Improved wear resistance of ultra-high molecular weight polyethylene by plasma immersion ion implantation

Surface modification of ultra-high molecular weight polyethylene (UHMWPE) has been explored using the novel non-line-of-slight plasma immersion ion implantation (PIII) with nitrogen. The modified surfaces were characterised by SEM and a Nano Test 600 testing machine. The tribological behaviour of PIII treated UHMWPE sliding against AISI 316L stainless steel counterfaces was evaluated using a pin-on-disc tribometer under water lubricated conditions. The experimental results show that PIII is a very promising surface engineering technique to improve such surface mechanical properties as surface hardness and elastic modulus of UHMWPE. As a result, the wear resistance of UHMWPE was significantly enhanced by a factor of three following PIII treatment, as compared with untreated material. It was found that the significantly improved wear resistance of PIII treated UHMWPE can be mainly attributed to ion bombardment induced cross-linking, and thus surface hardening.     

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.     

甘油润滑下CrCN涂层的超低摩擦特性

为开发与CrCN涂层具有良好配伍润滑性能的绿色润滑剂,使用磁控溅射技术在304不锈钢表面沉积CrCN涂层,利用场发射扫描电子显微镜、原子力显微镜、纳米压痕仪、维氏硬度计、X射线衍射仪、X射线光电子能谱仪分别对其表面形貌、涂层厚度、力学性能、物相组成以及元素化学价态进行分析,并借助多功能摩擦磨损试验机评价在甘油润滑下CrCN涂层的摩擦学性能,并与PAO6润滑下结果进行比较。利用磁控溅射技术在不锈钢表面构筑的CrCN涂层表面光滑致密,粗糙度仅为1.01 nm,硬度可达14.39 GPa。对比钢-钢和钢-CrCN体系的摩擦学性能发现,钢-CrCN体系在甘油润滑下展现出优异的润滑性能;当负载为0.5 N时,钢-CrCN体系在甘油润滑下的摩擦因数可低至0.01,大大低于PAO6润滑下的摩擦因数。对磨痕的XPS分析表明,在摩擦过程中,甘油发生摩擦化学反应,在CrCN涂层的接触表面生成一层FeOOH层,甘油分子及其降解产物可能进一步吸附在FeOOH层,形成流体润滑层,有效降低了摩擦和磨损。     

The Effect of FeS Solid Lubricant on the Tribological Properties of Bearing Steel under Grease Lubrication

In order to improve the tribological properties of 52100 steel under grease lubrication, FeS solid lubricant was used in two ways. Low-temperature ion-sulfurization technology was utilized to prepare solid lubricant iron sulfide (FeS) films on the surface of 52100 steel, and FeS particles were mixed into the lithium grease as additive. The friction and wear properties were examined systematically on a “ball-on-disc” testing machine. The results showed that the tribological properties of bearing steel under grease lubrication can be improved either by using ion-sulfurization technique or by adding FeS microparticles into the grease. The tribological performance of sulfurized surface lubricated by grease is better than that of a plain surface lubricated by grease containing FeS microparticles at lower load and speed. The plain surface lubricated by the grease containing FeS micropaticles possesses better antiwear property under harsher conditions. The mechanism of the experimental results is discussed in detail.     

Elastohydrodynamics and failure prediction

Many rolling and sliding contacts in industrial machineries are lubricated elastohydrodynamically to mitigate friction and wear. Predictions of tribological failures and performance have been greatly enhanced in the past two decades due to advancements in elastohydrodynamics. In this paper, the major physical features and principles of elastohydrodynamic lubrication (EHL) along with the major modes of tribological failures are summarized, first, for these contacts. Brief discussions are given to current predictability of lubricant film thickness, contact pressure, temperature, and friction in elastohydrodynamic contacts, and how these variables are used in predicting contact fatigue life and the threshold conditions for sliding failure.     

Coatings tribology—contact mechanisms and surface design

The fundamentals of coating tribology are presented by using a generalised holistic approach to the friction and wear mechanisms of coated surfaces in dry sliding contacts. It is based on a classification of the tribological contact process into macromechanical, micromechanical, nanomechanical and tribochemical contact mechanisms, and material transfer. The important influence of thin tribo- and transfer layers formed during the sliding action is shown. Optimal surface design regarding both friction and wear can be achieved by new multi-layer techniques which can provide properties such as reduced stresses, improved adhesion to the substrate, more flexible coatings and harder and smoother surfaces. The differences between contact mechanisms in dry, water- and oil-lubricated contacts with coated surfaces is illustrated by experimental results from diamond-like coatings sliding against a steel and an alumina ball. The mechanisms of the formation of dry transfer layers, tribolayers and lubricated boundary and reaction films are discussed.     

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.     

UHMWPE与橡胶共混水润滑轴承摩擦磨损性能试验研究

为改善丁腈橡胶水润滑轴承的摩擦学性能，以丁腈橡胶为基体，通过添加不同量的超高分子量聚乙烯（UHMWPE）粉末（分别为丁腈橡胶量的12%、50%、100%）制得3种复合材料；分析不同复合材料的结构，研究其在水润滑条件下的摩擦磨损特性，并与纯丁腈橡胶和纯UHMWPE材料进行对比。结果表明：制备的UHMWPE与丁腈橡胶复合材料中，UHMWPE以分散相的形式分布在丁腈橡胶基体中，分布较为均匀；UHMWPE的加入提高了丁腈橡胶材料的自润滑性能，其中UHMWPE的添加量为丁腈橡胶的50%和100%时复合材料在低速时的摩擦因数明显减小；UHMWPE的加入提高了丁腈橡胶基体的硬度，改善了复合材料摩擦表面的挤压变形，使得复合材料的磨损量有所降低。研究表明，一定添加量的UHMWPE添加量可明显改善丁腈橡胶水润滑轴承的摩擦学性能，其最佳添加量为丁腈橡胶的50%。     

Microstructural and sliding wear behaviour of a heat-treated zinc-based alloy

The effect of heat treatment on microstructure, hardness, tensile properties, fracture mode and wear behaviour during lubricated and dry sliding of the zinc-based alloy with 25 wt.%Al was studied. Microstructural investigation and chemical analysis of as-cast and heat-treated specimens, the fracture and worn surfaces, as well as wear debris were performed by scanning electron microscopy and energy dispersive spectroscopy. Wear tests were carried out using a disc-on block-type wear machine. By a relatively simple heat treating consisting of a short-term annealing in the single-phase region followed by water-quenching, the elongation has been markedly improved, while the strength was maintained high. The results indicate that the wear rate strongly depends on the microstructure, applied load and sliding conditions. The wear rate increases with load, and under dry sliding conditions the wear rate is approximately two orders of a magnitude higher than under lubricated conditions. During dry sliding the best wear behaviour was displayed by the water-quenched specimens, whereas slowly cooled specimens showed the higher wear rate. Lubrication strongly affects the wear behaviour. Contrary to dry sliding, slowly cooled specimens exhibit the best wear properties under lubricated conditions. The wear mechanisms were proposed for dry and lubricated sliding. An erratum to this article can be found at     

Thermomechanical wear modelling

It is assumed that the contact between bodies in sliding motion produces a stress field and frictional heat source that may induce severe wear from material yielding or fracture. For this situation, a thermomechanical wear model is used to develop a wear transition equation for identifying the dominant factors that will reduce or control such wear, by employing thermoelasticity analyses and contact mechanics. This equation is used to construct wear maps for ease of analysis. Studies are used to substantiate the thermomechanical wear model with experimental results that emphasise the transition from mild to severe wear for dry and lubricated metallic and ceramic sliding contacts under load.     

Performance evaluation for aged environmentally adapted lubricants in bronze‐steel sliding contacts

Environmentally adapted lubricants (EALs) are becoming of increasing interest to the industry as legislation demands the replacement of mineral oil lubricants. However, little or nothing is known about the influence of ageing on the performance of these fluids in mixed and boundary lubricated tribological contacts. In this study, samples of three fully formulated lubricating oils, both in their ‘unaged’ form and ‘aged’ by means of an oxidation process in the laboratory, were utilized in a detailed study whereby variations in relative lubrication performance were examined. Standard laboratory pin‐on‐disc equipment was utilized in order to allow comparisons to be made and the definition of conclusions for a sliding tin bronze on steel contact. This simulated the interaction between an oil‐lubricated bronze bushing and steel shaft as found in the vane adjustment mechanism of a Kaplan turbine. X‐ray photoelectron spectroscopy analysis was employed to assess the effect on surface layer structural chemistry. Results showed, for the specific application being investigated, that EALs continue to function well in terms of their friction and wear performance even at high acid numbers. Copyright © 2008 John Wiley & Sons, Ltd.     

Tribological properties of plasma nitrided AISI 4140 steel under dry and lubricated sliding conditions

In this investigation, the microstructural, mechanical and tribological properties of plasma and pulse plasma nitrided AISI 4140 steel have been investigated in comparison to hardened steel. The influence of nitriding case depth, as well as the presence of a compound layer, have been tribologically examined for both dry and lubricated sliding. Testing was carried out on a pin‐on‐disc machine in which surface‐treated pins were mated to hardened ball bearing steel discs. The surface treated samples were characterised using metallographic, SEM, microhardness and profilometric techniques, before and after wear testing. The resulting wear loss and coefficient of friction were monitored as a function of load and of test time. The results showed improved tribological properties of the AISI 4140 steel after plasma and pulse plasma nitriding as compared to the hardened steel, in both dry and lubricated sliding. However, the compound layer should be removed from the surface, either by mechanical means or by decreasing the amount of nitrogen in the nitriding atmosphere, in order to avoid impairment of the tribological properties by fracture of the hard and brittle compound layer, followed by formation of hard abrasive particles.     

Influence of surface texture on boundary lubricated sliding contacts

The friction and wear behaviour of boundary lubricated sliding surfaces is influenced by the surface texture. By introducing controlled depressions and undulations in an otherwise flat surface, the tribological properties can be improved. Lubricant can then be supplied even inside the contact by the small reservoirs, resulting in a reduced friction and a prolonged lifetime of the tribological contact.In the present paper, well-defined surface textures were produced by lithography and anisotropic etching of silicon wafers. The wafers were subsequently PVD coated with thin wear resistant TiN or DLC coatings, retaining the substrate texture. The size and shape of the depressions were varied and evaluated in reciprocating sliding under dry and boundary lubricated conditions.     

含污染物油润滑条件下的磨粒磨损研究

概述了含污染物油润滑条件下的磨损试验方法，分析了磨粒尺寸、磨粒含量；材料硬度和材料表面粗糙度等试验参数对含污染物油润滑条件下材料的磨损性能的影响，结果表明其磨损机理主要是点蚀、犁削和熔着磨损，并提出了解决措施。     

Wear and wear particles—some fundamentals

Each of the various processes by which material can be lost from a surface in service leaves its fingerprint both in the topography of the worn surface and in the size, shape and number of the particles which make up the wear debris. To use debris examination as a diagnostic aid in assessing the health of operating plant, which may contain many tribological contacts, requires not only careful and standardised procedures for debris extraction and observation but also an appreciation of the mechanisms by which wear occurs and the regimes in which each of the contacts of interest operates when displayed on an appropriate operational map.     

A system for wear prediction in lubricated sliding contacts

A system of analysis is developed to predict the rate of wear in sliding contacts. The essence of the approach is the proposal that the rate of wear can be predicted only in probabilistic terms. Therefore, the estimation of the probability of wear, which can be regarded as synonymous with the probability of surface asperity contacts, precedes the calculation of the wear rate. Further, recognising the fact that wear takes place within the actual area of contact, it is argued that this area consists of plastic and elastic contacts between asperities which, in turn, have different shear strengths and contribute differently to the wear process. In the case of lubricated contact, a frictional film defect represents the influence of a lubricant on the wear process. Moreover, as in this type of contact the load is supported by both lubricating film and contacting asperities, a special procedure is provided to estimate the load supported by the asperities, because it is only that part of the load which contributes to the wear. The catastrophic form of wear in lubricated contacts, that is termed ‘scuffing’, is also considered, and the probability of scuffing, under a given set of operating conditions, is estimated. The predictive system has been tested and its predictions are compared with available experimental results.     

不同含量盐水介质中丁腈橡胶水润滑轴承材料摩擦学特性分析

以水润滑轴承用丁腈橡胶(NBR)材料为研究对象,在CBZ-1摩擦磨损试验机上开展其在清水及不同盐分含量水介质中以及不同速度及载荷下的摩擦学试验,对比分析其摩擦因数、磨损量以及磨损表面形貌等摩擦学特性的变化规律。结果表明:盐水质量分数、速度和载荷对丁腈橡胶的摩擦学性能影响显著,其摩擦学特性的变化是盐水质量分数、载荷、速度以及丁腈橡胶的黏弹性等因素共同作用的结果;丁腈橡胶材料与锡青铜配副的摩擦因数随转速的升高而降低,随载荷的增加而降低;随着盐水质量分数的增加,摩擦副的摩擦因数和磨损量先增大而后均有所减小,这是因为盐水质量分数通过影响润滑介质的黏度来改变水润滑的效果,通过对铜盘的腐蚀作用来改变摩擦副的摩擦情况,从而在整体上影响摩擦因数和磨损量的变化。     

Sliding Wear of an Al Alloy SiC Whisker Composite

The tribological properties of a well-studied powder metallurgy metal-matrix composite, i.e., 20 volume percent SiC whiskers in 2124-T6 Al alloy matrix, were measured for the three principal orthogonal orientations under dry and lubricated sliding contacts. The sliding wear mechanisms were identified through analyses of wear tracks and subsurface microstructure by scanning and transmission electron microscopy techniques. The results for sliding wear of this 2124 Al-SiC whisker composite indicate a much higher wear when dry than when lubricated, and a strong wear anistropy, which is correlated with the ureal fraction of SiC whiskers on the wear plane. SEM and TEM analyses show direct evidence of adhesive wear through plastic deformation for dry sliding and abrasive wear through plowing and polishing for lubricated sliding.     

Tribology of titanium boride-coated titanium balls against alumina ceramic: Wear, friction, and micromechanisms

The tribological performance of titanium alloy (Ti–6Al–4V) balls coated with a dual boride layer comprised of titanium diboride (TiB₂) and titanium boride (TiB) whiskers mated against alumina ceramic disks has been determined using lubricated ball-on-disk wear testing. Measurements of coefficient of friction values and volumetric wear were made and electron microscopic investigation of wear spots and tracks was performed. The wear rate of the boride-coated titanium alloy balls was 40 times less than that of 97% dense alumina balls. Measurements of wear track width and depth corroborated this result. The superior wear resistance is attributed to the hardness and the unique structure of the dual (TiB₂ + TiB) whisker layer and the consequent smoothness of the wear surface created during the wear process. The material removal mechanism is abrasive in nature in the boride-coated balls compared to grain fracture and pullout in alumina.     

Fretting corrosion of lubricated tin plated copper alloy contacts: Effect of temperature

The fretting corrosion behaviour of lubricated tin plated copper alloy contacts at ambient and elevated temperatures is addressed in this paper. At 27 °C, lubrication is very effective and the contact resistance remains stable for several thousand fretting cycles whereas at elevated temperatures (155 °C) the performance of lubricated contact is not appreciable. Surface profile and surface roughness confirm that the lubricated contacts have a smoother profile and experience a lesser damage at the contact zone at ambient as well as at elevated temperatures. The mechanism of fretting corrosion of tin plated contacts appears to be similar with and without lubrication at all the temperatures studied. The difference in performance of the lubricated contacts at ambient and elevated temperatures is due to the faster wear rate of tin coating at elevated temperatures. Oxidation of the contact zone of the lubricated contacts is prevented at all temperatures studied. The study concludes that lubrication is effective in improving the life of the tin plated copper alloy contacts under fretting conditions at ambient temperatures whereas at elevated temperatures lubrication provides only a marginal improvement in performance. The decrease in performance of lubricated tin plated contacts at elevated temperatures is due to the higher wear rate of tin coating and not due to evaporation of the lubricant.