Tribological properties of nano-graphite as an additive in mixed oil-based titanium complex grease

Nano-graphite was chosen as an additive to improve the tribological properties of titanium complex grease. The influence of the concentration of nano-graphite (N-G) with three average diameter sizes (2 μm, 3.5 μm, and 6 μm) on the tribological properties of titanium complex grease was researched. It was determined that the optimum concentration of the three types of N-G is 0.8 wt%, 1.0 wt%, and 1.2 wt%. Futhermore, the titanium complex grease modified with nano-graphite with a concentration of 0.8 wt% is the optimum grease. Subsequently, the influence of load on the tribological properties of grease containing the optimum concentration (N-G) was studied. Compared to the base grease, the optimum grease showed a lower average friction coefficient, smaller diameter and better tribological performance under the same experimental load. The influence of dispersion homogeneity of N-G on the tribological properties of titanium complex grease was also investigated. The base titanium complex grease and titanium complex grease modified with nano-graphite were synthesized in the laboratory and their tribological properties were evaluated via the four-ball test. The worn surface of their wears scar was observed using SEM and the states of the typical elements were analyzed via XPS. It was uncovered that nano-graphite can improve the tribological properties of titanium complex grease due to the physical friction reduction by nano-graphite due to its interlayer slide and the supplemental effect of the tribochemical reaction anti-wear film composed of TiO₂ and Fe₃C.