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

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.

Normal Load and Counter Body Size Influence the Initiation of Microstructural Discontinuities in Copper during Sliding

“…However, these processes are not sufficiently understood 13 , 18 − 21 and most of the literature focuses on later stages in the lifetime of the contact. 13 , 15 , 22 …”

Scratching the Surface: Elastic Rotations Beneath Nanoscratch and Nanoindentation Tests

“…This abrupt change in rotation direction, could correspond with the tribologically induced discontinuity, known as a dislocation trace line, ubiquitously observed in various material systems. The origin of this has been attributed to the reorganisation of dislocations beneath a sliding contact as a result of the in-plane shear component of the stress field [69,39]. It appears that by incorporating a lateral component of force, a strongly inhomegeneous stress state subsurface, different to that under a statically loaded indent, activates slip systems that cause an outer rotation field to be formed whilst constraining the inner rotation field.…”

Variations in strain affect friction and microstructure evolution in copper under a reciprocating tribological load

“…In this layer, twins are observed. It is unlikely that these twin boundaries are due to heat treatment or recrystallization [40] and even though mechanical twinning is usually not observed in pure copper at room temperature [22,35], due to the extreme shear conditions induced by the tribological load [41], these twins must most probably be attributed to the mechanical tribological deformation.…”

“…The elementary mechanisms acting and dominating under different experimental conditions need to be studied in order to be able to strategically influence these complex processes. Our own recent work, for example, has identified three processes acting in the very early stages of sliding [35]: a simple shear of the subsurface area in sliding direction, a highly localized shear in sliding direction at a dislocation self-organization feature called the dislocation trace line, as well as a crystal rotation of the material between the sample surface and the dislocation trace line around an axes parallel to the transvers direction [13]. In light of these and other results, either by this group of authors or others, it is so far not fully understood how different elastic and plastic strains influence the subsurface microstructure evolution.…”