Tribological Properties of Few-layer Graphene Oxide Sheets as Oil-Based Lubricant Additives

The performance of a lubricant largely depends on the additives it involves. However, currently used additives cause severe pollution if they are burned and exhausted. Therefore, it is necessary to develop a new generation of green additives. Graphene oxide（GO） consists of only C, H and O and thus is considered to be environmentally friendly. So the tribological properties of the few-layer GO sheet as an additive in hydrocarbon base oil are investigated systematically. It is found that, with the addition of GO sheets, both the coefficient of friction（COF） and wear are decreased and the working temperature range of the lubricant is expanded in the positive direction. Moreover, GO sheets has better performance under higher sliding speed and the optimized concentration of GO sheets is determined to be 0.5wt%. After rubbing, GO is detected on the wear scars through Raman spectroscopy. And it is believed that, during the rubbing, GO sheets adhere to the sliding surfaces, behaving like protective films and preventing the sliding surfaces from contacting with each other directly. This paper proves that the GO sheet is an effective lubricant additive, illuminates the lubrication mechanism, and provides some critical parameters for the practical application of GO sheets in lubrication.

Lubrication properties of Nitinol 60 alloy used as high-speed rolling bearing and numerical simulation of flow pattern of oil-air lubrication

The friction and wear tests were performed using Nitinol 60 alloy pin sliding over GCr15 steel disk in a pin-on-disk tribometer system under PAO oil lubrication conditions. It was found that Nitinol 60 alloy can be lubricated well and has shown remarkable tribological performance. Average coefficient of friction （COF） of Nitinol 60 is 0.6 under dry friction; however, average COF decreases to 0.1 under PAO oil lubrication. SEM image of the worn surface shows that Nitinol 60 exhibits excellent wear resistance and the wear mechanism is mainly adhesive wear. Flow pattern of oil-air flow in oil pipe was simulated by FLUENT software with VOF model for acquiring working performance of oil-air lubrication. The optimum velocity of oil and air at the inlet was achieved, which provides the great proposal for the design of experiment of oil-air lubrication of Nitinol 60 alloy. The simulation results showed that the optimum annular flow of flow pattern was obtained when air velocity is 10 m/s and oil velocity is 0.05 m/s. The formation mechanism of annular flow was also discussed in the present study.

Analysis of Properties of Thrust Bearing in Ship Propulsion System

Thrust bearing is a key component of the propulsion system of a ship. It transfers the propulsive forces from the propeller to the ship＇s hull, allowing the propeller to push the ship ahead. The performance of a thrust bearing pad is critical. When the thrust bearing becomes damaged, it can cause the ship to lose power and can also affect its operational safety. For this paper, the distribution of the pressure field of a thrust pad was calculated with numerical method, applying Reynolds equation. Thrust bearing properties for loads were analyzed, given variations in outlet thickness of the pad and variations between the load and the slope of the pad. It was noticed that the distribution of pressure was uneven. As a result, increases of both the outlet thickness and the slope coefficient of the pad were able to improve load beating capability.

Microstructure and wear properties of the electroslag remelting layer reinforced by TiC particles

The electroslag remelting （ESR） layer reinforced by TiC particles was obtained by electroslag remelting. The microstructure and wear properties of the ESR layer were studied by means of scanning electron microscopy （SEM）, X-ray diffraction （XRD）, and wear test. The results indicate that TiC particles are synthesized by self-propagating high-temperature synthesis （SHS） reaction during the electroslag remelting process. The size of TiC particles is in the range of 1-10 μm, and the distribution of TiC particles is uniform, from outside to inside of the ESR layer, and the volume fraction and the size of TiC particles decrease gradually. Molten iron and slag flow into porosity due to the SHS process leading to rapid densification and the elimination of porosity in the ESR layer during the ESR process. TiC particles enhance the wear resistance of the ESR layer, whereas CaF2 can improve the high temperature lubricating property of the ESR layer.

Study on Lubrication Properties of Modified Nano ZnO in Base Oil

ZnO nanoparticles with an average size of 125 nm were prepared via homogeneous precipitation method and were characterized by SEM.The products were surface-modified by the surfactant SDS.Surface-modified nano particles were added at a mass ratio of 1.0%,2.0%,3.0%,and 4.0%,respectively,in base oil and their friction and wear behaviors were evaluated on a MRS-10D type four-ball wear tester.After four-ball wear tests,the morphology of the rubbing surfaces was evaluated with metallographic microscope.It was revealed that the modified nano ZnO had excellent behavior for improving anti-wear property and friction coefficient,which could greatly reduce the friction of machine parts.

THE LUBRICATING PROPERTIES OF ION-PLATING FILMS OF Pb-Sn ALLOY

Experimental results of the lubricating behaviour of Pb-Sn alloy films formed by ion-plating on brass substrates are given. It is shown that the film microhardness, friction coefficient and wear life per thickness are under the influence of the substrate. The wear failure of film appears to be film adhesion and transferring by the mating surface.

Study on Tribology Performance of Different Lubricant Additives under Atmospheric Pressure and High Vacuum Conditions

By using PAO-10 as the base oil, the tribological behavior of 11 additives under high vacuum condition was evaluated. By adopting some surface analytical instruments, such as scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS) and X-ray photoelectron spectroscopy(XPS), the tribological mechanisms of these additives were studied. In air, O_2 can react with metal to form metal oxide that can protect the surfaces of rubbing pair during the tribological tests. According to the theory of the competitive adsorption, the function of some active elements is weakened. In a vacuum environment, the additives contributed more to the lubrication performance. The sulfur-containing additives could react with Fe to produce Fe Sx and "M—C" bonds("M" represents metal). They both had contributions to the lubrication. As for the phosphorus-containing additives, they only generated the phosphates during the tests. When the sulfur and phosphorus-containing additives were applied, the generated phosphates and Fe Sx had the primary contribution to the lubrication performance during the tests.

Assessment of Lubrication Property and Machining Performance of Nanofluid Composite Electrostatic Spraying(NCES)Using Different Types of Vegetable Oils as Base Fluids of External Fluid

The current study of minimum quantity lubrication(MQL)concentrates on its performance improvement.By contrast with nanofluid MQL and electrostatic atomization(EA),the proposed nanofluid composite electrostatic spraying(NCES)can enhance the performance of MQL more comprehensively.However,it is largely influenced by the base fluid of external fluid.In this paper,the lubrication property and machining performance of NCES with different types of vegetable oils(castor,palm,soybean,rapeseed,and LB2000 oil)as the base fluids of external fluid were compared and evaluated by friction and milling tests under different flow ratios of external and internal fluids.The spraying current and electrowetting angle were tested to analyze the influence of vegetable oil type as the base fluid of external fluid on NCES performances.The friction test results show that relative to NCES with other vegetable oils as the base fluids of external fluid,NCES with LB2000 as the base fluid of external fluid reduced the friction coefficient and wear loss by 9.4%-27.7%and 7.6%-26.5%,respectively.The milling test results display that the milling force and milling temperature for NCES with LB2000 as the base fluid of external fluid were 1.4%-13.2%and 3.6%-11.2%lower than those for NCES with other vegetable oils as the base fluids of external fluid,respectively.When LB2000/multi-walled carbon nanotube(MWCNT)water-based nanofluid was used as the external/internal fluid and the flow ratio of external and internal fluids was 2:1,NCES showed the best milling performance.This study provides theoretical and technical support for the selection of the base fluid of NCES external fluid.

An inorganic–organic hybrid CQDs@PVP lubricant additive:Achieving low friction and wear in PEG and water

High-temperature lubrication has always been a hot topic in the lubricant and grease industry,and is also an essential concern in the high-end equipment sector to be addressed.Carbon quantum dots(CQDs)are an emerging material widely applied in the field of lubrication,owing to their exceptional lubricity and high load-bearing capacity.However,the vulnerability of CQDs to oxidation in air and reduced stability dramatically restrict their high-temperature application capability.In this study,a nanocomposite of amphiphilic polyvinyl pyrrolidone(PVP)homopolymer with excellent lubricating properties and thermal stability,which is hydrogen bonded to CQDs(CQDs@PVP),was designed to achieve low friction and wear of lubricants at high temperatures.The CQDs@PVP are consistently dispersed in both PEG400 and water,and exhibit superior lubricity compared to unmodified CQDs at high temperatures(ranging from 200‒150°C and 90‒50°C).Meanwhile,the dense carbon film on the wear surface and the chemically reactive film of iron compounds directly contribute to the enhanced lubrication performance.These analytical results demonstrate the powerful candidacy of CQDs@PVP as a lubrication additive and promote future high-temperature applications of CQDs in industrial production.

Preparation of tungsten disulfide motor oil and its tribological characteristics

Through using mineral oil and synthetic oil to deploy the semisynthesis base oil, modifying the surfaces of ultrafine tungsten disulfide grains by surface chemical embellishment and adsorption embellishment to make them suspended steadily in the base oil as solid lubricating additive, and adding some function additives, the tungsten disulfide motor oil was prepared. The tribological characteristics of this kind motor oil and the well-known motor oils in our country and overseas were studied. The results show that the oil film strength of this kind of motor oil is respectively 1.06 and 1.38 times of that of shell helix ultra motor oil and great wall motor oil, and its sintering load is 1.75 and 2.33 times of that of them, and when tested under 392 N, 1 450 r/rain and 30 min, the friction coefficients of friction pairs lubricated by the tungsten disulfide motor oil decrease with the increase of time, meanwhile, the diameter of worn spot is small, and the surface of worn spot is smooth, and no obvious furrows appear. The experiments indicate that the tungsten disulfide motor oil has the better antiwear, antifriction and extreme pressure properties than the well-known motor oils.

Thermal elastohydrodynamic lubrication of modified gear system considering vibration

The thermal elastohydrodynamic lubrication characteristics of a modified gear system under a dynamic load were investigated,including the influence of the modification coefficient and vibrations.Based on the dynamic theory of gear systems,a six-degree-of-freedom tribo-dynamics model was established.Thermal elastohydrodynamic lubrication characteristics of a modified gear system under vibrations and a static load were analyzed.The results showed that the positive transmission gear system exhibited the better lubrication effect compared with other transmission types.A thick lubricating oil film could be formed,and the friction coefficient between the teeth and the oil film flash temperature were the smallest.As the modification coefficient increased,the lubrication condition was continuously improved,and the scuffing load capacity was enhanced.The increment of the modification coefficient increased the meshing stiffness of the gear system but reduced the stiffness of the oil film.

Effects of Electropulsing Cutting on the Quenched and Tempered 45 Steel Rods

Electropulsing is introduced into the cutting process for quenched and tempered 45 steel, which is a novel method to improve the material machinability compared with the conventional cutting process. The effects of electropulsing on cutting performances, microstructure evolution, and surface qualities of 45 steel rods were studied. The results indicate that electropulsing is beneficial for the cutting process in 3 aspects as follows：（1） reducing the principal cutting force, surface microhardness and surface roughness of the machined sample dramatically;（2） improving the machining efficiency and prolonging the life of cutting tools;（3） decreasing the thickness of rheological layer which was usually caused by work hardening in the cutting process. The morphology and microstructure of the cutting chips showed that the length of the chips increased significantly with the increase of the current density. The advantage of electropulsing is that it can improve the plastic deformation capability as well as increase the lubricating property between the specimen and the cutting tool.

Comparison of Lubricities of Two Novel Benzotriazole Derivatives Used as Additives in Water-Glycol Hydraulic Fluid

Two kinds of benzotriazole derivatives with and without sulfur （abbreviated as BSC and BC, respectively,） were synthesized and their lubricating, anticorrosion and antirust properties were investigated, when they were used as additives in the water-glycol fluid. The morphology and chemical species of typical elements on the worn surface were examined by the scanning electron microscopy （SEM）, the energy dispersive spectrometry （EDS）, and the X-ray photoelectron spectroscopy （XPS） in order to reveal the tribological mechanisms. The results indicated that two synthesized additives could effectively improve the anti-wear, friction-reducing, load-carrying, anticorrosion, and antirnst properties of the base fluid. The surface analysis illustrated that stable nitrogen-containing absorption films generated by BC should be responsible for its facilitated anti-wear and friction-reducing performance, and the excellent lubricities of BSC should be attxibuted to the combined action of adsorption film and tribo-chemical film which were composed of iron oxides, iron sulfides and iron sulfates. The superior lubricating properties of BSC as compared to that of BC demonstrated the effectiveness of elemental sulfur in reducing friction and wear, especially under high loads. But corrosion wear is more obvious at a relative high concentration of elemental sulfur.

A Simple Way to Prepare Silicon Carbide Reinforced Graphite Composite Lubricating Materials

SiC reinforced graphite composites were prepared via introducing carbide silicon into the natural graphite flakes（NGF） by hot-pressing process. Their physical and mechanical properties, including density, open porosity, flexural strength, and friction behavior were investigated. The addition of 30vol% Si C increased the bending strength of composites materials to 127 MPa, 2 times higher than 60 MPa of commercial pure graphite block. What was particularly interesting was that the as-obtained graphite composite with 30vol% Si C kept the same low friction coefficient of about 0.1 as pure graphite, and the wear resistance of composites increased.

Effects of pore size on the lubrication properties of porous polyimide retainer material

An oil-impregnated porous polyimide(PI)retainer is used in space rolling bearings to improve the lubrication performance,which depends on the release of lubricant from the pores,and therefore is closely related to the pore size.To study the effect of pore size,in this work,PI materials with different pore sizes were prepared by preheating the retainer tube billet during the limit pressing process,and then the friction tests were conducted with the ball-on-ring mode.The results show that the applied load deforms the pores,allowing the lubricant to be squeezed out from the pore;the centrifugal effect induced by rotation also makes the lubricant migrate out of the pore.Therefore,for the same pore sizes,the friction coefficients decrease with the increasing loads and rotation speeds.In addition,it was found that there exists an optimal pore size for the best lubrication properties of porous PI material.Furthermore,the optimal pore size should be larger for lubricants with high viscosity.The microscopic mechanism for lubricant outflow from pores is clarified by molecular dynamic simulations.The insights gained in this study can guide the preparation of oil-impregnated porous retainers under different working conditions.

Synthesis of Fullerene-Acrylamide Copolymer Nanoball and Its Lubrication Properties

A novel fullerene-acrylamide copolymer was synthesized via radical polymerization. It is soluble in polar sol- vents such as water, dimethyl sulfoxide etc. The product was characterized by FTIR, UV-Vis and GPC. TEM analy- sis shows that the average particle diameter is about 46 nm. Four-ball tests show that the addition of a certain con- centration of the fullerene copolymer to base stock (2 wt% triethanolamine and 0.5 wt% OPZ aqueous solution) can effectively raise the load-carrying capacity (PB value) and the antiwear ability. SEM analysis shows that the addition results in reducing diameter of wear scar and decreasing wear.