Deformation Mechanisms in High-Purity Copper Induced by Sliding
The energy dissipated in mechanical systems due to friction and wear greatly contributes to global energy consumption. Materials tailored towards low friction and little wear may be further improved by studying fundamental mechanisms at metal sliding interfaces, where plastic deformation is classically mediated by dislocation activity. According to the seminal work by Bowden and Tabor, friction is in turn closely related to a material’s mechanical properties and thus, deformation behavior.
This work analyzes the microstructural changes induced by sliding of a sapphire sphere over high-purity copper in the vicinity of a twin boundary. Two characteristic horizontal line features (dislocation trace lines, DTL) are observed at a depth of less than half a micron beneath the sliding interface. Using automated crystal orientation mapping (ACOM), their interaction with the twin boundary is investigated. Three complementary fundamental deformation mechanisms are identified by employing the twin boundary as a marker: A simple shear process affecting the immediate subsurface area, a localized plastic shear process occurring at the lower DTL and a crystal rotation of the areas between the sliding interface and both DTLs. Crystallographic orientation analysis reveals that the three processes are physically compatible.
As these processes are considered instrumental for guiding future computational modeling of tribological contacts, they are further investigated. Scanning transmission electron microscopy and transmission Kikuchi diffraction (TKD) shed light on the influence of crystallographic orientation and experimental parameters such as the load regime on each process. Corresponding friction measurements demonstrate the interdependence of friction and deformation.