Microstructure Development and Tribological Behavior in AlCuFe Quasicrystalline Thin Films

A series of AlCuFe films were deposited by magnetron sputtering and subjected to X-ray diffraction and tribological testing to elucidate the correlation between quasicrystalline phase content and coefficient of friction. The sputter target was a pressed powder target comprised of a mixture of elemental powders combined in the ratio Al₆₅Cu₂₃Fe₁₂ and pressed at 400°C. This target was designed to produce film compositions within the single-phase icosohedral quasicrystalline regime. X-ray diffraction performed on the as-deposited coatings showed that they were comprised of a nanoscale/amorphous precursor phase with broad X-ray diffraction maxima. Anneals of the as-deposited films were performed at 450 or 500°C in argon for various times to cause partial or full development of the quasicrystalline microstructure, and films were tribo-tested in two separate systems. The first of these was an oscillating pin-on-flat system, in which a coated 2 mm diameter pin was used to test as-deposited films at temperatures of up to 220°C under vacuum and a 15 g load. The second system used a 0.25 diameter alumina ball and a load of 100 g to test films in air at temperatures of 25, 150, and 300°C. Various anneal conditions were also tested. For an as-deposited coating, a coating annealed for 2 h at 450°C, and a coating annealed for 1h at 500°C, the observed coefficients of friction were 0.45, 0.23, and 0.17, respectively. Correlation between quasicrystalline phase content, room temperature friction coefficient, and appearance of the wear track clearly showed that annealing to the fully developed quasicrystalline structure resulted in a harder film with a lower coefficient of friction.     

类金刚石薄膜水润滑摩擦学特性研究进展

综述类金刚石薄膜水润滑摩擦学特性的研究进展,评述薄膜在水环境中的摩擦磨损特性,分析薄膜种类、元素掺杂、对摩材料以及微结构对DLC薄膜水润滑摩擦学特性的影响,并阐述DLC薄膜在水中的摩擦磨损机制。指出:DLC薄膜水润滑摩擦学特性受薄膜制备参数和摩擦试验环境影响,通过与微结构的耦合可以进一步改善类金刚石薄膜的摩擦学特性。同时还展望了类金刚石薄膜水润滑摩擦学未来研究方向。     

Improved Tribological Behavior of DLC Films Under Water Lubrication by Surface Texturing

Textured diamond-like carbon (DLC) films with the pattern of parallel grooves were developed by depositing DLC on textured stainless substrates in a PVD system. The texturing effects on tribological performance of DLC in water-lubricated condition were investigated. Results show that introducing specific patterns into DLC film not only retains the low friction coefficients, but also dramatically extends coating lifetime through affecting the coating delamination behavior and graphitization process during friction. Besides the adherence difference induced by surface texturing which could influence the delamination, another possible mechanism, “buffer stripes”, which is characteristic of the lateral soft/hard periodical structure, was proposed by us based on the Micro-Raman spectroscopy and nanoindentation analysis. Additionally, a much lower graphitization for textured DLC during friction may also be responsible for the improved wear resistance.     

Lubrication with Sputtered MoS2 Films

Sputtered MoS₂films (2000–6500 Å) were deposited on highly polished metal surfaces. These films have a low coefficient of friction (0.03–0.04) at speeds of 40–80 rpm and loads of 250–1000 grams. At loads of 250 grams the wear lives are over 0.5 million cycles, but at 1000 gram loads, it decreases to 38,000 cycles. Friction experiments and tensile tests have indicated that sputtered films have a strong adherence to metal surfaces. Electron transmission, diffraction and scanning electron microscopy show that these films have an extremely small particle size, less than 30 Å in diameter, and are very dense and free from observable pinholes. The high kinetic energy of these sputtered species, the submicroscopic particle size and the sputter-etched substrate surface is responsible for strong adhesion and cohesion of the sputtered film.     

Lubrication of Metal Surfaces by Oxide Films

Experimental data obtained with sixteen metals suggest that hexagonal structured metals have low friction, while other metals have high friction unless a lubricating oxide layer is farmed. In order for an oxide to lubricate, it must not be much harder than the substrate, and the oxide thickness must be adequate. For pin-an-desk tests at loads of about 1 kg, the critical oxide thickness is 10^?6 cm, and the metals must be heated until this thickness is reached. Other solid lubricant films appear to obey the same criteria of not 100 hard, not too thin.     

Lubrication by Transferred Films of Solid Lubricants

Experiments are described to determine the lubricating ability of various solid films, particularly graphite and molybdenum disulfide, transferred from a compact to a steel surface. The amount of lubricant transferred depends markedly on the surface finish of the steel, and the most effective films are formed on relatively rough surfaces. In these conditions, bonding between the film and its substrate appears to be primarily mechanical. Determinations of the scuffing load and endurance tests show that replenishment of the lubricant film by continuous transfer to compensate for wear is only possible to a limited extent. With molybdenum disulfide, the film ultimately wears away, but with graphite, failure occurs when the mean surface temperature exceeds about 100 C. The load-carrying capacity of transferred films of molybdenum disulfide is appreciably greater than that of graphite films.     

自旋润滑油膜测量系统

设计制造了一种纯自旋弹流润滑油膜测量系统,介绍了其油膜厚度多光束干涉测量原理和主要的机械结构组成。初步测量结果表明接触区在纯自旋条件下可形成弹流润滑油膜,出现扇形的对称气穴区。     

水润滑橡胶轴承

对当前水润滑橡胶轴承的发展现状及存在的问题进行了深入剖析，并针对存在的问题进行了一些理论分析和实验研究工作。     

Application of Spectroscopic Reflectometry to Elastohydrodynamic Lubrication Films Study

Optical measurement techniques have been successfully used for elastohydrodynamic (EHD) lubricant films studies for several decades and have significantly helped to understand the lubrication mechanisms within highly loaded machine contacts. Nevertheless, there are still many phenomena waiting for the explanation and new experimental approaches and measurements techniques are developed. Recent studies have provided promising results as to the application of spectroscopic reflectometry to the study of EHD films. Nevertheless, some simplifications were introduced. The main aim of this study was to develop a physically correct approach that could provide the additional information about the properties of lubricant film within highly loaded contacts. The principal part of this article was devoted to the effort to develop and verify the optical design suitable for such applications. This verification was carried out within lubricated contact formed between a steel barrel and sapphire disc without any semi-reflective layer. This simplified optical arrangement has enabled to obtain the correct lubricant film data and verify the applicability of the spectroscopic reflectometry for EHD lubrication films study. It represents the first step in this application of spectroscopic reflectometry and further research in the field of the behavior of thin solid films under high contact pressures is necessary to enable thin film measurements.     

Nanostructure and Composition of Tribo-Boundary Films Formed in Ionic Liquid Lubrication

Since the idea of using ionic liquids (ILs) as lubricants was raised in 2001, many studies have been conducted in this area and results have demonstrated superior lubricating performance for a variety of ILs. It is widely believed that a protective tribo-boundary film is formed on the contact area by tribochemical reactions between the metal surface and the IL during the wear process and, as a result, reduces friction and wear. However, the study of this critical boundary film in the literature has been limited to two-dimensional topography examination and chemical analysis from the top surface. This study demonstrates a multi-technique three-dimensional approach to characterize the boundary films on IL-lubricated metallic surfaces. The complementary characterizations at the top surface, cross-section, and different layers of the boundary film provide direct measurement of the film thickness, visualization of the nanostructure, and analysis of the composition change. The boundary films observed on different alloys are substantially distinct from both physical and chemical perspectives. The measured mean film thicknesses for cast iron, steel, and aluminum worn surfaces are 300, 60, and 200 nm, respectively. The boundary films on ferrous alloys are dominated by amorphous phase mixing with well-dispersed very fine (a few nm) nanocrystals, while the film on aluminum contains many larger size (tens of nm) metallic particles in a less organized manner.     

不同润滑状态下游离水对点接触油润滑润滑性能的影响*

为研究水污染对润滑油性能的影响,通过点接触光干涉试验得到充分供油、轻微乏油及严重乏油3种润滑状态下的油膜光干涉图和膜厚形状曲线,研究游离水对接触区油润滑润滑性能的影响。结果表明:在充分供油条件下,游离水对点接触润滑油膜厚度的影响不大,主要影响中心膜厚;在乏油润滑状态下,游离水对点接触润滑油膜厚度有增益效果;但3种润滑状态下,游离水都会使气穴区边界变得模糊不清,提高了油润滑的弹流润滑性能。     

水液压元件的润滑和密封问题

用水作为工作介质的液压传动技术是近年来国内外液压领域普通关注的研究方向之一,也是前沿课题之一。本文描述了水液压元件的润滑和密封特性,并介绍了国内外水液压泵的润滑密封方式。     

Squeezing Molecularly Thin Alkane Lubrication Films: Layering Transitions and Wear

The properties of alkane lubricants confined between two approaching solids are investigated by a model that accounts for the curvature and the elastic properties of the solid surfaces. We consider linear alkane molecules of different chain lengths, C₃H₈, C₄H₁₀, C₈H₁₈, C₉H₂₀, C₁₀H₂₂, C₁₂H₂₆, and C₁₄H₃₀ confined between smooth gold surfaces. We observe well-defined molecular layers develop in the lubricant film when the width of the film is of the order of a few atomic diameters. An external squeezing-pressure induces discontinuous changes in the number n of lubricant layers. We find that with increasing alkane chain length, the transition from n to n - 1 layers occurs at higher pressure, as expected based on the increasing wettability with increasing chain length. We obtain good correlation between our theoretical results and wear experiments.     

发动机气门应用固体润滑薄膜研究

利用多层梯度复合技术,在气门表面制备出了低摩擦固体润滑薄膜,厚度为2.1μm,强度达13GPa,接合力为50N。与渗氮气门相比,强度提高了近2倍,磨损率降低了1/6。该技术具有自主知识产权,实现了气门批量化覆膜加工,并有望在发动机主要摩擦副上推广应用。产业化应用后,将使发动机的寿命提高2倍,油耗降低1%～3%,CO2排放降低2%～4%,可为开发环境友好的新型发动机提供技术保障,并提高自主品牌汽车在国内外市场上的竞争力。     

Water Lubrication of Silicon Nitride in Sliding

Several studies have shown that the coefficient of friction of self-mated silicon nitride in water decreases from an initially high value to about 0.002 after a certain run-in period. Since the worn surfaces become extremely smooth, the low friction is attributed to the initiation of hydrodynamic lubrication by a thin water film at the interface. The possibility of mixed lubrication, i.e., hydrodynamic lubrication by water and boundary lubrication due to the presence of colloidal silica on the wearing surfaces, has also been proposed. The purpose of our study is to investigate the influence of load, speed, and surface roughness on the duration of the run-in period. The results confirmed that a low coefficient of friction is obtained following a run-in period when a wear scar of sufficient size is developed to reduce the contact stress. The run-in period, during which the coefficient of friction is fairly high, was shorter for smoother surfaces and at higher loads and speeds. The low friction behavior was found to be unstable and occasional high friction spikes were observed. The surfaces of the wear tracks and wear scars contained a series of striations parallel to the sliding direction and exhibiting plastic deformation, delamination and fracture. The striations that appeared to be associated with the high friction spikes, could form as a result surface film breakdown. Although these results are consistent with the proposed mechanisms of hydrodynamic lubrication or mixed lubrication, it is proposed that the low friction behavior may be also related to fundamental interactions between two hard and elastically deforming surfaces covered with hydrogen-terminated oxide films.     

碳基薄膜水润滑性能的研究进展

评述了碳基薄膜如类金刚石薄膜(DLC)和非晶氮化碳(a-CNx)薄膜水润滑的研究现状和进展。分析了第2元素加入和摩擦副材料对碳基薄膜在水中摩擦磨损特性的影响,探讨了碳基薄膜在水中的磨损机制。指出:氢化或氮化碳基薄膜的磨损率与摩擦副材料的水合反应有关,若摩擦副材料易于摩擦水合反应,碳基薄膜的磨损率很低;3种DLC薄膜在水中的磨损率与DLC的种类和对磨钢球材料无关,都在10-8mm3/(N.m)的数量级上变动;a-CNx/Si基非氧化物陶瓷摩擦副显示很低的摩擦因数和低的磨损率;在相同条件下,a-CNx薄膜比a-C薄膜更能显示优异的水润滑性能。     

自旋对弹流油膜影响的试验研究

利用自制的旋滑式光干涉弹流薄膜测量系统,对带有自旋的钢球—玻璃盘接触副形成的弹流油膜形状和厚度进行试验研究。采用新的方法来获得自旋,即通过调节接触副与玻璃盘旋转中心的距离改变自旋分量的大小。试验结果表明,自旋导致油膜厚度降低,油膜形状也失去了经典的马蹄形相对卷吸中心线的对称性。当卷吸速度增加时,油膜厚度增加,油膜形状的非对称性增强;载荷增加,油膜厚度减小,油膜形状的非对称性增强;偏心距增加,油膜整体厚度增加,两侧油膜厚度差别减小,油膜形状的对称程度增加。     

双雷诺边界条件下水润滑橡胶轴承的弹流润滑特性

引入双雷诺边界条件研究水润滑橡胶轴承的弹流润滑特性。采用"负压充零"算法实现双雷诺边界条件,比较双雷诺边界条件和雷诺边界条件下水膜压力分布、承载力及摩擦力等的差异。结果表明:双雷诺边界条件下水膜起始位置比雷诺边界条件提前,水膜区域范围扩大,起始边界为抛物线形而非直线;在水膜破裂区,2种边界条件下的压力分布情况相近;在破裂区以外的区域,双雷诺边界条件下的水膜压力比雷诺边界条件下的大;由于水膜起始区和破裂区的水膜压力部分抵消,双雷诺边界条件下的承载力与雷诺边界条件下的承载力相差不大;双雷诺边界条件下的偏位角大于雷诺边界条件下的偏位角,摩擦力大于雷诺边界条件下的摩擦力。     

Some Aspects of the Mechanical Behavior of Films in Boundary Lubrication

In boundary lubrication, the wear process is often controlled by the formation of colloidal agglomerations in the contact. These agglomerations are due to collected products of chemical reactions between metal Surfaces and environment (1). They make a non-homogeneous thin film in the interface. Their accumulation gives rise to the formation of adherent films in the case of antiwear additives (zinc dithiophosphates and organophosphorous compounds).

The purpose of the paper is to show that small agglomerations (called lump), compressed between two solid bodies, can plastically deform the surface and can grooves when the two surfaces slide. Experiments involving plasticine are presented. The first shows that, during static compression, the thickness of the film and local friction coefficients are important parameters in explaining the plastic deformation of the substratum. The second shows the mechanical conditions that favor the entry of the lump into the contact area and give the give the mild scartch-type wear. The mechanical models are explained and disscussed.     

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。