Early deformation mechanisms in the shear affected region underneath a copper sliding contact

C Haug,A Kashiwar,F Ruebeling,C Greiner,C Kübel,P Gumbsch

doi:10.1038/s41467-020-14640-2

Abstract

Dislocation mediated plastic deformation decisively influences the friction coefficient and the microstructural changes at many metal sliding interfaces during tribological loading. This work explores the initiation of a tribologically induced microstructure in the vicinity of a copper twin boundary. Two distinct horizontal dislocation traces lines (DTL) are observed in their interaction with the twin boundary beneath the sliding interface. DTL formation seems unaffected by the presence of the twin boundary but the twin boundary acts as an indicator of the occurring deformation mechanisms. Three concurrent elementary processes can be identified: simple shear of the subsurface area in sliding direction, localized shear at the primary DTL and crystal rotation in the layers above and between the DTLs around axes parallel to the transverse direction. Crystal orientation analysis demonstrates a strong compatibility of these proposed processes. Quantitatively separating these different deformation mechanisms is crucial for future predictive modeling of tribological contacts.

Highlights

Dislocation mediated plastic deformation decisively influences the friction coefficient and the microstructural changes at many metal sliding interfaces during tribological loading
The elementary mechanisms governing the early stages of tribological loading have been studied less extensively, even though they seem elemental in deciding the future fate of a tribological contact
We have previously reported a distinct horizontal line feature at a uniform depth of about 150 nm below the surface of copper samples contacted in dry sliding conditions by a sapphire sphere[12]

Summary

Introduction

Dislocation mediated plastic deformation decisively influences the friction coefficient and the microstructural changes at many metal sliding interfaces during tribological loading. Crystal orientation analysis demonstrates a strong compatibility of these proposed processes Separating these different deformation mechanisms is crucial for future predictive modeling of tribological contacts. We have previously reported a distinct horizontal line feature at a uniform depth of about 150 nm below the surface of copper samples contacted in dry sliding conditions by a sapphire sphere[12] Since this line was found to consist of dislocations, it was named dislocation trace line (DTL). Detailed (scanning) transmission electron microscopy investigations including automated crystal orientation mapping (ACOM) shed light on the characteristics of this horizontal microstructural discontinuity They allow to decipher the characteristics of the plastic deformation occurring during early-stage sliding beneath the sliding interface. Three distinct concurrent shearing and grain rotation processes are identified

Methods

Results

Conclusion