The tribological performance and lubrication mechanism of graphene oxide (GO) aqueous lubricants with different pH levels on the strip surfaces during cold rolling were investigated. And triethanolamine (TEA) was used to adjust the pH levels of GO lubricants. The morphology of GO and physical characterization of GO lubricants were carried out. Four‐ball tribological tests and cold rolling experiments were conducted to obtain the tribological behaviors of GO lubricants on the strip surfaces. To figure out the lubrication mechanism, the surfaces of the rolled strips using GO lubricants were analyzed utilizing a series of experiments. The increase in the pH value of lubricants changed the intrinsic structure of GO, resulting in better dispersibility and wettability. The change of physical characteristics significantly improved the antifriction and antiwear properties of lubricants, and the alkaline lubricant (pH 9.0) exhibited the best lubrication performance. A diameter–height ratio (λd) applied by a calculation method was proposed to approximatively ascertain the lubrication regime during the cold rolling. The λd and the surface quality of the rolled strips indicated that the lubrication regime was the boundary lubrication when using the alkaline lubricant. Moreover, GO particles in the alkaline lubricant could repair the strip surface by mending effect and form the physically adsorbed layers. The layers prevented direct contact between rolled surfaces, further amending the surface quality of the rolled strips.
A facile and modified hydrothermal method was reported for the simultaneous reduction and functionalization of graphene oxide without any reductant. The lubrication mechanisms of nanomaterials were analyzed based on tribological experiments and molecular dynamic simulation. Tribological studies indicated that triethanolamine functionalized graphene oxide exhibited excellent friction-reducing performance and the optimal concentration was 0.15 wt.%, while 0.25 wt.% of triethanolamine functionalized graphene oxide showed best wear resistance in the pin-on-disk experiment. An anti-wear and friction-reducing coefficient τ was proposed to evaluate the tribological properties of lubricants for a uniform standard. Molecular dynamics simulation results revealed the influence of different functional groups on the anti-wear and friction-reducing performance. The sliding distance between graphene oxide layers with COOH functional groups was the longest, it was conducive to reduce the friction coefficient but decrease the wear life. The order of diffusion coefficients of graphene oxide containing different functional groups was DCOOH (4.02 × 10–11 m2 s−1) > DC-OH (1.42 × 10–11 m2 s−1) > DC–O–C (5.24 × 10–12 m2 s−1). It was proposed and verified that the structure of graphene oxide could be optimized by grafting triethanolamine molecules on the C–O–C functional groups to ameliorate the tribological properties.
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