| Friction and wear are the most common problems in industrial machinery and equipment,which lead to severe economic and energy consumption.In China,with the development of industrial technology,more and more key components are exposed to multiple environments and complex working conditions for a long time during service,such as high/low temperature,high speed,heavy/alternating load and other harsh working conditions,which are more likely to cause wear and fatigue damage.That will affect the reliability,safety,practicability and maintainability of the whole life cycle,and even possibly result in catastrophic accidents.Lubricating oils are widely used in the relative motion lubrication of equipment to reduce the friction and wear of mechanical equipment under very harsh friction conditions.In order to improve the lubricating performance of the oil samples,the common method is to add various additives.Graphene is a kind of carbon-based material with a two-dimensional layered structure,which has not only outstanding properties,but also unique wear and friction properties that are not available to traditional materials.It is a promising application direction to use graphene as lubricant additive,but there are still various key issues such as operating condition adaptability and long-term dispersion stability.If not solved,it is still difficult to realize the industrialization and large-scale development of graphene lubricants.Therefore,aiming at the dispersion stability of graphene in industrial lubricating oils,through functional modification,layer number regulation and structure regulation of graphene-based material,the high dispersion and excellent tribo-lubrication performance of graphene in lubricating oil can be achieved to meet the requirements of industrial application.The main research contents and conclusions are as follows:（1）The dispersion stability of graphene in hydraulic oil was improved by modification technology.The graphene oxide was modified with titanate coupling agent,and long-chain alkanes were successfully grafted onto the surface of graphene oxide to obtain functionalized graphene（T-GO）.The results show that the obtained functionalized graphene has high dispersibility in industrial lubricating base oils（hydrostatic oil and anti-wear hydraulic oil）,and will not precipitate when stored at room temperature for 30 days.0.08 wt%T-GO hybrid hydraulic oil displayed excellent tribological properties,and the friction coefficient is reduced by about 50%,and the wear volume is decreased by about 20%compared with pure oil.High dispersty ensures the continuous supply of the friction interface,and the graphene-like solid protective film deposited at the interface improves the load-carrying capacity and reduces friction and wear.（2）Regulating graphene layers enhances their tribological properties in transmission oil.Single-layer graphene（SLG）,few-layer graphene（FLG）,multi-layer graphene（MLG）and nano-graphene sheets（Nano G）are added to the transmission oil to explore the influence of the number of flakes on dispersibility and lubrication performance.The results show that SLG exhibits the best dispersion stability compared with FLG,MLG and Nano G due to its high specific surface area,and the friction test shows that SLG displays the best tribological performance,with a friction coefficient reduction of up to 43.7%.The high layer spacing and friction-induced multilayer structure of SLG favor interlayer shear sliding,while the high dispersion and ordered structural transition result in the formation of uniform and compact graphene-based lubricaton thin film,thus having the lowest friction coefficient and the best wear resistance.（3）The construction of graphene incommensurate heterogeneous structure realizes its ultra-low friction in gear oil.Graphene/Mo S2heterostructure material（r GO-Mo S2-1）was synthesized by hydrothermal method,in which molybdenum disulfide grew vertically and evenly on the surface of reduced graphene oxide.The heterostructure nanocomposite material was added to gear oil to investigate their dispersion stability and tribological properties.The results show that 0.04 wt%r GO-Mo S2-1 has good dispersion stability in gear oil,and it can uniformly disperse for 15 days without sedimentation.Four-ball friction experiments show that it has excellent tribological properties.Compared with pure oil,friction coefficient and scar diameter decrease by 16.7%and 22.6%.The excellent friction reduction and wear resistance performance depends on the synergistic effect of the outstanding dispersion stability of r GO-Mo S2-1 material in base oil,the lubrication protective thin film formed in the friction process,and the low interlaminar shear force caused by the unique structure of heterostructured material. |
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