Graphene Nano-Lubricant for the Improved Rolling Contact Fatigue (RCF) Life of AISI 4140 Steel under Rolling with Slip Conditions

Rolling and sliding contacts are common tribological interactions between surfaces in high-speed rotating components such as bearings, gears, and rail wheels. If the bearing is operated under mixed/boundary lubrication conditions, the major failure mechanism would be micro-pitting and wear, and its extent depends on the percentage slide between the contact pairs. This work compares the rolling contact fatigue (RCF) behavior of AISI 4140 steel under pure rolling (zero slip) and slip conditions by using base lubricant and formulated lubricant with graphene nanoadditives. Rolling contact fatigue performance under pure rolling and slip conditions shows a significant improvement with graphene lubrication compared to base lubrication. Under pure rolling conditions, the RCF L 10 life improved 3-fold with graphene lubricant compared to base lubricant. Similarly, under the slip condition, a significant improvement in the anti-wear performance was observed for the graphene lubrication compared with the base lubrication. A detailed wear track analysis was performed using scanning electron microscopy and Raman spectroscopy. The results reveal that the formation of tribo-films on the surface is the major reason for the improved anti-wear performance with graphene nanolubrication. According to the working conditions, the physical tribo-film was observed under pure rolling conditions, and the chemical tribo-film was observed under slip conditions.