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nanostructures (OLCs). Combining with atomistic molecular dynamic (MD) simulations, we elucidate the tribochemical mechanism of formation of OLC with pure iron NPs and how that depends sensitively on the core-shell chemistry of the nanoparticle. Interestingly, the formed OLCs lead to the near-zero friction (superlubricity) during sliding in dry conditions, thus demonstrating great potential to be used as a solid lubricant for various tribological applications.

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Conventional solid lubricants such as MoS2, graphite, or diamond-like carbon films demonstrate excellent tribological performance but only in specific environments due to their inherent materials properties. This limitation prohibits using these solid lubricants in environments that change dynamically. This study presents the results of a novel solid lubricant that was developed using a combination of solution-processed 2D-molybdenum disulfide and graphene-oxide (GO) that can be deposited on to stainless steel substrates using a simple spray-coating technique and show exceptional performance in multifarious environments namely, ambient (humid) atmosphere, dry nitrogen, and vacuum. The tribological performance of the coatings was evaluated using a ball-on-disc sliding test and demonstrated an excellent wear/friction performance in all environments and coating survived even after 44 km of linear sliding. Transmission electron microscopy and Raman spectroscopy analysis of the tribolayers suggested in-operando friction-induced re-orientation of MoS2 layers that were protected by GO layers and, an absence of MoOx peaks indicate a strong resistance to intercalation with moisture and oxygen. The simplicity and robustness of the hybrid MoS2–GO solid lubricant in mitigating wear-friction behavior of steel-on-steel tribopair in a multifarious environment is a game-changing and is promising for various applications.

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.

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