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Developing functional additive resistant to space atomic oxygen (AO) irradiation through simple molecular design and chemical synthesis to enhance the lubricating performance of multialkylated cyclopentanes (MACs) oil is a significant challenge. Herein, sulfur-containing polyhedral oligomere silsesquioxane (POSS) were synthesize via a click-chemistry reaction of octavinyl polyhedral oligomeric with alkyl sulfide. The reduce-friction (RF), anti-wear (AW) properties and anti-AO irradiation of POSS-S-R as MACs base oil additives in atmospheric and simulated space environments were systematically investigated for the first time. Results demonstrate that POSS-S-R not only possesses outstanding anti-AO irradiation capacity but also effectively improves the RF and AW of MACs in atmospheric or simulated space surroundings. This improvement is due to the excellent anti-AO irradiation properties of the POSS structure itself and the high load-carrying ability of silicon-containing and sulfur-containing compounds generated by tribo-chemical reactions, which effectively separates the direct contact of the friction interface. We believe that this synthesized POSS-S-R is a promising additive for space lubricants. [ABSTRACT FROM AUTHOR]

This study presents a nitrogen-doped microporous carbon nanospheres (N@MCNs) prepared by a facile polymerization–carbonization process using low-cost styrene. The N element in situ introduces polystyrene (PS) nanospheres via emulsion polymerization of styrene with cyanuric chloride as crosslinking agent, and then carbonization obtains N@MCNs. The as-prepared carbon nanospheres possess the complete spherical structure and adjustable nitrogen amount by controlling the relative proportion of tetrachloromethane and cyanuric chloride. The friction performance of N@MCNs as lubricating oil additives was surveyed utilizing the friction experiment of ball-disc structure. The results showed that N@MCNs exhibit superb reduction performance of friction and wear. When the addition of N@MCNs was 0.06 wt%, the friction coefficient of PAO-10 decreased from 0.188 to 0.105, and the wear volume reduced by 94.4%. The width and depth of wear marks of N@MCNs decreased by 49.2% and 94.5%, respectively. The carrying capacity of load was rocketed from 100 to 400 N concurrently. Through the analysis of the lubrication mechanism, the result manifested that the prepared N@MCNs enter clearance of the friction pair, transform the sliding friction into the mixed friction of sliding and rolling, and repair the contact surface through the repair effect. Furthermore, the tribochemical reaction between nanoparticles and friction pairs forms a protective film containing nitride and metal oxides, which can avert direct contact with the matrix and improve the tribological properties. This experiment showed that nitrogen-doped polystyrene-based carbon nanospheres prepared by in-situ doping are the promising materials for wear resistance and reducing friction. This preparing method can be ulteriorly expanded to multi-element co-permeable materials. Nitrogen and boron co-doped carbon nanospheres (B,N@MCNs) were prepared by mixed carbonization of N-enriched PS and boric acid, and exhibited high load carrying capacity and good tribological properties. [ABSTRACT FROM AUTHOR]

Lubricants are often contaminated by water in different ways. Water-polluted lubricants extremely accelerate wear corrosion, leading to the deterioration of lubricity performance. Recently, multiphase media superwettability has been developed to endow one surface with compatible functions, such as on-demand separation of oily wastewater. However, realizing the robustness of the dual superlyophobic surface to solve water-caused lubricant deterioration and water contamination as needed remains challenges. Herein, a robust dual superlyophobic membrane is presented to realize on-demand separation for various lubricant—water emulsions. Compared to pure lubricants, the purified lubricants have equivalent tribology performance, which are much better than that of water-polluted lubricants. The as-prepared membrane maintains dual superlyophobicity, high-efficient for water or lubricant purification, and excellent tribology performance of the purified lubricant, even after immersion in hot liquids for 24 h, multicycle separation, and sandpaper abrasion for 50 cycles. Water-polluted lubricant extremely accelerates wear corrosion to promote catalytic dehydrogenation of lubricants, generating too much harmful carbon-based debris. This work shows great guiding significance for recovering the tribology performance of water-polluted lubricants and purifying water by the dual superlyophobic membrane. [ABSTRACT FROM AUTHOR]

This present study aimed to clarify the effect of contact scale and surface topography of substrates with different roughnesses on the actual contact area, tangential stiffness, and tangential deformation of the substrate at micro- and macro-scales via finite element method (FEM) simulations, as well as the final tribological performances of MoS2 coatings by experiments. The MoS2 coatings were deposited on stainless steel (SS) substrates with different roughnesses, and the settings in the simulation models were based on the roughness of the SS substrates. The predicted tribological behavior of the simulation results was confirmed by the morphological and compositional analysis of the wear track using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), 3D profilometer, and Raman spectroscopy. The results showed that the substrate with a surface roughness of Ra 600 nm (R600), coated by MoS2 nanosheets, exhibited excellent tribological properties at both micro- and macro-scales. At the micro-scale, the lubrication lifetime of R600 was as long as 930 cycles, while the substrates with surface roughnesses of Ra 60 nm (R60) and Ra 6 nm (R6) had a lubrication lifetime of 290 cycles and 47 cycles, respectively. At the macro-scale, the lifetime of the substrate R600 was 9509 cycles, which was nearly six times longer than the 1616 cycles of substrate R60. For the rough surface of substrate, the surface grooves could not only effectively preserve the lubricant but also continuously release them, ensuring that the lubricants with low shear strength were always present in the contact interface. It was further verified that the high surface roughness of the substrate reduced friction and wear by reducing the actual contact area and enhancing the tangential stiffness of asperities, thereby prolonging the lubrication lifetime. The wear mechanisms were discussed in terms of the morphology and chemical composition of the wear tracks. [ABSTRACT FROM AUTHOR]

The WS2/P201 hybrid lubrication system was constructed with a combination of WS2 film deposited by magnetron sputtering and P201 oil. The tribological properties of the WS2/P201 hybrid system with atomic oxygen (AO) irradiation are inferior compared to WS2 film and the WS2/P201 hybrid system without AO irradiation. Mainly the effects of AO irradiation on the components and tribological performance of the WS2/P201 hybrid system were studied. AO irradiation not only leads to breakage of chemical bonds and formation and volatilization of small molecular compounds, but also triggers crosslinking reaction between molecular chains, which results in an increase of molecular weight and broadening of the distribution of molecular weight. The loose columnar crystal pores are filled with viscous oil and the S/W ratio decreases notably after AO irradiation. The lubricating and failure mechanisms of the WS2/P201 hybrid system under AO irradiation were revealed. It is found that WO3 formed during AO irradiation plays an important role in the sliding process. [ABSTRACT FROM AUTHOR]

Two-dimensional compounds combining group IV A element and group V A element were determined to integrate the advantages of the two groups. As a typical 2D group IV–V material, SiP has been widely used in photodetection and photocatalysis due to its high carrier mobility, appropriate bandgap, high thermal stability, and low interlayer cleavage energy. However, its adhesion and friction properties have not been extensively grasped. Here, large-size and high-quality SiP crystals were obtained by using the flux method. SiP nanosheets were prepared by using mechanical exfoliation. The layer-dependent and velocity-dependent nanotribological properties of SiP nanosheets were systematically investigated. The results indicate the friction force of SiP nanosheets decreases with the increase in layer number and reaches saturation after five layers. The coefficient of friction of multilayer SiP is 0.018. The mean friction force, frictional vibrations, and the friction strengthening effect can be affected by sliding velocity. Specially, the mean friction force increases with the logarithm of sliding velocity at nm/s scale, which is dominated by atomic stick-slip. The influence of frequency on frictional vibration is greater than speed due to the different influences on the change in contact quality. The friction strengthening saturation distance increases with the increase in speed for thick SiP nanosheets. These results provide an approach for manipulating the nanofriction properties of SiP and serve as a theoretical basis for the application of SiP in solid lubrication and microelectromechanical systems. [ABSTRACT FROM AUTHOR]

The high specific-strength of glass fibers and exceptional self-lubrication of polytetrafluoroethylene (PTFE) fibers promote the potential application of hybrid PTFE/glass fabric composites in the tribological field, but their weak interfacial adhesion and inferior thermal properties significantly inhibit their tribological performance and reliability. Herein, a hybrid of polydopamine/silicon carbide/polyethyleneimine (PDA/SiC/PEI) functional coating was co-deposited onto the hybrid PTFE/glass fabric surface through a one-step impregnation method, leading to increased surface roughness and abundant amine groups. Tensile and peeling tests showed that this functional coating offered 47.8% enhancement in the fabric/matrix interfacial adhesion without compromising the strength of the pristine fabric. Moreover, the additional incorporation of WS2, and aluminum nitride (AlN) micro-fillers contributed to the development of a high-quality tribofilm and improved the thermal properties of fabric composites. The results of wear tests proved that the hybrid-fabric composites, after the introduction of functional coating and micro-fillers, exhibited outstanding tribological performance, which was attributed to the superior interfacial adhesion as well as the synergistic enhancement effects between WS2 and AlN micro-fillers. [ABSTRACT FROM AUTHOR]

Ionic liquids (ILs) have emerged as potential lubricants in 2001. Subsequently, there has been tremendous research interest in ILs from the tribology society since their discovery as novel synthetic lubricating materials. This also expands the research area of ILs. Consistent with the requirement of searching for alternative and eco-friendly lubricants, IL lubrication will experience further development in the coming years. Herein, we review the research progress of IL lubricants. Generally, the tribological properties of IL lubricants as lubricating oils, additives and thin films are reviewed in detail and their lubrication mechanisms discussed. Considering their actual applications, the flexible design of ILs allows the synthesis of task-specific and tribologically interesting ILs to overcome the drawbacks of the application of ILs, such as high cost, poor compatibility with traditional oils, thermal oxidization and corrosion. Nowadays, increasing research is focused on halogen-free ILs, green ILs, synthesis-free ILs and functional ILs. In addition to their macroscopic properties, the nanoscopic performance of ILs on a small scale and in small gaps is also important in revealing their tribological mechanisms. It has been shown that when sliding surfaces are compressed, in comparison with a less polar molecular lubricant, ion pairs resist "squeeze out" due to the strong interaction between the ions of ILs and oppositely charged surfaces, resulting in a film that remains in place at higher shear forces. Thus, the lubricity of ILs can be externally controlled in situ by applying electric potentials. In summary, ILs demonstrate sufficient design versatility as a type of model lubricant for meeting the requirements of mechanical engineering. Accordingly, their perspectives and future development are discussed in this review. [ABSTRACT FROM AUTHOR]

Fabric composites are widely applied as self-lubricating liner for radial spherical plain bearings owing to their excellent mechanical and tribological properties. Nevertheless, the poor interfacial strength between fibers and the resin matrix limits the performance of composites utilized as tribo-materials. To overcome this drawback, a mild layer-by-layer (LbL) self-assembly method was successfully used to construct hybrid fabric composites in the present work. In addition, this investigation addressed the effect of self-assembly cycles on the friction and wear behaviors of hybrid fabric composites under dry sliding condition. The results demonstrate that fabric composites with three or more self-assembly cycles have significantly enhanced surface activities and anti-wear performances. The results obtained in this work can provide guidance in the preparation of selflubricating liner composites and highlight how the LbL self-assembly techniques could influence the properties of hybrid fabric composites. [ABSTRACT FROM AUTHOR]

In this work, Al-20Si-5Fe-2Ni/ZrB2 composites with 0-20 wt% ZrB2 were fabricated by spark plasma sintering. The effects of ZrB2 content on the microstructure, mechanical properties and high-temperature tribological behavior of the composites were investigated. The results indicate that Si, Al5FeSi, and ZrB2 particles are uniformly distributed in the aluminum matrix. The density, hardness, and compressive strength increase with increasing ZrB2 content. The friction coefficient and wear rate are dependent on the ZrB2 content and test temperature. At a certain temperature, the friction coefficient increases with an increase in ZrB2 content, whereas the wear rate shows a reverse trend. Due to the improvement in thermal stability and high-temperature softening resistance, the composite shows improved wear resistance and increased transition temperature from mild wear to severe wear. [ABSTRACT FROM AUTHOR]

Plasma electrolytic oxidation (PEO) coatings were prepared on low carbon steel from electrolytes with different silicate concentrations. The microstructure, elemental and phase compositions of the PEO coatings were analyzed by scanning electron microscope, energy-dispersive spectrometer, and x-ray diffraction, respectively. The adhesion of PEO coatings with low carbon steel substrate was qualitatively examined by thermal shock tests. The tribological properties were evaluated by a reciprocating tribometer sliding against a Si3N4 ceramic ball. The corrosion behaviors of PEO coatings were investigated in 3.5 wt.% NaCl solution by electrochemical impedance spectra and potentiodynamic polarization. Results indicated that all the PEO coatings were comprised of amorphous SiO2 and Fe-containing oxides; however, the silicate concentration in electrolyte showed significant influence on the growth and the performance of PEO coatings. The PEO coating prepared from the electrolyte with silicate concentration of 30 g/L had the highest Fe content because the substrate was more readily oxidized and showed a dense structure, resulting in the best comprehensive performance of adhesion, wear resistance, and corrosion resistance. [ABSTRACT FROM AUTHOR]

The plasma electrolytic oxidation (PEO) coatings were prepared on low carbon steel from silicate electrolyte without and with Al nanoparticles, respectively. The structure, composition, anti-wear and anti-corrosion properties of the PEO coatings were investigated. The results indicated that the Al nanoparticles in the silicate electrolyte turned into alumina during the PEO process and reduced the amount of iron oxides in the coating. The PEO coating prepared from silicate electrolyte with Al nanoparticles showed enhanced wear resistance due to the formation of alumina. Furthermore, the coating was characterized by sealed pores on the surface, different from the open pores on the surface of PEO coating prepared from silicate electrolyte without Al nanoparticles. The modified structure and the changed composition of PEO coating by introducing Al nanoparticles in the electrolyte significantly improved the corrosion resistance of the coating, demonstrated by the electrochemical corrosion and salt spray tests. [ABSTRACT FROM AUTHOR]

The friction and wear properties of supramolecular gel lubricant impregnated into the laser surface texturing steel fabricated by laser micromachining were investigated, with that impregnated with commercial oil PAO10 as a comparison. Scanning electron microscopy characterization shows the gel lubricant have been successfully pumped into the pores of laser surface texturing steel from liquid state and solidified afterwards via supermolecular assembly. The friction was measured on an Optimal SRV-IV oscillating reciprocating friction and wear tester. It is shown that laser surface texturing steel impregnated with gel lubricant exhibited outstanding friction reduction and antiwear performance than impregnated with PAO10. The gelator molecules act not only to solidify lubricating oil, but also contribute to boundary lubrication by strong adsorption on substrate surface. The instant self-assembly of gelator to solidify lubricating oils makes impregnation of lubricants easier and helps to keep lubricating oils retention for long-term functioning. [ABSTRACT FROM AUTHOR]

Molybdic acid–modified phenolic resin (Mo-PF) had been synthesized and was used to prepare fabric composites. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) indicated that the thermal properties were improved when the phenolic resin was modified by molybdic acid. The tribological properties of the fabric composites were evaluated by a pin-on-disk tribometer. Compared to the unmodified ones, the result showed that the fabric composites made by Mo-PF displayed a lower wear rate under all tested conditions. The optimal content of molybdic acid to modify the phenolic resin was obtained, as the correspondingly produced fabric composite displayed improved tribological properties. The effect of applied load, sliding speed, and environment temperature on tribological properties of the fabric composites and the related mechanisms were also discussed. [ABSTRACT FROM PUBLISHER]

Purpose - The aim of this paper was to inhibit the serious corrosion of conventional ionic liquids, a series of new ionic liquids (ILs) containing the triazole functionality, as the anti-corrosion groups were synthesized in this work. Design/methodology/approach - It is well known that nitrogen and sulfur containing organic compounds have been traditionally used as corrosion inhibitors. Among them, triazole derivatives are most often used as corrosion inhibitors. To alleviate the corrosion of the ILs and further improve the anti-wear property, the authors prepared a series of imidazolium ILs modified with the triazole functionality in the present study. Findings - The corrosion behavior of the ILs was evaluated with the iron disk corrosion test and their tribological properties were investigated on an Optimol SRV IV oscillating friction and wear tester at elevated temperatures. The results showed that the ILs with the triazole functionality could effectively reduce the corrosion and exhibit a smaller friction coefficient and wear volume than the unmodified counterpart. The ILs containing the triazole functionality can be used as the single component anti-corrosion base oils even at elevated temperatures. Originality/value - The results showed that the ILs with the triazole functionality could effectively reduce the corrosion and exhibit a smaller friction coefficient and wear volume than the unmodified counterpart. The ILs containing the triazole functionality can be used as the single component anti-corrosion base oils even at elevated temperatures. [ABSTRACT FROM AUTHOR]

The tribological behaviors of hybrid polytetrafluoroethylene (PTFE)/Nomex fabric/phenolic composite under dry sliding condition and water-bathed sliding conditions were investigated using a pin-on-disk type tribometer. The results showed that this hybrid fabric reinforced composite exhibited a higher wear rate and a lower friction coefficient under water-bathed sliding conditions compared to that measured under dry sliding condition. Scanning electron microscopy (SEM) and X-ray photoelectron microscopy (XPS) analysis demonstrated that under water-bathed sliding conditions the transfer films formed on the counterpart pins surface were of high roughness and less PTFE transferred onto the pin surface, compared to that under dry sliding condition. Moreover, the hybrid fabric composite displayed varied tribological behaviors when distilled water-bathed sliding condition and seawater-bathed sliding condition were applied separately. [ABSTRACT FROM AUTHOR]

To improve the tribological properties of WS film both in vacuum and in humid air conditions, its microstructure was optimized by doping different concentrations of Cu via radio frequency co-sputtering method. The film microstructure and composition were investigated by field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, grazing incidence X-ray diffraction and high-resolution transmission electron microscopy. It was verified that Cu was presented in amorphous phase in the WS matrix and could also induce amorphization and densification of the composite films gradually. The film microstructure changed from coarse columnar platelet structure at low Cu content (0-5.8 at.%) to transition structure with two separate layers at increased Cu content (11.5-16.2 at.%) and to a featureless structure at high Cu content (above 24.4 at.%). The mechanical and tribological properties of films were evaluated using the scratch tester and ball-on-disk tribometer, respectively. It was found that the incorporation of a suitable content of Cu dopant could significantly improve the film toughness, but excess amount of Cu dopant lead to high brittleness. All the composite films exhibited much lower wear rate and longer wear life than those of pure WS film both in vacuum and in humid air conditions. The wear mechanisms were proposed after correlating the mechanical performance with film microstructure. [ABSTRACT FROM AUTHOR]

The titanium/silicon mono- and co-doped amorphous carbon films were deposited by mid-frequency magnetron sputtering Ti target, Si target, and Ti80S20 alloy target, respectively. The effects of doped elements on the composition, surface morphology, microstructure, and mechanical and tribological properties of the films were investigated. The results reveal that the ratio of sp3 and sp2 carbon bonds of the films is regulated between 0.28 and 0.62 by a combination of Ti and Si dopant. The addition of small amounts of silicon leads to an increase in sp3 bonds and disorder degree of the sp2 carbon. The co-doped film exhibits significantly superior friction performance than the mono-doped films. The ultra-low friction (μ < 0.01) was achieved under a load of 2 N in ambient air with 40% RH. By comparing to the mono-and co-doped films, it is thought that the sp3/sp2 ratio of the films may play a key role for the superlow friction. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper, we investigated the effect of counterface of AISI 52100 steel and ceramics of SiC, AlO, and SiN on the tribological behavior of TiAlC at ambient. The results showed that the tribological properties of TiAlC are strongly dependent on the counterfaces. Under present test conditions, the tribocouple of TiAlC/SiC exhibits lower coefficient of friction (CoF) 0.40, TiAlC/AISI 52100 steel shows a rising CoF from 0.1 to 0.63, both TiAlC/SiN and TiAlC/AlO tribopartners exhibit higher CoF of 1.22 in average. The TiAlC exhibits the lowest wear rate sliding against AISI 52100 steel, the wear rate of TiAlC sliding against AlO, SiN, and SiC are higher and comparable. The morphologies of the worn surfaces of the TiAlC are observed by scanning electron microscopy, and the element states are analyzed by X-ray photoelectron spectroscopy. The wear mechanisms are discussed. [ABSTRACT FROM AUTHOR]

ABSTRACT Nano-calcium borate (NCB) with an average particle size of about 70 nm was synthesised via ethanol supercritical fluid drying technique, and the morphology and microstructures of as-prepared particles were characterised by means of scanning electron microscope (SEM, JEOL LTD., Tokyo, Japan) and X-ray powder diffraction. The friction and wear behaviour of the NCB as additive in lithium grease were evaluated with an Optimol-SRV IV (Optimol Instruments Prüftechnik GmbH, Munich, Germany) oscillating friction and wear tester (SRV tester). The morphology and surface composition of the worn surfaces of lower discs after SRV test were analysed by SEM and X-ray photoelectron spectroscopy (XPS, Physical Electronics, Inc., USA). The result demonstrated that the anti-wear and load-carrying capacities of the lithium grease were significantly improved, and the friction coefficient of the lithium grease decreased with the addition of NCB additive. The analytical results of XPS indicate that the good tribological performance of NCB is attributable to the formation of a boundary lubrication film composed of deposited NCB and the tribochemical reaction products such as B2O3, CaO and iron oxides on the rubbing surface. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to study the antirust, tribological performance and anti-wear (AW) mechanism of the of soybean lecithin (SL) as a kind of multifunctional lubricant additive. Design/methodology/approach – As a kind of multifunctional lubricant additive, the antirust performance of SL was tested according to ASTM D 665, and meanwhile, its tribological performances were also evaluated by Optimol SRV-I oscillating reciprocating friction and wear tester and four ball tester. The worn steel surfaces were investigated by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS). Findings – The results showed that the SL exhibited excellent antirust properties in different base stock, and could effectively improve the AW and extreme pressure (EP) performances. The results of SEM and XPS indicated that a protective film was formed between steel-steel friction pair during the tribological test. Originality/value – This paper first investigated the antirust properties and the tribological mechanism of the SL as a kind of multifunctional lubricant additive, which can be very useful and will promote the application of SL in lubricant industry. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to investigate the tribological properties of Si3N4 sliding against Dy-sialon ceramics lubricated by two novel phosphazenes bridged fluorophenoxycyclotriphosphazene (coded as L-2P) and metal halide-stabilized linear phosphazene derivatives (coded as LMZn-3). The traditional phosphazene tetrakis (3-trifluoromethylphenoxy)-bis(4-fluorophenoxy) – cyclotriphosphazene (X-1P) was also tested as the reference. Design/methodology/approach – The lubricity characteristics of phosphazene derivatives were evaluated on an Optimol SRV oscillating friction and wear tester. The morphology of the worn sialon surface was analyzed with a scanning electron microscope (SEM) and X-ray photoelectron spectroscope (XPS). Findings – The two novel phosphazenes are effective lubricants for Dy-sialon and show superior tribological properties to traditional phosphazene X-1P and glycerol. Among all lubricants, linear phosphazene LMZn-3 exhibits the lowest wear volume loss at 20°C or 100°C. Moreover, LMZn-3 and L-2P show much better antiwear ability than X-1P under higher load than 60N. The decreased friction coefficient and wear volume of Dy-sialon ceramics under lubrication of the phosphazene lubricants are attributed to the tribochemical products mainly consisting of organic oxyfluoride or carbonfluoride species and silicon fluoride. Research limitations/implications – The paper deals with only limited compounds. The paper works on the subject progressively to explore more combinations for better tribological properties. Practical implications – The phosphazene derivatives present better tribological performance used as base oils and additives. Originality/value – There are few data about other phosphazene with different structures, such as bridged cyclotriphosphazene and metal halide-stabilized linear phosphazene, used as lubricants for ceramics materials. [ABSTRACT FROM AUTHOR]

It is a challenge to design self-lubricating materials that exhibit and maintain reduced friction coefficient as well as high strength over a wide range of temperatures. A high-temperature self-lubricating nickel-alloy-based composite was created using the hot pressing technique. The composite exhibited high relative density, and simultaneously superior lubricating properties, average friction coefficient below 0.25 from room temperature to 800 °C, and high strength, 470 MPa of tensile strength and 1500 MPa of compressive strength. The composite was very promising in high-temperature tribology. [ABSTRACT FROM AUTHOR]

Dry sliding wear behavior of nanocrystalline Fe88Si12 alloy has been investigated compared with coarse grained counterpart. The friction coefficient of the Fe88Si12 alloy changes slightly with grain size. But the wear resistance of the Fe88Si12 alloy improves as the grain size decreases to 40 nm, and then weakens when the grain size decreases from 40 nm to 10 nm. The grain size has significantly effect on the tribological behavior of Fe88Si12 alloy by modifying the hardness and the tribo-chemical interaction on the sliding zone during the wear process. [ABSTRACT FROM AUTHOR]

Three kinds of protic ionic liquids with ammonium salts, dodecylamine salt of S-(1-carboxyl)-propyl- N, N-diethyldithiocarbamate (coded as DDED), dodecylamine salt of S-(1-carboxyl)-propyl- N, N-dibutyldithiocarbamate (coded as DDBD), dodecylamine salt of S-(1-carboxyl)-propyl- N, N-dioctyldithiocarbamate (coded as DDOD) were synthesized, characterized, and their tribological behaviors as additives in lithium complex grease were studied for steel/steel contact. The tribological properties were evaluated on an Optimol SRV-I oscillating reciprocating friction and wear tester and a MRS-10A lever-type fourball tester in details. The results of tests demonstrated that the novel additives were able to remarkably improve the extreme pressure, friction-reducing, and anti-wear properties of the base lithium complex grease when added at a low adding concentration (<3 %). Based on the performance comparison of three novel additives with different chain lengths in DTCs groups and a commercial additive with similar DTCs groups but no PILs groups, methylene bis dibutyldithiocarbamate (T323), a number of primary conclusions were drawn. The carboxylic acid ammonium salts, the typical function groups of the PILs existing in the molecule structures of three additives, could not only greatly enhance the physical and/or chemical adsorption on the metal surface to reduce friction of the base grease, and also have better synergism with DTCs groups in improving anti-wear performance of base grease. Based on the characterization and analysis of the worn surface by a PHI-5702 multifunctional X-ray photoelectron spectrometer (XPS) and a JSM-5600LV scanning electron microscope (SEM), a protective film consisting of FeS, organic compound was formed on the surface. The ordered adsorbed film and chemical reactive film on the sliding steels contributed to the main factor in improving the tribological properties of base lithium complex grease. [ABSTRACT FROM AUTHOR]

The tribological behavior of a Ti-46Al-2Cr-2Nb alloy prepared by hot-pressed sintering was investigated under liquid paraffine lubrication against AISI 52100 steel ball in ambient environment and at varying loads and sliding speeds. For comparison, the tribological behavior of a common Ti-6Al-4V alloy was also examined under the same testing conditions. The worn surfaces of the two alloys were analyzed using a scanning electron microscope. The friction coefficient of the Ti-46Al-2Cr-2Nb alloy in the range of 0.13-0.18 was significantly lower than that of the Ti-6Al-4V alloy (0.4-0.5), but comparable to that under dry sliding, which indicated that TiAl intermetallics could be more effectively lubricated by liquid paraffine than titanium alloys. Applied load and sliding speed have little effect on the friction coefficient of the Ti-46Al-2Cr-2Nb alloy. The wear rate of the Ti-46Al-2Cr-2Nb alloy was about 45-120 times lower than that of Ti-6Al-4V alloy owing to Ti-6Al-4V alloy could not be lubricated effectively. The wear rate of the Ti-46Al-2Cr-2Nb alloy increased with increasing applied load, but decreased slightly at first and then increased with increasing sliding speed. The wear mechanism of the Ti-46Al-2Cr-2Nb intermetallics under liquid paraffine lubrication was dominated by main plowing and slight flaking-off, but that of the Ti-6Al-4V alloy was plastic deformation and severe delamination. [ABSTRACT FROM AUTHOR]

The tribological behaviour of Fe-28Al-5Cr and its composites containing 15, 25 and 50 wt% TiC (corresponding to 19.3, 31.2 and 57.6 vol%), produced by hot-pressing process, was investigated under liquid paraffine lubrication against an AISI 52100 steel ball in ambient environment at varied applied loads and sliding speeds. It was found that the wear resistance increased and friction coefficient decreased with increasing of TiC content. The coefficients of friction are in the range of 0.09-0.14 at the given testing conditions. The wear rates of all the materials except the 50% composite are on the order of 10-10 mm m, the wear rate for the 50% composite is too low to quantify under the two sliding conditions, (50 N, 0.04 m/s) and (100 N, 0.02 m/s). The wear rates of all the materials increase as applied load increases and the increasing extent diminishes with the increase of TiC content, but first increase slightly and then nearly remains steadiness with increasing sliding speed. The 50 wt% composite has wear resistance about 7-20 times better than pure Fe-28Al-5Cr at different sliding parameters. The enhanced wear resistance by TiC addition is attributed to the high hardness of the composites, as well as support of the oil lubrication film/layer by the hard TiC phase. The worn surfaces of all the materials are analyzed by a scanning electron microscope. The dominant wear mechanism of the Fe-28Al-5Cr and 15% composite is grooving and flaking-off, but those of the 25 and 50% composites are mainly shallow grooving. [ABSTRACT FROM AUTHOR]

The self-lubricating composites NiAl-BaF-CaF-Ag-Cr, which have varying fluoride contents, were fabricated by the powder metallurgy technique. The effect of fluoride content on the mechanical and tribological properties of the composites was investigated. The results showed that an optimal fluoride content and a balance between lubricity and mechanical strength were obtained. The NiAl-6.2BaF-3.8CaF-12.5Ag-10Cr composite showed the best friction coefficients (0.29-0.38) and wear rates (4.2 × 10-2.19 × 10mm N m) at a wide temperature range (room temperature to 800°C). Fluorides exhibited a good reduced friction performance at 400 and 600°C. However, at 800°C, the formation of BaCrO on the worn surface due to the tribo-chemical reaction at high temperatures provided an excellent lubricating property. [ABSTRACT FROM AUTHOR]

Five room temperature ionic liquids (ILs), 1-butyl-3-methylimidazolium hexafluorophosphate (L-P104), 1-hexyl-3-methylimidazolium hexafluorophosphate (L-P106), 1-octyl-3-methylimidazolium hexafluorophosphate (L-P108), 1-decyl-3-methylimidazolium hexafluorophosphate (L-P110), and 1-hexyl-3-methylimidazolium tetrafluoroborate (LB106) were studied as 1 wt% additives of polyurea grease for steel/steel contacts. Their tribological behaviors as additives of polyurea grease for steel/steel contacts were evaluated on an Optimol SRV-IV oscillating reciprocating friction and wear tester and an MRS-1J (G) four-ball tester at room and high temperatures. The friction test results showed that the ILs, as 1 wt% additives in polyurea grease for steel/steel contacts, had better friction reduction and anti-wear properties at high temperature than at room temperature, and ILs can significantly improve the friction reduction and anti-wear properties of polyurea grease compared with base grease containing 1 wt% of zinc dialkyldithiophosphate (T204). The excellent tribological properties are attributed to the formation of a surface protective film composed of FeF, nitrides, and compound containing the P-O bonding on the lubricated metal surface by a tribochemical reaction. The ordered adsorbed films and good miscibility of ILs with the base grease also contributed to the excellent tribological properties. Wear mechanisms and worn steel surfaces were studied by a PHI-5702 multifunctional X-ray photoelectron spectrometer and a JSM-5600LV scanning electron microscope. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to prepare water-soluble TiO2 nanoparticles and evaluate the tribological properties as additives in water. Design/methodology/approach – Nanoparticles present excellent friction-reducing and antiwear properties as additives in base oils. However, there are seldom literatures about the nanoparticles as additives in water as yet. In this work, water-soluble TiO2 nanoparticles were prepared by sol-gel method and characterized with transmission electron microscopy and selected area electron diffraction. The tribological properties as additives in water were investigated by SRV and the surface analysis by scanning electron microscope and X-ray photon electron spectroscope. Findings – TiO2 nanoparticles modified with polyethylene glycol have uniform size about 10 nm and easily dissolve in water. The tribological experiments showed TiO2 nanoparticles exhibit excellent friction-reducing and antiwear properties. Research limitations/implications – The paper is restricted to only TiO2 nanoparticles. Some other water-soluble nanoparticles also should be prepared and their tribological properties investigated. Practical implications – Water-soluble TiO2 nanoparticles could be used as water additives and improve the tribological properties. Originality/value – This paper emphasises that the water-soluble nanoparticles are prepared and could be used as water additives. [ABSTRACT FROM AUTHOR]

Abstract: The tribological properties of Ni-17.5Si-29.3Cr alloy against Si3N4 were studied on a ball-on-disc tribotester between room temperature and 1000°C. The effects of temperature on the tribological properties of the alloy were investigated. The worn surfaces of the alloy were examined using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results indicated that the tribological behavior of the alloy expressed some differences with increase in testing temperature. At low and moderate temperatures (below 800°C), the alloy showed excellent wear and oxidation resistances, and the wear rate of the alloy remained in the magnitude of 10−5 mm3/Nm; but at elevated temperature (800–1000°C), the wear and oxidation resistances decreased, and the wear rate of the alloy increased up to 10−4 mm3/Nm. The friction coefficient decreased from 0.58 to 0.46 with the rising of testing temperature from 20 to 600°C, and then remained nearly constant. The wear mechanism of the alloy was mainly fracture and delamination at low and moderate temperatures, and transformed to adhesive and oxidation at elevated temperatures. [Copyright &y& Elsevier]

Abstract: The tribocorrosion property of a Ni-17.5Si-29.3Cr alloy against a Si3N4 ball was studied in comparison with AISI321 stainless steel using a ball-on-disk reciprocating tribotester in 1M sulfuric acid (H2SO4) solution. The effects of load and sliding speed on the tribocorrosion properties of the alloy were investigated. The results indicated that the wear rate of the alloy increased while the friction coefficient decreased with increasing load. The wear rate of the alloy increased linearly with increasing sliding speed and the friction coefficient increased in the initial stages and then remained constant with increasing sliding speed. The wear mechanisms were mainly microploughing, uniform corrosion and pitting corrosion. Under the experimental conditions of the present study, the Ni-17.5Si-29.3Cr alloy showed excellent corrosion-resistence and anti-wear ability compared with AISI321 stainless steel. [Copyright &y& Elsevier]

Abstract: TiO2, SiO2, hydroxyapatite (HA), TiO2–HA and SiO2–HA thin films with good biocompatibility were grown on Ti–6Al–4V (coded as TC4) substrate by sol–gel and dip-coating processes from specially formulated sols, followed by annealing at 500°C. The chemical states of some typical elements in the target films were detected by means of X-ray photoelectron spectroscopy (XPS). High-resolution scanning electron microscopy (SEM) is applied to characterize the surface and cross-sectional morphologies of obtained films. Various phases of the films were characterized by XRD. The tribological properties of thin films sliding against an AISI52100 steel ball were evaluated on a reciprocating friction and wear tester. As a result, the target films were obtained. Compared with the TC4 substrate, all the sol–gel ceramic films are superior in resisting wear. Among all, HA film shows the best resistance while SiO2 film shows the worst wear resistance both under higher (3N) and lower load (1N). TiO2 shows a good wear resistance under lower load but higher load. Compared with TiO2, the wear resistance of the dual film TiO2–HA can be improved under 3N but deteriorated under 1N. Compared with SiO2, the wear resistance of SiO2–HA is improved both under 3N and 1N. Compared with HA, the wear resistances of dual films are deteriorated both under 3N and 1N. Under 0.5N, a very long wear life for TiO2–HA is also obtained, illustrating that the lower wear resistance of dual films is closely related to the applied load. SEM observation of the morphologies of worn surfaces indicates that the wear of TC4 is characterized by abrasive wear. Differently, abrasion, plastic deformation and micro-crack dominate the wear of ceramic films. The superior friction reduction and wear resistance of HA films are greatly attributed to the slight plastic deformation of the film. Sol–gel is a potential method being applied to implant materials for wear protection according to proper process designs. The single HA film and the dual TiO2–HA film is suggested for biomedical application from the point of view of wear protection. [Copyright &y& Elsevier]

The electrical contact resistance (ECR) measuring techniques were applied to study the deposit film forming process in the presence of Ag nanoparticles under boundary lubricating condition (abbreviated as NA) and the tribological performance of polyethylene glycol (PEG 300) containing different concentration of Ag nanoparticles were also evaluated. ECR values between tribo-pairs lubricated with PEG 300 containing Ag nanoparticles and blank PEG 300, which was used as a comparison, were detected on a reciprocating "ball-on-disk" mode wear tester and boundary lubricating conditions can be achieved. Aseries of tests were performed to investigate the effect of rubbing conditions such as normal load, frequency, and surface roughness on the ECR value. SEM and XPS were used to analyze the worn surface to confirm the results of ECR. Results showed that the use of the ECR measuring techniques permits visualization and synchronous study of deposit film formation. Variations in test conditions can only slightly affect the ECR lubricated with PEG 300 containing Ag nanoparticles but affect the ECR lubricated with blank PEG 300 significantly. It is realized that the anti-wear property is related to the formation of a deposited film of Ag nanoparticles. [ABSTRACT FROM AUTHOR]