Multiscale analysis of the tribological role of the molecular assemblies of synovial fluid. Case of a healthy joint and implants

The aim of this work is to identify the coupled role of the biological components of synovial fluid in the remarkable tribological operation of a healthy natural joint, as well as in the friction of steel and polythene implants. It uses a realistic ex vivo model capable of reproducing the mechanical and physicochemical characteristics of the entire tribological triplet of the joint, whether healthy or implanted. It particularly focuses on the lipidic bilayers and vesicle structures associated with synovial fluid. The analysis of the friction measurements and fluorescence microscopy images confirm the role of lipidic bilayers in maintaining a very low friction coefficient. In addition, we observe that the substitute cartilage favours the formation and maintenance of these bilayers, which is not the case of implant materials.     

磁控溅射制备高熵碳化物(AlTiVCrNb)C涂层摩擦学性能

为改善高熵合金涂层的摩擦学性能,通过石墨与AlTiVCrNb高熵合金靶共溅射制备(AlTiVCrNb)C涂层,采用扫描电子显微镜(SEM)、X射线衍射仪(XRD)分析涂层的成分、表截面形貌和物相,采用纳米压痕仪、球盘式摩擦磨损试验机测试涂层的硬度、弹性模量和摩擦学性能,采用白光干涉三维形貌仪表征涂层的磨损情况。试验结果表明：随着涂层中碳含量增加,高熵组分从BCC/FCC双相向单一FCC结构转变,且涂层的微观组织结构也随之变化;由于碳化物的形成和固溶强化,涂层呈现良好的摩擦学性能;在涂层碳原子分数为20.83%时,涂层的摩擦性能和力学性能达到最优,此时摩擦因数最低,为0.35,涂层硬度与弹性模量最高,分别为17.84、182.72 GPa。研究表明,在磁控溅射工艺中石墨与AlTiVCrNb高熵合金共溅射,可以获得摩擦学性能良好的高熵碳化物(AlTiVCrNb)C涂层。     

Comparative Investigation on Tribological Properties of Ion-Sulfuration Layers Under Dry Friction

Four kinds of steel, including high-speed steel (M2), die steel (L6), stainless steel (420) and plain carbon steel (1045), were treated by low-temperature ion sulfuration. Sulfide layers, dominated by the FeS phase, were produced on the surfaces of the four steels. The tribological properties of sulfide layers were investigated on a block-on-ring test rig under dry friction conditions. The results showed that the tribological properties of all sulfurized steels were remarkably improved. The tribological properties decreased in the order of high-speed steel—die steel—1045 steel—stainless steel. The hardness, microstructure and corrosion resistance of the substrate determined the differences in the tribological properties of different steels.     

Role of the biomolecular interactions in the structure and tribological properties of synovial fluid

The analysis of healthy rat synovial fluid (SF) by electron microscopy proved the existence of lipid multilamellar vesicular discontinuities of several hundred nm in diameter. To understand the discontinuities’ role in biolubrication, their intermolecular and tribological properties were studied using AFM and biotribological techniques. Hyaluronic acid and lubricin exhibited high affinity and high friction coefficients for lipid bilayers while biomimetic SF vesicles including glycoproteic components conferred low friction coefficients. These results suggest that SF’s volume is composed by a network of vesicles containing glycoproteic gel separated by lipid multilayers, lubricin’s role being devoted to anchor lipid layers on the cartilage.     

Friction and Wear Behaviors of Ni-based Composites Containing Graphite/Ag2MoO4 Lubricants

In order to improve the tribological properties of Ni-based composites, novel adaptive Ni-based composites containing multiple lubricants were prepared via a mechanical alloying and hot-press sintering technique. The phase constituents and microstructure of the composites were characterized and the tribological properties were evaluated from room temperature to 700 °C. The results showed that the Ag₂MoO₄ phase decomposed and new phases of Mo₂C, Ag, and MoO₃ formed in the sintered composites, which can be attributed to the solid state reaction of silver molybdate lubricant during the sintering process. The wear test results indicated that the Ni-based composites containing graphite and silver molybdate lubricants exhibited superior tribological properties at ambient and high temperatures. Subsequently, the Raman results demonstrated that the composition of the tribo-layers on the worn surface of the Ni-based composites was varied with increasing temperature. Combined with the wear test results, it can be proposed that the improvement of tribological properties is due to the synergistic lubricating action of silver molybdate, iron oxide, and nickel oxide. Furthermore, Raman results of the composite containing silver molybdate and silver/molybdenum trioxide lubricants revealed that the silver molybdate lubricant can reproduce easily by the direct reaction between molybdenum trioxide and silver in the agglomerate state.     

深过冷Ni-Pb-Cu固体自润滑材料摩擦行为研究

采用深过冷快速凝固方法制备了均质N i-Pb-Cu偏晶合金,用扫描电镜对其组织进行了观察,在摩擦试验机上对其试样进行了摩擦性能测试,并分析了其摩擦磨损机制。结果表明:制备的N i-Pb-Cu偏晶合金其凝固组织为硬基体上均匀地分布着软质点;N i-Pb-Cu合金的摩擦学特性随过冷度的提高而呈上升趋势,从而在理论上证实采用深过冷技术制备难混熔偏晶合金固体自润滑材料是可行的;N i-Pb-Cu偏晶合金与45#钢的磨损为磨屑磨损、粘着磨损。     

Electron Affinity Calculations For Thioethers

Previous work indicated that polyphenyl thioethers possessed chemical properties, related to their electron affinities, which could allow them to function as vapor phase lubricants (VPL). Indeed, preliminary tribological tests revealed that the thioethers could function as vapor phase lubricants but not over a wide temperature and Hertzian pressure range. Increasing the electron affinity of the thioethers may improve their VPL properties over this range. Adding a substituent group to the thioether will alter its electron affinity in many cases. Molecular orbital calculations were undertaken to determine the effect of five different substituent groups on the electron affinity of polyphenyl thioethers. It was found that the NO₂, F, and I groups increased the thioethers electron affinity by the greatest amount. Future work will involve the addition of these groups to the thioethers followed by tribological testing to assess their VPL properties.     

Comparison of the effects of ionic liquid and anti‐wear additives on the tribological properties of Cr―Mo―N coatings

Cr―Mo―N coating was prepared by magnetron sputtering, and its crystallinity and phase structure were analysed by X‐ray diffraction. The tribological properties of the coating separately lubricated with L‐P106 ionic liquid was compared with poly‐alpha‐olefin (PAO) and PAO‐containing MoDTP and ZnDTP additives with a ball‐on‐disc reciprocal friction and wear tester. It was found that the tribological properties of as‐prepared Cr―Mo―N coating vary with varying lubricant systems. Namely, the results indicated that the L‐P106 has better friction‐reducing and wear resistance properties than that of MoDTC and ZnDTP. The analyses indicated that Cr―Mo―N coatings and lubrication films can be considered as a solid–liquid duplex lubricating systems. Copyright © 2014 John Wiley & Sons, Ltd.     

Preparation and Tribological Properties of Surface-Capped Copper Nanoparticle as a Water-Based Lubricant Additive

Cu nanoparticle surface-capped by methoxylpolyethyleneglycol xanthate was synthesized using in situ surface-modification technique. The size, morphology and phase structure of as-prepared Cu nanoparticle were analyzed by means of X-ray diffraction and transmission electron microscopy. The tribological properties of as-synthesized Cu nanoparticle as an additive in distilled water were investigated with a four-ball machine, and the morphology and elemental composition of worn steel surfaces were examined using X-ray photoelectron spectroscopy and scanning electron microscope equipped with an energy-dispersive spectrometer attachment. Results show that as-synthesized Cu nanoparticle as a water-based lubricant additive is able to significantly improve the tribological properties and load-carrying capacity of distilled water, which is ascribed to the deposition of Cu nanoparticles on steel sliding surfaces giving rise to a protective and lubricious Cu layer thereon. In the meantime, they may also tribochemically react with rubbing steel surfaces to generate a boundary lubricating film consisting of Cu, FeS and FeSO₄ on the rubbed steel surface, which helps to result in greatly improved tribological properties of distilled water, thereby reducing friction and wear of the steel–steel pair.     

The tribochemical performance of nano/micrometre borate modified by an N‐containing compound as an oil additive

An N‐modified nano / micrometre borate (MNMB) as an oil additive was synthesised by an ultrasonic dispersion and emulsion reaction in the microemulsion phase. The particles of the MNMB additive were between 20 and 500 nm in diameter. The tribological properties of the MNMB as an oil additive were investigated using a four‐ball tester. The results reveal that the MNMB possesses good tribological properties. When the boron concentration is 0. 05 wt. %, the wear‐scar diameter is smallest and the seizure load is highest. The antiwear and extreme‐pressure properties of the MNMB were best at a viscosity of 65. 3 mms2. Small‐area X‐ray photoelectron spectroscopy (XPS) and electron probe microanalysis (EPMA) indicate that the MNMB additive can form a tribological mixed reaction film containing C, O, B, N, and Na on a rubbing surface. The elemental boron exists in four different chemical states, but is mainly present in the form of BN on the rubbing surface.     

离子渗硫模具钢的摩擦磨损机理研究

对模具钢5CrNiMo进行低温离子渗硫处理，表现得到了厚约10μm的渗硫层。在MM－200型摩擦磨损试验机上进行了渗硫层干摩擦条件下的摩擦学试验。利用原子力显微镜（AFM）和扫描电镜（SEM）观察了渗硫层的表面、截面与磨痕形貌；利用X射线衍射仪（XRD）分析了渗硫层的相结构；利用扫描俄歇微探针（SAM）分析了表面元素沿深度的分布。渗硫层表面多孔且不平，由纳米尺度的微粒随机叠嵌而成。渗硫层的纳米结构有利于改善其减摩耐磨性能。摩擦磨损结果表明，模具钢渗硫层的摩擦学性能明显优于未渗表面。     

网络结构增强金属基复合材料的研究进展

网络结构增强是一种全新的复合材料增强方式,其特征是增强相与基体在复合材料中形成各自连续且相互贯穿的三维网络结构,增强相因与之相互贯穿的基体所具有的韧性而得到增韧,基体则由于硬质网络结构增强相的骨架刚性承载作用而得到增强。主要评述了国内外网络结构增强金属基复合材料的制备工艺、特点及组织结构,重点介绍了复合材料的力学、热学、摩擦学性能及其今后发展趋势。     

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。     

Tribological behavior of plasma electrolytic oxidation coatings on the surface of Mg–8Li–1Al alloy

Plasma electrolytic oxidation coatings were fabricated on the surface of Mg–8Li–1Al. The tribological behavior of the coated and uncoated Mg–Li alloy was investigated under dry friction conditions against a Si₃N₄ ball as counter-face material. The results indicated that the tribological behavior is greatly affected by the microstructure and phase compositions of the coatings. The PEO coatings significantly improved the properties of friction and wear of Mg–Li alloy.     

The Effect of Concentration on Lubricating Properties of Aqueous Solutions of Sodium Lauryl Sulfate and Ethoxylated Sodium Lauryl Sulfate

The objective of this study was to formulate new ecological lubricating substances, primarily water-based, and to verify their tribological and physicochemical properties. Initially, simple binary solutions were investigated. Then, various additives were added depending on application targets. Two alkyl sulfates were selected as additives modifying lubricating properties of water: sodium lauryl sulfate (SLS) and ethoxylated sodium lauryl sulfate (ESLS). They have an identical hydrophobic part in the form of an alkyl chain consisting of 12 carbon atoms. The SO₄ ²⁻ anion forms the hydrophilic part in SLS molecules, whereas an ESLS molecule also contains two mers of ethylene oxide which cause an increase in its hydrophilicity relative to SLS. Both SLS and ESLS exhibit high surface activity measured by their surface tension. Micelles form in aqueous solutions of alkyl sulfates at low concentrations of the order of 1%, whereas the presence of liquid crystalline phases can be found at the concentrations of 40 and 70%. High surface activity and formation of structures in the solutions (micelles, mesophases) formed the basis for application of the compounds as additives modifying lubricating properties. Tribological properties of aqueous solutions of alkyl sulfates were verified with a four-ball machine (T02 tester) at a constant load of 2 kN. The values of friction coefficient (μ) were a measure of motion resistance, while the wear scar diameter (d) was a measure of wear. Alkyl sulfates significantly improve tribological properties of water. The coefficient of friction decreased sixfold and the wear scar diameter decreased by as much as twofold relative to the base. Non-monotonic changes in the tribological properties measured were observed as a function of concentration of additives. An attempt was made to relate those atypical changes with the presence of micelles and mesophases in both the surface phase and the bulk phase. In the model proposed the whole concentration range was divided into four areas in which tribological properties correspond well with physicochemical properties, particularly with the structures formed in solutions and at the interface.     

Poly-<Emphasis Type="Italic">p</Emphasis>-phenyl sulfide as the material for oil-lubricated sliding bearings

Tribological analysis of two different poly-p-phenyl sulfides, with melt viscosity differing more than twofold, is performed. The tribological properties of the poly-p-phenyl sulfides are compared with those of the composites based on minced carbofibers with 0.5% of fullerene C₆₀ by mass added into the matrix of the composites. In interpreting the tribological dependences it is especially noteworthy that the load-bearing capacity of the materials allows consideration of many of these dependences as phase diagrams.     

MoS2的表面修饰与摩擦学性能研究

分别用油酸（OA）、司班-60（Span-60）、十六烷基三甲基溴化铵（CTAB）-二烷基二硫代磷酸吡啶盐（Py-DDP）对MoS2纳米微粒进行表面修饰,考察了修饰后微粒的形貌、在液体石蜡中的分散稳定性和润滑性能,并采用四球摩擦磨损机测试了其摩擦学性能。结果表明,选用不同修饰剂所得到的修饰MoS2纳米微粒的稳定性和摩擦学性能均有不同程度的提高,其中以CTAB—PyDDP修饰MoS2纳米微粒的分散稳定性更佳,摩擦学性能最好。     

Surface modifications in tribological contacts

A characteristic of almost any type of dry or boundary lubricated tribological contact is that the composition and tribological properties of the original interface will change during use. The modifications include topography changes (smoothening or roughing), formation of micro-cracks, phase transformations, deformation hardening, formation of oxides, formation of solid films by reactions with lubricant additives, transfer of material from the counter surface, and so on. The thickness of these layers and films range from atomic monolayers (e.g., hydrogen termination of diamond surfaces) to tens of μm (e.g., plastic deformation of metals).Since the tribological properties of tools, wear parts and mechanical components then are determined by these modified surfaces rather than by the original, they deserve attention and careful assessment. Without the knowledge about how these surface layers are formed and how they modify the tribosystem, it is not possible to predict the friction and wear properties of a material in a given tribological situation. Thus, post-test evaluation including microscopy and analysis of both surfaces and cross-sections is required.A number of surface modifications selected from a wide variety of tribosystems is briefly presented. The corresponding surface modifications range from the most well known and simple to the more complex and relatively unexplored. Finally, the potential of designing materials and lubricants for improved surface modification is discussed and examples are given of current research projects on promoting formation of protecting low-friction tribofilms in boundary-lubricated systems.     

Tribological properties of nickel-base nanocrystalline coatings sputter-deposited on austenitic stainless steel

500 nm-thick films are deposited on austenitic stainless steel by neutral (Ar⁺) or reactive (N⁺) ion beam sputtering of Ni or NiTi targets, with (or without) high energy 160 keV-Ar⁺ ion beam assistance. Most of the time the coatings are nanocrystalline and induce a large (excellent in some conditions) increase of the wear resistance. Only Ar⁺ ion beam sputtering of a NiTi target gives an amorphous deposit which does not improve the substrate tribological properties. The hardness and wear resistance of ion beam assisted films are larger than those obtained with non-ion beam assisted coatings. The presence of a hard TiN phase inside a ductile Ni phase, of grains with preferential orientation beneficial to slip, as well as film densification are the main factors which increase the wear resistance. The best results are obtained when the structure is composed of two phases, Ni and TiN. The TiN phase strengthens the already good tribological Ni properties and the Ni ductility induces mechanical accommodation during the friction process.     

Development of evaluation technique for microcharacteristics of thixoforged wrought aluminum alloy by nanoindention and atomic force microscopy

This study demonstrated nanoindentation techniques of investigating the effects of size and feature in a microstructure on the mechanical properties of thixoforged aluminum alloy. Mechanical properties and tribological characteristics of rheology-forged Al2024 wrought aluminum alloy in terms of T6 heat treatment were investigated by varying the aging time by nanoindentation and nanoscratch techniques. By nanoindentation/nanoscratch tests and atomic force microscopy, it was demonstrated that the 4-h aged material exhibited the highest hardness because of the intermediate precipitate phase θ″, which was precipitated by T6 heat treatment. Moreover, the friction coefficients in the precipitates in the eutectic phase region were lower than those in the primary α phase region.