and not specific to gold or metals.

Abstract

Properties of twist grain boundaries (TGB), long known structurally but not tribologically, are simulated under sliding and load, with Au(111) our test case. The load-free TGB moir\'e is smooth and superlubric at incommensurate twists. Strikingly, load provokes a first-order structural transformation, where the highest energy moir\'e nodes are removed -- an Aubry-type transition for which we provide a Landau theory and a twist-load phase diagram. Upon frictional sliding, the transformation causes a superlubric-locked transition, with a huge friction jump, and irreversible plastic flow. The predicted phenomena are robust, also recovered in a Lennard-Jones lattice TGB, and not exclusive to gold or to metals.