Anti-friction Effect Research Articles

Frictional Performance of an Ionic Liquid/Graphene Composite Additive in Lubricating Oil

In this study, we used a four-ball friction and wear testing machine to test the tribological properties of [HPy]BF4 ionic liquids (ILs), low-layer graphene (G), and IL and G compounds (IL/G) as lubricant additives at variousconcentrations, loads, and speeds. The morphology of the wear scar was characterized by a white-light interferometer and a scanning electron microscope (SEM). The results showed that the optimal concentrations of IL and G were 0.10[Formula: see text]wt.% and 0.05[Formula: see text]wt.%, respectively. When the IL concentration was 0.10[Formula: see text]wt.%, the friction coefficient and the wear scar diameter (WSD) reduced by approximately 18% and 8%, respectively, compared to the base oil. When the concentration of G was 0.05[Formula: see text]wt.%, the friction coefficient and WSD reduced by approximately 23% and 12%, respectively, compared to the base oil. After adding the optimal concentration of the IL/G composite additive under the same test conditions, the average friction coefficient of the steel ball reduced by approximately 30%, and the average WSD reduced by approximately 18%. IL/G nanoadditives could be easily attached to the pit area on the friction surface of the steel ball, which made the contact surface of the friction pair smoother and the area of the oil film bearing the load larger, compared to those using the base oil. These two combined phenomena promoted synergistic antifriction and antiwear effects, which significantly improved the frictional performance of the base oil.

Characterization and Tribological Performances of Graphene and Fluorinated Graphene Particles in PAO.

Graphene has been widely used as a lubricating additive to reduce the energy consumption of engines and improve fuel economy because of its unique crystal structure. Herein, graphene (GR) and fluorinated graphene (F-GR) nanoparticles were prepared by ball milling and liquid-phase exfoliation. The SEM/EDS, HRTEM, XPS, Raman spectrometer, X-ray spectrometer, FTIR were used to investigate the morphologies, surface groups, and crystal structure of two kinds of graphene materials. The influence of loads on the tribological properties of two kinds of particles was investigated in Poly Alpha Olefin (PAO6) using a UMT-2 reciprocating tribometer. Results showed that the crystal structure of GR is better than F-GR. F-GR can improve the lubrication performance of PAO6. For PAO6 containing 1 wt% F-GR at 10 N, the average friction coefficient and average wear rate decreased by 12.3% and 87% relative to pure PAO6, respectively. However, the high load resulted in an inconspicuous anti-wear and anti-friction effect. The influence of F-GR on the tribological behavior of PAO6 was more substantial than that of GR. The friction and wear mechanisms attributed to F-GR quickly entered the interface between the friction pairs. Friction-induced F-GR nanosheets mainly took the tribo-chemical reactions to participate in the lubrication film formation and helped achieve a low friction coefficient and wear rate.

Coating-thickness-dependent physical properties and cutting temperature for cutting Inconel 718 with TiAlN coated tools

IntroductionCoating-thickness-dependent physical properties can induce different cutting temperatures with physical vapor deposition (PVD) titanium aluminum nitride (TiAlN) ceramic-coated tools. The determination of the optimal TiAlN coating thickness is important to obtain superior coating physical properties and decrease the cutting temperature of Inconel 718 alloy. ObjectivesThe present study investigates the effects of coating thickness on the physical properties of TiAlN coatings and the cutting temperature during the machining of Inconel 718 alloy. The optimal coating thickness is also determined. MethodsFirst, the direct-current-arc method was utilized to deposit PVD Ti0.55Al0.45N coatings with thickness of 1.6 µm, 2 µm, 2.5 µm, and 3 µm, onto a cemented carbide substrate. Second, the coating-thickness-dependent physical properties were characterized and estimated with a radar chart. Third, the effects of coating thickness on coating antifriction were analyzed with the tool-chip friction coefficient when cutting Inconel 718 with PVD TiAlN coated tools. Both the maximum cutting temperature generated in the chip and the cutting temperature of the tool bodies were measured for analyzation of the thermal barrier effect of coating. Finally, the topographies of the deformed chip and tool-chip contact area were obtained and investigated to determine the effects of coating thickness on the cutting temperature. ResultsThe tool-chip friction coefficient and coating thermal barrier effect were affected by the coating thickness. Ti0.55Al0.45N coated tools with moderate coating thickness had fine antifriction effect with Inconel 718. The thermal barrier effect of Ti0.55Al0.45N coating was positively related to the coating thickness. ConclusionsThe optimal TiAlN coating thickness was determined as 2 μm, which resulted in superior physical properties and reduced the cutting temperature of Inconel 718.

Research progress of nano lubricating additives

Nano-materials are ultra-fine materials with nano-sized particles, and their unique structure also makes nano-materials have different physical and chemical properties. Nano-materials can be added to a variety of lubricants, play a good anti-wear and anti-friction effect, and can be used in many fields, such as bearing lubrication, gear transmission, cutting processing. At present, the types of nano-lubricating additives include metal element nanoparticles, oxide and hydroxide nanoparticles, nano-carbide and its derivatives, nano-sulfide, nano-rare-earth compound, nano-boron series, polymer nano-beads, etc. This article reviews the research status of nano lubricating additives.

Preparation, characterization and tribological properties of coal indirect liquefied diesel soot modified by oleylamine

Coal indirect liquefied diesel soot (Fischer-Tropsch synthesis diesel soot, F-T DS) was collected by burning coal indirect liquefied diesel (F-T Diesel) with a self-made soot trap device in the laboratory. F-T DS was modified with oleylamine modification method to obtain oleylamine modified F-T DS (F-T DS-OLA). The effect of 10# white oil with F-T DS or F-T DS-OLA on the lubrication performance was investigated using a long-time four-ball friction and wear tester. The composition, structure, morphology and tribological mechanism for F-T DS and F-T DS-OLA had been studied by using FTIR, XPS, Raman, XRD and other instruments. The results show that F-T DS modified by oleylamine can increase lipophilic groups. The average particle size of F-T DS and F-T DS-OLA are 64 nm and 38 nm respectively. The main structure component is amorphous carbon with a small amount of graphite crystallites. The average friction coefficient (AFC) first decreases and then increases as the mass fraction of F-T DS and F-T DS-OLA increases in 10# white oil. When the mass fraction of F-T DS is 0.6 wt%, the AFC reaches the minimum, and the AFC reaches the minimum when the mass fraction of F-T DS-OLA is 0.8 wt%. The average wears scar diameter (AWSD) of the steel ball also decreases first and then increases. F-T DS reaches the minimum at 0.6 wt%, and F-T DS-OLA reaches the minimum at 0.8 wt%. Comprehensive AFC and AWSD analysis, the antifriction and anti-wear effect of F-T DS is greatly improved after oleylamine modified. Through the analysis of the surface morphology of the upper ball wear scar and valence state of the surface elements, it can be obtained that the wear scar of the upper test ball becomes shallow after adding F-T DS-OLA. A lubricating film containing C, O and iron oxides is formed on the surface, which can improve the antifriction and anti-wear effects of 10# white oil.

Influence of Mo Doping on the Microstructure, Friction, and Wear Properties of CrAlN Films

In this study, closed-field unbalanced magnetron sputtering ion-plating technology is used to deposit CrAlMoN and CrAlN nanomultilayer films on the surfaces of M2 tool steel and single-crystal Si. Energy-dispersive spectroscopy, scanning electron microscopy, x-ray photoelectron spectroscopy, transmission electron microscopy, x-ray diffraction, scratch tester, nanoindenter, and pin-on-disk wear tester are used to study the influence of Mo doping on the composition, microstructure, mechanical properties, and friction properties of CrAlN films. Results show that CrAlMoN films have a nanomultilayer structure, CrN/Mo2N/CrN/AlN, with a modulation period of 10.5 nm. After Mo doping, the face-centered cubic structure of CrAlMoN films remains the same as that of CrAlN films. The chemical valence of each element in CrAlN films does not change with Mo doping. At room temperature, the wear resistance of CrAlMoN films is significantly improved compared with that of CrAlN films. This is attributed to the significant antifriction effect of MoO3 that forms on CrAlMoN films doped with Mo during the friction process.

Tribological properties and releasing behavior of solid lubricant WS2 in the dimples on cylinder liner surface of diesel engine

Modified WS2 by silane coupling agent were encapsulated in the dimples fabricated on the surface of cylinder liner samples by hot-pressing method. The tribological properties, anti-adhesion performance of the samples as well as the releasing behavior of modified WS2 in the dimples were tested by a reciprocating tribotester. Moreover, the anti-erosion performance of modified WS2 was examined by ultrasonic vibration test. The results indicate that the composite lubrication structure has good anti-friction and anti-adhesion effects. Furthermore, the release rate of WS2 in the dimples is decreased by 102.2% due to the introduction of silane coupling agent. Additionally, the synergistic effect among the dimples, the solid lubricant and the silane coupling agent can explain the anti-friction and sustained release mechanisms.

Effect of ambient temperature on the formation mechanism of PTFE liner transfer film of spherical plain bearings

The relationship between the formation of the transfer film and the tribological properties of the self-lubricating spherical plain bearing was studied at the ambient temperature of 25–145 °C. The results show that the wear, friction coefficient and friction temperature increase of the spherical plain bearings all decreased first and then increased with the increase of the ambient temperature. The general trend is that the bearing has the most excellent anti-friction and wear resistance at 55–85 °C. An increase in ambient temperature will accelerate the formation speed of PTFE transfer film and shorten the running-in period of the bearing, but the ambient temperature above 85 °C will shorten the duration of the PTFE transfer film, thus accelerating the bearing into the degradation period. The transfer film coverage of the liner after wear was characterized, and it was found that the transfer film coverage was the largest when the ambient temperature was 85 °C. The wear form of the bearing is mainly abrasive wear and adhesive wear, and the aramid fiber is more prone to adhesive wear. The anti-friction effect of the bearing is determined by the PTFE transfer film. Elevated ambient temperature can promote the formation of PTFE transfer film and enhance the antifriction effect, but if the ambient temperature is too high, the wear resistance of the PTFE transfer film will be reduced, thus reducing the friction reduction effect.

Mathematical regularities of the sliding friction process of a porous material based on iron impregnated with lubricating oil with dispersed particles of fluorinated graphene

The paper presents the results of a study of the sliding friction process of a porous material based on iron impregnated with lubricating oil with dispersed particles of fluorinated graphene. It is established that the regularities of the kinetics of external sliding friction have a sigmoidal and sigmoidal-linear character. Experimental results have been obtained showing that with an increase in the concentration of aggregates from flakes of fluorinated graphene in the lubricating oil, the average force and coefficient of friction decrease, while a good anti-friction effect is observed.

Mathematical regularities of changes in the characteristics of the friction process of a porous composite material based on copper containing oil with graphene particles

The paper presents the results of a study of the sliding friction processes of a porous copper-based material impregnated with lubricating oil with dispersed particles of fluorinated graphene. Mathematical regularities of changes in the characteristics of the friction interaction are established. It is shown that the regularities of changes in the average friction force have a sigmoid-step character. Experimental results have been obtained showing that with an increase in the concentration of aggregates from flakes of fluorinated graphene in the lubricating oil, the average friction force and coefficient of friction decrease, while a good anti-friction effect is observed. It is shown that the average work of the friction force, and consequently the energy losses due to friction, when adding 0.01% of aggregates from fluorinated graphene flakes to the lubricating oil decreases by 3721 j, and when adding 0.1% — by 4098 j. It was found that the average coefficient of friction when adding 0.01% of fluorinated graphene flake aggregates to the lubricating oil decreases by 27%, and when adding 0.1% — by 30%.

Influence of Different Surface Texture Parameters on the Contact Performance of Piston Ring‐Sleeve Friction Pair of Hydraulic Cylinders

The surface texture, a major way to decrease friction and wear of the cylinder‐piston ring friction pair, was conducted on cylinder‐piston ring friction pair specimen using the orthogonal experimental design method to investigate the effect of different texture parameters (size, depth, shape, and surface density) of the friction and wear characteristics. Through simulation analysis, the texture parameters that affect the friction and wear characteristics are obtained. Using the evaluation method of friction coefficient and mass wear rate, the influence sequence and optimal values of texture parameters that affect friction and wear characteristics are obtained through range analysis. The results show that, after surface texture treatment under mixed lubrication conditions, the friction characteristics of the friction pair have changed and the friction coefficient and friction and wear rate have been significantly reduced. The results show that the triangular texture has a good antifriction effect, the texture depth is deepened, and the surface density and the size increases have a positive effect on the improvement of friction and wear. An ultra‐depth microscope was used to observe the wear morphology of the friction and wear tests. The results show that the weakening of the third body wear by the texturing treatment and the maintenance of oil lubrication are the main reasons for reducing friction and wear.

Friction properties of suspended graphene

Minimizing friction is a goal that has long been pursued in history. The role of micro-electromechanical system and nano-electromechanical system (MEMS/NEMS) in electronic devices is becoming more and more important. Due to the increasingly small size of the device, large surface-to-volume ratio leads to severe friction and wear problems of the device, thus limiting its performance. Graphene is considered as a good lubricating material in MEMS/NEMS due to its extremely thin size and excellent anti-friction effect. The study of nano-friction properties of graphene is of great significance in further developing the MEMS/NEMS. In this work, microporous arrays are prepared on a SiO<sub>2</sub>/Si substrate, and graphene is stripped on the micropores to form a suspension structure. The friction properties of suspended graphene and supported graphene are measured by using atomic force microscope. The results show that the nanofriction on suspended graphene is significantly reduced compared with that on supported graphene. The supported graphene experiences a frictional enhancement effect because of the puckering effect, while the friction enhancing effect disappears in the suspended graphene. With the increase of graphene thickness, the out-of-plane stiffness increases gradually, and the friction difference between suspended graphene and supported graphene decreases gradually. In addition, the nanofriction properties of suspended graphene under new tip and pretreated tip are also different. The friction between the pretreated tip and graphene is significantly higher than that between the new tip and graphene. The surface friction difference between the suspended graphene and the supported graphene decreases when the pretreated tip is used compared with the new tip. This work demonstrates that the deformability of atomic-scale structures can provide an additional channel of regulating the friction of contact interfaces. By comparing the changes of surface friction between the suspended graphene and the supported graphene with different thickness and tip sizes, the influence of out-of-surface deformation on the friction of graphene is revealed, thus providing theoretical guidance for effectively improving the friction performance of graphene solid lubricant.

ВЛИЯНИЕ ДВУХСЛОЙНОГО ПОКРЫТИЯ «АЛМАЗОПОДОБНЫЙ УГЛЕРОД + TIN/ ALTIN» НА ТРИБОЛОГИЧЕСКИЕ ХАРАКТЕРИСТИКИ МАСЕЛ ПРИ ГРАНИЧНОЙ СМАЗКЕ

The application of monocrystalline carbon to steel surfaces of rubbing bodies significantly increases the anti-friction and anti-wear properties of lubricants. (Research purpose) The research purpose is in choosing the optimal intermediate layer material based on the evaluation and comparison of the physical, mechanical and tribological characteristics of two-layer coatings obtained using titanium nitride and titanium aluminitride, respectively, as a solid intermediate layer, and compare them with each other. (Materials and methods) The cylindrical surfaces of 100Cr6 steel rollers with a diameter of 8 mm were coated with titanium nitride and titanium alumonitride, using the latest technologies, and on top of these coatings by pulsed condensation of carbon plasma with additional bombardment with argon ions - monocrystalline carbon. The micromechanical and microgeometric characteristics of the studied surfaces were evaluated using NanoScan-4D and SNeox devices. Pure base oil PAO-4, oil with the addition of oleic acid as a surface-active additive, and zinc dialkyldithiophosphate as a chemically active additive were used as a lubricant. (Results and discussion) The use of intermediate layers of titanium nitride and titanium aluminitride improves the adhesion of the carbon coating, which has a positive effect on its wear resistance. The main role in the antifriction effect of two-layer coatings is performed by a thin-layer carbon coating. (Conclusions) The article shows that the use of composite coatings from monocrystalline carbon + heat-resistant coating in friction units operating in the boundary lubrication mode serves as a reserve for improving the lubricating properties of oils, without requiring chemically active additives containing elements that negatively affect the environment. As an intermediate coating, the best result was shown by titanium aluminitride, it is more resistant to wear, and also provides lower friction.

Research on a New Type of Antifriction and Antiwear Cutting Fluid Based on Superlubricity Theory

Based on the superlubricity theory, a new type of cutting fluid with excellent anti-friction and anti-wear effects is developed. Using the existing superlubricity agent, several new environmentally friendly water-based cutting fluids have been formulated; Further, the high-speed cutting tests of a new type of cutting fluid were carried out for titanium alloy. Finally, a large number of comparative analyses were performed based on the test results. Studies have shown that the friction coefficient obtained using the cutting fluid with solid lubricant is generally large, however, the lower friction coefficient can be obtained when using the cutting fluid with glycerol-acid and hexadecyl dimethyl ammonium bromide, also the better cooling and lubricating effects were obtained.

Tribological performance of Mn3(PO4)2 coating and PC/MoS2 coating in Rolling–Sliding and pure sliding contacts with gear oil

The tribological performance of Mn.P coating and PC/MoS2 coating was investigated and compared with that of the reference steel (AISI52100) with different surface roughness. A mini traction machine and SRV tribometer were used to measure the COF under rolling–sliding and pure sliding conditions. Mn.P and PC/MoS2 exhibited a significant antifriction effect. The COF of the coated samples were less affected by the change in slide-to-roll ratio than that of the uncoated samples. As the wear time was prolonged, the running performance of the Mn.P coating improved relative to that of PC/MoS2. The effects of roughness, rolling speed and contact loads of coatings on wear mechanisms were discussed. Only one of the contact pairs treated with Mn.P coating showed improved tribological behaviour.

Preparation and tribological properties of micro-textured diamond/WSx coatings

Severe friction is the primary cause of fracture and delamination of diamond coating in tribological applications. Therefore, a surface technology is urgently needed to improve the tribological behavior of diamond coating. The synergistic antifriction effect of transition metal sulfides and texture can alleviate this issue. Micro-textures with precise parameters (width and area ratio) were prepared by Inductively Coupled Plasma Etching techniques (ICP) on the silicon substrate and then coated with diamond and WSx coating. The influence of texture parameters on friction under different normal loads was studied by orthogonal experiments. Results revealed that, compared with the width and load, the area ratio of the texture has a more significant influence on the friction coefficient. The textured diamond/WSx coating with the area ratio of 30% and width of 30 μm showed relatively low friction coefficient (~0.0457) under 5 N load. Then the reducing friction mechanism of the textured diamond/WSx coatings was analyzed based on the variation law of friction coefficient and wear marks. In addition, building on those tests an analytical model for the friction was developed to explain the differences in friction coefficient and predict the optimal texture parameters under different loading conditions.

Acoustic induced antifriction and its effect on thermo-mechanical behavior in ultrasonic assisted friction stir welding

The developed ultrasonic assisted friction stir welding (UaFSW) process can reduce the welding load and improve the joint quality, but the interaction mechanism between the exerted ultrasonic vibration and the thermo-mechanical behavior induced by friction stir welding is not yet elucidated. In this study, the classical Norton friction model is modified with the acoustic stress work, and the effect of ultrasonic vibration on the contact state at the tool/workpiece interface is analyzed. The relative velocity between the tool and its adjacent contacting material is taken as one of the main influencing factors to calculate the interfacial friction shear stress. A non-uniform interfacial friction model is combined with the modified constitution equation. And a fully coupled model of UaFSW process is developed to analyze the ultrasonic field, interfacial contact state, heat generation, plastic material flow and heat transfer phenomena. It is found that ultrasound can effectively reduce the interfacial friction stress, and this antifriction effect is more obvious in the welding direction which coincides with ultrasonic vibration. The ultrasound exerted along the radial direction of tool in UaFSW process results in acoustic softening of base material and friction reduction at the tool/material interface. Both effects change the heat generation, material flow and temperature field in UaFSW. Thus, the torque and traverse force are lowered with the ultrasonic induced reduction of interfacial stress, and the high quality of welds are obtained with the improvement of material flow. The model is experimentally validated by comparison of predicted and measured tool torque, heat input and thermal cycles.

Nano-Magnesium Silicate Hydroxide/Crumpled Graphene Balls Composites, a Novel Kind of Lubricating Additive with High Performance for Friction and Wear Reduction.

In this study, crumpled graphene balls (CGB), a kind of nano-material, was used as an additive to improve the tribological properties of base oil. Nano-magnesium silicate hydroxide (MSH)/CGB composites were prepared by ultrasound-assisted liquid-phase exfoliation. The loading of MSH significantly increased the number of pleats and reduced the lamellar thickness of CGB. Then, in order to improve the compatibility with the base oil, the MSH/CGB composites were decorated with oleic acid and stearic acid to get modified lipophilic composites (ML-MSH/CGB). The ML-MSH/CGB were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM). In addition, the tribological properties of the ML-MSH/CGB in base oils were investigated using a ball-on-disc setup tribometer. It indicated that the fantastic tribological behavior of the ML-MSH/CGB in base oil may contribute to a smaller and extremely wrinkled laminated structure. Furthermore, the base oil with 0.005 wt% ML-MSH/CGB composites exhibited the best anti-friction effect, and its average friction coefficient, wearing capacity and wear scar diameter were reduced by 25.4%, 22.1% and 16.7%, respectively. The introduction of ML-MSH/CGB composed materials is an excellent strategy to optimize the friction performance of lubricating oil.

An Innovative VCN Coating for High-Temperature Tribological Applications via Orthogonal Research

An innovative vanadium carbonitride coating with C element doped in a vanadium nitride (VN) matrix was developed on Inconel 718 and Si (100) substrates using a multi-arc ion plating technique. The micromorphology and microstructure of the as-deposited VCN coating were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The results show that the incorporation of C-dopant with the VN matrix can produce both sp2 C-C and sp3 C-C hybridized structures besides VC and VN phases. Furthermore, tribological testing was performed on a ball-on-disc tribometer with an Al2O3 ball as the counterpart. The main mechanisms of friction factors and C-dopant that affect the tribological properties of VCN coating were studied under some designed orthogonal parameters. The optimal solutions for VCN and VN coatings to attain the lowest friction coefficient and wear rate were suggested by orthogonal analysis, and the order of importance of friction factors that influence the tribological performance of VCN and VN coatings was clarified for each situation. In addition, the lubricant mechanisms of sp2 hybridized carbon and V2O5 crystal were focused on due to their special graphite-like structure as well as Magnéli phase, which can enhance the antiwear and antifriction effect of VCN coating under test conditions. Finally, the wear morphologies of all tested samples were observed by SEM, and the phase composition in the worn area was investigated by micro-Raman spectrometry.

Enhancing the tribological properties of boron nitride by bioinspired polydopamine modification

Boron nitride (BN) shows obvious anti-wear performance as additives in lubricants, ceramics and polymers, however, the strong interlayer interactions lead to the weak anti-friction effect compared to those of carbon-based materials. In this work, we obtained the hydroxylated BN (BNO) via annealing the bulk material in air at high temperature. Utilizing the self-polymerization reactions of dopamine (DA) on the hydroxyls of BNO, the polydopamine (PDA) modified BNO (BNO-PDA) was formed, which has a good dispersity in water. The tribological tests indicate that both the hydroxylation and PDA modification can effectively lower the coefficient of friction (COF) and wear rate of the BN as additives in water, but the letter seems to present lower COF values when the testing time is increased. We also studied the influence of polymerization time on the tribological behaviors of BNO-PDA, and it was concluded that the 6 h modification gained the lowest wear rate and the 24 h modification yielded the lowest average COF value. It is believed that the favorable tribological performance of BNO-PDA as additives in water lubrication is resulted from the improved dispersity and the formation of organic layers on the surface of BN.