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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]

Here, reported is a new, simple, and nonsynthetic way of in situ preparation of bi‐component supramolecular gel lubricants, which are formed by supramolecular self‐assembly of bis(2‐ethylhexyl) sulfosuccinate (AOT) and aromatic acid derivatives via the noncovalent interaction in the base lubricating oil. The formation mechanism of the gel lubricant was investigated by experimental and theoretical calculations. The results of 1H nuclear magnetic resonance, ultraviolet, and molecular dynamics simulations show that they formed a network structure through intermolecular hydrogen bonding and π–π stacking, thereby solidifying the base oil to form gel. The rheological and thermal analysis results show that these gels have shear thinning, creep recovery, and excellent thermal stability, and such characteristics make them potential as a lubricant for special mechanical working conditions. Indeed, tribological data also show that compared with commercial mineral oil 500SN, the gel lubricant has excellent lubricity, anti‐wear, and load‐carrying capacity, which is attributed to the introduction of the anionic surface active agent AOT molecules. Quartz crystal microbalance and X‐ray photoelectron spectrometer characterization proves that AOT forms an effective adsorption film and tribochemical reaction film on the contact surface in the process of friction. Here, reported is a new, nonsynthetic way of preparation of bi‐component gel lubricants, which are formed by supramolecular self‐assembly of bis(2‐ethylhexyl) sulfosuccinate (AOT) and aromatic acid derivatives via the noncovalent interaction in 500SN oil. Compared with 500SN, the gel lubricant has excellent lubricity, anti‐wear, and load‐carrying capacity, which is attributed to the introduction of anionic surface active agent AOT molecules. [ABSTRACT FROM AUTHOR]

Titanium boride (TiB 2 ) particles with different sizes were introduced into the hybrid Nomex/PTFE fabric composites to explore the high-temperature tribological properties. The thermal, mechanical and tribological properties of the filled fabric composites were investigated. Results showed that the presence of TiB 2 improved the thermal and mechanical properties obviously. High-temperature friction and wear tests also proved that the anti-wear ability of TiB 2 filled fabric composites was enhanced sharply without sacrificing the friction coefficients. Meanwhile, the effects of fillers content and size, applied load and temperature on tribological properties and wear mechanisms were also investigated. XRD and XPS were employed to analyze the worn surfaces and demonstrate the fabrication of tribofilm composed of TiO 2 and B 2 O 3 , which played a vital role in the excellent tribological behaviors. [ABSTRACT FROM AUTHOR]

Rotational speed has an important influence on the performance of coating materials. The a-C:Ta composite coatings were prepared by controlling the substrate rotational speed during deposition process using PVD technique. The results showed that the coating transformed from dense structure to columnar structure. Due to the changes of deposition time and the vapor incident angle of the sputtering ions, the sp2 hybrid structure increased and the C–Ta bonds contents decreased as a function of the rotational speed, which led to the improvement of adhesion force. The average friction coefficient of the composite coatings did not fluctuate significantly for the amorphous carbon matrix and the transfer films formed during friction, while the wear rates were gradually increased. The sample at 0.5 rpm possessed the lowest wear rate, which was mainly associated with the cooperative behavior of the dense structure and the formation of TaC nanoclusters in the composite coating. [ABSTRACT FROM AUTHOR]

The (CrAlTiNbV)N x coatings are fabricated by controlling the substrate bias via magnetron sputtering method. Under low substrate bias, the coating tends to form a loose columnar crystal structure with (200) preferred orientation. However, when the substrate bias increases, the coating transforms into a dense nanocrystalline structure, and the (111) orientation is enhanced. As the substrate bias increases, the residual stress and hardness of the coating gradually increase, while the adhesion strength decreases slightly. Friction tests show that the coating possesses the lowest average friction coefficient (about 0.06) and wear rate (8.7 × 10-9 mm3/N·m) in 4050# aviation lubricant, which is achieved under the substrate bias of -96 V and -126 V, respectively. [ABSTRACT FROM AUTHOR]

Elucidating the tribological behaviors of CoCrNi-based high-entropy alloys (HEAs) at cryogenic temperatures is crucial for their practical application. This work uncovers the correlation between the wear-induced microstructural evolutions and tribological properties of single-phase CoCrFeNiMn HEA and heterogeneous CoCrFeNiAl HEA upon two contact conditions at 173 K. When CoCrFeNiMn HEA matches with GCr 15 rather than Si 3 N 4 , low contact stress and high flash temperature suppress the inhomogeneous deformation initiated by martensitic transformation and in turn create a gradient nanograined tribo-layer activated by high-density dislocations and nano-scale deformation twins, which progressively accommodates the frictional strain and reduces wear by an order of magnitude. Instead, the tribological properties of the CoCrFeNiAl HEA sliding against Si 3 N 4 are slightly superior to those sliding against GCr 15 , owing to the elevated contact stress and reduced flash temperature thicken the protective recrystallized nanocrystalline tribo-layer. Our findings offer guidance for optimizing the tribological properties of HEAs in cryogenic environments. [ABSTRACT FROM AUTHOR]

The PEEK fabric-reinforced polyimide resin containing microcapsules with excellent mechanical and lubrication properties is reported. The GO-COOH/TiO 2 @PAO double-wall microcapsules (Capsule) were prepared by interfacial condensation polymerization of titanium butoxide (TBT) and self-assembly between GO-COOH and TiO 2 shell. A double crosslink of chemical bond (amide or ester) and hydrogen bond were constructed between microcapsules and polyimide (PI) to improve the mechanical properties of PEEK fabric-reinforced polyimide resin (PEEK/PI). It was identified that the addition of Capsules induced a 12.98% decrease in friction coefficient and 56.85% in the wear rate of the composites. This superior frictional behavior was primarily attributed to the combined effect of the boundary lubrication of PAO6, load-bearing effect of TiO 2 and PEEK fabric, and friction-reducing of GO-COOH. • Developed a novel containing oil microcapsules applied in lubrication. • The chemical bond and hydrogen bond was constructed between microcapsules and polyimide. • The microcapsules demonstrate good lubrication. • Regular fluctuations were observed in the friction curve of the samples containing microcapsules. [ABSTRACT FROM AUTHOR]

The poor dispersion stability of nanoparticles in oils limited their application. To address this problem, diverse of nanoparticles were introduced to supramolecular gels to fabricate a new lubricant (Nano-Gel). The results of molecular dynamics simulation show that gelators adsorbed onto the surface of nanoparticles at the non-covalent interaction. Besides, the intricate networks of supramolecular gels show spatial confinement to nanoparticles, which improved the dispersion stability of nanoparticles. Compared with supramolecular gels lubricant, Nano-Gel shows good anti-friction and anti-wear properties. The excellent tribological properties would be contributed to the self-repairing and tribo-film formed by nanoparticles and gelators. The Nano-Gels provide effective solution to the application of nanoparticles in lubricating oil, which have great values to prolong the life of mechanisms. [Display omitted] • The manuscript reported a new lubricant that diverse of nanoparticles were introduced to supramolecular gels. • The supramolecular gels realized the long-term dispersion stability of different nanoparticles in lubricants. • Dispersion stability mechanism of nanoparticles in supramolecular gels were penetrated by molecular dynamic simulations. • Nanoparticles as lubricant additives improved the anti-friction and anti-wear performances of supramolecular gels. [ABSTRACT FROM AUTHOR]

Abstract High concentration hydrogen peroxide solutions (HCHP) have been attractive as potentially future fuels. However, preparing inner moving-parts with both good compatibility and tribological properties under HCHP remains to be a challenge. Here, the high entropy alloys (HEAs)/Si 3 N 4 tribol-pair with compatible alloy and self-lubricating counterpart was researched. The wear-mechanisms and alloy-structure effects were studied. As a result, the realization of lubricated friction depends on whether the condition meet V formtion (formation velocity of colloidal films)- V attrition (attrition velocity of colloidal films)> V pit (increase velocity of pit depth and amount). HEAs with poorer corrosion resistance and higher strength could more easily achieve effective lubrication. The component inhomogeneity of different structures could promote the corrosion behavior. Graphical abstract Image 1 Highlights • Tribological properties of high entropy alloys under 90 wt. % H 2 O 2 solutions are studied. • The wear-mechanism variations and alloy-structure effects are exploited. • Wear mechanisms depend on the competition between V formtion , V attrition and V pit. • High entropy alloys with poor corrosion resistance and high strength easily achieve lubrication. [ABSTRACT FROM AUTHOR]

[Display omitted] • MXene@Fe 3 O 4 @PNA reduce the COF of water from 0.559 to 0.218, the wear volume decreased by 78.7%. • The excellent lubricating properties are attributed to the tribofilm and hydration layer. • MXene@Fe 3 O 4 @PNA can be heated to 73.1 °C and 123 °C in water and dry state under infrared light. Improving the tribological performance of water via designing nanomaterials as lubricant additive has garnered mounting interest. In this work, the poly-(N-isopropylacrylamide) microgel is grafted onto Fe 3 O 4 nanoparticles surface (Fe 3 O 4 @PNA) via free radical polymerization. Then, the Fe 3 O 4 @PNA can self-anchored on the MXene nanosheets via hydrogen bonding interaction to obtain MXene@Fe 3 O 4 @PNA composite. The as-prepared MXene@Fe 3 O 4 @PNA can effectively reduce friction and wear when used as a water-based lubricant additive. Compared with pure water, the average coefficient of friction (COF) and wear volume decrease by 61% and 78.7%, respectively. The lubrication mechanism was analyzed by focused ion beam technique-TEM (FIB-TEM) and X-ray photoelectron spectroscopy (XPS). The outstanding tribological performance of MXene@Fe 3 O 4 @PNA is attributed to the synergistic lubrication effect of MXene and Fe 3 O 4 @PNA. Interlayer shear of MXene and spherical Fe 3 O 4 @PNA can make MXene@Fe 3 O 4 @PNA play a full role of sliding friction and rolling friction mechanism, which can induce tribo-chemical reactions to form a protective film on the contact area of the friction pair. In addition, the hydrophilic groups of the MXene@Fe 3 O 4 @PNA can adsorb a large number of water molecules and form a hydration layer, reducing the agglomeration of nanosheets and acting as a boundary lubrication film. Moreover, the as-prepared MXene@Fe 3 O 4 @PNA exhibit excellent photothermal conversion performance in both underwater environment and dry state. Based on this characteristic, infrared light can be collected efficiently and stored quickly. Then, convert and utilize it. Therefore, the multifunctional MXene@Fe 3 O 4 @PNA has a broad application prospect as a water-based intelligent lubrication additive. [ABSTRACT FROM AUTHOR]

TiN-doped Sialon matrix composites are potential candidates for high temperature applications due to their excellent mechanical and tribological properties. The objectives of this work are to thoroughly research the mechanical properties and tribological behaviors of the TiN reinforced Sialon composites and reveal their toughening and wear mechanisms. Results show that the fracture toughness can be obviously enhanced by doping TiN. The fracture toughness of the composite with 10 wt% TiN reaches the maximum value of 6.2 MPa m 1/2 and 4.4 MPa m 1/2 at 25 °C and 800 °C, respectively. Moreover, TiN reinforced Sialon composites exhibit excellent tribological properties at a wide temperature range. Especially for the composite with 30 wt% addition of TiN at 200–800 °C, the friction coefficient reduces to 0.46–0.60, and the wear rate decreases about 15–50 times as compared to the material without TiN. In addition, the toughening and wear mechanisms are revealed on the basis of the crack propagation behavior and tribological properties. The crack propagation behavior indicates that crack deflection is the principal toughening mechanism. The enhancement of heat-conducting property, mechanical properties, and the tribo-chemical reaction are the main friction-reducing and anti-wear mechanisms. [ABSTRACT FROM AUTHOR]

As is well known, it is hard to prepare ceramic-Ag composites, owing to the lower melting temperature of silver. In this paper, Si 3 N 4 -based composites reinforced with in situ formation of Ag particles were successfully fabricated by sintering Si 3 N 4 and AgNO 3 , and their microstructure, elevated-temperature mechanical and tribological properties were investigated. It can be found that Ag particles about 1 µm were uniformly dispersed into the Si 3 N 4 matrix and there was no outflow of silver during the sintering. Meanwhile, S 3 N 4 /Ag composite containing 5.1 wt% silver exhibited the best fracture toughness, 7.05 MPa m 1/2 and 6.12 MPa m 1/2 at 25 °C and 600 °C, respectively, and the plastic deformation and crack bridging of silver were responsible for the high toughness. Besides, the friction coefficient and wear rate of composites were continuously reduced as the silver content increases. Especially at 200 °C, the friction coefficients reached the lowest value due to the formation of an amorphous silicon oxide film. And the wear resistance was enhanced by the cooperative strengthening effect of silver toughening and lubricating. [ABSTRACT FROM AUTHOR]

Poor interfacial adhesion and inferior UV resistance severely inhibit the development of hybrid Meta-aramid/Polytetrafluoroethylene (Nomex/PTFE) fabric composites for distinguished solid self-lubrication materials, especially under high exterior load and long-term UV irradiation conditions. Herein, glycidyl polyhedral oligomeric silesquioxanes (POSS) nanoparticles are covalently grafted onto the hybrid Nomex/PTFE fabric with a polydopamine/polyethylenimine (PDA/PEI) intermediate layer. The microstructure and chemical characteristics of Nomex and PTFE fibers before and after modification are investigated and the results manifest an obvious increase in surface functional groups and roughness, as well as resin compatibility. Tensile and peeling testing results show that the obtained fabric composites, denoted as hybrid-fabric@PDA/PEI-POSS composites, exhibit 24.3% and 46.8% enhancements in tensile and interfacial bonding strength without discernable decrease in pristine hybrid-fabric strength. In addition, the PDA/PEI-POSS hierarchical coating imparts the hybrid-fabric with excellent UV-shielding properties. As a result, the tribological performance of hybrid-fabric@PDA/PEI-POSS composites presents an obvious improvement under high load and UV irradiation conditions. [ABSTRACT FROM AUTHOR]

This research into environmentally-friendly ionic liquids (ILs) used a series of choline amino acid ILs ([Ch][AA] ILs) prepared from choline cations and several amino acid anions. Their physicochemical and tribological properties were tested, and the results showed that [Ch][AA] ILs had good lubricating properties for different friction pairs at room temperature (RT). Their toxicities were checked against three aquatic organisms: brine shrimp, zebrafish and green algae. The results showed that they have a remarkably low toxicity. Versus traditional IL 1-butyl-3-methyl imidazolium tetrafluoroborate (L-B104), the [Ch][AA] ILs had comparable or even better physicochemical and tribological properties. More importantly, they had the environmentally features of biodegradability and non-toxicity. [ABSTRACT FROM AUTHOR]

Ti:WS 2 films with duplex-layer structure were deposited by magnetron sputtering. The mechanical properties and tribological performance of Ti:WS 2 film were improved after Ti incorporation. Ti:WS 2 /P201 hybrid system constructed by combination of Ti:WS 2 film and P201 oil displays a synergistic lubricating effect, significantly prolonging lubricating lifetime compared to the single film. It is attributed to the effectively repairing function in some wear areas owing to the debris acted as an additive in oil. However, the AO irradiation can decrease the tribological performance of Ti:WS 2 /P201 hybrid system to different extent, depending on dose of irradiation. The high-dose AO irradiation rapidly deteriorates the tribological properties of the hybrid system, dramatically shortening the lubricating lifetime. It is found that the AO irradiated oil caused the severe tribo-oxidation reaction with the increase of sliding distance, resulting in forming numerous W oxides and carbide. Finally, failure mechanism of Ti:WS 2 /P201 hybrid system under AO irradiation were revealed. • Ti:WS 2 films with duplex-layer structure were deposited, showing better mechanical property and tribological performance after Ti incorporation. • Ti:WS 2 /P201 system constructed by combination of Ti:WS 2 film and P201 oil, significantly prolonging lubricating lifetime, which attributes to the effectively repairing function in wear areas owing to the debris acted as additive. • AO irradiation decreases the tribological performance of Ti:WS 2 /P201 system to different extent, depending on dose of irradiation. • The high-dose irradiation rapidly deteriorates the tribological properties which mainly atrributed to tribo-oxidation reaction. [ABSTRACT FROM AUTHOR]

AlMgB 14 based composites are promising candidates for use as cutting tool etc. In this respect, tribological behavior is one of the most important performances among all the criteria. In this work, a novel AlMgB 14 -30 wt% Si composite (referred to as BMAS30) was prepared by Spark Plasma Sintering. and its tribological property was investigated under different counterface materials (316 L and Si 3 N 4 ) and loads in ambient environment. Besides, the fracture toughness and the hardness were measured. We found that BMAS30 has a good fracture toughness of 5.90 MPa m 1/2 and a super-high hardness of 27 GPa. In terms of the tribological properties, BMAS30 shows good tribological properties when sliding against 316 L, i.e., a lower friction coefficient of 0.19–0.28 and wear rate of 7.00–8.00 × 10 −6 mm 3 /N m, while it presents a relatively high friction coefficient of 0.35–0.46 and wear rate of 3.80–9.00 × 10 −5 mm 3 /N m when sliding against Si 3 N 4 . In the former case, large numbers of Si grains pull-out pits formed on the worn surface that can store wear debris, which is conducive to lower the friction and wear; the latter produces severe fatigue fracture under high Hertz contact stress and thereby aggravates the friction and wear. [ABSTRACT FROM AUTHOR]

In aerospace, some moving parts will meet with simultaneous high temperature and vacuum environments. In this study, the tribological behavior of a nickel alloy matrix solid lubricant composite was contrastively investigated under both air and vacuum conditions from room temperature to 800 °C. Results showed that both the friction coefficient and the wear rate of the composite were highly dependent on testing temperature and atmosphere. The friction coefficient in vacuum was lower than that in ambient air. The compositions of the frictional surfaces were analyzed, based on which, the mechanism of friction and wear was proposed. [ABSTRACT FROM AUTHOR]

In this paper, the tribological behaviors of 20 and 40 vol% in situ TiB 2 reinforced TiAl-based composites sliding against SiC balls were investigated in artificial sea water, and TiAl alloy was also studied as a comparison. The results showed that the TiAl-TiB 2 composites are lubricated in artificial sea water and TiB 2 is effective to improve the wear resistance of the TiAl alloy. Also, it was found that the tribological behaviors have a dependency on the applied loads and sliding speeds. Worn surface morphologies and composition together with electrochemical behaviors of the materials were evaluated and related to the tribological behaviors. [ABSTRACT FROM AUTHOR]

Al matrix composites reinforced with Ti 3 AlC 2 and Cu coated Ti 3 AlC 2 were prepared by hot-press sintering approach. It was confirmed that Ti 3 AlC 2 displayed poor wettability with Al, resulting in the poor interfacial bonding strength between Ti 3 AlC 2 and Al matrix. However, Al 2 Cu layer could be formed due to the reaction between Cu and Al during the sintering process, when Cu coated Ti 3 AlC 2 was incorporated in Al matrix. Because of the formation of enhanced Al 2 Cu interface, the mechanical and tribological properties were significantly improved. The Al 2 Cu layer could bridge Ti 3 AlC 2 particle and Al matrix effectively, which contributed to absorbing energy when load was applied, to provide better mechanical properties. Moreover, Ti 3 AlC 2 particle could exhibit powerful pinning effect to inhibit two-body abrasion and adhesion wear, which was favorable for forming smooth tribo-oxidation surface to yield low friction coefficient. The wear mechanism was believed to be oxidation and fatigue wear. [ABSTRACT FROM AUTHOR]

WS 2 films with duplex-layer structure were deposited by magnetron sputtering. The tribological differences of as-deposited, AO-irradiated WS 2 films and WS 2 /P201 hybrid system were mainly investigated for the same film. In comparison with as-deposited WS 2 film, AO-irradiated WS 2 film exhibits the lower initial friction coefficient and lower wear rate, and longer service longevity. Meanwhile, WS 2 /P201 hybrid system significantly extended service life further. It is found that the generated WS 2 debris act as lubricating agent with different participation states and air isolation in the different lubricating systems affect the tribological property of WS 2 film. Eventually, different lubrication mechanisms for AO-irradiated WS 2 film and WS 2 /P201 hybrid system in vacuum were revealed. [ABSTRACT FROM AUTHOR]

The thermal stability of polymer matrix composite could effectively improve by incorporation of highly thermally conductive ceramic materials into polymers. In present work, hybrid PTFE/Nomex fabric/phenolic composite specimens were prepared with zirconium diboride (ZrB 2 ) particles for the improvement its high-temperature tribological performances. The thermal stability of hybrid PTFE/Nomex fabric/phenolic composite was investigated by TGA. The result showed that the thermal stability was improved because of addition of ZrB 2 particles. In addition, it was found that 9 wt% ZrB 2 reinforced hybrid PTFE/Nomex fabric/phenolic composite exhibited optimal tribological performances compared to unfilled fabric composite under all test conditions. [ABSTRACT FROM AUTHOR]

We report a new type of zwitterionic gelator, which cannot only gelate base lubricating oils by supramolecular self-assembly, but be used as additive in oils for significantly improved the tribological performances. The self-assembly mechanism is confirmed by NMR. The as-prepared zwitterionic gels have good thermoreversible and thixotropic characteristics, which make them as potential high performance semi-solid lubricants. The tribological results showed that the gel lubricants possessed excellent friction-reducing and anti-wear properties compared with blank 500SN and Li-base grease with 2 wt% MoS 2 . The morphologies of the worn surfaces were analyzed by scanning electron microscope (SEM). The lubrication mechanism is proposed according to in-situ electrical contact resistance and the surface composition analysis at the worn surfaces. [ABSTRACT FROM AUTHOR]

Tribological properties of AlCoCrCuFeNi and AlCoCrFeNiTi 0.5 alloys under 90% H 2 O 2 solution rubbing against 1Cr18Ni9Ti steel, ZrO 2 ceramic and SiC ceramic were investigated. The tribological behavior is dependent on the counterparts and the structure of high entropy alloys. The high entropy alloys exhibit significantly lower friction coefficient and wear loss sliding against SiC ceramic than 1Cr18Ni9Ti steel and ZrO 2 ceramic, which can be attributed to the lubricating colloidal film formed by tribo-chemical reaction between H 2 O 2 and SiC. Moreover, the AlCoCrFeNiTi 0.5 /SiC tribo-pair preserves better tribological properties than AlCoCrCuFeNi/SiC tribo-pair, as results of high strength and hardness of AlCoCrFeNiTi 0.5 alloy. [ABSTRACT FROM AUTHOR]

The tribological behaviors of the (W 0.67 Al 0.33 )C 0.67 –Co/fluoride (CaF 2 , BaF 2 , CaF 2 /BaF 2 ) composites against SiC ball from room temperature to 600 °C were investigated. A marked increase in the friction coefficient resulting from fluoride oxidation was observed as the temperature increased. The composites containing BaF 2 or (Ca, Ba)F 2 displayed better integrated wear resistance over a wide temperature range compared with (W 0.67 Al 0.33 )C 0.67 –Co/CaF 2 . The high temperature tribological characteristics of the three composites were distinct, which originated from the composition difference on the worn surfaces. First, the SiO 2 /SiC film formed on the worn surfaces of the composites with BaF 2 or (Ca, Ba)F 2 was favorable for their wear resistance. Second, the oxidation of WC matrix was an important factor influencing the wear resistance of the composites. When mixture oxides of WO 2 and WO 3 appeared on the surface, wear is severe. In addition, single WO 3 formed on the worn surfaces, appeared more adhesive to the underlying substrate and decreased the wear rate. [ABSTRACT FROM AUTHOR]

The tribological behavior of nanocrystalline Fe 88 Si 12 alloy in vacuum environment has been investigated compared with coarse grained counterpart. The results demonstrated that the friction coefficient of the Fe 88 Si 12 alloy reduced with the decrease of both grain size and oxygen partial pressure. The wear resistance of the Fe 88 Si 12 alloy improved more effective in vacuum than in air as the grain size decreased. As the hardness and oxidation activity of the Fe 88 Si 12 alloy decreased, the wear mechanism changed from adhesion and oxidation to plastic deformation and adhesion when the grain size and oxygen partial pressure decreased. [ABSTRACT FROM AUTHOR]

Ni 3 Al matrix composites with addition of silver and barium salt (BaCrO 4 , BaMoO 4 ) were fabricated by powder metallurgy. It was found that from room temperature to 800 °C, Ni 3 Al matrix composite with addition of Ag and BaCrO 4 offers the continuous lubrication properties, and its friction coefficient ranges from 0.29 to 0.38; Ni 3 Al matrix composite with addition of Ag and BaMoO 4 also offers the favorable lubricating properties; the friction coefficient ranges from 0.28 to 0.35 in a wide temperature range. The low friction coefficient in a wide temperature range could be attributed to the synergistic effect of Ag and barium salts. [ABSTRACT FROM AUTHOR]

In this paper, the dry-sliding tests of Ti 3 AlC 2 /SiC tribopairs were conducted from 25 °C to 1000 °C in both air and argon atmospheres for confirming the roles of tribo-oxidation and laminate structure of Ti 3 AlC 2 . The characteristics of the worn surfaces of the Ti 3 AlC 2 were contrastively examined and the corresponding tribological mechanisms were discussed. Ti 3 AlC 2 showed distinctive tribological behaviors and mechanisms in the two atmospheres. Here, the tribo-oxidation film played a very vital role for the tribology of Ti 3 AlC 2 . In air, Ti 3 AlC 2 showed moderate wear at 25–400 °C and Ti 3 O 5 was the major phase of the tribofilms. At 600–1000 °C, the wear-resistant tribo-oxidation films, consisting of TiO 2 and Al 2 O 3 , were believed to be responsible for the negligible wear. In argon, Ti 3 AlC 2 exhibited heavy wear in the whole temperature range. Abrasive and adhesive wear caused the poor tribological performances at 800 °C and below. At 1000 °C, Ti 3 AlC 2 displayed plastic flowing and large furrows under the shear stress. [ABSTRACT FROM AUTHOR]

The mechanical and tribological properties of the Fe–15.88Al–5.46Cr (wt.%) based composites reinforced with 15, 25, 35 wt.% novel W 0.5 Al 0.5 C 0.5 particulates (referred to FA15, FA25 and FA35), produced by hot-press sintering, were evaluated. The hardness of the composites increased with the W 0.5 Al 0.5 C 0.5 content but the bending strength firstly decreased and then increased. The wear resistance of the composites was dramatically superior to Fe–15.88Al–5.46Cr alloy (FA0) without mass density gain. Interestingly, the wear resistance increased with W 0.5 Al 0.5 C 0.5 concentration from 15 to 25 wt.%, but then slightly declined when W 0.5 Al 0.5 C 0.5 content was up to 35 wt.%. It is also surprised that FA25 displayed the lowest friction coefficient, while that of other composites was much higher than Fe–15.88Al–5.46Cr alloy. These abnormal mechanical and tribological behaviors would be associated with the microstructure of the composites and the composition of the worn surfaces. The wear mechanism of the composites was abrasion and oxidation wear. [ABSTRACT FROM AUTHOR]

Ag films, deposited by arc ion plating, had been exposed for 43.5 h in real low earth orbit (LEO) space environment by a space environment exposure device (SEED) aboard the China Shenzhou-7 manned spaceship. The structure, morphology, composition and tribological property of the Ag films after the space environment exposure (SEE) were investigated using X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), X-ray photoelectron spectroscope (XPS) and ball-on-disk tribometer, respectively. Depth XPS and XRD analysis revealed that after the SEE, the surface layer of Ag films was partially oxidized to Ag 2 O, the cracking and flaking phenomena could be observed from the film surface by FESEM, and so the Ag films lose its metallic shine and became gray. As a result, the tribological performance was deteriorated and the high/unstable friction was obtained. [ABSTRACT FROM AUTHOR]

Producing fabric composites with improved high-temperature tribological property is highly desired for their use in practical application, yet still challenging. Herein, we employed MoSi 2 as anti-oxidant and filled it into the hybrid PTFE/Nomex fabric/phenolic composite. The high-temperature tribological properties of the fabric composites were evaluated on a pin-on-disk tribometer. The results showed that the MoSi 2 filled fabric composites displayed much lower wear rates in high-temperature environment, comparing to that of unfilled fabric composite. Moreover, the antiwear property of the MoSi 2 filled fabric composite can be further improved by treating the fabric with air-plasma, as the bonding strength between the fabric and resin was evidently enhanced. The wear behaviors and the corresponding wear mechanisms of the composites were discussed based on the characterizations. [ABSTRACT FROM AUTHOR]

• Preparation of gallate ionic liquids (GAILs). • Their lubricating performances for copper and aluminum friction pairs are discussed. • The GAILs show prominent friction reduction and wear resistance properties. • The properties are attributed the formed physicochemical adsorbing films. In this study, four kinds of GAILs were prepared and used to lubricate copper and aluminum friction counterfaces. Their physicochemical and tribological properties were systematically investigated. The results showed that the GAILs have better performances with regard to viscosity-temperature characteristic, corrosiveness and hydrolytic stability as compared with the two traditional halogen-containing IL lubricants L-B104 and L-F104. Moreover, the most prominent nature of the GAILs are their excellent friction reduction and wear resistance properties as lubricants for copper and aluminum friction counterfaces, while traditional halogen-containing ILs are generally found to be unsuitable for lubricating these counterfaces. The excellent tribological properties of the GAILs are conjectured to be largely attributed to the physical/chemical adsorbed films formed by the GAIL molecules on the friction surfaces, which is further verified by QCM and XPS analysis results. [ABSTRACT FROM AUTHOR]

[Display omitted] • The (CrAlTiNbV)N x high-entropy coatings are prepared by magnetron sputtering method. • All coatings exhibit columnar growth morphology and own a single FCC structure. • The S-38 owns a friction coefficient of 0.096 and wear rate of 1.8 × 10−7 mm3/(N·m). • The excellent wear resistance of S-38 is mainly attributed to its dense structure. (CrAlTiNbV)N x high-entropy nitride coatings are deposited via tuning nitrogen flow rates, and evaluating their influence on the microstructure, mechanical and tribological properties of the coatings. All deposited coatings exhibit columnar growth morphology and own a single face-center-cubic structure. As the nitrogen flow rate increases, the preferred orientation of the coating gradually transfers from (1 1 1) to (2 0 0) and (2 2 0), and then changes back to (1 1 1) with the nitrogen flow rate continues to increase. The S-38 sample possesses the optimal plastic deformation resistance and adhesion strength. Friction and wear results show that the (CrAlTiNbV)N x coating deposited at nitrogen flow rate of 38 sccm owns the best tribological properties with a friction coefficient of 0.096 and wear rate of 1.8 × 10−7 mm3/(N·m) in 4050# aviation oil. [ABSTRACT FROM AUTHOR]