Enhancement of friction performance enabled by a synergetic effect between graphene oxide and molybdenum disulfide

Graphene-related materials and molybdenum disulfide (MoS2) are good candidates as solid lubricants owing to their easy-shear property between lattice layers. However, the coefficients of friction (COFs) of graphene or graphene oxide (GO) are not sufficiently low at the macroscale and the friction and wear performance of MoS2 is significantly deteriorated by humidity. Herein, GO-MoS2 nanocomposite film is fabricated on a stainless steel (SS) substrate by a simple electrophoretic deposition (EPD) method in water. The deposited nanocomposite film can reduce the COF to 10% of that for a SS substrate and 50% of that for a pristine GO film and can extend the lifetime in comparison to a MoS2 film under ambient conditions. A tribofilm forms in the wear track where GO nanoflakes wrap MoS2 nanoflakes in the tribofilm; furthermore, a MoS2 transfer layer forms on the steel ball surface during the friction test. This excellent lubrication performance arises from the synergetic effect between GO and MoS2, where the layered MoS2 dominates the lubrication performance owing to its easy-shear property and the surrounding GO protects MoS2 from humidity and oxidation. This has implications for developing nanocomposite films with excellent lubrication and wear-resistance performance for industrial applications. (C) 2019 Elsevier Ltd. All rights reserved.