On the physical nature of tribolayers and wear debris after sliding wear in a superalloy/steel tribosystem at 25 and 300 °C

Dry sliding wear of metals is strongly affected by the formation of oxide particles and their incorporation into compacted oxide layers, so-called glaze layers. A high-temperature reciprocating pin-on-disc tribometer was used to study the tribological response of a Ni-based Alloy 80A pin on a cast iron disc at ambient temperature and at 300 °C. Alloy 80A is used for valves and specific cast irons are used for valve seat-inserts in automotive diesel engines, where wear limits the service life of the valve/seat-insert tribosystems. Measurements of the friction coefficient, the total linear wear and the electrical contact resistance were used to monitor the formation of oxide layers during the experiments. Electron dispersive X-ray (EDX) element mappings from the surface regions with wear scars provide clear evidence for the formation of glaze layers and material transfer between pin and disc. Focused ion beam (FIB) micromachining was used to cut out thin lamellae from specific surface regions of glaze layers and from metallic wear particles. These lamellae were investigated in a transmission electron microscope (TEM). It was shown that the glaze layers generated at 25 and 300 °C exhibit distinct differences, which led to a reduction in wear rate by a factor of five at the higher temperature. We also report on the mechanical mixing of oxide particles and metal matrix that results in a metal/oxide nanocomposite directly below the sliding surfaces. Such composite structures were also observed inside of metallic wear debris.