Tribological Characterisation Of The Solid-Liquid Interface For Magnetic Fluid Lubrication

As one of the important basic components,bearing is great important to the development of high-end equipment,marine ships and offshore wind power and other fields.Due to the continuous innovation of industrial technology,the requirements of mechanical equipment for lubricant lubrication performance are increasing.Traditional lubricants in the application of advanced equipment have many shortcomings such as high pollution,non-adjustable viscosity and insufficient material stability.It is difficult to meet the requirements of precision for high reliability,high precision and non-pollution of bearings.With the rapid development of nanotechnology,the magnetic liquids containing magnetic nanoparticles as lubricants have attracted more and more attention in the field of high-end equipment.Magnetic nanoparticles in magnetic fluids can transform sliding friction between frictional contact surfaces into a mixed friction of sliding and rolling,which not only helps to improve the lubricant’s lubrication performance between frictional subsets,but also fills the pits and scratches on the contact surface to protect the friction surface.Therefore,in order to better understand the working mechanism of the friction reduction and anti-wear effect of magnetic fluids,this paper investigates the tribological characteristics of the solid-liquid interface of magnetic fluid lubrication by preparing oil-based magnetic fluids as follows:The effect of magnetic particle content on the lubrication performance of the solid-liquid interface of magnetic liquids was investigated by simulations using molecular dynamics methods,and the magnetic liquid model with different volume fractions of Fe₃O₄ was established respectively to construct the lubrication model of the solid-liquid interface of magnetic liquids.In order to ensure the stability of the simulation process,the structural and energy optimisation of the constructed model was carried out,and the simulation of the established lubrication model was carried out after the completion of the optimisation.The effect of the variation of magnetic particle content on the lubrication performance of magnetic liquids was investigated at the microscopic level through the simulations,and the mechanism of the tribological behaviour of the solid-liquid interface of magnetic liquids was revealed.The oil-based magnetic fluid was prepared by a two-step method,and the distribution,morphology and particle size of the magnetic particles were analysed,showing that the Fe₃O₄ nanoparticles were sphere-like in appearance and relatively uniformly dispersed,with an average particle size of 14.3 nm.Characterisation of the stability and magnetisation properties of the magnetic liquids with different mass fractions showed that the magnetic liquids were superparamagnetic and could maintain good dispersion over a certain period of time,with no significant delamination observed.The tribological properties of the prepared magnetic fluid were investigated by using multi-functional tribological and wear test instrument,and the friction and wear behaviors of oil lubrication and magnetic fluid were compared.The worn surface was analyzed by scanning electron microscope and ultra-depth of field 3D microscopy,and the wear mechanism was studied.In order to investigate the effect of external magnetic field on the friction behavior of magnetic liquid,Nd Fe B permanent magnet was selected as the magnetic source to investigate the frictional wear performance of magnetic fluids with and without magnetic field.Based on the Box-Behnken response surface design,the tribological performance of magnetic fluid lubrication under the effect of different factors（magnetic particle mass fraction,magnetic field strength and load）was studied.The effects of mass fraction,magnetic field strength and load on the mean friction coefficient were assessed using response surface analysis and a mathematical regression model of the mean friction coefficient was developed by ANOVA.