Influencing factors on high temperature tribology

Abstract

This study investigates the influence of temperatures, normal force, displacement, frequency and sliding distance on the tribological material behaviour of an unlubricated cobalt-based material pairing, as well as the effects resulting from a change of atmosphere from ambient air to a low-oxygen CO₂/N₂/O₂-atmosphere. The subsequent identification of empirical wear correlations should enable a transfer to other material systems. Reciprocating wear tests were carried out at up to 800 °C with a cylinder-on-plate contact geometry. The test conditions and the material are based on the application as exhaust gas flap plain bearings for combustion engines.

The temperature has a major influence on the wear behaviour, as it induces the change of tribological mechanisms from abrasion to oxidation and adhesion of wear particles to the formation of a glaze layer in the HT range. The wear particles, required for the tribologically induced sintering process of the glaze layer, are already present in fully oxidised form at low temperatures of 200 °C. The formation of a wear-reducing glaze layer is therefore mainly dependent on the temperature, as this directly influences the sintering process, according to a key finding of this work. The atmospheric influence on the tribological material behaviour is dependent on the temperature related wear regime. For lower temperatures, a mechanism change from abrasion to adhesion takes place in the oxygen-reduced CO₂/N₂/O₂-atmosphere. In contrast, the formation of the glaze layer is not influenced by the change in atmosphere. Moreover, the influence of normal force, displacement and sliding distance differs between the various temperature sections and the related tribological mechanisms.