Friction and Wear Phenomena of Vegetable Oil–Based Lubricants with Additives at Severe Sliding Wear Conditions

The tribological responses of palm oil and soybean oil, combined with two commercial antiwear additives (zinc dialkyl dithiophosphate and boron compound), were investigated at a lubricant temperature of 100°C and under severe contact conditions in a reciprocating sliding contact. The friction coefficient of palm oil with zinc dialkyl dithiophosphate was closest to the commercial mineral engine oil, with a 2% difference. The soybean oil with zinc dialkyl dithiophosphate produced a 57% improvement in wear resistance compared to its pure oil state. The existence of boron nitride in vegetable oils was only responsive in reduction of wear rather than friction. The response of commercial antiwear additives with vegetable oils showed a potential for the future improvement in the performance of vegetable oils.     

Improvement of tribological performance of steel by solid lubricant shot-peening in dry rolling/sliding contact wear tests

The effect of shot-peening treatment with the particulate MoS₂ solid lubricant on the wear resistance of steel in the dry rolling/sliding contact wear tests was investigated. The duplex shot-peening treatment with ceramic balls and the particulate MoS₂ solid lubricant provided excellent wear resistance under a severe loading and sliding condition because the uniform and minute surface roughness given by shot-peening treatment with ceramic balls could keep shot-peened MoS₂ particles with a low friction coefficient on the sample surface. Furthermore, the sample surface was covered with shot-peened MoS₂ particles by a MoS₂ layer formed during the rolling/sliding contact wear test.     

Tribological Behavior of Micrometer- and Submicrometer-Size Cenosphere Particulate-Filled Glass Fiber–Reinforced Vinylester Composites Under Dry and Water-Lubricated Sliding Conditions

In this work, the tribological behavior of micrometer and submicrometer cenosphere particulate–filled E-glass fiber–reinforced vinylester composites have been investigated on a pin-on-disc tester under dry sliding and water-lubricated sliding conditions. Three different uniform sizes of cenosphere particles (2 μm, 900 nm, 400 nm) were used as fillers in the glass fiber–reinforced vinylester composites. The weight fraction of cenosphere particles has been varied in the ranges from 5, 10, 15, to 20 wt%. The experimental results show that all of the composites exhibited lower coefficient of friction and lower wear resistance under water-lubricated sliding conditions than under dry sliding. It has been noted that the submicrometer size (400 nm) cenosphere particulates as fillers contributed significantly to improve the wear resistance. It has also been noted that 10 wt% of the cenosphere particles is the most effective in reducing the wear rate and coefficient of friction. Effects of various wear parameters such as applied normal loads, sliding speeds, particle size, and particle content on the tribological behavior were also discussed. In order to understand the wear mechanism, the morphologies of the worn surface were analyzed by means of scanning electron microscopy (SEM) for composite specimens under both dry and water-lubricated sliding conditions.     

Effects of Microscale Particles as Antiwear Additives in Water-Based Slurries with Abrasives

Abrasive wear is the dominant cause of tool failure in the process of mining and petroleum/gas drilling. This research investigated the effects of two additives, polystyrene and silicon nitride, on the tribological properties of water-based slurries with silicon dioxide or alumina abrasives. A pin-on-disk configuration was utilized to evaluate the performance of the additives for a steel–steel contact. Experimental results showed that polystyrene particles were able to reduce wear but friction increased simultaneously. On the contrary, silicon nitride particles exhibited excellent performance on both wear resistance and friction reduction. Results in this study indicated that the addition of appropriate additives was able to improve the tribological properties of slurries with abrasives.     

Tribological Behavior of Deagglomerated Active Inorganic Nanoparticles for Advanced Lubrication

The tribological behavior of novel, deagglomerated, and active molybdenum disulfide (MoS₂) nanoparticles as additives in paraffin oil is presented. In a novel approach, the MoS₂ nanoparticles were activated by their intercalation with organic molecules, particularly triglycerides (canola oil) and lecithin (source of phosphorus). A four-ball tribological test setup was used to measure the wear scar diameter, the coefficient of friction, and the extreme pressure properties of such formulated paraffin oils. The results showed significant influence of this uniquely designed MoS₂ nanostructured additive on the coefficient of friction (0.07), the wear scar diameter, and the extreme pressure (315 kg) properties of the paraffin oil. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive x-ray spectroscopy (EDS) were also used for investigating size, the surface morphology, and the elemental composition of the nanoengineered lubricant. The characterization revealed a particle size less than 100 nm and the elemental composition analysis of the wear track showed the presence of Mo, S, and P in the tribofilm, explaining the observed improvements in the tribological properties.     

金属陶瓷粒子添加剂对摩擦副表面的影响

用MMW-1型销盘式摩擦磨损试验机,对含有金属陶瓷添加剂润滑油对气缸套-活塞环摩擦学特性的影响进行了模拟试验研究;用表面粗糙度仪测量了缸套试样的表面粗糙度;用原子力显微镜对缸套试样表面的微观形貌和摩擦力形貌进行了测试;用韦氏硬度仪测量了缸套试样的表面硬度变化。研究结果表明,气缸套试样表面在这种添加剂作用下,其表面粗糙度和峰高都大幅度降低,展现了金属陶瓷粒子良好的自修复能力,并且这种能力随载荷的增大而增强。表面硬度分析结果也表明,添加剂粒子与摩擦表面的作用也与载荷有关。     

六方氮化硼负载纳米铜润滑添加剂的制备及其摩擦学性能研究

采用水热吸附及热解还原制备六方氮化硼负载纳米铜复合润滑添加剂(Cu/h-BN),利用透射电镜(TEM)、X射线衍射仪(XRD)、热重分析仪(TGA)以及红外光谱仪(FT-IR)对样品进行表征.将纳米润滑添加剂分散到聚α-烯烃(PAO10)中,采用球盘摩擦试验考察其摩擦学性能.采用扫描电子显微镜(SEM)对典型的磨痕进行...     

硼类化合物极压抗磨润滑油添加剂的研究进展

对硼类化合物润滑添加剂的制备、性能和研究现状进行了总结，着重介绍了其摩擦学性能、抗磨减摩作用和摩擦化学机理，特别是渗硼作用、稀土元素对渗硼的催化作用、添加剂问的协同抗磨减摩作用；给出了提高其抗水解性能的方法，如对硼酸盐进行表面修饰、在有机硼酸酯分子中引人钛原子；简单介绍了多功能硼类化合物润滑油添加剂和硼化硫代磷酸酯；指出了硼类添加剂的环境污染效应。     

Formation of Low-Friction Particle/Polymer Composite Tribofilms by Tribopolymerization

Inorganic fullerene-like (IF) solid lubricant particles based on MoS₂ or WS₂ have recently gained attention in various tribological applications, for instance incorporated in coatings, porous materials, greases and dispersed in oils. However, their effect in oil can be limited often due to inadequate penetration into the contact zone. Meanwhile, tribopolymerization of monomer additives in oil have proven to be efficient to reduce wear, but without significantly reducing the friction. This investigation combines these two lubrication techniques in order to form particle/polymer composite tribofilms, aimed to give low friction and wear in high-pressure sliding contacts. A cyclic amine, caprolactam, was used as the monomer together with IF as well as normal 2H WS₂ particles. Zn-DTP was used as a reference antiwear additive and poly-alfa-olefin (PAO) was used as the base oil. Reciprocal ball-on-flat sliding test results found that monomer plus particles reduced the friction by 10–50%, depending on sliding speed and type of particles, compared with particles or monomer alone. And the scattering between different tests was also considerably lower. The wear rate was also substantially reduced to a level similar to that of Zn-DTP. The particle/polymer composite tribofilms were generally much larger than the actual contact area and its thickness varied from below a few nanometres in the contact centre to several micrometers in the outer parts. Consequently, the reduced friction is believed to come from two effects: one being a trapping of particles in the contact zone, which reduces the boundary friction level; and the other a shift in lubrication regime towards EHD-lubrication due to reduced contact pressures accompanied with the formation of the composite tribofilm.     

Study of wear resistance of thermal-diffusion boron nitride coatings on titanium

The wear resistance of commercially pure titanium VT1-0 covered with boron nitride coatings in pair with steel U8 is studied. It is found that the boron nitride coatings deposited from amorphous boron by thermal-diffusion saturation in molecular nitrogen at temperatures of 800?C850°C using the noncontact method improve the wear resistance of titanium during boundary sliding friction. Their characteristics are compared with those of boride coatings on titanium deposited by the same method. It is shown that the high-gradient strengthened layers formed during contact thermal-diffusion boronitriding within the 900?C950°C temperature range affect adversely the tribological performance of the boron nitride coating-steel pair.     

Tribological Properties of Friction Pairs in Lubricant Contaminated with Particles under High Temperature

A liquid–solid lubricant with sand particles of different sizes and concentrations is prepared in advance. The viscosity of the lubricant is measured by a capillary viscometer to determine its relationship to the concentration or size of the sand particles. The relationships between friction and concentration or size of the sand particles are also identified with a UMT2 tribometer. Results indicate that the size of sand particles plays an important role in the lubrication performance; when the size of sand particles is 1–5 μm, the friction coefficient of the liquid–solid lubricant is reduced at low concentration and low load. Contaminant concentration greatly influences the tribological behavior of such a lubricant. The failure probability of the part surface decreases with a reduction in particle concentration; moreover, a high temperature aggravates the friction and wear of this surface. The friction coefficient is 0.14 at 200°C, which is well above the friction coefficient at room temperature (0.078), and the wear volume also increases by 30% compared to the normal temperature. When the temperature is 300°C the wear volume is two times that under room temperature.     

The lubricated wear of ceramics : Part II: The wear and friction of silicon nitride and steel in the presence of mineral oil or an ester based lubricant

The friction and wear characteristics of combinations of silicon nitride, alumina and AISI 52100 steel in the presence of mineral oil containing anti-wear, dispersant and detergent additives have been investigated in a tri-pin-on-disc machine. The tests were carried out at a nominal temperature of 100°C for a range of sliding speeds, loads and total sliding distances. In Part II of this two-part paper a comparison will be made between the tribological performance of these sliding pairs of materials in mineral oil and ester based lubricant environments. The results of the investigation showed that the alumina performed relatively poorly under these test conditions, whereas silicon nitride showed good potential as an improved wear resisting material compared with 52100 steel. Wear factors of the order of 10⁻¹⁰ mm³/Nm were deduced for the alumina, while values as low as 10⁻¹¹ mm³/Nm were typical of the silicon nitride sliding against 52100 steel discs. The alumina pins wore by a process of brittle fracture at the surface, whereas the silicon nitride pins wore primarily by a tribochemical polishing mechanism. The rate of tribo-chemical wear was found to be proportional to the nominal contact area.     

Ionic Liquid Lubrication Effects on Ceramics in a Water Environment

Ionic liquids were studied to determine their effectiveness as boundary lubricant additives for water. The chemical and tribochemical reactions that govern their behavior were probed to understand lubrication mechanisms. Under water lubricated conditions, silicon nitride ceramics are characterized by a running-in period of high friction, during which time the surface is modified causing a dramatic decrease in friction and wear. Two mechanisms have been proposed to explain the friction and wear behavior. Si₃N₄ sliding against itself may result in tribochemical reactions that form a hydrated silicon oxide layer on the surface of the sliding contact. This film has been suggested to mediate friction and wear. Others have suggested that tribo-dissolution of SiO₂ results in an ultra smooth surface and after a running-in period of high wear, the lubrication mode becomes hydrodynamic. The goal of this study was to examine the effects that ionic liquids have on the friction and wear properties of Si₃N₄, in particular their effects on the running-in period. Tribological properties were evaluated using pin-on-disk and reciprocating tribometers. The tribological conditions of the tests were selected to produce mixed/hydrodynamic lubrication. The relative lubrication mode between mixed and hydrodynamic was controlled by the initial surface roughness. Solutions containing 2 wt% ionic liquids were produced for testing purposes. Chemical analysis of the sliding surfaces was accomplished with X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The test specimens were 1 in diameter Si₃N₄ disks sliding against 1/4 in Si₃N₄ balls. The addition of ionic liquids to water resulted in dramatically reduced running-in periods for silicon nitride from thousands to the hundreds of cycles. Proposed mechanisms include the formation of BF_x and PF_x films on the surface and creation of an electric double layer of ionic liquid.     

Boron in Tribology: From Borates to Ionic Liquids

Boron compounds are widely used in a range of tribological applications such as friction modifiers, antioxidants, antiwear additives, and in many cases as environmentally friendly lubricants. The chemical nature and structure of boron compounds provide multifunctionality. They are used as (1) solid lubricants such as boric acid and hexagonal boron nitride, (2) liquid lubricants such as ionic liquids, (3) lubricant additives such as borate derivatives of various organic and inorganic compounds, and (4) coatings such as cubic boron nitride and different metal borides. Boron is also one of the most favorable elements for coatings and thin films in biotribological and biomedical applications. This review outlines the growing role of boron in lubrication over the past several decades, summarizes the main findings, and identifies future challenges related to boron chemistry.     

A study on the tribological characteristics of graphite nano lubricants

Many researchers have tried to improve the tribological characteristics of lubricants to decrease friction coefficients and wear rates. One approach is simply the use of additives in the base lubricant to change its properties. Recently, nanoparticles have emerged as a new kind of additive because of their size, shape and other properties. A nano lubricant is a new kind of engineering lubricant made of nanoparticles, dispersant, and base lubricant. In this study, graphite nanoparticles were used to fabricate nano lubricants with enhanced tribological properties and lubrication characteristics. The base lubricant used was industrial gear oil, which has a kinematic viscosity of 220 cSt at 40°C. To investigate the physical and tribological properties of nano lubricants, friction coefficients and temperatures were measured by a disk-on-disk tribotester. The surfaces of the fixed plates were observed by a scanning electron microscope and an atomic force microscope to analyze the characteristics of the friction surfaces. The results show that when comparing fixed plates coated with raw and nano lubricants, the plate coated with a nano lubricant containing graphite nanoparticles had a lower friction coefficient and less wear. These results indicate that graphite nanoparticle additives improve the lubrication properties of regular lubricants.     

Various MoS2-, WS2- and C-Based Micro- and Nanoparticles in Boundary Lubrication

Various solid lubricant particles have been experimentally evaluated as possible additives to oils. However, information in terms of a direct comparison of their tribological properties is still missing. In this study, we have compared the tribological properties of seven different solid lubricant micro- and nanoparticles as additives in polyalphaolefin (PAO) oil: MoS₂ nanotubes, MoS₂ platelets (2 and 10 μm), WS₂ nanotubes, WS₂ fullerene-like nanoparticles, graphite platelets (20 μm) and multi-walled carbon nanotubes. The experiments were performed in the boundary lubrication regime under a contact pressure of 1 GPa (Hertz, max) using a ball-on-disc tribotester. In general, the particles significantly decreased the friction and wear compared to the base PAO oil. We found that it was the material of the particles that largely determined their tribological performance. The effect of the size of the particles was much less important, and the morphology (shape) of the particles had little or no influence. We have also investigated the effect of ultrasonication during suspension preparation on particle damage and found that the solid lubricant particles were not notably affected, except the MoS₂ and WS₂ nanotubes, which became somewhat shorter.     

Tribological Characterisation of Graphene Oxide as Lubricant Additive on Hypereutectic Al-25Si/Steel Tribopair

The performance of a lubricant greatly depends on the additives it involves. However, recently used additives produce severe pollution when they are burned and exhausted. Therefore, it is necessary to develop a new generation of green additives. Graphene oxide (GO) is considered to be environmentally friendly. The scope of this study is to explore the fundamental tribological behavior of graphene, the first existing 2D material, and evaluate its performance as a lubricant additive. The friction and wear behavior of 0.5 wt% concentrations of GO particles in ethanol and SAE20W50 engine oil on a hypereutectic Al-25Si alloy disc against steel ball was studied at 5 N load. GO as an additive reduced the wear coefficient by 60–80% with 30 Hz frequency for 120 m sliding distance. The minimum value of the coefficient of friction (0.057) was found with SAE20W50 + 0.5 wt% GO. A possible explanation for these results is that the graphene layers act as a 2D nanomaterial and form a conformal protective film on the sliding contact interfaces and easily shear off due to weak Van der Waal's forces and drastically reduce the wear. Scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and Raman spectroscopy were used for characterization of GO and wear scars.     

Textured surfaces in sliding boundary lubricated contacts – mechanisms,possibilities and limitations

Abstract

The mechanisms of friction and wear in boundary lubrication are complex with influences from the surface roughness and hardness of surfaces, the lubricant and the wear products. Introduction of a texture on either surface can influence several important parameters. Wear particles can be collected or produced by the surface texture. A lubricating film can suffer or gain and the lubrication regime might change. This paper presents an overview of the tribological effects and important parameters of textured surfaces in sliding boundary lubricated contact, based on the experience of the authors and on published results. Examples of successful and less successful textured contacts are given and some recommendations regarding size, orientation and textured area fraction are presented.     

Microstructure and surface chemistry of amorphous alloys important to their friction and wear behavior

An investigation was conducted to examine the microstructure and surface chemistry of amorphous alloys, and their effects on tribological behavior.

The results indicate that the surface oxide layers present on amorphous alloys are effective in providing low friction and a protective film against wear in air. Clustering and crystallization in amorphous alloys can be enhanced as a result of plastic flow during the sliding process at a low sliding velocity and at room temperature. Clusters or crystallites with sizes up to 150 nm and a diffused honeycomb-shaped structure are produced on the wear surface. Temperature effects lead to drastic changes in surface chemistry and friction behavior of the alloys at temperatures up to 750°C. Contaminants can come from the bulk of the alloys to the surface on heating and impart to the surface oxides at 350°C and boron nitride above 500°C, The oxides increase friction while the boron nitride reduces friction drastically in vacuum.     

Effects of Using Alternative Extreme Pressure (EP) and Anti-Wear (AW) Additives with Oxy-Nitrided Samples

Oxy-nitriding is a widely used industrial process aiming to improve the tribological properties and performance of components. Previous studies have shown the effectiveness of the treatment with friction and wear performance, but very few have focussed on optimising this behaviour. The lubrication properties of several EP and AW additives were examined to investigate their effectiveness in improving the tribological properties of the layers formed after treatment. Previous studies showed the presence of an oxide layer on the sample could improve the effectiveness of the sulphurised olefin (SO) and tricresyl phosphate (TCP) additives. The friction and wear behaviour of oxy-nitrided samples were analysed using a tribometer and surface profiler. Scanning electron microscope, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy were employed to identify the morphologies and chemical compositions of the treated surface before and after testing. No real effect on friction was observed when using the SO or TCP additives, mostly due to lack of interaction with the less reactive iron nitride layer and their roles as anti-wear additives. However, when the zinc dialkyldithiophosphate-containing lubricant was used, a higher friction coefficient was observed. Greater improvements in anti-wear properties with the presence of additives in comparison with only using base oil were reported, with the TCP additive producing the lowest wear rates. The study effectively demonstrated that the additive package type used could impact the tribological and tribochemical properties of oxy-nitrided surfaces.