Oleylamine (hereinafter referred to as OM)-modified CeO 2 nanoparticles were synthesized by a one-pot pyrolysis method. The tribological properties of the as-prepared CeO 2 nanoparticles as the lubricant additive in poly-alpha olefin (PAO) were investigated with a four-ball machine, and their lubricating mechanism was discussed in relation to worn surface analyses by SEM, EDS, and XPS. Findings indicate that these nanoparticles exhibit good dispersibility as well as excellent anti-wear ability in PAO. This is because OM-modified CeO 2 nanoparticles can catalyze the oxidation of metallic Fe to form ferrite oxide-containing tribo-film. Under the condition of ASTM D2266-2001, the same lowest WDS was obtained at the concentration of 0.2 wt% and 1.8 wt%. When the concentration of CeO 2 is 0.2 wt%, a compact catalytic oxidation tribo-film is formed, which has more outstanding long-term anti-wear ability. When 1.8 wt% CeO 2 is added, the tribo-film formed is the combination of catalytic oxidation film and ceria deposition film, which has more significant bearing capacity.

CeO2 nanoparticles are potential anti-wear additives because of their outstanding anti-wear and load-bearing capacity. However, the shear-sintering tribo-film formation mechanism of oxide nanoparticles limits the tribo-film formation rate and thickness greatly. In this study, by compounding with zinc dioctyl dithiophosphate (ZDDP), ultra-fine CeO2 nanoparticles modified with oleylamine (OM) can quickly form 2 µm ultra-thick tribo-film, which is 10–15 times thicker than that of ZDDP and CeO2, respectively. The ultra-thick tribo-film presents a nanocomposite structure with amorphous phosphate as binder and nano-CeO2 as filling phase, which leads to the highest loading capacity of composite additives. The results of adsorption experiments tested by dissipative quartz crystal microbalance (QCM-D) showed that the PB value of additive has nothing to do with its equilibrium adsorption mass, but is directly proportional to its adsorption rate in 10 s. The compound additive of CeO2 and ZDDP presented the co-deposition mode of ZDDP monolayer rigid adsorption and CeO2 viscoelastic adsorption on the metal surface, which showed the highest adsorption rate in 10 s. It is found that the tribo-film must have high film forming rate and wear resistance at the same time in order to achieve super thickness. Cerium phosphate was formed from ZDDP and CeO2 through tribochemistry reaction, which promotes the formation of an ultra-thick tribo-film with nanocomposite structure, which not only maintains the low friction characteristics of CeO2, but also realizes high PB and high load-carrying capacity.

In this investigation, micro crystalline diamond (MCD) and nanocrystalline diamond (NCD) films are deposited on cemented carbide (WC-Co) balls by hot filament chemical vapor deposition (HFCVD) technique. After deposition, MCD and NCD films are characterized by field emission scanning electron microscopy (FESEM) and Raman spectroscopy. Then frictional tests are carried out between CVD diamond coated balls and graphite. The results show that the MCD-graphite and NCD-graphite tribo-pairs exhibit comparable frictional coefficients, while the wear rate of graphite in MCD-graphite working pair is much higher than that of graphite in NCD-graphite working pair. Furthermore, the element oxygen is detected in the wear groove of graphite, suggesting the oxycarbide of working materials at the increased temperature due to the heat generated from the mechanical friction.