High‑Temperature Tribo‑Oxidative Wear of a Cu‑Based Metal‑Matrix Composite Dry Sliding Against Heat‑Treated Steel

The tribo-oxidative wear of a Cu-based metal-matrix composite, dry sliding against a steel counterface, was investigated at 400 °C by means of pin-on-disc sliding tests. The applied pressure was 0.5 and 1 MPa, and the sliding velocity was 1.57 and 7 m/s. Special emphasis was given to the determination of the characteristics of the friction layers, whose constituents were identified and quantified by means of SEM and XRD measurements, and using the Rietveld analysis of the XRD patterns. The pin friction layers were found to be mainly made by compacted CuO/Cu2O oxides and by Fe oxides (mainly Fe3O4) transferred from the disc surface. The disc friction layers were made by CuO transferred from the pin surface and Fe3O4- rich regions, formed by direct asperity oxidation, due to the quite high (600 °C or more) flash temperatures achieved during sliding. This information was used to explain the experimental dependency of the coefficient of friction and the wear rate with the adopted tribological parameters.