Atomic-scale insights into the mechanical and tribological properties of graphullerene

Abstract

Graphullerene (GF) as an emerging two-dimensional nanomaterial exhibits excellent flexibility properties and superlubricity potential, but current research on its mechanical and tribological properties still lacks in-depth insights from the microscopic scale. Herein, the mechanical strength of GF was explored and its tribological mechanisms as a lubricant additive in fluid and boundary lubrication states were revealed by indentation, tensile, and friction molecular dynamics simulations using graphene (GR) as a comparative object. The results revealed that compared with GR, covalent bond mixed hybridization reduced the mechanical strength of GF, but the robust spherical structure enhanced its bending stiffness. Under fluid lubrication, GR promoted adsorption film formation and rapid flow to induce low-shear strength solid-liquid interfacial slip. GF inhibited this characteristic and thus induced liquid-liquid interlayer slip with high frictional resistance. Under boundary lubrication, GR exhibited superior tribological performance compared to GF, with the bilayer outperforming the monolayer. This was attributed to the high bending stiffness of GF inhibiting the bending deformation releasing stresses and thus deteriorating the mechanical contact with the asperity. However, friction-induced interlayer slip of bilayer nanoparticles with low shear strength. This study provides valuable insights into the mechanical and tribological properties of GF.