Effect of Urea-Containing Imidazole Halogen-Free Ionic Liquid on Tribological Properties of Composite Lithium Grease

Two urea based-functionalized imidazole halogen-free ionic liquids (IL), DOSS-1 and DOSS-4 were synthesized. As reduce friction and anti-wear additives for 2^# lithium complex grease (G), their tribological properties were investigated using friction and wear tester (SRV-V) and surface non-contact optical 3D profiler (Bruker-NPFLEX). The friction test results show that lithium complex grease with addition of ILs had excellent friction-reduction and anti-wear performance. The addition of 3% DOSS-4 (or DOSS-1) produced excellent improvement for friction and wear. The tribological property of DOSS-4-G is superior to DOSS-1-G of equivalent addition amount of IL. The surface morphology of the worn surface was analyzed by a Bruker-NPFLEX 3D surface profile and scanning electron microscopy. The chemical states of the main elements of wear spot was determined by X-ray photoelectron spectroscopy and the lubrication mechanism was clarified. The significant effects for IL on the friction-reduction and anti-wear performances were attributed to the formation of tribofilm containing elements N and S on the worn surfaces.