Dry lubrication and transfer lubrication of rolling contacts by self-regenerating molybdenum oxide coating systems

• Applicants: Professor Dr.-Ing. Kai Möhwald; Professor Dr.-Ing. Gerhard Poll
• Subject Area: Engineering Design, Machine Elements, Product Development
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 524080913

The research work in the planned project opens up the possibilities of operationally reliable solid lubrication of tribological contacts subjected to rolling loads via Mo-based coatings. A stable coating process was developed which can be transferred to different systems. Nanowear tests were used to characterize and model the wear behavior of the individual coating components. In the rolling bearing tests with axial cylindrical roller bearings on the FE8 test rig with Hertzian pressures of up to 1 GPa, a significant increase in operating life was demonstrated for the dry-lubricated bearings compared to unlubricated standard bearings; the results were even better than those obtained for bearings coated by means of WC/C. It was shown that the combination of Mo and MoO3 represents a new type of dry lubricant. In rolling contact, the MoO3 is finely dispersed as a lubricant and is continuously formed from the Mo reservoir by tribo-oxidation. In addition, transfer lubrication was demonstrated in a hybrid bearing. In this case, a running-in process took place in the transfer phase, which subsequently led to a stable operating condition. The focus in the requested funding will now be to scale the results to more complex bearing geometries and larger bearings, to understand the lubrication mechanisms more deeply and to control them better, and thus to make the operating behavior of the components predictable. The IMKT's extensive experience in the analysis of tribological layers will be used for further research into MoO3 transfer lubrication. The central research objective is to clarify the mechanism of action of transfer lubrication by MoO3 in more detail and to investigate the influence on the edge zones of the microstructure in greater depth. The description of the transfer film formation is realized by an extended wear model, which describes the layer build-up by a "negative" wear and subsequently the steady state phase until the layer degradation.

• DFG Programme: Research Grants
• Co-Investigator: Dr.-Ing. Florian Pape