| Friction is inevitable in daily life and industrial production,especially in high-speed rotating motorized spindle,the friction heat generation of bearing pair directly affects the service life of motorized spindle.How to reduce bearing friction is the focus of scholars'research.Hybrid ceramic ball bearings have been widely used in high-speed motorized spindles in order to reduce the friction of the bearing friction pairs.Many scholars have tried to add nano-additives to the lubricating oil to reduce friction and improve lubrication.Graphene is an additive that has been found by scholars in recent years to have good lubricating properties.In this thesis,the effects of graphene content,pressure and shear velocity on the tribological behavior of Si3N4-GCr15s friction pair were studied by experimental methods.The molecular dynamics simulation was used to explain the antifriction mechanism of the graphene additive on the Si3N4-GCr15 friction pair.The research contents and results are as follows:(1)Based on the multi-functional friction and wear tester,the effects of graphene content,Pressure and shear velocity on the friction characteristics of Si3N4-GCr15 friction pair were investigated.The results show that when the pressure is large and the shear velocity is large,the lubricating oil with a graphene molar mass of 2.5%has a good lubricating effect.(2)A molecular dynamics model of the lubricating body is established.It is assumed that the main component of the lubricating oil is n-hexadecane(C6H.2),and graphene is added to form a lubricating body.A two-layer molecular model between the lubricating body and silicon nitride(Si3N4)(or bearing steel(GCr15))is established to calculate the adsorption energy between the lubricating body and Sb3N4 or between the lubricating body and GCr15.The changes of adsorption energy between the lubricating body and Si3N4 or between the lubricating body and GCrls before and after graphene addition is analyzed.The results show that the adsorption energy between the lubricating body and Si3N4 or between the lubricating body and GCrls increases after the addition of graphene,which proves that graphene has good adsorption.(3)A three-layer molecular model along GCrls,lubricating body and Si3N4 is established to investigate the influence of different graphene molar mass fraction on the lubrication and friction of Si3N4-GCrl 5 friction pair by confined shear motion.The results show that the friction is minimum when graphene molar mass is 2.5%and the appropriate graphene content can achieve the best lubrication effect.(4)The molar mass of graphene was fixed at 2.5%to analyze the influence of different pressures and shear velocities on the lubrication characteristics of van der Waals,shear stress and the solid film thickness in Si3N4-GCr15 friction pair.The results show that graphene as an additive can increase the van der Waals and the solid film thickness in the lubrication region and reduce the shear stress.(5)A three-layer molecular model of GCrls,lubricating body and Si3N4 was used to investigate the antifriction mechanism of graphene additive to Si3N4-GCr15 friction pair.The results show that the solid film formed on the surface of Si3N4 and GCrls can reduce the shear stress and reduce the friction force. |
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