Three regimes in the tribo‐oxidation of high purity copper at temperatures of up to 150°C

Surface oxidation of high-purity copper is accelerated under tribological loading. Tribo-oxide formation at room temperature is associated with diffusion processes along defects, such as dislocations or grain boundaries. Here, the additional influence of temperature on the tribo-oxidation of copper is investigated. Dry, reciprocating sliding tests were performed with a variation of the sample temperature between 21 – 150 °C. Microstructural changes were monitored and analyzed with state-of-the-art electron microscopy techniques. Oxide layer formation through thermal oxidation was observed for 150 °C, but not for lower temperatures. As the temperature increases from room temperature up to 100 °C, a significantly stronger tribo-oxidation into deeper material layers and an increase in the amount of formed pores and oxides was detected. Up to 75 °C, diffusional processes of oxygen along grain boundaries and dislocation pipes were identified. Starting at 100 °C, CuO was detected. Hence, tribological loading significantly alters the CuO formation in comparison with static oxidation. Along with the CuO formation at temperatures ≥ 90 °C, the oxide layer thickness decreased while the friction coefficient increased. ... mehrThe observations broaden the understanding of the elementary mechanisms of tribo-oxidation in high-purity copper. Eventually, this will allow to systematically customize surfaces showing tribo-oxidation for specific tribological applications.