Scientific challenges which connect the field of tribology with other disciplines of materials science, such as oxidation, are interesting since they generate a new access to an interdisciplinary point of view. Understanding the fundamental mechanisms of tribo-oxidation is very important for future modelling of the tribological contacts evolution. The change in microstructure or chemical composition during different stages of sliding results in a difference in friction response and wear of a tribo-system. The formation of tribo-oxides, especially in the very early stages of the sliding contact, is poorly understood.
In order to understand these mechanisms, a model test setup with high-purity copper as a model material in contact with a sapphire sphere in reciprocating sliding experiments is used. Our results show the formation of amorphous cuprous-oxide (Cu2O) patches which grow to hemispherical amorphous/nanocrystalline cuprous-oxide clusters. The patches are randomly distributed at the sample surface indicating that the oxide islands might form at surface defects which are areas with a locally lower energy barrier. We relate the growth of the clusters to the diffusion of oxygen on and in copper but the exact pathways of the oxygen are still elusive. After the island growth they coalescence and form an oxide layer on the surface. Additionally, in order to characterize the tribological performance once the whole surface is covered by the oxide, copper oxides such as Cu2O and CuO are tested. Different electron microscopy techniques are applied on the copper samples in order to reveal the fundamental mechanisms of tribologically-induced oxidation. Once understood, it will allow for tailoring the materials properties for little wear and low friction.