Superlubricity in rolling/sliding contacts

Rolling element bearings and gears are critical components of mechanical systems such as wind turbines and automotive engines and transmissions that use oil-based lubricants. Oil-based lubricants used in these applications many times need periodic replacement, which not only adds more cost but also affects overall productivity. More importantly, the used oil generates hazardous waste creating huge environmental problems. In this study, we demonstrated that nanomaterials can be employed as solid lubricants in combination with diamond like carbon (DLC) films in a dry nitrogen environment under rolling/sliding contacts. Using a micropitting rig which is generally used to test and qualify materials and lubricants for bearings and gear systems for industrial applications, we have tested diamond like carbon (DLC) material pairs in an oil-free, dry nitrogen environment along with two-dimensional MoS2 combined with nanodiamond as a solid lubricant. We show that superlubricity (traction coefficient of friction is 0.003) was achieved through the formation of a carbon rich superlubricious tribolayer at the interface reducing the overall friction by a minimum of 20 times, and no surface damage was observed as compared to Steel-Steel contacts lubricated with oil (0.06-0.07). The current work paves the way for developing oil-free solid lubricants in a variety of applications involving rolling/sliding contacts.