Contrasting Lubrication Properties of Imidazolium-Based Ionic Liquids Affected by the Nature of the Surface Under High Vacuum

The lubrication performance of imidazolium-based ionic liquids was evaluated under high vacuum using a ball-on-disk tribometer. A ball and a flat disk made of SUS440C stainless steel were used as specimens. A surface of the as-received flat disk specimen was covered with a thick oxide layer (>40 nm). For an examination of the effect of the surface oxide layer on the tribological performance of the ionic liquids under high vacuum, another specimen with a thin oxide layer (approx. 4 nm thick) was prepared. The ionic liquids with the TFSA anion showed better lubrication performance with the thicker oxide layer specimen, whereas the ionic liquids with the BF4 anion showed superior performance with the thinner oxide layer specimen. These results are discussed based on the HSAB principle. It is shown that the mechanism of the opposite tribological characteristics can be reasonably explained in terms of the chemical hardness by the HSAB principle.     

基于原位和RNT技术的摩擦试验机及其实验研究

针对目前传统摩擦磨损试验机的不足之处,开发了一种基于原位和RNT技术的摩擦磨损试验机。在合理设计和选取试验机工作系统及主要部件的基础上,采用原位全息显微技术和放射性核素技术,实现了对摩擦过程中材料磨痕表面微观形貌的在线原位观察和磨损量的实时精确测量。利用试验机对CuZ n20/100Cr6进行摩擦磨损性能实验,并对试验后试样进行了X射线电子能谱分析(XPS)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)分析研究。结果表明,磨痕表面形成耐磨层和晶粒细化是CuZ n20具有良好耐磨性的主要原因;试验机的实验结果精确,能为深入研究材料摩擦学行为提供重要参考依据。     

Improved additives for multiply alkylated cyclopentane‐based lubricants

Multiply alkylated cyclopentanes (MACs) are replacing heritage (mineral oil‐based) spacecraft lubricants because of their excellent performance and low volatility. While MACs have acquired an increasingly prominent role, soluble additives with similarly low volatility are lacking. In this study, the performance of specially designed candidate high‐molecular‐weight/low‐volatility phosphate additives was compared with the performance of conventional phosphate and lead naphthenate additives currently used in space. The candidate additives were equivalent or superior to the currently used additives in both conventional (atmospheric) and vacuum wear tests. Volatility studies revealed superior candidate additive performance compared with currently used additives. In addition, surface chemical analysis of the wear surfaces provided a better understanding of the anti‐wear protective films formed by these additives. Copyright © 2008 John Wiley & Sons, Ltd.     

Effects of Using Alternative Extreme Pressure (EP) and Anti-Wear (AW) Additives with Oxy-Nitrided Samples

Oxy-nitriding is a widely used industrial process aiming to improve the tribological properties and performance of components. Previous studies have shown the effectiveness of the treatment with friction and wear performance, but very few have focussed on optimising this behaviour. The lubrication properties of several EP and AW additives were examined to investigate their effectiveness in improving the tribological properties of the layers formed after treatment. Previous studies showed the presence of an oxide layer on the sample could improve the effectiveness of the sulphurised olefin (SO) and tricresyl phosphate (TCP) additives. The friction and wear behaviour of oxy-nitrided samples were analysed using a tribometer and surface profiler. Scanning electron microscope, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy were employed to identify the morphologies and chemical compositions of the treated surface before and after testing. No real effect on friction was observed when using the SO or TCP additives, mostly due to lack of interaction with the less reactive iron nitride layer and their roles as anti-wear additives. However, when the zinc dialkyldithiophosphate-containing lubricant was used, a higher friction coefficient was observed. Greater improvements in anti-wear properties with the presence of additives in comparison with only using base oil were reported, with the TCP additive producing the lowest wear rates. The study effectively demonstrated that the additive package type used could impact the tribological and tribochemical properties of oxy-nitrided surfaces.     

Tribological Performance and Surface Analysis of a Borate Calcium as Additive in Lithium and Polyurea Greases

In this work, a borate calcium additive was added to lithium and polyurea greases to investigate the tribological performance. Friction and wear tests were conducted on a four-ball machine under higher load and a reciprocating tribometer under lower load. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) analyses were performed on the worn surface after the tests. It was found that the tribological performance affected the boundary layers formed by the additive and the soap fibers. The boundary films in lithium grease mainly consist of ferrum hydroxide, and more oxide can be found in polyurea-based films. SEM analyses of soap fibers show that the soap fibers in polyurea-based grease were more separated than those in lithium-based grease. Compared to the base grease, the soap shows smaller and shorter fibers.     

Effects of Sulfur Additive EP in Ester Coolants during Friction with CBN

A study was undertaken to investigate the effects of the EP additives during tribological tests using a CBN tool against steel. Ester oil with and without sulfur additive were used as lubricants in a tribometer. Tribochemical interactions between the S additive and steel have been investigated under boundary lubrication conditions by SEM and EDX analysis. The relative abundance of different elements on the surface of the CBN tools, which are present in the workpiece material such as Fe (iron) and Cr (chromium), suggests that adhesion occurred when the ester oil without sulfur additive was tested. Tribochemical interactions between the additive and the steel could be observed when using the ester oil containing the sulfur additive. These interactions contribute to the formation of a uniform layer on the CBN tool. This layer is composed by S (sulfur), Fe, and O (oxygen). The presence of these elements indicate that FeO (iron oxide) and FeS (iron sulfide) were formed.     

A Nano- to Macroscale Tribological Study of PFTS and TCP Lubricants for Si MEMS Applications

The reliability and lifetime of cyclic contacting Si MEMS is limited by adhesion and their tribological performance. In this study, the tribological effects of adding a lubricant (tricresyl phosphate, TCP) to a bound self-assembled monolayer (perfluorodecyltrichlorosilane, PFTS) at different length scales were examined using a quartz crystal microbalance (QCM), an atomic force microscope (AFM), a reciprocating microtribometer, and a macroscopic reciprocating tribometer. The results showed that the addition of TCP to a PFTS layer increased the number of cycles possessing low friction and wear by at least a factor of four in the macroscopoic tribometer. Differences in friction response over the range of experimental scales were correlated to contact size and pressure. QCM measurements of TCP on PFTS showed a non-zero slip time, which suggests favorable tribological performance in larger length-scale regimes. This non-zero slip time also may indicate TCP mobility.     

Consideration of Test Parameters in Reciprocating Tribometers Used to Replicate Ring-On-Liner Contact

The use of horizontal reciprocating tribometers to model ring-on-liner contact in engines is common practice. The steady reduction of lubricant viscosity to improve fuel economy has produced a consequential reduction in film thicknesses at these interfaces. As a result reciprocating tribometer tests are now more often testing the resultant surface film formed in the contact by the lubricant additive package as opposed to the bulk lubricant. This has made understanding the interlinked nature of the parameters that can be set on the tribometer more essential than previously due to the increasing complexity of the tribochemistry. In this article, the parameters that can be set on these reciprocating tribometers are discussed, how they potentially impact upon the test, the interactions between the parameters and the level of representation of the engine conditions that can be achieved.     

Study of the tribological performance of a rare earth naphthenate as a lubricant additive

The tribological behaviour of a rare earth naphthenate (REN) as a lubricant oil additive in VG26 white oil and the complexes of REN and organo‐sulphur or organo‐phosphate compounds have been evaluated with a four‐ball friction and wear tester. The chemical features and elemental composition of the boundary lubricating film were examined by means of Auger electron spectroscopy (AES) and X‐ray photoelectron spectrometry (XPS). The results show that REN exhibits good antiwear, load‐carrying, and friction‐reducing properties in the base stock. When 2.0% REN is added, the wear‐scar diameter value reduces to 54.7% of that for the base stock alone and the maximum non‐seizure load increases 2.95 times. A synergistic effect is found for the load‐carrying capability of the complex of REN and organo‐sulphur while poor compatibility is exhibited for the complex of REN and organo‐phosphate. The analytical results of AES and XPS indicate that the good performance of REN is attributable to the formation of a boundary lubricating film mainly composed of naphthenic acid, rare earth oxide, and complexes of rare earth metals, which is formed on a rubbed surface when lubricated by oil containing the REN additive.     

The tribological properties of several silahydrocarbons for use in space mechanisms

Silahydrocarbons are members of a relatively new class of liquid lubricants with great potential for use in space mechanisms. They are unimolecular species consisting of silicon, carbon, and hydrogen. They possess unique wear, viscosity, and volatility properties while retaining the ability to solubilise conventional additives. The tribological properties of several members of this class, including tri‐, tetra‐, and penta‐compounds, are presented. These properties include viscosity‐temperature, viscosity—pressure, vapour pressure, lubricant life, traction, and reciprocating and four‐ball wear rates. Lubricant lifetimes were determined using a vacuum ball bearing simulator, the spiral orbit tribometer. Wear was measured using a Cameron Plint reciprocating tribometer and wear rates with a vacuum four‐ball tribometer. Conventional viscometry was used for viscosity—temperature measurements and a Knudsen cell for vapour pressure. Thermogravimetric analysis was also used for volatility measurements. Pressure—viscosity coefficients (α—values) were estimated from elastohydrodynamic lubrication film thickness measurements. These properties are compared to those of existing state‐of‐the‐art space lubricants.     

基于人工神经网络技术的环块试验机智能测控系统

针对目前大多数摩擦磨损试验机环境因素不可控、线速度不能实时优化调控的缺点,利用虚拟仪器开发平台LabVIEW开发一种基于人工神经网络技术的摩擦磨损试验机智能测控系统。该智能测控系统以工控机为核心,集数据采集、数据处理和实验环境控制为一体,既可实现温度、载荷、摩擦力、线速度和摩擦因数等参数的实时检测,又能对线速度进行实时调控。该试验机可更好地模拟现实工况条件,可开展多种环境因素的摩擦学实验研究。     

Long-term surface restoration effect introduced by advanced silicate based lubricant additive

Long-term effect (up to 300 h) of an advanced silicate based lubricant additive on the tribological properties is studied using a newly designed pin-on-disk tester. With the additive, the coefficient of friction was reduced by ∼40%. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) examinations showed that a smooth and high C-content outer layer was formed on the specimen surfaces, suggesting possible formation of diamond-like carbon (DLC) films. Using nano-hardness measurements, the hardness of the layer on the disk and the pin were 10.2 GPa and 16.7 GPa respectively. Wear loss and ferrographic analyses indicated that a “negative wear” occurred when the additive was applied, suggesting the debris particles were captured by the specimen to form a self-repairing layer.     

Tribological performance of PTFE- and PEEK-based coatings under oil-less compressor conditions

Due to favorable tribological performance, PTFE- and PEEK-based polymeric coatings have received interest in air-conditioning and refrigeration compressor applications, as a potential solution to supplement and potentially replace conventional oil lubricants. The literature in this area is somewhat scarce, especially on the tribological performance of PTFE- and PEEK-based polymeric coatings under aggressive conditions simulating compressor operation. In this work, several PTFE-, PEEK-, resin- and fluorocarbon-based polymeric coatings, coated on gray cast iron were tribologically evaluated using a specialized tribometer under compressor specific conditions, that included oscillatory motion (simulating piston-type compressors) and unidirectional motion (simulating swash plate compressor operation). The coatings showed good to excellent tribological performance, and in general PTFE-based coatings exhibited better friction and wear behavior than the rest of the coatings, including PEEK-based coatings. Long-term durability experiments also showed the superiority and suitability of PTFE/Pyrrolidone coating for potential use in oil-less compressors (where oil-less conditions refer to operation in the absence of any liquid lubricant).     

Halogen-free borate ionic liquids as novel lubricants for tribological applications

The unique properties of ionic liquids favour their applications in diverse fields, such as synthesis, catalysis, electrochemistry and nanotechnology. Their application as lubricants in several systems has found that these substances are able to provide remarkable protection against wear and significantly reduce friction whether they are used as additives or in the neat form. Therefore, in the present work, a further approach to provide halogen-free ionic liquids as lubricants for steel–steel contacts is discussed. The special chemical compositions of two imidazolium borane ionic liquids selected allowed the replacement of hetero-elements such as fluorine and sulphur that are usually found in ionic liquids. Their tribological properties were evaluated with a Schwing–Reib–Verschleiss (SRV) tribometer using an oscillating steel–steel contact with ball-on-disc geometry under boundary conditions. The addition of a phosphate based ionic liquid significantly improved the tribological properties of the imidazolium borane ionic liquids in comparison to a reference halogen containing ionic liquid (used as neat and lubricant additive). XPS analyses of the wear scars confirmed the formation of a phosphate based tribofilm that significantly improved the friction reducing properties and anti-wear performance of the lubricants.     

Tribological Performance and Anticorrosion Stability of Co-Cr-Mo Alloy with Thermal Oxidation Layer under Bovine Serum Albumin Solution

Co-Cr-Mo alloy used for an artificial hip joint prosthesis was treated in a vacuum tubular furnace to obtain a thermal oxidation layer with anticipated surface properties. The tribological performance of the thermal oxidation layer was subsequently characterized under bovine serum albumin (BSA) lubrication by suitable accelerating wear with a pin-on-plate tribometer. The influence of (1) BSA concentration in range of 2–20 mg/ml and (2) load in the range of 2–10 N on wear was analyzed. Stability of the oxidation layer was also studied by electrochemical testing to analyze its corrosion resistance. The change in microstructure of the substrate, after removal of the oxidation layer, was also evaluated. Results should that (1) the coefficient of friction (COF) under the applied load of 10 N fluctuated by about 0.15, (2) a higher value of wear loss 4.23 × 10^?4 mm³ in 20 mg/ml BSA, and (3) a decrease in the COF and increase in wear loss under a load of 2 to 8 N. It was suggested that the corrosion potential of the oxidation layer of ?0.25 V in BSA solution and ?0.13 V in NaCl solution moves further toward positive values and the corrosion current density is reduced, implying that the specimens with a thermal oxidation layer gave better corrosion resistance than the controlled Co-Cr-Mo alloy specimen.     

Additive Mechanism Investigation of Perfluoropolyether Lubricants with a Phosphazene Additive

The tribological characteristics of magnetic thin film media coated with perfluoropolyether (PFPE) lubricants (ZDOL and AM300J) and a phosphazene additive (X-IP) were investigated in this study. The drag test results show that under ambient and hot/wet conditions the media coated with AM300J lubricant have higher retention on the test track than those coated with ZDOL 2000 PFPE lubricant. The phosphazene additive X-IP was observed to strongly anchored to the surface and was not as easily removed as PFPE lubricants alone. The retention characteristics of X-IP are independent of either AM or ZDOL. Secondary Ion Mass Spectroscopy (SIMS) depth profile data and Angle-Resolved X-Ray Photo-electron Spectroscopy (XPS) reveal that X-IP molecules were distributed near the disk surface in the X-IP and PFPE lubricants mixed layer, indicating a strong bonding/adhesion of X-IP to the disk surface. Together with the drag testing data, the authors conclude that the preferential distribution of X-IP close to the disk surface in the mixed layer helps to improve lubricant retention performance at the head-disk interface.     

Lubrication of CrN Coating With Ethyl-Dimethyl-2-Methoxyethylammonium Tris(pentafluoroethyl)Trifluorophosphate Ionic Liquid as Additive to PAO 6

This paper studies ethyl-dimethyl-2-methoxyethylammonium tris(pentafluoroethyl)trifluorophosphate ionic liquid [(NEMM)MOE][FAP] as 1 wt% additive to a polyalphaolefin (PAO 6) in the lubrication of CrN PVD coating. The tribological behavior of this mixture has also been compared with a traditional oil additive, such as zinc dialkyldithiophosphate (ZDDP). Friction and wear tests were performed by means of a ball-on-plate reciprocating tribometer, and XPS was used to analyze wear surfaces. The experimental results showed that both additives substantially improve the anti-friction and anti-wear performance of the base oil. However, the tribological behavior of the ionic liquid as oil additive does not reach that of ZDDP. The interactions of each additive with the surface and tribofilm formation contributed to improve the tribological behavior of the lubricants.     

Development of atmosphere-controlled tribometer and fail-safe analysis

The design of existing tribometer mainly focuses on normal pressure and environmental conditions, and aims to measure the effect of load and speed on material performance. The effect of gas pressure and environmental condition on performance of materials is usually not considered. Thus, data from friction tests are not precise. In this paper, a new atmosphere tribometer is developed to study the tribological behavior of materials under severe rugged atmosphere. A fail-safe analysis is performed through reproducibility, comparability, and sensitivity tests. The tribometer allows tests to be performed in block-circle disc line contact, pin-circle disc line contact, and block-circle disc face contact configurations at controlled atmosphere and gas pressure. A self-centering plant is designed to settle the poor contact problem. A pin-on-disk test is conducted, and the test results indicate that the proposed design is efficient. A combined sealing style is introduced to control gas leaks. Compared with other sealing styles, the combined sealing is found to meet the experiment requirements best. And the reproducibility, comparability, and sensitivity tests validate the performance of the tribometer. The designed atmosphere tribometer reliably simulates the friction test under extremely harsh conditions, enhances the ability for material tribological properties test, and ensures accuracy of the tribological data.     

环烷酸稀土化合物作为润滑油添加剂的摩擦磨损性能

用四球摩擦磨损试验机考察了环烷酸稀土(REN)在26#白油中的摩擦学性能，并与当前普遍使用的抗磨剂ZDDP进行了比较，对REN与硫系、磷系润滑油添加剂的复配效果以及它们的摩擦磨损机理也进行了探讨。     

X-ray Photoelectron Spectroscopy Analysis of Tribostressed Samples in the Presence of ZnDTP: A Combinatorial Approach

The influence of load on the chemistry of tribofilms formed on a steel surface in solution of pure di-isopropyl zinc dithiophosphate (i-ZnDTP) in n-decane has been investigated by means of a combinatorial tribological experiment involving X-ray photoelectron spectroscopy. The experiment consisted of the preparation of a set of spatially separated areas, produced under various tribological test conditions, and the subsequent spectroscopic probing of the chemical composition of the tribofilm. The experiment was carried out at room temperature under boundary-lubrication conditions and revealed a physically adsorbed layer of the additive in the non-contact area and a thin (ca. 5nm), inhomogeneous phosphate film covering the tribostressed areas. The total amount of phosphate present in the tribostressed area was found to increase with increasing load. In the contact areas, iron oxides and metal sulfides have also been detected.