Fluorinated Graphene-Based Functional Lubrication Materials:Design,Preparation,Interface Modulation,and Their Tribological Performances

In recent years,two-dimensional（2D）nanomaterials have exhibited low friction,easy film formation,and high load-bearing properties due to advantages of the combination of low slip shearing strength from weak interlayer van der Waals forces,film formation capacity from the high specific surface area,and high in-plane mechanical strength from in-plane covalent bonding.Among them,fluorinated graphene（FG）,a new essential member of the 2D nanomaterials,exhibits better lubricity and load-bearing properties due to the introduction of fluorine atoms and the construction of carbon-fluorine bonds（C-F）.However,the presence of C-F and the resulting low surface energy properties prevent FG from being directly applied to the application in water-based lubricant additives and solid lubrication films like graphene oxide（GO）.To address these issues,this thesis introduced suitable modification reagents to modulate the interfacial properties of FG using the physical and chemical properties of C-F bonds and solved the problems of water-based dispersion and substrate film formation.The main research contents and results are drawn as follows.1.To meet the demand for lubricating performance and environmental protection of current water-based lubricants,a hybrid lubricating additive system of physically modified FG and soluble starch（SS）with excellen t friction-reduction,anti-wear,and high load-bearing capacities was designed and prepared.Firstly,the physically modified FG nanosheets with good water dispersibility and dispersion stability were obtained from graphite fluoride by using the selective adsorption of surfactant alkyl chains on the fluorinated graphite（FGi）surface and the shear exfoliation effect of a high-speed shear mixer.The as-prepared modified FG basically maintained the original fluorine content and exhibited good thermal and chemical stability.Subsequently,the tribological properties of the SS and FG hybrid lubricating additive system were systematically investigated,and the results showed that SS and FG exhibited excellent synergistic lubrication in water.The addition of modified FG significantly improved the load-bearing and boundary lubrication performance of the water-based lubricant,while the addition of SS further improved the friction-reduction and anti-wear performances of the system.At the amounts of 0.3 wt.% FG and 0.6 wt.% SS,the hybrid system showed the best frictionreduction and anti-wear performances,which reduced the corresponding friction coefficient and wear rate by one order of magnitude compared with pure water.Besides,wear scar analysis shows that in the 30 min friction test process,the first 5 min of the running-in process accounts for more than 80% of the wear.The boundary lubrication film formed by FG during the friction process is crucial to the friction-reduction and anti-wear performances,while the introduction of SS further improves the structural integrity of the boundary lubrication film of FG.Finally,a water-based lubrication additive system with good substrate adaptability was obtained.2.To improve the lubrication and anticorrosion performances of mechanical equipment in the salty,hot,and humid marine environment,a composite coating with friction-reduction,anti-wear,and anticorrosion properties was designed and prepared.First,using the ultrasound-assisted solvothermal method,the FG/CeO₂ nanocomposite was successfully obtained by structurally compounding zero-dimensional（0D）cerium dioxide（CeO₂）nanoparticles with the two-dimensional（2D）FG nanosheet.It was shown that the modification of FG by CeO₂ was a physical process and did not damage the FG structure.Then,by using the chemical affinity among the nitrogen-hydrogen bonding in ethylenediamine（EDA）,the C-F bond in FG,and the metal atoms on the metal substrate surface,the substrate binding behavior and interlayer force during the FG film formation process were regulated,and the FG composite coating was successfully constructed on the metal substrate surface.Subsequently,the effects of FG,CeO₂,and EDA on the physicochemical and tribological properties of the coating were systematically investigated,and the results showed that the coating with the synergy of FG,CeO₂,and EDA has lower friction coefficient and longer lubrication duration time.In addition,the electrochemical corrosion performance of each coating was al so investigated using an electrochemical workstation system.The results showed that the composite coating has a higher corrosion potential and a lower corrosion current than the single coating,it is mainly attributed to the lamellar barrier effect of FG nanosheets,the corrosion inhibiting effect of CeO₂ and EDA.Finally,the FG-based composite coating with integrated lubrication and corrosion protection performances was obtained,and a new idea for constructing FGbased composite coating was posed.