The science of interacting surfaces in relative motion, called tribology, is of great importance in modern life. In general, friction and wear play a critical role in energy efficiency and product lifetime. The tribological performance of metallic tribo-systems is influenced by the microstructure of the material under the contact. The ability to tailor materials that combine low friction and little wear, will allow to increase the energy efficiency of many engineering systems. Up to now, mechanisms for microstructure evolution in tribological processes, regarding friction, adhesion, lubrication and wear, are not sufficiently investigated and understood. In our unlubricated experiments, a sapphire sphere is sliding over an oxygen-free high-purity copper plate in a linear reciprocating fashion. Tests were performed for various normal loads (2…100 N), cycle numbers (1…5000) and sapphire sphere diameters (1…10 mm). For evaluating the microstructure evolution, the copper samples were examined using scanning electron and focused ion beam microscopy. At 100 N normal load, the FIB cross-sections show a strongly deformed microstructure with a high number of grain boundaries and dislocations. With increasing cycle number, the tribologically deformed layer increases in thickness. The size of the sphere correlates with the gradient of the contact pressure: the smaller the spheres’ diameter, the bigger is the gradient. Additionally, the number of cycles was found to have no influence on the depth of the wear track at the loading point under a constant normal load.
One aim of this study is the formulation of a model description for the microstructural changes in order to predict and tailor tribological properties like friction coefficient and wear rate.