Superlubricity Of Graphene And Tribological Properties Of Graphene Composites

Nowadays,one-third of the fuel energy is used to overcome friction and 80%mechanical equipment damage is caused by wear.Thus,effectively reducing the friction between the relative motion interfaces and improving the tribological performance of mechanical components are problems to be solved urgently.Superlubricity is highly desirable for achieving sustainable development in the context of global energy and resource shortages.Until now,however,superlubricity can only be achieved at microscale and under special atmosphere environment,and has not been able to make a breakthrough at macroscale.Secondly,polymer composites have been widely used in the high precision and performance moving parts due to their light weight,high strength and excellent chemical stability.However,its tribological performance still can’t meet extreme requirements due to the limited enhancement of the existing material reinforcing material.Graphene,because of its high specific surface area,excellent mechanical and tribological properties,has great advantages in achieving macroscopic superlubricity and enhancing the tribological properties of polymers.In this study,a superlubricity tribological system was fabricated by graphene-coated quartz plate,graphene-coated SiO2 microsphere,and graphene-coated quartz ball.The friction coefficient of this tribological system is 0.0075 in air under 35 mN at a sliding speed of 0.2 mm/s.To the best of the knowledge,for the first time,macroscale superlubricity under ambient conditions is reported.The mechanism of macroscale superlubricity,which demonstrated by the experimental measurements,ab initio,and molecular dynamics simulations,is concluded that the addition of silica spherical particles reduces the stress of the graphene layer resulting in no wrinkled and cracked graphene layer,which contributing to additional energy dissipation.Secondly,this paper used a blending method to prepare graphene/epoxy composites.The results show that the wear resistance of graphene/epoxy composites with 5 wt%graphene content is shown to be 628 times as stronger as pure epoxy resin at 10 N normal load.Furthermore,MD simulations on tribological properties for crosslinking between dispersed graphene and the polymer matrix,and blending dispersed graphene randomly in was established for the first time.The indenter is composed of Fe atoms.The results show that the improved tribological performance is due to the formation of lubricant film consist of graphene flakes exfoliated from the epoxy matrix during the friction process.Finally,in order to fully utilize the anisotropic properties of graphene,highly aligned graphene/epoxy composites with horizontally oriented structure have been fabricated via an improved vacuum filtration method.The results show that the compact lubricant film is easier to formed by the graphene sheets aligned in the epoxy matrix,thereby significantly reducing the friction coefficient of the graphene epoxy resin composite.Moreover,it has a lower wear rate than the randomly arranged graphene epoxy composites when normal load is lower than 8 N.The results of this paper are helpful for the application of superlubricity at the macroscale,as well as the design and manufacture of high-performance devices based on graphene polymer composites...