Friction and wear of some engineering materials against hard chromium plating

Using a simple pin on disc machine the friction and wear characteristics of grey cast iron, aluminium bronze and phosphor bronze rubbing against channel type and conventionally ground surfaces of chromium plating were studied. The results are discussed and microscopical investigations of tested specimens used to illustrate the conclusions derived.     

Lubricating materials with additives (problems and perspectives)

One of many possible directions of further improvement of lubricating compositions with additives is considered. It consists in joint use of additives to oil in the form of powdered remetallisants and mineral friction modifying agents, and this allows realization of a synergistic effect in the structure of protective metal-ceramic coatings significantly increasing the operating ability of tribojoints.     

Synthesis of butyl-octyl-diphenylamine as lubricant antioxidant additive by ionic liquids

Ionic liquid used in Friedel-Crafts reaction catalytic of dialkyl diphenylamine is a green environmental method. In this paper, butyl-octyl-diphenylamine (BODPA) was synthesized by the series of 1-butyl-3-methylimidazolium chloroaluminate (BMIM-AlCl₃) ionic liquids catalysts. Pressure differential scanning calorimetry (PDSC) was used to test antioxidant properties of BODPA in lubricating oil. The influences of various reaction parameters such as dosage of catalysts, molar ratio of diphenylamine to chloralkane, reaction temperature, and time on the alkylation catalyzed by BMIM-AlCl₃ have been studied. The molecular structure and content of alkyl diphenylamine were also characterized by FT-IR/GC-MS.     

Thermo-oxidative stability and corrosion properties of ammonium based ionic liquids

Ionic liquids (ILs) as a novel and potential type of lubricants possess partly superior properties over traditional classes of lubricants. Their extremely low vapor pressure, generally high thermal stability and non-flammability suggest them for high performance applications. However, their tendency towards corrosiveness is neglected in general. The selection of three ILs was based on the aim to achieve relevant lubricant properties, in particular high oxidation stability and low corrosiveness, as well as high environmental benignity. The cations were in all cases ammonium based with and without functionalization. Bis(trifluoromethylsulfonyl)imide (NTF₂) was chosen as anion and has been replaced for one IL by methanesulfonate. Artificial aging was carried out to obtain knowledge about the lubricant long-term performance under both oxidative and humid conditions while being in contact with CuSn8P and 100Cr6 commonly used in tribology. For the evaluation of IL corrosion potential, the metal content in the IL was monitored by ICP-OES, metal specimens were examined optically and by SEM-EDX analysis. To find out the IL suitability for the long-term applications the thermo-oxidative stability of the IL has been analyzed by several mass spectrometric techniques. In this study, NTF₂ based IL - regardless of the cationic moiety - showed superior performance over methanesulfonate based IL under all conditions. In the case of 100Cr6, dry conditions lead to the lowest corrosion whereas CuSn8P caused the lowest corrosion under humid conditions. The degradation process based on thermally induced transmethylation of the IL investigated occurred only at the cationic moiety of methanesulfonate based IL This is based on mass spectrometric investigations and indicates a contribution to the enhanced corrosiveness by means of the IL reduced stability.     

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.     

Influence of structural variations on imidazolium‐based ionic liquids

In this work, a fundamental study of ionic liquids (ILs) is shown. The main goal was to establish relationships between rheological and tribological properties of ILs and to understand how these properties are linked to the molecular structure of ILs. Of particular interest were the effects occurring to a frictional system due to variations of the anions and the alkyl chain length of the imidazolium‐based cations. Tribological experiments were performed using a reciprocating ball‐on‐disc test machine. To understand the effects resulting from a variation of the structural characteristics of the used ILs on the rheological properties, studies were performed using a rheometer. The results obtained are very promising in terms of improving friction and wear behaviour by using ILs as lubricants. Copyright © 2012 John Wiley & Sons, Ltd.     

Thermo‐oxidative stability of ionic liquids as lubricating fluids

Thermo‐oxidative stability of ionic liquids was evaluated by three bulk‐scale tests. The changes in chemical and physical properties such as viscosity, deposit formation, weight loss and TAN were obtained. The results are discussed in terms of chemical structure of ionic liquids. TFSI derivatives exhibit good thermo‐oxidative stability in comparison with BF4 derivatives. As chain length of alkyl group in imidazolium‐cationic moiety increases, the thermo‐oxidative stability of the molecule decreases. Water contaminant promotes the thermo‐oxidative degradation of ionic liquids. Reaction mechanism via radical intermediates is proposed herein. Copyright © 2007 John Wiley & Sons, Ltd.     

Effect and mechanism of additives for ionic liquids as new lubricants

Ionic liquids are unique compounds, which exhibit low viscosity, non-flammability, low vapor pressure, and extremely high thermal stability. Therefore, they are expected as candidates for advanced lubricants. Several ionic liquids, derived from cations such as imidazolium, pridinium, ammonium, and anions such as , bis(trifluoromethylsulfonyl)imide (TFSI^-) were examined under boundary conditions. It was found that tribological properties of ionic liquids are better than those of conventional lubricants such as synthetic hydrocarbons, synthetic esters, and fluorinated ethers. Careful analysis of worn surface revealed that tribochemical reactions of ionic liquids take place under these conditions. For example, organic fluoride, iron fluoride, iron sulfate derived from anionic moiety of the ionic liquids were detected by the instrumental surface-analysis with TOF-SIMS and XPS. Tricresylphosphate (TCP) and dibenzyldisulfide (DBDS) were found to improve anti-wear properties of ionic liquids to some extent. Interestingly, both additive-derived compounds and anionic moiety derived ones were detected on the worn surface. Moreover, additive response of ionic liquids was found to be superior to those for conventional lubricants. It was speculated that the unique tribochemical reactions will lead us to design tailor-made lubricants. Lubrication mechanism of ionic liquids is discussed from the viewpoint of tribochemistry.     

Mechanism of tribofilm formation with P and S containing ionic liquids

Mechanism of tribofilm formation with two ionic liquids (IL), choline bis(2-ethylhexyl)phosphate and choline dibutyldithiophosphate was studied. XANES analysis of tribofilms indicates that the underlying mechanism of tribofilm formation with ionic liquids is similar to that formed when ZDDP is used. The chain length of glassy polyphosphates with IL in base oil is longer in length in comparison to that formed with ZDDP under identical conditions indicating a higher level of networking. In fully formulated oils, Ca replaces Zn and Fe (in the case of ZDDP) or Fe (when IL׳s are used) as the primary cationic species present in the polyphosphate network. The sulfur is present in the form of sulfates of different cationic species including Fe and Ca.     

硬质合金材料的应用与发展

在回顾硬质合金材料的历史发展和现状的基础上,重点介绍了在该领域中上海材料研究昕取得的典型实际成果及工业应用概况。最后,提出了硬质合金材料今后值得重视的若干发展方向。     

Benzotriazole as the additive for ionic liquid lubricant: one pathway towards actual application of ionic liquids

In this paper, we report on the first tribological evaluation of the room temperature ionic liquids (RTILs) compatible lubricant additive. Benzotriazole (BTA) was chosen for study in that it shows good miscibility with imidazole ionic liquids because of similar molecular structure. BTA can greatly improve the tribological behaviors of ionic liquids carrying hexafluorophosphate anions for Steel/Cu–Sn alloy sliding pair mainly because of the alleviation of corrosion. The worn surface of the bronze was investigated by X-ray photoelectron spectroscopy (XPS), which revealed complex tribochemical reactions during the sliding process. A protective film comprised of [Cu(–C₆H₅N₃)] and Cu₂O is formed. Strong interaction between benzotriazole and the surface of Cu alloy was proposed to account for the excellent anti-wear and anti-corrosion improvement capability.     

Preparation of functional ionic liquids and tribological investigation of their ultra-thin films

Novel ionic liquid materials based on 1-alkyl-4-[5-(alkylsulfanyl)-1,3,4-oxadiazol-2-yl] pyridinium tetrafluoroborate derivatives were synthesized. Ultra-thin ionic liquid films were prepared on silicon wafers by means of spin-coating and their tribological properties were investigated. The wear life increases when the chain length decreases. Under low load, they show good tribological properties which are closely related to the interaction between ionic liquid and substrate surface, especially the film of 1-ethyl-4-[5-(ethylsulfanyl)-1,3,4-oxadiazol-2-yl] pyridinium tetrafluoroborate, it has low friction coefficient and long wear life. So, this kind of ionic liquid can be potentially applied as ultra-thin lubricating coating.     

Lubricant film formation properties of alkyl imidazolium tetrafluoroborate and hexafluorophosphate ionic liquids

The film thickness and friction properties of four imidazolium ionic liquids (1-butyl-3-methyl tetrafluoroborate and hexafluorophosphate and 1-hexyl-3-methyl tetrafluoroborate and hexafluorophosphate) were measured for mixed rolling-sliding conditions and the results compared to an additised mineral oil. Film thickness results showed that three of the fluids demonstrated classical EHL behaviour; however, the 1-butyl-3-methyl fluids gave anomalously thick, time-dependent films at low speeds (<0.3 m/s). Post-test inspection of the specimens revealed a loosely bound brown film deposited in the track. Film formation appeared to originate in the bulk fluid where brown “fibrous” agglomerations were observed. These were flocculated by shear flow and deposited in the track after passing through the contact. Overall the RTIL friction coefficients were less than the mineral oil for all conditions investigated. In the absence of thick film formation all RTILs gave a similar friction coefficient of 0.03 in the boundary regime, which is thought to be due to electrical double layer formation. In the fluid film regime traction was determined by the nature of the anion.     

Hard-alloy metal-cutting tool for the finishing of hard materials

The creation of a hard-alloy metal-cutting tool for the finishing of materials that are hard to machine is considered. To improve the machining quality and productivity, the use of a tool with 1-μm sharpness is proposed.     

冷硬材料的硬车削技术浅析

分析了硬车削的定义、所需的条件以及硬车削技术在生产中的实际应用，指出硬车削技术具有广泛的应用前景。     

Insight into degradation of ammonium-based ionic liquids and comparison of tribological performance between selected intact and altered ionic liquid

Due to lack of experimental work clearly describing ionic liquids (ILs) degradation which could take place under application conditions, specially designed artificial alteration experiments were performed to derive degradation mechanisms most probably taking place under long-term thermo-oxidative stress. The use of mass spectrometry enabled identification of IL degradation products both in liquid and gas phases. The mechanisms of intermolecular transmethylation in ammonium ILs proceeding via anion-derived intermediates have been identified. Hence, care has to be taken for applying ILs in processes, e.g. in lubrication applications, as it is shown that IL altered products can negatively influence friction and wear performance as well as can lead to build-up of vapour pressure in otherwise non-volatile ILs.