  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, we
embark on investigating the additional influence of temperature on the
tribo-oxidation of copper. Dry, reciprocating sliding tests were performed with
a variation of the sample temperature between 21 - 150 $^\circ$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 $^\circ$C, but not for lower temperatures. As the
temperature increases from room temperature up to 100 $^\circ$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
$^\circ$C, diffusional processes along grain boundaries and dislocation pipes
were identified. Starting at 100 $^\circ$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 $^\circ$C,
the oxide layer thickness decreased while the friction coefficient increased.
The observations broaden our 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.
