Three Regimes in the Tribo‐Oxidation of High Purity Copper at Temperatures of up to 150 °C

Abstract

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. Herein, the additional influence of temperature on the tribo‐oxidation of copper is investigated. Dry, reciprocating sliding tests are performed with a variation of the sample temperature between 21 and 150 °C. Microstructural changes are monitored and analyzed with state‐of‐the‐art electron microscopy techniques. Oxide layer formation through thermal oxidation is 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 is detected. Up to 75 °C, diffusional processes of oxygen along grain boundaries and dislocation pipes are identified. Starting at 100 °C, CuO is 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 decreases while the friction coefficient increases. The observations broaden the understanding of the elementary mechanisms of tribo‐oxidation in copper. Eventually, this will allow to systematically customize surfaces showing tribo‐oxidation for specific tribological applications.

Performance of Austenitic High-Nitrogen Steels under Gross Slip Fretting Corrosion in Bovine Serum

“…From the severe plastic deformation (SPD) literature that we know of, such strain rates require distinctly different deformation mechanisms than under hardness or tensile tests [72]. Finally, the differences in the stacking fault energies [73] or the tendency of the materials to form shear bands might have an influence [74], as well as other micro-and nanostructural effects that are still under investigation [25,75,76]. Including the contribution of the tribomaterial appears impossible, for we do not know its structural, mechanical, and fluidic properties under high shear rates at all.…”