High diffusivity pathways govern massively enhanced oxidation during tribological sliding

TL;DR

This study reveals that tribological loading creates high diffusivity pathways like dislocations, significantly accelerating oxidation in metals, with oxidation controlled mainly by test duration rather than sliding speed.

Contribution

It uncovers the role of deformation-induced defects as diffusion pathways in tribo-oxidation, providing a physics-based understanding of oxidation mechanisms during sliding.

Findings

Oxidation is governed by test duration, not sliding speed.

Dislocations and grain boundaries act as high diffusivity pathways.

Enhanced atomic diffusion around defects accelerates oxidation.

Abstract

The lifetime of moving metallic components is often limited by accelerated oxidation. Yet, the mechanisms and pathways for oxidation during tribological loading are not well understood. Using copper as a model system, tribologically-induced oxidation is systematically investigated by varying the sliding speed and test duration under mild tribological loading. We demonstrate that tribo-oxidation is controlled by test duration rather than the number of cycles or the sliding speed. Plastic deformation from tribological loading creates dislocations, grain and phase boundaries that act as high diffusivity pathways. A combination of electron microscopy and atom probe tomography revealed significantly enhanced atomic concentration of the diffusing species around dislocations. Oxygen diffusion into the bulk as well as of copper towards the free surface along these defects control the oxide formation kinetics. Our work paves the way for formulating a physics-based understanding for tribo-oxidation, which is crucial to develop strategies to prevent oxidation and to strategically tailor surfaces to increase the lifetime of engineering systems.