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

• Applicants: Professorin Dr.-Ing. Kirsten Bobzin; Professor Dr.-Ing. Bernd Sauer
• Subject Area: Engineering Design, Machine Elements, Product Development ; Coating and Surface Technology
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 450064527

Chain drives are used in a variety of applications in the mobility sector and in the industrial field, and can be distinguished in drive chains and transport chains. Drive chains are usually used in powertrains and transport chains can serve as conveyor chains in farming machines, industrial production and food production. The resulting loads on chain drives are mainly determined by the forces and torques, environmental and operating conditions (continuously, intermittent) as well as the lubrication. Drive chains and transport chains are often operated with an initial lubrication and only re-lubricated by demand. The friction and wear behaviour of chain drives is strongly affected by the tribological contact between chain pin and bushing. Especially in initially lubricated chains, only a limited amount of lubricant can be provided to the contact. This leads to increased tribological loads. In industrial applications, increased lifetimes of the chains can be achieved by physical vapour deposition (PVD) coated chain pins. Nitride hard coatings can reduce the chain elongation, which is caused by wear of the chain pin and the bushing. However, investigations in a chain test bench with coated chain pins show high initial chain elongations during the first hours of operation and is ascribed to the wear of uncoated bushings. Increased wear resistance of the bushings bears therefore a high potential to increase the efficiency of chain drives. However, a direct coating of the inner bushing surfaces is not possible by means of PVD technology. An alternative is the indirect increase of the wear resistance of the inner bushing surfaces by means of tribochemical reaction layers that form under tribological load and are transferred from the chain pin on the bushing. Promising approaches are triboactive (Cr,Al,X)N PVD coatings (X = Mo, Cu) and amorphous diamond-like carbon (DLC) coatings. Triboactive coatings can interact with lubricant additives and lead to tribochemical reaction layers. DLC coatings can lead to the transfer of graphite on the counter part. The proposed research project IOT and MEGT focuses on fundamental research regarding the transfer layer formation on chain bushings to reduce wear and friction in initially lubricated drive chains.

• DFG Programme: Research Grants