Tribologically Induced Deformation Mechanisms and Friction as a Function of Crystal Orientation in Copper

Minimizing friction and wear in technical systems requires a detailed understanding of the fundamental mechanisms occurring at tribologically loaded metal surfaces. Crystal orientation is an important factor governing dislocation-mediated plastic deformation. Using sapphire spheres in dry sliding contact with high-purity copper bi- and single crystals, this work explores the influence of crystal orientation on deformation mechanisms and friction both in the early and later stages of sliding. Detailed 3D-profilometry and electron microscopy – including large-scale, non-destructive EBSD as well as high-resolution transmission Kikuchi diffraction – reveal fundamental insights into early-stage, tribologically induced crystal rotation kinematics and demonstrate a systematic long-term influence of the initial crystal orientation on wear track topography. While relations to the initial orientation increasingly vanish inside a developing nanocrystalline subsurface layer, friction anisotropy seems to increase during continued sliding. In conclusion, this work provides an important contribution to the fundamental understanding of the influence of crystal orientation on tribologically induced deformation mechanisms and friction.