Dry lubrication of rolling contacts by self-regenerative molybdenum oxide coating systems

Due to the worldwide economic and ecological change, there is an increasing demand for the use of innovative environmentally friendly and resource-saving technologies. The current shortage of valuable energy and raw material resources, such as fossil fuels and rare alloy elements, requires an optimal and sustainable use of these resources. This can be achieved by a combination of design and production processes of technical goods and products of mechanical engineering. In SPP 2074, the aim is to achieve resource conservation on structural elements subjected to rolling loads by eliminating fluid-based lubrication, extending service life time and reducing friction loss. This objective is pursued by using molybdenum oxides as solid lubricants with regenerating properties. As layered systems, these provide a hard, wear-resistant surface and elastic properties in the carrier layer and reservoir. In the event of material erosion, the underlying layers react with atmospheric oxygen to provide a surface with good wear properties. The application limits of this novel solid lubricant system are explored in this research project and compared with conventional grease-lubricated bearings. The joint research activity of the Institute of Materials Science (IW), the Institute of Machine Design and Tribology (IMKT) and the Institute of Forming Technology and Machines (IFUM) makes it possible to develop a self-regenerating solid lubricant layer that ensures wear resistance under highly loaded rolling contacts. To this end, PVD processes are used to apply molybdenum oxide-based coating systems as solid lubricant formers on the rolling surfaces. The properties of MoO2 and MoO3 predestine these materials as possible coating materials for rolling contacts. MoO3 in particular is suitable as a solid lubricant due to its layer structure, while MoO2 is particularly suitable as a reservoir and carrier layer. In the operation of highly loaded rolling/roller contacts, layer degradation occurs continuously due to wear processes. The processes in the rolling contact are analysed via bench tests. The wear processes are to be investigated in greater depth using an FE model in combination with a numerical wear calculation. The work should make it possible to understand the wear behaviour of the coatings used and to draw conclusions about the service life time of the coatings in operation.