Analysis of transfer layer formation in initially lubricated, coated drive chains

• Applicants: Professorin Dr.-Ing. Kirsten Bobzin; Professor Dr.-Ing. Oliver Koch
• Subject Area: Engineering Design, Machine Elements, Product Development
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 564002863

Tribological measures to reduce wear and friction offer great potential for increasing energy efficiency and sustainability. One machine element with open potential in this respect is the chain. The chain joint is the decisive element that determines the majority of friction losses and the wear-related service life. Basic research focuses on triboactive CrAlMoCuN chain pin coating under lubrication with grease. Through interactions of Mo and Cu with the lubricating grease and its sulphur and phosphorus-containing additives, friction- and wear-reducing transfer layers are formed on the uncoated sleeves, which in the case of sulphur-added lubricants contain the dry lubricant MoS2. It is assumed that copper has a catalytic effect. In the current project, it was demonstrated that CrAlMoN-coated chain pins achieve a reduction in friction and wear in the chain joint. In pin-on-disc tests, this was increased by a CrAlMoCuN coating, which was attributed to a transfer layer containing MoS2. Furthermore, wear analyses in individual chain joints have shown that a CrAlMoN coating with a sulphur-containing lubricating grease achieves extremely low running-in wear and low wear rates over the service life. The research objectives of the proposed project are: 1) To systematically investigate the presumed catalytic effect of Cu on transfer layer formation, 2) To investigate a “two-stage” conditioning process in the form of the initial production of a two-dimensional contact and subsequent reaction layer formation with regard to wear and friction reduction over the service life and 3) To transfer the findings to real, entire chains and to verify the service life prediction by means of wear simulation. The solution includes simplified tribological model tests. The focus here is on the investigation of transfer layer formation through chemical, crystallographic and structural analyses of the transfer layers in order to investigate the catalytic effect of Cu. Chain link tribometers are used to investigate running-in processes in real, coated chain links and a two-stage conditioning process is designed. This is then validated with regard to wear and friction reduction in long-term tests. The condition of the chain pins and sleeves after conditioning is analyzed and forms the basis for the wear simulation. The wear prediction is validated using tests on real, complete chains and the transferability of the findings on the catalytic effect of Cu, transfer layer formation and the associated reduction in wear and friction is investigated.

• DFG Programme: Research Grants