A series of high solid content (30 wt%) epoxy resin (EP) composite coatings reinforced with differently sized cubic boron nitride (CBN) particles were fabricated successfully on 304L stainless steel. Polydopamine (PDA) was used to improve the dispersibility of CBN particles in EP. The structural and morphological features of the CBN particles and the composite coatings were characterized by Raman spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Moreover, a UMT-3 tribometer and surface profiler were used to investigate the tribological behaviors of the as-prepared composite coatings. Electrochemical impedance spectroscopy (EIS) and Tafel analysis were used to investigate the coatings' anti-corrosion performance. The results demonstrated that the CBN fillers could effectively enhance the tribological and anti-corrosion properties of the EP composite coatings. In addition, when the additive proportion of the microsized (5 μm) and nanosized (550 nm) CBN particles was 1:1, the tribological property of the EP composite coatings was optimal for dry sliding, which was attributed to the load carrying capability of the microsized CBN particles and the toughening effect of the nanosized CBN particles. However, when the additive proportion of the microsized and nanosized CBN particles was 2:1, the tribology and corrosion resistance performance were optimal in seawater conditions. We ascribed this to the load-carrying capacity of the microparticles, which played a more important role under the seawater lubrication condition, and the more compact structure, which improved the electrolyte barrier ability for the composite coatings.

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The preparation of TiO2/F-rGO nanocomposites by an in situ synthesis method was discussed, and the nanocomposites were used as lubricant additives. The morphology and structure of TiO2/F-rGO nanocomposites showed that there was an excellent link between TiO2 nanoparticles and F-rGO nanosheets. The tribological results showed that TiO2/F-rGO nanocomposites as lubricant additives displayed a low coefficient of friction and excellent wear resistance capacity. Furthermore, it was illustrated that the TiO2 nanoparticles and the F-rGO nanosheets in the TiO2/F-rGO nanocomposites had a synergistic lubricating effect. The coefficient of friction­(COF) and wear rate of the TiO2/F-rGO nanocomposites decreased by 33.67% and 88.38%, respectively, compared with those of pure oil, suggesting that these nanocomposites display excellent application prospects as novel lubricant additives.

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Fluorographene, a new alternative to graphene, it not only inherits the 2-dimensional (2D) layered structure and outstanding mechanical properties, but also possesses controllable C–F bonds. It is meaningful to reveal the evolution processes of the tribological behaviors from graphene to fluorographene. In this work, fluorinated reduced graphene oxide nanosheets (F–rGO) with different degree of fluorination were prepared using direct gas-fluorination and they were added into gas to liquid-8 (GTL-8) base oil as lubricant additive to improve the tribological performance. According to the results, the coefficient of friction (COF) reduced by 21%, notably, the wear rate reduced by 87% with the addition of highly fluorinated reduced graphene oxide (HF–rGO) compared with rGO. It was confirmed that more covalent C–F bonds which improved the chemical stability of HF–rGO resisted the detachment of fluorine so the HF–rGO nanosheets showed less damage, as demonstrated via X-ray photoelectron spectroscopy (XPS), Raman spectra, and transmission electron microscopy (TEM). Meanwhile, the ionic liquid (IL) adsorbed on HF–rGO successfully improved the dispersibility of F–rGO in GTL-8 base oil. The investigation of tribofilm by TEM and focused ion beam (FIB) illustrated that IL displayed a synergy to participate in the tribochemical reaction and increased the thickness of tribofilm during the friction process.

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