Amino-ionic liquid functionalized graphene: A dual-purpose additive for lubrication and electrical erosion resistance

To address electrical erosion in rolling bearings of the motor systems of electrical vehicles, this study presents an in situ functionalization of graphene oxide (GO) with an amino-functionalized ionic liquid, [Bmim]PF₆, resulting in a reduced graphene oxide–ionic liquid composite (rGOIL) with excellent electrical conductivity and outstanding friction-reducing and anti-wear performances. A series of conductive urea-based greases are formulated by optimizing the rGOIL content. The structure and morphology of rGOIL are characterized by FTIR, XRD, Raman spectroscopy, SEM, TEM, and XPS. Tribological tests using an SRV tribometer and electrical erosion evaluation on a bearing test rig show that grease containing 0.5 wt% rGOIL maintains a low and stable friction coefficient (0.102) under a 200 N load at 50 °C, with a 93 % reduction in wear volume compared to conventional polyurea grease. In electrical erosion tests, the bearing vibration amplitude stabilizes at 1.1 mm/s², only 15 % of that measured for the reference grease. XPS and TEM analyses reveal the formation of a tribochemical film consisting of graphene nanosheets, ionically bonded liquid layers, and metal fluorides and phosphates. This film forms a conductive lubrication layer through a synergistic "lubrication–conductivity–lubrication" mechanism, effectively mitigating electrical erosion and enhancing bearing durability.