A comprehensive evaluation of DLC coating on gear bending fatigue, contact fatigue, and scuffing performance

Modern advanced equipment demands higher reliability and longer service life, imposing increasingly stringent requirements on loading capacity of gears. Diamond-like carbon (DLC) coating significantly improves the friction and wear performance, which has potential to be applied to gears to enhance their loading capacity. In this study, a comprehensive evaluation of the DLC coating treatment on the loading capacity of 18CrNiMo7-6 gears was conducted. The surface morphology, hardness gradient, residual stress, and material microstructure of the DLC coated gears have been characterized. Additionally, bending fatigue, contact fatigue, and scuffing tests on the gears were performed, which took more than 1000 h. The results demonstrate that DLC coating significantly enhances surface microhardness, reaching up to 2000 HV, and surface residual compressive stress shows an increase of approximately 200 MPa. The DLC treated gear contact fatigue limits from 1570 MPa to 1770 MPa, and the scuffing limit temperature rises from 224.6 °C to 348.6 °C compared with grinding state. Although DLC coatings do not exhibit an improvement in gear bending fatigue strength, the composite treatment of shot peening combined with DLC coating still enhances its bending fatigue performance.