Study On Friction-Reduction & Anti-Wear And Vibration & Noise Suppressing Properties Of Nitrogen Doped Graphene Lubricant Additives

With the advancement of modern industry,the construction machinery is increasingly subjected to extreme working conditions,consequently,the requirements for lubrication between mechanical components are becoming progressively more critical.Graphene,as a two-dimensional nano material with excellent properties such as high mechanical strength,has attracted attention in the field of lubrication.It has been shown that the tribological properties and even other performance of graphene can be further improved by structural design or structural modification to meet different applications.Therefore,this study focuses on nitrogen-doped graphene nano additives to explore their tribological properties and vibration and noise reduction performance under low-speed and heavy-duty conditions,as well as to reveal the corresponding lubrication and vibration and noise reduction mechanisms.In this work,the tribological properties of 3D HPG,MWCNT and mixed nanoparticles of both in castor oil are investigated under heavy load conditions.The characterization results for steel wear marks show that the friction-reduction and anti-wear properties of the hybrid nano lubricant could be improved by 26% and 48% respectively(4 Hz-2.7 GPa).The mechanism of synergistic lubrication is that the multi-walled carbon nanotube nanoparticles form a smoother friction surface by filling the grooves and pits,making it easier for the suspended 3D HPG nanoparticles to adsorb into the rubbing interface to form a protective film.3D HPG is disintegrated into a 2D graphene flake structure,resulting in a 2D graphene nanosheet/multi-walled carbon nanotube/2D graphene nanosheet composite structure.The "rolling bearing" effect of this composite structure significantly reduces friction and wear on the friction surfaces.Secondly,it is investigated the effect of common graphene and nitrogen-doped graphene nano additives on the tribological properties of PAO6 base oil under high temperature conditions.The experimental data from the analysis of wear marks by means of the characterisation instrument indicate that the friction-reduction and anti-wear performance of PAO 6 base oils at100°C are improved by 22.4% and 56.9% in the case of 0.4 wt%nitrogen-doped graphene concentration,respectively.The introduction of nitrogen element enhances the adsorption properties of nitrogen doped graphene in high temperature environments.In addition,the filling effect of the nitrogen-doped graphene results in a flat friction surface,which greatly reduces the collision between the micro bumps on the friction surface.The smooth friction surface and the ordered few-layer structure facilitate the inter-layer slip of nitrogen-doped graphene sheets along the parallel motion direction.Finally,the effect of nitrogen-doped graphene/C60 hybrid nano additives on vibration and noise reduction performance is also investigated.The underlying relationship between wear and vibration and noise reduction properties is analysed from a tribological point of view.The evaluation of the wear and vibration signals demonstrates that the nitrogen-doped graphene/C60 hybrid nanoparticles exhibit excellent tribological properties.The corresponding friction-reduction and anti-wear properties are enhanced by60% and 57% respectively.The friction-induced vibration signal(root mean square value of Z-axis acceleration)and noise sound pressure level(d B(A))are reduced by 81% and 19% accordingly.On the one hand,the adsorption effect of nitrogen-doped graphene and the filling effect of C60 decrease the frequency of direct collisions between surface grooves and microbumps during motion,thus indirectly suppressing friction-induced vibration and noise;On the other hand,the sandwich roller bearing structure formed by nitrogen-doped graphene and C60 hybrid nanoparticles can play a buffering role,greatly reducing the noise caused by adhesion and abrasive wear.In summary,nitrogen-doped graphene nanoparticles can improve the tribological properties of base lubricant.In addition,it exhibits excellent vibration and noise reduction properties as well,which holds a broad prospect in the field of engineering lubrication.