The Adsorption Mechanism Of Cu Nano-additives And Its Influence On Tribological Properties

Additives will interact with the surface of the friction pair through physicochemical adsorption or tribochemical reaction to achieve the purpose of reducing friction and abrasion under boundary conditions.However,regardless of the formation of an adsorption film or a friction reaction film,the adsorption of additives on the surface of the friction pair is the prerequisite and basis for lubrication.With the rapid development of new lubricating materials,nano-additives have exhibited unique and outstanding lubricating properties such as ultra-slip,extreme pressure,and self-repair.However,the adsorption behavior of nanoadditives in oil systems is different from the behavior of small molecules and aqueous solutions,and will be affected by many factors such as surface properties,particle size and so on.At the same time,new types of friction pair materials are constantly emerging.How to properly design and optimize the shape,size and surface properties of nano additives for different friction pair materials to achieve the efficient application of nano additives? At present,there is still a lack of the study of adsorption characteristics for nano additives.Therefore,this study takes Cu nano-additives as the research object,systematically studies the adsorption behavior and tribological properties of Cu nano-additives with different surface properties and agglomerated particle sizes on the surfaces of metal and DLC film friction pairs in an oil lubrication system.Reveal the law of nanoparticle adsorption rate,equilibrium adsorption quality and other adsorption characteristics on its tribological performance,establish realistic friction mechanism models,quantitatively explore the impact of nano-additives adsorption characteristics on the boundary friction performance in oil lubrication system and to establish its structure-effect relationship.The main research contents and results are as follows:(1)Adsorption behavior and tribological mechanism of Cu nano-additives on metal surfaceThe Cu nano-additives with a particle size distribution of 4,5 nm were treated by the solvent induction method to change their surface properties and agglomeration particle size distribution.On the premise of ensuring the stable dispersion of Cu nano-additives in dodecane,as the induced solvent polarity increases,the surface potential of Cu nano-additives increases from-103 m V to-246 m V,and the zeta potential change from-1.7 m V to-9.6 m V,and the maximum agglomeration particle size increased from 6 nm to 60 nm.For Cu nano-additives with the same surface potential,the agglomeration particle size in oil increased with increasing concentration.Quartz crystal microbalance(QCM-D)was used to study the effect of the surface potential and agglomeration size of Cu nano-additives on their adsorption behavior and tribological properties on the surface of metal friction pairs.The results show that the adsorption mass of Cu nanoadditives on the surface of the metal friction pair is only related to the surface potential when the agglomeration particle size is the same.The higher the surface potential,the greater the electrostatic attraction,and accordingly the greater the equilibrium adsorption mass;When the surface potential is the same,as the agglomeration particle size increases,the fluid driving force received increases,resulting in a decrease in the adsorption mass.Finally,Cu nano-additives with agglomeration of 20 nm and surface potential of-246 m V have the maximum equilibrium adsorption mass on the metal surface.The tribological properties of dodecane lubricants with different surface properties and concentrations of Cu nano-additives in a steel/steel(GCr15 steel)friction partner system were studied using a friction and wear tester(UMT).tudies have shown that the addition of Cu nano-additives reduces the friction coefficient of the system by 35% and the wear rate by nearly 36%.The anti-friction mechanism is that Cu nano-additives form a rich lubricating film on the steel surface to reduce the adhesion wear between friction pairs.The tribological properties of Cu nano-additives have a good consistency with their adsorption behavior.When the adsorption mass of Cu nano-additives is larger,the wear rate of GCr15 steel is lower.When lubricant with agglomeration particle size of 20 nm and surface potential of-246 m V Cu nano-additives is added,the minimum wear rate of GCr15 steel reaches 6.73×10-6 mm/(N·m);In addition,the greater the adsorption rate of Cu nano-additives,the shorter the run-in period of the lubrication system,and the easier the friction to reach a stable state.(2)Study on the adsorption behavior and tribological mechanism of Cu nano-additives on the surface of carbon filmUsing QCM-D to study the influence of the surface potential and agglomeration size of Cu nano-additives on their adsorption behavior and tribological properties on DLC surface.Studies have shown that the increase of oxygen-containing groups on the surface of DLC is beneficial to the adsorption of Cu nano-additives on the surface of DLC.The hydroxyl group and polar polar groups on the surface of DLC have a weaker dipole effect on Cu nano-additives than on the metal surface.Electrostatic attraction makes its equilibrium adsorption quality on the DLC surface lower than the metal surface.For the same DLC surface,the adsorption law of Cu nano-additives on the DLC surface is consistent with the adsorption behavior on the metal surface.The higher the surface potential of Cu nano-additives,the greater the corresponding equilibrium adsorption mass;when the surface potential is the same,with the agglomeration particle size increase,the equilibrium adsorption mass decreases.When the surface potential is the same,as the agglomeration particle size increases,the equilibrium adsorption mass decreases.t was also found that the adsorption behavior of Cu nano-additives on the DLC surface is consistent with its tribological properties.As the equilibrium adsorption mass of Cu nano-additives on the surface of DLC increases,the wear rate of DLC first decreases and then tends to a constant value.The analysis of the friction mechanism shows that when the equilibrium mass of Cu nanoparticles reaches 3000 ng/cm2,the adhesive wear between DLC and GCr15 can be completely isolated,and the surface of DLC can be graphitized,thereby reducing wear.Since the solid lubrication mechanism of DLC is not changed,although the equilibrium adsorption mass of Cu nano-additives is further increased,the wear rate remains constant.Therefore,Cu nano-additives and DLC produce a synergistic lubrication mechanism,which promotes the saturation value of Cu nano-additives on the wear resistance of DLC/dodecane solid-liquid composite lubrication system.In the DLC solid-liquid composite lubrication system,the compound tribological properties of Cu nanoadditives and various commercial additives such as antifriction agents,antiwear agents,antioxidants,dispersants,detergents,viscous agents,etc.were studied.By improving the surface properties of Cu nanoadditives,it was found that high surface potential Cu nano-additives can better overcome the competitive adsorption problem of detergents and dispersants,and the antiwear performance of commercial carbon film engine special lubricants has been improved by nearly 30%.