Toward Robust Macroscale Superlubricity on Engineering Steel Substrate

Abstract

“Structural superlubricity” is an important fundamental phenomenon in modern tribology that is expected to greatly diminish friction in mechanical engineering, but now is limited to achieve only at nanoscale and microscale in experiment. A novel principle for broadening the structural superlubricating state based on numberless micro‐contact into macroscale superlubricity is demonstrated. The topography of micro‐asperities on engineering steel substrates is elaborately constructed to divide the macroscale surface contact into microscale point contacts. Then at each contact point, special measures such as pre‐running‐in period and coating heterogeneous covalent/ionic or ionic/ionic nanocomposite of 2D materials are devised to manipulate the interfacial ordered layer‐by‐layer state, weak chemical interaction, and incommensurate configuration, thereby satisfying the prerequisites responsible for structural superlubricity. Finally, the robust superlubricating states on engineering steel–steel macroscale contact pairs are achieved with significantly reduced friction coefficient in 10−3 magnitude, extra‐long antiwear life (more than 1.0 × 106 laps), and good universality to wide range of materials and loads, which can be of significance for the industrialization of “structural superlubricity.”

Macroscale superlubricity achieved via hydroxylated hexagonal boron nitride nanosheets with ionic liquid at steel/steel interface

“…Nowadays, superlubricity, including solid superlubricity [5] and liquid superlubricity [6], has attracted continuously attention in many fields including machinery, energy, aerospace, and biology [7][8][9][10]. As for solid superlubricity, the achievement of extremely low COF (< 0.01) usually relied on a specific structure (e.g., graphite, MoS 2 , a-C:H, and diamond like carbon (DLC) film) [11][12][13][14][15] or a certain atmosphere (e.g., inert gas and vacuum) [16][17][18]. However, for liquid superlubricity, it is much easier to obtain common friction pairs in the atmosphere; therefore, it has wider application.…”

Environmental Molecular Effect on the Macroscale Friction Behaviors of Graphene

“…Therefore, the difference in the friction coefficient of the graphene coating is mainly determined by the microstructure of the graphene at the sliding contact interface. The highly flat ordered layer-by-layer slip structure at the sliding interface can be formed in a short time in air ( Figures 8A,B ), and the formed layer-by-layer slip structure is the structural prerequisites for graphene to obtain the low friction coefficient ( Song et al, 2017 ; Li et al, 2020 ). At the macroscale, the slip occurs between the nanosheets of graphene, and the intrinsic friction is dependent on the interaction between its nanosheets and the layers of graphene nanosheets.…”

“…The macroscale friction coefficient of graphene is also dependent on its microstructure, so it can be presumed that graphene with intact nanosheets can show excellent lubricating performance. In particular, the highly ordered slip structure at the sliding interface lets graphene obtain macroscale superlow friction ( Song et al, 2017 ), and ideal layered slipping microstructure is the prerequisite for graphene to exhibit outstanding macroscale tribological behaviors ( Li et al, 2020 ; Gao et al, 2020 ). In recent years, research on the tribological properties of graphene are mainly focused on the microscale and in theory ( Hirano and Shinjo, 1990 ) ( Dienwiebel et al, 2004 ; Song et al, 2018 ) and can provide guidance for macroscale research.…”

Friction reduction mechanisms of TiN film sliding in graphene aqueous dispersion

“…The weak interaction between water molecules and graphene can lead to the appearance of superlubricity. Li et al 19 achieved the structural super-lubricity at macroscale on steel substrate, the macroscopic surface contact was transformed into a large number of microscopic contact points by laser etching, then superlubrication was achieved at each microscopic contact point by pre-running and 2D lubricating materials additive. Finally, the robust super lubrication was achieved at macroscale with extra-long anti-wear life (1.0 Â 10 6 laps) and high contact stress (1.37 GPa).…”