Wear protection for high-load chain drives by CrAlMoN coatings via PVD

Chain drives experience significant wear between pins and bushings, which promotes chain elongation. Hard coatings deposited with Physical Vapour Deposition (PVD) could improve wear resistance. However, coating the inner surface of chain bushings presents economic and technological challenges. Triboactive CrAlMoN coatings on chain pins offer an innovative approach by interacting with lubricants to form protective tribofilms that transfer to uncoated bushings. For the first time, three chains were tested with uncoated, CrAlN and CrAlMoN coated pins on a test bench using a grease with sulfur additive and polytetrafluoroethylene (PTFE) under medium (1.8 kW) and high load (23.8 kW) conditions. The total wear was qualitatively evaluated by measuring chain elongation at defined time intervals. Ex situ analysis included visual inspection, wear related roundness measurement, remaining coating thickness and tribofilms. Under medium load, all systems indicate comparable wear rates. At high loads, the CrAlMoN chain exhibits the lowest wear rate. Half of the CrAlMoN coated pins show nearly no wear in contrast to references. The tribofilm composition correlates with this wear reduction. Coating elements were found on uncoated bushings indicating a transfer of tribofilms. The results display effective wear protection for the CrAlMoN system demonstrating high potential for high load chain drives. • CrAlMoN coatings show superior wear protection compared to CrAlN and uncoated systems. • Wear resistive coatings for chain pins demand resistance against surface fatigue. • Formation of tribofilms consisting disordered graphite with high order. • Transfer or tribofilms from chain pin to inner surface of the bushing. • Correlation of tribofilm properties with wear reduction.