Exploring Pristine Graphene as a Solid Lubricant Coating Film for Its Macroscale Application under Various Environments

Solid lubricants have been used not only as an alternative to liquid lubricants under extreme environments such as extremely high and low temperatures, and vacuum environments but also for applications to mechanical systems under ambient conditions at the macroscale. Graphene, one of the representative two-dimensional nanomaterials, has been extensively explored as a solid lubricant due to its excellent tribological properties from the nanoscale to the macroscale. However, since graphene has its own unique properties under various conditions, it is essential to investigate its tribological performance under various conditions. Also, although several researchers have attempted to achieve a super low coefficient of friction at the macroscale tribo-test, achieving low COF doesn’t always correspond to good tribological performance. In real mechanical applications, the service lifetimes of the coating film can be more important. For achieving prolonged service lifetimes of the solid lubrication coating film, it is essential to form the rigid and stable transfer layer onto the counterpart surface after sliding. However, since pristine graphene has a chemical inertness, it cannot easily form the transfer layer, leading to its poor durability. In this study, we provide a material design strategy to realize the graphene-based solid lubricant to prolong the service times and a low COF simultaneously for applications to both ambient and extreme conditions. We simply stacked the graphene oxide on the pristine graphene film using a drop-casting method and achieved the formation of the transfer layer on the counterpart contact surface which can lead to an enhanced tribological performance under ambient conditions. In addition, to explore the tribological performance of graphene-based coating film under space environments where no oxygen exists, we conducted the tribo-test with the introduction of argon gas to mimic the space environments. Finally, we provided a possible strategy for the application of solid lubricants under various environmental conditions by unveiling the lubrication mechanism of the graphene-based heterogeneous solid lubrication coating film.