The Influence on Boundary Friction of the Permeability of Sintered Bronze

Components made of sintered bronze are often used in tribological systems. Examples of applications are self lubricated bearings, wet clutches and brakes and synchromesh components for manual gearboxes. The bronze material in these applications is often porous and permeable. However, the required level of permeability i.e., the ability for a fluid to flow inside the material varies widely for different applications. This implies the need to investigate if the permeability can influence the properties of a tribological system. Various studies have been performed in order to investigate the permeability of different materials but a possible relationship between permeability and boundary lubrication performance has not yet been thoroughly investigated. In this article this relationship has been investigated in a pin-on-disk apparatus for test specimens with a permeability that is well-defined. Materials with three different permeabilities were investigated together with non-permeable test specimens. The results indicate that permeability has a small influence on the friction coefficient when the tribological system is operating with good lubrication of the contact. The function of the tribological system when working under starved conditions is also investigated and a very clear relationship between permeability and the ability to cope up with starved running conditions is shown. This is explained in terms of the varying ability of the materials’ to store lubricant in pores. Non-porous test specimens were also tested as a comparison with the permeable test specimens in the investigation with starved running conditions . The results show that a material with high permeability works much better under starved running conditions than that with low permeability.     

硅油润滑对莫来石基陶瓷摩擦磨损性能的影响研究

莫来石基陶瓷具有一系列优异的性能,其在摩擦学领域中的应用越来越广泛。本文研究了硅油润滑对该类陶瓷摩擦磨损性能的影响规律。研究结果表明,硅油可明显地降低莫来石基陶瓷的摩擦系数和磨损率,但却使摩擦系数在稳定阶段的波动幅度增加。硅油润滑条件下,莫来石基陶瓷的磨损机理主要是微观断裂和磨料磨损。     

Changes in Friction Properties of Monolayer Lubricant Films Induced by Development of Molecules’ Bonding

Functional perfluoropolyether (PFPE) films consisting of mobile and bonded molecules are widely used for lubrication of magnetic disks. In order to clarify the influence of film composition (mobile/bonded) on tribological performance, we measured the friction properties of two types of 2 nm-thick PFPE films (functional Zdol2000 and nonfunctional Z03) under lightly loaded (loading force: 0–1 mN) and quasi-static (low rotational speed: 2.1 mm/s) conditions as a function of elapsed time. The friction force of Z03 remained unchanged with time and increased linearly with loading force as described by Amontons’ law. In contrast, induced by the development of the molecules’ bonding in time, the friction force of Zdol2000 increased and transited to a nonlinear increase with loading force as time proceeded. The nonlinear friction-load relationship of Zdol2000 in the equilibrium state was characterized by the Johnson-Kendall-Roberts model.     

半金属基粉末摩擦片摩擦磨损性能研究

在不同工况下研究半金属基粉末摩擦片与淬火45#钢配副时,载荷和转速对其摩擦磨损性能的影响,并分析其磨损机制。结果表明,在油润滑和水润滑下,半金属基摩擦片高速下的磨损量要明显低于低速下的磨损量,而干摩擦下其高载高速下的磨损要高于高载低速时的磨损量。油润滑下随载荷的增大,半金属基摩擦片的摩擦因数逐渐升高;水润滑下随载荷的增大,高速时摩擦因数先增大后减小,低速时则逐渐降低;干摩擦下随载荷的增大,高速时摩擦因数呈现出先升高后降低再升高的趋势,低速时则先升高后降低。干摩擦时摩擦面十分粗糙,有比较明显的沟状磨痕和硬质颗粒脱落后残留的凹坑;而水润滑和油润滑时摩擦面较为光滑。     

Friction and Wear Properties of Micro Textured DLC Coated Surfaces in Boundary Lubricated Sliding

In the present study, the friction and wear properties of boundary lubricated textured surfaces were investigated. The capability to feed lubricant into the interface of a sliding contact and to isolate wear particles was related to the shape, size and orientation of the texture patterns. Well-defined surface textures of square depressions or parallel grooves of different widths and distributions were produced by lithography and anisotropic etching of silicon wafers. Subsequently the wafers were PVD coated with thin, wear resistant DLC coatings, retaining the substrate texture. The surfaces were evaluated in reciprocating sliding against a ball-bearing-steel ball under starved or amply lubricated boundary lubrication conditions.     

可动微机电器件摩擦磨损测试方法研究

为比较真实地模拟可动微机电器件侧面间的摩擦磨损状况,进而研究MEMS器件的摩擦磨损规律,设计和研制了一种基于单晶硅材料的微摩擦试验模块,利用微机械体硅工艺及键合技术,将摩擦磨损测试单元、加载单元以及微力传感元件集成在单一的芯片上。最后,在大气环境下借助数字光学显微镜和图像处理技术对该试验模块的静、动态摩擦因数及磨损状况进行了测试。试验结果表明:随着正压力的增加,该摩擦副的摩擦因数相应减小,在较长时间的摩擦过程中磨粒表面出现了比较严重的氧化现象。     

润滑剂对轮轨摩擦与磨损的影响

利用MMS-2A磨损试验机模拟轮轨系统在润滑油、二硫化钼锂基脂、植物油和石墨钙基脂4种润滑剂润滑下的摩擦与磨损行为,研究润滑剂对轮轨副摩擦、磨损特性的影响.结果表明:与干态相比,4种润滑剂均使摩擦副的摩擦因数减小,表面磨痕深度减小,磨损量降低,其中石墨钙基脂的减摩和抗磨效果最好;试验结束后,轮轨试样接触表面的硬度均有不同程度的增加,其中涂有石墨钙基脂的轮轨试样的表面硬度增加最小.     

仿生非光滑结构的摩擦磨损试验研究

研究了非光滑表面形态对摩擦磨损的影响规律。通过对9种仿生非光滑形态模型试块在JF150DⅡ-型定速式摩擦试验机上进行的润滑摩擦试验表明,光滑试块的润滑及耐磨效果最差,沉坑形试块的耐磨性和润滑性提高不大,而通孔倒角形和通孔形试块能显著提高耐磨性和润滑性,证明了仿生非光滑结构具有良好的耐磨润滑性能,并通过正交试验分析了仿生非光滑形态、分布等因素对润滑的影响效应。     

水润滑塑料轴承的摩擦性能研究

用MPV—200型摩擦磨损试验机测定了超高分子量聚乙烯(简称UHMW—PE)塑料合金轴承水润滑条件下的摩擦学性能，考察了载荷、速度、运行时间等因素对轴承摩擦系数和磨损率的影响，得出了摩擦学性能随各种因素的变化规律。并对作用机理进行了系统的分析，为水润滑超高分子量聚乙烯塑料合金轴承的实际应用提供理论依据。     

超固体润滑及其在微机械电子系统中的应用前景

介绍了超固体润滑的概念 ,综述了超固体润滑的研究现状和近年来的研究成果 ,通过对微机械电子系统摩擦学问题的讨论 ,分析了超固体润滑在微机械电子系统中应用的前景 ,阐述了超固体润滑技术在微机械电子系统中应用的发展趋势     

边界润滑条件下表面微细织构减摩特性的研究

表面织构(Surface texture)已被证明是一种提高表面承载力和改善表面摩擦学特性的有效方法。然而在边界润滑条件下,织构对表面摩擦性能的影响机制仍未明确。利用纳米压痕仪在碳钢表面制作了具有不同密度和深度(125~500nm)的划痕的点阵,并通过改进的四球试验机对其在边界润滑下的摩擦性能进行了评价。试验载荷为100~300N,相对滑动速度为0.19~1.33m/s。研究发现:在边界润滑条件下,深度为125nm的低密度"划痕"点阵具有良好的减摩效果。     

Silicon Nitride Boundary Lubrication: Lubrication Mechanism of Alcohols

This paper describes the lubrication mechanism of alcohols with silicon nitride under boundary lubrication conditions. Dynamic wear tests and static chemical reaction studies were conducted to study the chemical interaction between alcohols and silicon nitride. Direct evidence of chemical reactions occurring between alcohols and silicon nitride was collected. Gel-permeation-chromatography-graphite-furnace-atomic-absorption (GPC-GFAA) analysis detected the presence of high molecular weight (HMW), silicon-containing, metallo-organic compounds in the wearing contact. Secondary ion mass spectrometry (SIMS) analysis of the reaction products from wear tests revealed the formation of silicon alkoxides. These alkoxides subsequently reacted to form HMW products which had been independently verified as capable of lubricating silicon nitride surfaces. A two-ball collision test was used to verify the lubricating quality of the film generated from the wear test. A lubrication mechanism is proposed in which alcohols adsorb and react with the oxide/hydroxide layer of Si₃N₄ to produce a bonded surface silicon alkoxide. Subsequent tribochemical reactions prompted by the surface disruption from the wearing contact cause the formation of free silicon alkoxides. These species then proceed to form a variety of silicon-containing high molecular weight products that have demonstrable lubricating ability. This mechanistic understanding provides a framework of Si₃N₄ lubrication.     

激光微造型表面摩擦磨损性能研究

采用声光调Q二级管泵浦固体光源（DPSS）Nd：YAG激光器对缸套试件表面进行了,微造型州纹加工。在往复式活塞环-缸套摩擦磨损模拟试验机上进行了激光造型缸套试件与未造型光滑缸套试件的摩擦磨损性能对比试验研究。试验结果表明,在重载高速条件下,激光网纹试件与未造型试件相比,摩擦因数降低23％,磨损量降低66％。说明激光网纹沟槽具有贮油、积屑和动压润滑作用,同时激光加工的网纹淬火效应也有利于提高支承表面的耐磨抗擦伤性能。     

Anomalous Low Friction Under Boundary Lubrication of Steel Surfaces by Polyols

We present here anomalous low friction obtained with highly polished steel on steel hard contact lubricated by glycerol under severe mixed and boundary regimes (λ ratio below 1). We investigated the effects of contact pressure, sliding speed, and temperature on friction coefficient and electrical contact resistance. The mechanism of low friction (typically below 0.02) is thought to have two origins: first a contribution of an ultrathin EHL film of glycerol providing easy shear under pressure, second the chemical degradation of glycerol inside the contact when more severe conditions are attained, generating a nanometer-thick film containing shear-induced water molecules. This new mechanism, called “H-bond Network model”, is completely different from the well-accepted “Monolayer” model working with polar molecules containing long aliphatic chains. Moreover, we show outstanding superlubricity (friction coefficient below 0.01) of steel surfaces directly lubricated by a solution of myo-inositol (also called vitamin Bh) in glycerol at ambient temperature (25 °C) and high contact pressure (0.8 GPa) in the absence of any long chain polar molecules. Mechanism is still unknown but could be associated with friction-induced dissociation of inositol and H-bond interactions network of water-like species with steel surface.     

磨屑对润滑油摩擦性能的影响

通过实验和模拟研究磨粒对润滑油摩擦性能的影响。首先通过微纳米压/划痕试验测量含磨屑润滑油的摩擦因数。同时,建立边界润滑体系模型,采用分子动力学方法模拟含磨屑润滑油膜在不同载荷下沿膜厚方向的压缩率和密度分布;对体系的上下固体壁面施加方向相反的剪切速度,计算出壁面原子的应力、摩擦力、正压力和摩擦因数;分析不同粒径磨屑的动态行为特征;通过减少润滑油分子数量,探究乏油工况下含磨屑润滑体系的摩擦性能。结果表明,润滑体系摩擦因数的模拟值与试验值一致;磨屑的存在会降低油膜的压缩率,同时在高载下磨屑的存在会对油膜的分层产生破坏,影响磨屑附近的密度分布;含小粒径磨屑的润滑体系的摩擦因数比含大粒径磨屑的润滑体系的小,表明磨粒聚集长大现象会恶化润滑油的润滑性能;磨屑在剪切过程中同时存在滚动和滑动,含小粒径磨屑的润滑体系剪切过程中表现出波动幅度更大的角速度;随着载荷的增大,磨屑角速度减小,波动幅度降低;在乏油工况下,磨屑会在剪切过程中出现变形破碎现象。     

硅化石墨的摩擦性能的试验研究

在 ＭＰＸ２００型环／环试验机上，对油和水介质润滑下的硅化石墨／硅化石墨、２０Ｃｒ钢／硅化石墨的摩 擦性能进行了实验评价。结果表明，水润滑下硅化石墨的摩擦系数为 ０．０１～０．０２左右，远小于油润滑下 的摩擦系数。对其摩擦化学作用机理进行了探讨。     

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.     

Thin-Film Properties of Some Functionalized Perfluoropolyether Boundary Lubricants Based on the n-Perfluoropropylene Oxide Monomer Unit

The thin-film properties of some perfluoropolyether boundary lubricants based on hydroxyl-termination of the n-perfluoropropylene oxide monomer units are investigated as a function of molecular polarity. The n-perfluoropropylene oxide monomer units provide a stiffer main chain than perfluoropolyethers comprised of a copolymer of perfluoro-methylene oxide and -ethylene oxide monomer units. Terraced flow and bonding kinetics show that the stiffer main chain reduces lubricant mobility on the disk surface but provides a lower profile lubricant film. The lack of mobility attributed to the main chain can be compensated for by decreasing the number of OH end groups. The Hamaker constants, derived from surface energy vs. thickness measurements are larger than the corresponding flexible main chains, suggesting an increased adhesion to the underlying carbon surface.     

Embedding Wear Models into Friction Models

Frictional behavior in dry or boundary-lubricated tribosystems is commonly time-dependent. Examples include phenomena like running-in, scuffing initiation, adhesive transfer, coating wear-through, and lubricant starvation. Fundamental models for the sliding friction coefficient usually focus either on determining a steady–state value or on predicting periodic behavior like stick-slip. They often neglect the details of long- and short-period frictional transients, some of which are quite repeatable. In addition to generating heat, frictional work is known to be dissipated in several ways, including roughness changes, wear particle generation, tribomaterial evolution, and microstructural alteration. Pairs of materials can display identical average friction coefficients but significantly different wear processes because frictional work is dissipated differently from one pair of materials to the next. The attributes of friction-versus-time behavior for combinations of metals, ceramics, and polymers can be comprised of stages whose understanding may require the development of piecewise friction models that include wear. This paper discusses past work on the subject, exemplifies embedding a simple wear model into a friction-versus-time model, and indicates how friction process diagrams can play a role.     

The Effect of Metal 8-Hydroxyquinolinates as Lubricant Additives on the Friction Process

This paper presents an investigation of tribological properties of lithium grease with 8-hydroxyquinoline complexes with copper, zinc, cobalt, cadmium, lead and manganese. The tribological tests were performed on a T-02 four-ball machine produced at the Institute for Terotechnology (ITeE) in Radom. The influence of the applied additive on the friction coefficient and wear was discussed. Compositions containing complexes of copper, cadmium and lead show the most significant effect on the reduction of motion resistance and wear, especially at high loads. The results of seizure tests performed according to the procedure of M. Szczerek [1,2] are also presented. The highest seizure load was obtained for lubricants containing copper and cadmium, while the highest limiting pressure of seizure—for the copper complex. The observed changes in antiseizure properties can be interpreted as a result of destruction of complexes and formation of protective metallic layers. The presence of deposited metal from the complexes was confirmed by X-ray microanalysis surface tests.