Friction and wear behaviour of hard coatings in vibrating contacts

The friction and wear behaviour of thin hard coatings, such as TiN and the promising class of C-based coatings (a-C, a-C:H, and diamond for example), are compared under oscillating and reciprocating sliding conditions. The typical effects of test parameters, such as stroke, frequency, normal force, relative humidity and test duration, are described as a basis for the proper selection of test conditions or, conversely, for the selection of suitable coatings for particular practical applications. Friction and wear data from over 1000 vibrating tests using thin hard coatings against 100Cr6 and against Al₂O₃ have been compiled in a database. This allows easy manipulation and comparison of test results. Using selection criteria and filter procedures (e. g., lifetime of coatings, friction limits, and critical wear rate), suitable coating systems for different test conditions can be chosen from the database. The effects of test parameters on friction and wear behaviour and changes have anyway to be known for meaningful tribotesting, as well as for the selection of coatings.     

SY-1型真空摩擦磨损试验机的研制

研制了SY-1型真空摩擦磨损试验机,可以提供4×10~(-3)Pa的压力环境,速度在0～2800r/min范围内可调,并且可以自动进行数据采集和处理。该机可以在真空、充不同气体、加热及冷却等多种条件下进行材料的摩擦学性能测试。     

The Tribological Properties of Low-friction Hydrogenated Diamond-like Carbon Measured in Ultrahigh Vacuum

In this paper, we investigate the sliding friction and wear behavior of a hydrogenated diamond-like carbon (DLC) film in ultrahigh vacuum (UHV) and under partial pressures of water vapor, oxygen, nitrogen and hydrogen. The initial friction coefficient of the film in UHV was ~0.15, but decreased steadily to values as low as 0.03 after about 30 sliding passes. During longer duration tests, the friction coefficient increased again to values as high as ~0.15 and such an increase in friction coincided with hydrogen desorption from the contacting surfaces (as detected by a mass spectrometer). Heating DLC to temperatures higher than 360 K also caused desorption of hydrogen and a resulting marked increase in friction. The presence of molecular nitrogen, oxygen and hydrogen in the test chamber did not have any noticeable effect on friction, but the presence of thermally dissociated or ionized hydrogen within the close proximity of sliding surfaces had a beneficial effect by restoring the low friction behavior of the DLC films. The introduction of water vapor into test chamber had an adverse effect on friction. The results of this study confirm that hydrogen is key to low friction behavior of hydrogenated DLC films and that the presence of water molecules has an adverse effect on their friction behavior.     

The Frictional Properties of Thin Inorganic Halide Films on Iron Measured in Ultrahigh Vacuum

Friction coefficients are measured in ultrahigh vacuum using a tungsten carbide tribopin against thin films of sodium chloride and potassium iodide deposited onto clean iron. It is found, in accordance with previous measurements for potassium chloride on iron, that the friction coefficient falls from an initial value of 2 for the clean iron surface to a minimum value after a few tens of Ångstroms of the halide have been deposited onto the surface, and remains constant for thicker films. The minimum friction coefficient is independent of applied load and therefore obeys Amontons' law. Simple theories for the effect of a low-shear-strength film suggest that the friction coefficient should depend on the shear strength of the film. This idea is tested by plotting the minimum friction coefficient versus the hardness of the film material, which is proportional to its shear strength, where a linear correlation was found. The lack of dependence of friction coefficient with film thickness for thicker films implies that ploughing forces do not contribute significantly to the friction coefficient.     

A Study of the Static/Kinetic Friction Behavior of PTFE-Based Fabric Composites

Three different polytetrafluoroethylene (PTFE)-based fabric composites were prepared. The static/kinetic friction behaviors of these composites under different loads and speeds were studied. A 3D laser microscope and profile measurement apparatus were used for analysis of the morphology and weave structure of the composites, and the contact temperature of these composites under different loads and speeds was monitored continuously using a high-precision thermal resistor. In addition, a dynamic mechanical analysis (DMA) apparatus was used to explore the thermal and mechanical properties of PTFE-based fabric composites. The results demonstrated that speed/load, weave structure, and fiber form have an important influence on static and kinetic friction behavior of the fabric composites. Generally, the static friction coefficient is greater than the kinetic friction coefficient, except when considering light load conditions. Under light load conditions, the static friction coefficient is equal to the kinetic friction coefficient. In addition, the kinetic friction coefficient first increased and then decreased with increased speed, but the static coefficient increased first and then remained at an almost constant value. At all sliding speeds, the static and kinetic friction coefficients of tape yarn composites are better than those of the multifilament yarn composites. Weave structure has no effect on the static friction coefficient, but it has a significant influence on the kinetic friction coefficient.     

On the influence of surface finish of SSiC on the results of tribological laboratory tests in the case of water lubricated oscillating sliding

The development of materials for tribological applications requires characterisation of their friction and wear behaviour. This characterisation is often based on tribological model testing, working with simple shaped specimens, running under well-defined conditions. Discrepancies in test results may arise from the fact that non-standard tests with different sets of operational parameters are used. An essential starting point for the development of tribological standards is knowledge of the main parameters that influence the tribological properties. One aspect that is not often adequately taken into account is the surface finish of the test specimens. Results are presented of friction and wear tests with self-mated SSiC couples (ball on disc), running in water in an oscillating sliding mode. The surfaces of the disc were ground, lapped, or polished, respectively, running against a polished ball. For certain test conditions, the influence of the surface finish on wear is found to be negligible, while for other conditions, the wear rate can differ by one order of magnitude or even more. The consequences for the standardisation of wear tests of ceramic materials are discussed.     

聚四氟乙烯基固体润滑剂摩擦表面的X-光光电子能谱研究

利用扫描电镜(SEM)对聚四氟乙烯基固体润滑剂摩擦表面及在45^#钢表面所形成的润滑转移膜形貌进行表征；采用X-光光电子能谱(XPS)仪测定了聚四氟乙烯基固体润滑剂烧结前后、在45^#钢表面摩擦试验前后，试样表面的元素组成及价态的变化。结果表明：摩擦过程中固体润滑剂在45^#钢表面形成了润滑转移膜，在烧结及摩擦过程中发生了化学反应，并产生磨粒磨损、腐蚀金属等现象。     

Ultrastructure of Tracheal Surface Liquid: Low-Temperature Scanning Electron Microscopy

A layer of liquid lines the airways in the lung. Previous microscopic studies have suggested that it is in two phases, with a mucous gel lying above a periciliary sol. However, shrinkage artifacts due to chemical fixation, dehydration, and drying have prevented reliable estimates of the depth of these layers. To avoid such problems, we have studied the surface liquid of bovine trachea by low-temperature scanning electron microscopy (LTSEM). A polished copper probe cooled to liquid nitrogen temperature was applied to the mucosal surface of sheets of excised tracheal epithelium to effect rapid freezing of surface liquid. Tissue sheets were then mounted in an LTSEM (AMRay 1000A with Biochamber) which maintains samples at -180°C with a Joule-Thompson refrigerator built into the stage. Tissues were fractured at right angles to the epithelial surface, coated with gold, and viewed, all at 10^?5 to 10^?6 torr without transfer through air. The sample was stable under the electron beam at accelerating voltages up to 20 kV. Epithelial features (nuclei, cilia, microvilli, mucous granules) were well preserved. The mucosal surface of the cells was covered with material on the order of 8 μm in depth. The mucous gel and periciliary sol could be seen as distinct layers and could be distinguished by the size and pattern of ice crystal voids generated by radiant-etching of the fractured surface of the sample.     

拉锻式摩擦塞焊的热力耦合解析模型和试验验证

为快速得到拉锻式摩擦塞焊的焊接工艺参数,对焊接过程进行预测,建立了摩擦塞焊过程的扭矩、轴向力、功率和能量等指标的力学模型和热力耦合解析模型。模型的输入量为焊接塞棒的几何参数、材料属性、焊接转速和进给速度,输出量为焊接过程的扭矩、轴向力、功率和能量等。在自主设计的拉锻式摩擦塞焊设备上进行了焊接试验。通过将试验数据的输入和输出指标与理论模型值进行对比分析,验证了理论解析模型的可行性。     

不同介质下ER8车轮钢滑动摩擦磨损性能

为探讨车轮在不同环境下服役时摩擦因数的变化机制,通过滑动摩擦试验机考察不同载荷下,ER8车轮钢分别在干燥空气、纯水、3.5%氯化钠溶液3种环境下的摩擦磨损性能。利用光学显微镜、扫描电子显微镜、非接触三维表面轮廓仪、X射线衍射仪对磨痕及元素组成进行了分析,探讨不同环境下ER8车轮钢的摩擦磨损机制。结果表明：随着载荷的增大,ER8车轮钢的摩擦因数明显增大;列车的服役环境对车轮的摩擦磨损性能有较大影响,在干燥空气环境下,ER8车轮钢无腐蚀状况,磨痕宽度最小,但摩擦因数最大,可达0.503;在盐水环境下,ER8车轮钢出现腐蚀现象,磨痕宽度最大,但摩擦因数最小;干摩擦下ER8车轮钢的磨损机制为黏着磨损、磨粒磨损和氧化磨损,纯水摩擦和3.5%NaCl溶液环境下的磨损机制为磨粒磨损和氧化磨损。     

耗材摩擦焊技术及其应用前景

耗材摩擦是一项高效、优质、低成本的焊接／堆焊技术,应用该技术可在材料表面获得无稀释、结合完整性的焊敷层,对于解决无法采用常规摩擦焊接的大型或异形构件,以及难焊材料的焊接与堆焊问题具有应用价值。介绍了耗材摩擦焊技术原理、工艺特点及其应用前景。     

表面形貌在乏油润滑时的最大静摩擦力研究

采用磨削和刮研方法加工了2种表面形貌,并在乏油情况下进行了这2种形貌的最大静摩擦力实验。结果表明,刮研形貌的最大静摩擦力较磨削形貌小,约为后者的77%。且刮研表面有鱼鳞状浅坑形貌,实验观察到小气泡在刮研形貌上的浅坑中稳定存在。分析认为,该小气泡在一定的条件下有助于承载并减小最大静摩擦力。     

镀锡马口铁表面污染的XPS分析

本文利用XPS方法对受海水浸泡的镀锡马口铁进行了表面分析。结果表明,经海水浸泡及在海水蒸气下放置的镀锡马口铁表面都会受到不同程度的污染。同时也表明,XPS作为一种重要的表面分析技术将会在商品检验和产品检验中得到有效地应用。     

The Tribological Properties of Monolayer KCl Films on Iron in Ultrahigh Vacuum: Modeling the Extreme-Pressure Lubricating Interface

The friction coefficients of thin KCl films deposited onto clean iron in ultrahigh vacuum are measured using a tungsten carbide tip. A rapid decrease is found in the friction coefficient from 2 for clean iron to 0.27 ± 0.03 after the deposition of 40 Å of KCl. Based on previous contact resistance measurements, this was proposed to be due to the completion of the first layer of KCl. The first-layer KCl coverage was measured by adsorbing deuterium onto an iron surface partially covered by KCl, where deuterium selectively adsorbs onto the iron. This revealed that the first monolayer is complete after the deposition of 40 Å of KCl and that the first-layer KCl film coverage _KCl ⁽¹⁾ is given by _KCl ⁽¹⁾ = 1 - exp(-0.39±0.02t), where t is the film thickness. XPS data suggest that heating a KCl film to 550 K causes it to wet the surface. This leads to decreases in the friction coefficients for thin KCl films in accord with the idea that friction is reduced by the first monolayer of KCl on iron. Temperature-programmed desorption data indicate that KCl in the first monolayer is 5 kJ/mol more stable than the multilayer consistent with the wetting behavior. Finally, the kinetic data are analyzed to suggest that the first-layer film is 2.6 Å thick.     

Friction and wear of PTFE seal materials

Shaft seals made from polytetrafluoroethylene (PTFE) materials, called PTFE lip seals, have been successfully used for decades in the chemical industry. Owing to their chemical and thermal stability, PTFE lip seals are used instead of elastomeric lip seals in many automotive and hydraulic applications. This paper deals with the fundamental tribological properties and effects of filled PTFE materials employed in rotary shaft seals, mainly on the basis of experimental work done in the authors' laboratory. The tribological components of a sealing system and the main influences on the sealing function are briefly surveyed. The test methods and conditions used are also described. The experimental results show that the fillers used in the PTFE compounds, as well as the topography of the shaft, play a crucial role in fluid sealing.     

滑动干摩擦的热机理浅析

分析了在高速滑动干摩擦过程中热的产生和扩散机理、摩擦温度的测定与分析，讨论了摩擦热效应对配副材料摩擦磨损性能的影响。结果表明：在摩擦过程中，摩擦热的形成是显著的；由粗糙表面产生的摩擦热作用在粗糙表面进而影响粗糙表面的形貌；摩擦热是影响摩擦副摩擦性能变化的主要因素；在研制摩擦材料时应充分考虑配副材料的耐热性与散热性等物性，进行优化选材。     

Friction and Wear of Self‐Lubricating Polyimides in Vacuum and Air to High Temperatures

In an increasing number of tribosystems, liquid lubrication cannot be applied or its application has to be avoided for environmental reasons. Examples include both plain bearings and linear guides used in space applications and in industrial vacuum production devices, e.g., for flat screens. Demand has also grown to raise the upper working temperatures of tribosystems and vacuum tribometers to around 300°C. For these reasons, a new formulation of polyimide (P84‐HT) for higher temperatures has been developed. Composites (Sintimid) with selected fillers (MoS₂, graphite, polytetrafluoroethylene, carbon fibres) were previously tested as to their general properties (physical, thermal, mechanical, vacuum stability) in temperatures up to 300°C and as regards the ECSS requirements for materials for operation in space (vacuum). The Sintimid compounds were successfully qualified according to these considerations. This paper reports a study of their mechanical properties and friction and wear behaviour. In particular. the influence of environmental parameters ‐ atmosphere and temperature ‐ and load are discussed and compared to other known materials, e.g., Vespel SP3. The tribological results are discussed in terms of the different filler types and their combinations.     

水压摩擦副中的压力与流量特性

水的低粘度使得水压润滑间隙中的惯性力与粘性力几乎处于同一数量级,因此研究摩擦副的润滑特性时,不能忽略惯性力的影响。惯性力的作用可能改变间隙流场的局部甚至全局流态,从层流变为紊流,因此应用经典润滑理论所得的计算结果将产生太大的误差。采用CFD方法从N-S方程出发对水压摩擦副中压力与流量特性的惯性影响和表面粗糙度效应进行了研究,并与经典润滑理论结果进行了对比,发现表面粗糙度和惯性力对润滑间隙中的压力和流量特性均有一定的影响。其中,惯性力对端面摩擦副中的压力分布具有一定的影响,对端面副和径向副的泄漏流量均有影响,并且惯性力使得表面粗糙度对流场流态的影响得以体现,因此以N-S方程而不是雷诺方程为模型所得的计算结果更加准确。     

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.     

铝合金气缸内表面摩擦涂覆处理工艺的研究

为了提高铝合金气缸的表面硬度及耐磨性能,改善其高温性能,本文利用涂覆材料经过摩擦作用发生塑化和塑性流动后形成改质层的原理,对铝合金气缸内表面的摩擦涂覆工艺进行了研究。研究结果表明,在铝合金气缸内表面采用Al-Si13%合金和Al-Cu35%合金作为改质材料经过摩擦涂覆处理后,可形成比较稳定的硬质膜,涂覆层的细化更加均匀,结合界面和气缸内表面的形状都非常圆滑,改善了气缸的耐磨性,有利于发动机的小型轻量化。