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• Lattice distortion mediated superlubricity of MoS 2 /BN and MoS 2 /graphene moiré interfaces is revealed. • Special contributions of 2p z orbital electrons are yielded by specific atomic stackings. • Periodic distribution of π bonds and interfacial hybridization are related to the potential corrugations. • Evaluation of potential energy barrier is proposed by coupling electron structure and twisted angle. Superlubricity, a novel lubricity mode ascribing to moiré superlattice (MSL), has attracted attention in ultra-precise manufacture, microelectronic devices, and national defense areas. Based on incommensurate MSL, nearly zero friction can be achieved by eliminating sliding lock-in and offsetting lateral force in principle, and the theoretical foundations are still under extensive investigation. Here, the effects of MSL-induced lattice distortion on π bond and tribological performance in twist MoS 2 /graphene and MoS 2 /BN heterointerfaces were studied by first-principles calculations comprehensively. Various contributions of 2p z orbital electron polarization among AA-, AB-, and AC-stacking symmetry areas in different MSL were reflected by band structures to explain the sensitivity of π bond to MSL. The π bond perpendicular to the atomic plane depended closely on interfacial distortion, which can not only influence the local distribution of intralayer bond strength but also determine the interlayer charge redistribution. Meanwhile, the interfacial potential energy was changed with the interlayer interaction fluctuation caused by twist angle and atomic stacking modes. Through evaluating the energy barriers and lateral force, MoS 2 /BN with a twist angle of 20.79° exhibited superlubricity. Moreover, the connection among sliding energy barriers, twist angles, and specific electronic structures has been bridged paving a path to reveal the superlubricity mechanism of two-dimensional materials with π bond. [Display omitted] [ABSTRACT FROM AUTHOR]

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Although a large number of water- and oil-based gel lubricants have found extensive potential applications in industrial and biomedical fields, developing new-type emulsion-based gel lubricants that may effectively integrate their characteristics and preponderances remains a significant challenge. Here a water-in-oil Pickering emulsion gel lubricant that is able to combine the high colloidal stability of traditional Pickering emulsions, the good swelling and corrosion resistance of oil-based gel lubricants, and the high cooling capacity of water-based gel lubricants prepared from a binary mixture of aqueous graphene oxide (GO) dispersion and diamino-functionalized polydimethylsiloxane oil solution in a broad concentration, pH, and water volume fraction range is reported. It can provide favourable lubrication for the Si3N4/steel and Si3N4/silicone tribopairs either in air or under water owing to the formation of a sturdy adsorbed oil film and ball-bearing actions of the GO particles. It can also be printed into various colourful 2D and 3D geometries upon direct extrusion into water, thanks to its water-in-oil nature and inherent shear-thinning and thixotropic properties, which further shows good prospects in underwater operations and artificial biomimetic organs. Our study may provide new insights into the design and preparation of novel semi-solid materials for diverse industrial, engineering, and biomedical applications.

Reducing the coefficient of friction (COF) and wear rate is significant for triboelectric nanogenerators (TENGs). Here, we devised a new macroscale superlubric triboelectric nanogenerator (SL-TENG) that can withstand high-contact stress with ultralow COF (<0.01) and ultralow wear rate based on a hydrogenated diamond-like carbon (DLC) film from the tribological perspective. Specifically, the SL-TENG produced an output with the peak short-circuit current of approximately 60 nA and a power density of up to 5.815 W/m2during the friction of DLCversus steel ballwith a Hertz contact stress of 1.37 GPa. Moreover, first-principle calculations demonstrate that the ultralow friction on DLC is mainly due to the hydrogen-terminated surface. The SL-TENG can generate direct current (DC) output caused by tribovoltaic effect and can light up several light-emitting diodes (LEDs) without rectification. Online superlubric friction monitoring and early warning can be realized, owing to the close correspondence between tribology and triboelectricity.

• The (CrNbTiAlV)N x high-entropy nitride films were fabricated by magnetron sputtering. • The films transformed from amorphous to nanocrystalline structures with the increment of nitrogen. • The tribocorrosion mechanism of the high-entropy nitride films was discussed. • The film deposited at nitrogen flow of 38 sccm exhibits the best comprehensive mechanical and tribocorrosion performance. The (CrNbTiAlV)N x high-entropy nitride films were fabricated by adjusting nitrogen flow via magnetron sputtering. The microstructure, mechanical, electrochemical and tribocorrosion performances of the films were studied. The results show that the films transform from amorphous to nanocrystalline structure as nitrogen flow increased. The nanocrystalline films show super hardness (> 40 GPa) and adhesion strength (> 50 N). The amorphous film has a pretty anti-corrosion in static corrosion, while not in tribocorrosion condition. The film deposited at nitrogen flow of 38 sccm exhibits the optimal tribocorrosion performance in artificial seawater, with the highest open circuit potential (∼ − 0.1 V vs. Ag/AgCl), the lowest friction coefficient (∼ 0.162) and wear rate (∼ 7.48 × 10−7 mm3 N−1 m−1). [ABSTRACT FROM AUTHOR]

Atomic oxygen (AO) has an important influence on the performance of solid lubricating materials applied in space. The tribological behaviors of both sputtered WS2films without and with a dense layer were mainly investigated under the ex situ AO irradiation condition. AO irradiation results in the worse tribological property for the WS2film without a dense layer. On the contrary, it is surprising that the WS2film with the dense layer exhibits a lower friction coefficient after irradiation, which is different from the reported results that the solid lubricating films always increased the friction and wear because the surfaces of the films were oxidized by AO. Meanwhile, it is found that the generated W oxides contributes to the partial surface of the wear track becoming smooth because of the shear and slip of crystal planes for WS2crystals on the surface of the dense layer. Eventually, the lubricating mechanisms of the irradiated WS2films are also revealed via correlating the friction and wear characteristics of the films.

La2Zr2O7nanocrystals doped with Er3+were prepared from curing and pyrolysis of La2Zr2O7preceramic precursor modified by erbium acetylacetonate for the purpose of photoluminescence applications. The crystallisation behaviour, microstructure and photoluminescence of the generated ceramics were investigated. The nanocrystals derived from the precursor annealed at 900 °C for 2 h exhibit a single-phase solid solution with an average crystallite size of about 20 nm. The emission band centred at 528 nm was attributed to the 2H11/2→4I15/2transition, while those at 550 and 562 nm were ascribed to the 4S3/2→4I15/2transition. The optimal molar ratio of Er3+/Zr4+for max emission intensity was between 0.04 and 0.06.

La2Zr2O7nanocrystals doped with Er3+were prepared from curing and pyrolysis of La2Zr2O7preceramic precursor modified by erbium acetylacetonate for the purpose of photoluminescence applications. The crystallisation behaviour, microstructure and photoluminescence of the generated ceramics were investigated. The nanocrystals derived from the precursor annealed at 900 °C for 2?h exhibit a single-phase solid solution with an average crystallite size of about 20?nm. The emission band centred at 528?nm was attributed to the 2H11/2?4I15/2transition, while those at 550 and 562?nm were ascribed to the 4S3/2?4I15/2transition. The optimal molar ratio of Er3+/Zr4+for max emission intensity was between 0.04 and 0.06.

Doped graphite-like coating (GLC) has aroused great interest as one of the most promising protective materials in marine applications. However, there is a lack of systematic research on the tribocorrosion and antifouling performance of doped GLC coatings in harsh marine environments. Herein, a multifunctional (Cr, Cu)-GLC coating with combined antifouling and tribocorrosion properties was prepared via a magnetron sputtering method. The experimental results indicate that the resultant coatings changed from a dense structure to a loose columnar structure with the increment of Cr and Cu doping amount. At the same time, the hardness of the coating gradually decreases, but the contact angle between coating and seawater gradually increases. The algae adhesion test reveal that the algae density on the surface of the (Cr, Cu)-GLC coating decreases from about 565 to 70/mm2as the amount of doping increased. However, on the contrary, the friction coefficient of the coating under OCP condition increases from 0.06 to about 0.35. Overall, the mild doped (Cr, Cu)-GLC coating exhibits the best comprehensive properties, combining antifouling and tribocorrosion properties. The corresponded mechanisms are discussed in terms of the coating microstructure, antifouling, and tribocorrosion behavior.

For improving the wear resistance, thick silicon doped hydrogenated amorphous carbon (a-SiC:H) coatings were deposited on cold working tool steels by plasma-enhanced chemical vapor deposition (PECVD) technology. The increase of the acetylene (C2H2) flow rate distinctly tuned the microstructure of a-SiC:H coatings, including an increase in the coating thickness (>15 µm), a decrease in the silicon content, a greater sp2/sp3 ratio, and higher degree of graphitization. The highest hardness of 19.61 GPa and the greatest critical load of 50.7 N were obtained. The coating showed low wear rate against different friction pairs and presented excellent abrasive wear resistance at high applied load and the wear rate decreased with increasing loads, which exhibited an outstanding application prospect in cold working tool steels.

Zeolitic imidazolate framework-8 (ZIF-8) was fabricated as a lubrication container to encapsulate lubrication oil, which was added to epoxy resin (EP) as a filler to get the self-lubricating ZIF-8/EP composites coating. The antiwear and anticorrosion peculiarities of EP can be significantly improved by the encapsulation method. The antiwear peculiarities of EP were evaluated by the macroscopic ball-disk friction tests with the 9Cr18 steel ball as the counterface material. The result demonstrates that the coefficient of friction (COF) and wear rate of the self-lubricating ZIF-8/EP composites were reduced by 82.1% and 93.5% compared with that of the pure EP, respectively. Importantly, the ZIF-8/EP composite shows anticorrosion performance in the artificial seawater (ASW). The constant phase element and effective capacitance of the coating containing ZIF-8 fillers are lower than that of the non-containing coating. In addition, the diameter of the capacitive arc and the impedance modulus of the coating containing ZIF-8 + YR1800 are higher than those of the coating non-containing, which proved that the corrosion resistance of the EP is improved by the ZIF-8 + YR1800.

Cr doped MoS2 films were deposited by magnetron sputtering. The tribological properties of Cr doped MoS2 films under vacuum (VC) and air (AR) environments were investigated. The results show that Cr doped MoS2 film with Cr target power of 0.2 A (0.2 A Cr:MoS2 film) exhibits low friction coefficient and long wear life under both VC and AR environments. The chemical compositions of the films were analyzed by energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). With the increases of Cr target power, the content of Cr increases. The cross-sectional field emission scanning electron microscopy (FESEM) morphologies show that the structure of the films changed from granular particles to column when the Cr target power increases from 0.2 A to 0.4 A. The wear mechanism has also been discussed based on the characteristics of worn surface. The 0.4 A Cr:MoS2 film has the lowest wear volume among these films, which can be attributed to the compact microstructure. The bandgap of Cr doped MoS2 films were measured by XPS and the tribological performance of the film is found to be best when there is a modest bandgap. It can be speculated that the tribological performance of Cr doped MoS2 films are closely related to the width of bandgap.