Synergistic lubrication mechanism of CeO2 nano-additives and friction modifiers in PAO/DLC solid-liquid composite lubricating system

Abstract

Nano additives exhibit efficient anti-wear and friction reducing properties for various friction materials, thus having broad application prospects in engine oil. The synergistic mechanism between friction modifiers and nano additives is a key issue in the development of energy-saving engine oil. In this paper, the tribological properties of oleylamine (OM) modified CeO₂ nanoparticles and commercial organic friction modifiers glyceryl monooleate (GMO), glycol oleate (T403B), benzotriazole aliphatic amine (T406E) and molybdenum dithiocarbamate (MoDTC) in PAO/DLC solid-liquid composite lubricating system were investigated. It was found that only when CeO₂ nanoparticles were combined with GMO, the anti-wear and friction reduction performance of the system was better than that of nano additives, any friction modifiers, and their combination additives. The synergistic effect was demonstrated in the boundary lubrication range under reciprocating sliding conditions and fully lubricated range in the S-curve experiment under rotating sliding mode. Three-dimensional topography, EDS typical element distribution, and Raman analysis were performed on the worn surface, and the adsorption behavior of additives on metal and DLC surfaces was studied using quartz crystal microbalance (QCM-D). It was found that only lubricated with CeO₂ + GMO, a viscoelastic composite adsorption layer with both high adsorption quality and high adsorption layer density could be formed on the metal and DLC surfaces simultaneously. The adsorption layer has excellent tribological properties of high load-bearing capacity and low friction, which not only overcomes the high friction problem of CeO₂ nanoparticle solid tribofilm, but also avoids the high wear defect of tribofilm formed by friction modifier.