Controlling friction by light field is a low-cost, low-energy, non-polluting method. By applying ultraviolet light on the surface of photosensitive materials, the properties of the friction pairs or ...lubricant can be influenced, thus achieving the purpose of reducing friction. In this study, TiO2, an inorganic photosensitive material, was selected to investigate the modulating effect of light fields on friction lubrication when using polyalphaolefin (PAO) base oil as a lubricant, and the modulation law of light fields on the friction lubrication behavior was investigated under different loads (1–8 N), different speeds (20–380 mm/s), and different viscosities (10.1–108.6 mPa·s) of PAO base oil. The experimental results showed that light treatment could reduce the friction coefficient of PAO4 base oil lubrication from 0.034 to 0.016, with a reduction of 52.9% under conditions of 3 N-load and 56.5 mm/s-speed, and the best regulation effect could be achieved under the mixed lubrication condition. After TiO2 was treated with ultraviolet light, due to its photocatalytic property, PAO molecules were oxidized and adsorbed on the TiO2 surface to form an adsorption layer, which avoided the direct contact of rough peaks and thus reduced the friction coefficient. This study combines photosensitivity, photocatalysis, and friction, presenting a method to reduce the friction coefficient by applying a light field without changing the friction pairs or lubricants, which provides a new direction for friction modulation and gives new ideas for practical applications.
Deterioration of the lubricant performance of oils due to water incorporation is a major cause of failure during prolonged operation of mechanical assemblies. However, early indication of lubricant ...failure is challenging. In this work, a quartz crystal microbalance (QCM) technique was used to sense changes in oil characteristics and degradation upon water incorporation. The results obtained during runs at different temperatures indicate stronger signs of oil degradation with larger amount of water mixed in it. The observations on the lubrication performance of water-containing lubricants were confirmed by evaluating the effect of water incorporation on the tribological performance of steel surfaces immersed in synthetic oil. Macroscale tribological analysis indicated an increase in friction and wear of sliding steel components lubricated with water-containing oil after longer durations of tests. The results of this study provide new insights into how early signs of oil degradation can be sensed using the QCM technique toward minimizing the potential negative impact of such changes on the lubrication characteristics of oils.
In response to the challenges posed by friction and wear of tribo-components exposed to boundary and mixed lubrication conditions, there is increasing interest in the development of polymer-based, ...self-lubricating composites. This investigation addressed the effect of various fillers (i.e. short carbon fibers (SCF), short glass fibers (SGF), ZnS sub-micrometer particles and combinations of respective fibers with ZnS particles), on the friction and wear of polyimide (PI) when lubricated by poly-alpha-olefins (PAO). A sliding plate-on-ring geometry, using GCr15 steel rings, was used. It was demonstrated that the reinforcing fibers greatly improved the composites’ wear resistance. SGF was observed to be more effective than SCF in respect to friction- and wear-reduction. Moreover, an obvious synergism between SGF and ZnS was identified. The hybrid composite ZnS/SGF/PI exhibited excellent tribological performance under oil lubrication. With respect to the hybrid formulation, the glass fibers imparted their high abrasion resistance to the composite; while ZnS led to complex tribo-chemical reactions. A stable tribofilm consisting of transferred materials and various tribo-chemical products improved the boundary lubrication capability of the sliding system.
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•Tribological properties of PI composites under oil lubrication were studied.•SGF and ZnS led to a synergetic role in friction reduction and wear resistant.•Short glass fibers imparted their high abrasion resistance to the composite.•ZnS led to complex tribo-chemical reactions on the worn surface.•A tribofilm was formed on the counterface when being slid against ZnS/SGF/PI.
Laser texturing with a dimple pattern was applied to modify a Ti6Al4V alloy at the micro level, aiming to improve its friction and wear resistance in combination with oil lubrication to optimize the ...performance in demanding industrial environments. The tribological analysis was performed on four different dimple-textured surfaces with varying dimple size and dimple-to-dimple distance and under lubrication with three different oils, i.e., T9, VG46, and VG100, to reflect the oil viscosity’s influence on the friction/wear of the laser-textured Ti6Al4V alloy. The results show that the surfaces with the highest texture density showed the most significant COF reduction of around 10% in a low-viscosity oil (T9). However, in high-viscosity oils (VG46 and VG100), the influence of the laser texturing on the COF was less pronounced. A wear analysis revealed that the laser texturing intensified the abrasive wear, especially on surfaces with a higher texture density. For low-texturing-density surfaces, less wear was observed for low- and medium-viscosity oils (T9 and VG46). For medium-to-high-texturing densities, the high-viscosity oil (VG100) provided the best contact conditions and wear results. Overall, reduced wear, even below the non-texturing case, was observed for sample 50–200 in VG100 lubrication, indicating the combined effect of oil reservoirs and increased oil-film thickness within the dimples due to the high viscosity.
Quenched cast iron with different hardness values, as substrates of biomimetic samples from different hardened layers, were selected for this study. To improve the oil - lubrication wear resistance ...(OWR) of quenched cast iron (QCI) with different hardness values, QCI samples were modified by a two-step laser treatment (TLT) to imitate the shell nacreous layers alternating between soft (substrate) and hard (units) phases. Compared to untreated samples, these modified samples with various soft-hard combinations exhibited different wear patterns, and their wear loss was not always proportional to the average hardness of the corresponding surfaces, while the hardness difference (HDV) between units and substrates had a major impact. For understanding the relationship between the HDV and OWR, three types of substrates coupled with four types of units with a HDV combination variety, where the units were alloyed of C/Cr powders with four types of ratios through TLT, were subjected to reciprocating wear tests under lubrication.
In order to study the tribological properties of V-shaped texture under oil lubrication conditions, the loading force and speed are selected as the influencing factors, each factor selected six ...levels. Experimental study on friction and wear of V-shaped texture with ring arrangement is finished by MMG-10 Multifunctional Friction and Wear Testing Machine, and the data of the experimental results are analyzed by using Matlab. The results show that there is a near linear relationship between the friction coefficient and the loading force and velocity. The relationship between the friction coefficient and the loading force and velocity can be expressed by a functional equation. The loading force has a greater influence on the friction coefficient than the speed. The SEM images of the post-test specimens show that the main weared zone of the V-shaped texture is the tip part. Create a single V-shaped texture model with Solidworks and use CFD to divide the mesh into the Fluent solution. According to the pressure distribution cloud diagram and the turbulence intensity cloud diagram, the stability of the oil film is improved due to the enhanced fluidity of the oil film and the small change in the oil pressure. The tip portion is also the region with a large turbulence intensity value. The improvement of the stability of the oil film is the key to reduce the friction coefficient of the V-shaped texture when the loading force increases.
为了研究V字型织构在油润滑条件下的摩擦学性能，选取加载力和速度为影响因素，每个因素选取6个水平，通过MMG-10多功能摩擦磨损实验机对环形排列的V字型织构进行摩擦磨损实验研究。并利用Matlab软件对实验结果进行数据整理和分析，结果表明摩擦因数与加载力和速度存在近线性关系，它们之间的关系可以通过一个函数方程式表示，并且加载力对摩擦因数的影响能力要大于速度。实验后试件的SEM图像表明了V字型织构的主要磨损区为尖端部分。通过Solidworks建立单个V字型织构模型并使用CFD划分网格，导入到Fluent中求解。通过压力分布云图以及湍流强度云图可知，油膜的稳定性提高是由于油膜流动性增强和油压值波动小导致的，尖端部分也正是湍流强度值较大的区域。而油膜稳定性的提高正是V字型织构能在加载力增加的情况下降低摩擦因数的关键。
•W-doped DLC coating with various W contents was fabricated.•Friction and wear of DLC coated sample was studied.•The lubricant additive was T307.•The influence of W content on friction under ...lubrication was unveiled.•The influence of W content on wear under lubrication was studied.
The influence on tungsten content on the structure, mechanical properties and tribological performance of W-doped diamond-like carbon (DLC) coatings was studied by X-ray photoelectron spectroscopy, nano-indentation, scratch test, and ball-on-disk friction test. It was found that with increasing W content, the content of WC and free W in the coatings is increased while the content of sp3-C in the coatings is decreased. The effect of W content on the hardness and elastic modulus of the coatings is indistinctive, but there exists the highest critical load of scratch test of above 100N when W content is 3.08at.%. With the increase of W content, the friction coefficients of W-doped DLC coatings under dry friction conditions are increased while the friction coefficients of W-doped DLC coatings under polyalpha olefin (PAO) lubrication are decreased. With the increase of W content, the wear rates of the DLC-coated samples under dry friction conditions show a minimum value; under pure PAO lubrication, the influence of W content on the wear rates of the DLC-coated samples is indistinctive when the W content is below 10.73at.% while the wear rates are increased with increasing W content from 10.73at.% to 24.09at.%; when lubricated by PAO+thiophosphoric acid amine (T307) salt, the samples coated with the undoped DLC or the W-doped DLC with high W content exhibit low wear rates.
Titanium‐doped diamond‐like carbon (Ti‐DLC) coatings with Ti concentration of 4 at.% (Ti4at.%‐DLC) and 27 at.% (Ti27at.%‐DLC) were prepared by a hybrid ion beam deposition system for comparison. The ...tribological behaviors of Ti‐DLC coatings under dry friction and boundary lubrication conditions were systematically investigated. Results showed that, under dry friction, the Ti4at.%‐DLC coating displayed lower friction coefficient (0.07) and wear rate due to the continuous transfer film formed in the sliding interface, while Ti27at.%‐DLC coating was worn out at initial stage due to severe abrasive wear. And under boundary lubrication, both the Ti4at.%‐DLC and Ti27at.%‐DLC coatings showed excellent tribological properties attributing to the formation of oil film between sliding interface. In particular, Ti27at.%‐DLC performed the lowest wear rate of 1.12 × 10−16 m3 N−1 m−1 in this friction case. In conclusion, compared with Ti27at.%‐DLC coating, Ti4at.%‐DLC coating exhibited better tribological performances both under dry friction and boundary lubrication. The present result provides guidance for the selection of DLC coatings according to the realistic environment of starved‐oil and rich‐oil conditions.
•For MoDTC, DLC coating showed better anti-friction and worse anti-wear behaviors.•The improved anti-friction property was due to graphitization and MoS2.•Formation of MoOx resulted in a high wear ...volume.•For ZDDP, DLC coating showed the best anti-wear and the worst anti-friction behaviors.•Absence of friction reducing product and graphitized layer resulted in a higher friction.
The tribological behaviors of hydrogenated diamond-like carbon (DLC) coatings under varied load conditions lubricated with polyalpha olefin (PAO), molybdenum dithiocarbamate (MoDTC) and zinc dialkyl dithiophosphate (ZDDP) additives were investigated in this paper. Hydrogenated DLC coatings were synthesized through the decomposition of acetylene by the ion source. The tribological performances were measured on a SRV tribometer. The morphologies and chemical structures of the DLC coatings were investigated by the scanning electron microscope (SEM), Raman spectrometer (Raman) and X-ray photoelectron spectroscope (XPS). It was shown that the low friction and high wear were achieved on the hydrogenated DLC coating under MoDTC lubrication, while low wear was found on the hydrogenated DLC coating lubricated by ZDDP. The primary reason was attributed to different tribofilms formed on the contact area and the formation of graphitic layer. Both factors working together leaded to quite different tribological behaviors.
The synergistic effect of different types of solid particles in liquid lubricants is of great interest. In this work, g-C3N4 nanosheets were initially prepared using a calcination method and then ...as-prepared, and h-BN were used as lubricating additives to the white oil. A comparison between the mixed additives and the single g-C3N4 or h-BN additives revealed that the base oil with the addition of g-C3N4 and h-BN showed the best lubricating properties. The results show a 12.3% reduction in friction coefficient, resulting in a 68.6% reduction in wear rate compared to the white oil when filled with 0.5 wt% g-C3N4 and h-BN (1:1 by weight). Moreover, the addition of g-C3N4 and h-BN improves the high-temperature lubrication properties of the white oil. However, the friction coefficient and wear rate increase with increasing oil temperature. The large contact area between g-C3N4 and its sliding counterpart and the strong adhesive force between h-BN and its sliding counterpart improve the film formation efficiency, leading to enhanced tribological properties under oil lubrication conditions.
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