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Dense Ti3SiC2/ZnO composites were sintered at different temperatures by spark plasma sintering (SPS). The effects of sintering temperature on composition and mechanical properties of Ti3SiC2/ZnO composites were studied. The tribological behaviors of Ti3SiC2/ZnO composites/Inconel 718 alloy tribo-pairs at elevated temperature from 25 °C to 800 °C were discussed. The experimental results showed that the initial decomposition temperature of the Ti3SiC2/ZnO composite was 1150 °C, and Ti3SiC2 decomposed into TiC. When the decomposition temperature was higher than 1150 °C, the compositions of the Ti3SiC2/ZnO composites were Ti3SiC2, ZnO, and TiC. It was found that Ti3SiC2/ZnO composites had better self-lubricating performance than Ti3SiC2 at elevated temperature from 600 °C to 800 °C, which was owing to material transfers of tribo-pairs and sheared oxides generated by tribo-oxidation reactions. [ABSTRACT FROM AUTHOR]

Ten kinds of self-lubricating composites with different amounts of sintering aids and solid lubricants in Al2O3 matrix were fabricated by hot-pressed sintering. Their friction and wear behaviours in unlubricated sliding against Al2O3 were tested by using a pin-on-disk wear tester at 650°C. It was shown that the amount of sintering aids strongly affected friction coefficient and wear rate of the Al2O3–20Ag20CaF2 composite, the appropriate amount of sintering aids was 10 wt% for beneficial effect on the reduction of wear at 650°C. Also it was shown that the addition of equal quantities of Ag and CaF2 in Al2O3 matrix can promote the formation of the well-covered lubricating film, and effectively reduce the friction and wear. The composite with 40 wt% of lubricants (20 wt% Ag, 20 wt% CaF2) presented an optimum tribological behavior at 650°C (friction coefficient μ is about 0.3, wear rates are about 4 x 10-6 mm3/N,m and 5 x 10-7 mm3/N,m for the disk and pin, respectively). [ABSTRACT FROM AUTHOR]

The tribochemistry and transfer film formation at the metal/polymer interface plays an essential role in surface protection, wear reduction, and lubrication. Although the topic has been studied for decades, challenges persist in clarifying the nanoscale mechanism and dynamic evolution of tribochemical reactions. To investigate the tribochemistry between iron and polytetrafluoroethylene (PTFE) in ambient and cryogenic environments, we have trained and expanded a ReaxFF reactive force field to describe iron-oxygen-water-PTFE systems (C/H/O/F/Fe). Using ReaxFF molecular dynamics simulations, we find that mechanical shearing of single asperity induced the degradation of PTFE molecules and radicals, showing subsequent oxidation and hydroxylation reactions of the radicals initiated by C-C bond cleavage, in agreement with previous experimental observations. Furthermore, we studied mechanisms of interfacial tribochemical reactions and formation of transfer films. We found that tribochemical wear and Fe-C and Fe-F bonding networks are important mechanisms for anchoring molecular chains to form a transfer film on the iron countersurface. Hydroxyl groups can dehydrogenate to form short and strong chelation bonds with the Fe 2 O 3 countersurface. A friction-induced oriented molecular layer plays a key role in reducing friction, which is responsible for the excellent lubrication property. By varying temperatures in the range of 10-300 K, we found a nonmonotonic change in friction with a maxima at 100 K. At cryogenic temperatures, the molecular mobility was obviously suppressed, while the chain rigidity was enhanced, resulting in the less oriented interface and brittle-like shear interface, which is responsible for nonmonotonic friction. This work elucidates mechanisms of tribochemical reactions and transfer film formation between iron and PTFE at the atomistic level, facilitating design and development of self-lubricating materials, especially under harsh conditions.

Three-dimensional (3D) printing of porous polyimide (PI) with good oil storage capability for self-lubricating is realized by direct ink writing of poly(amide acid) (PAA) precursor ink followed by post thermal treatment and template removal. The ink is comprised of PAA and polymethyl methacrylate (PMMA) microspheres, where the PMMA microspheres serve as both the pore-forming agent and the rheology modifier to realize high-precision porous PI objects. The printed porous PI exhibited good mechanical performance and thermal stability, and good oil storage capability to various lubricant oils to achieve self-lubricating. Importantly, various parts with desirable complex structures, bearing retainers for example, can be readily accomplished. It is therefore promising for manufacturing high-performance lubricating parts, especially those with high complexity. [Display omitted] • Porous polyimide with good comprehensive properties was achieved by 3D printing. • 3D printed polyimide shows good self-lubricating performance with oil impregnated. • 3D printing porous polyimide is promising for parts with high complexity and special shape. [ABSTRACT FROM AUTHOR]

A novel yttria stabilized zirconia (YSZ) - polytetrafluoroethylene (PTFE) - silicone composite coating was fabricated by the atmospheric plasma spraying (APS). Results showed that this coating exhibited dense texture and surface uplift feature due to the thermal-mechanical shock synergistic effect, and showed good hydrophobicity with a contact angle of 150.65°. The sliding wear test confirmed that the coating showed excellent self-lubricating property, reflected by a low friction coefficient of 0.12. This coating also showed good marine weatherability, and possessed excellent corrosion resistance with a high potential which a value is closed to 0 V. These current results clearly demonstrated that APS technique possessed a huge advantage for the one-step fabrication of the ceramic doped PTFE-based composite coating with considerable wear resistance and corrosion resistance. • The polytetrafluoroethylene based composite coating was fabricated by APS. • Thermal-mechanical shock synergistic effect resulted in dense growth texture. • The coating exhibited excellent self-lubricating effect and hydrophobicity. • The coating showed considerable marine weatherability and corrosion resistance. [ABSTRACT FROM AUTHOR]

Pure iron has recently been identified as the material basis of many high-tech industries due to its high toughness, plasticity as well as superior electromagnetism. However, the rather poor machinability has limited the wider applications of pure iron. Nano-laminated multilayer graphene-carbide tool (MLG/WC-Co) was produced employing two-step sintering. This study applied towards investigate the microstructure and mechanical properties of this MLG/WC-Co tool, highlighting its machining performance through dry turning pure iron. Results showed that compared with commercially available YG6 tool, MLG/WC-Co tool yielded reduced cutting forces, cutting temperature and friction coefficient at the tool-chip interface together with enhanced shear angle and tool life. The MLG/WC-Co tool developed cooperative adaptive mechanism for the coupled and interacted thermal-mechanical-chemical multi-fields were determined thoroughly. For one thing, the wear resistance was significantly enhanced as a function of the MLG introduced strengthening and toughening mechanisms. For another, cutting force induced tensile stress could be compensated by the residual compressive stress on the rake face resulting from the laminated structure. Furthermore, extensive MLG film formed at tool-chip interface at high-speed cutting conditions, endowing the cutting tool self-lubricating function coupled with exceptional adhesive-wear and oxidation resistance. Besides, the orientation conduction of cutting heat was proposed by associated consideration of tool structure as well as orientation distribution and anisotropic heat conductivity of MLG, so as to effectively slow down the heat accumulation and temperature rise. This research can ease the overwhelming pressure associated with sustainability by eradicating or circumventing the undesirable effects of traditional cutting fluids for economy, healthy coupled with environment through advancing dry machining techniques. [Display omitted] • The tool life of graphene-carbide was about three times that of commercial YG6 cutting tool. • Wear resistance was significantly enhanced as a function of the graphene introduced strengthening and toughening mechanisms. • Residual compressive stress was introduced on rake face through laminated structure design of the tool. • Graphene lubricating film formed at both tool-chip and tool-workpiece interfaces. • Orientation conduction of cutting heat was proposed. [ABSTRACT FROM AUTHOR]

High entropy alloys (HEAs) have provided a unique opportunity to design novel structure-function integrated materials through modulating chemical composition and tailoring microstructural features. In this study, a novel self-lubricating CoCrCu 1-x FeNi x (x = 0, 0.1, 0.3 and 0.5) HEA coating was in-situ prepared by laser cladding. The adequate amount of nearly pure copper segregated into the interdendritic regions could effectively smear the surface of the alloy and provide a Cu-rich protective oxide layer during dry sliding condition at an intermediate temperature of 400 °C. These findings serve as a proof of concept for the application of laser cladding as a high throughput process to rapidly fabricate self-lubricating HEA coatings through combining the intrinsic features of HEAs and additive manufacturing. Image 1 • A self-lubricating CoCrCu 1-x FeNi x HEA was designed by tailoring microstructural features. • A novel route for designing self-lubricating HEAs without the addition of solid-lubricating agents. • The mechanism of formation of Cu-rich protective oxide layer was outlined. • The wear resistance significantly increased upon the formation of oxide layer. [ABSTRACT FROM AUTHOR]

The development of hard-yet-tough ceramic coatings with self-lubricating behavior is an urgent technological requirement to reduce mechanical friction losses and energy consumption. However, traditional ceramics possessing the limited self-lubricating ability and poor toughness have limited their practical applications. To tackle the above-mentioned problems, we modified ceramic material vanadium nitride (VN) to prepare the catalytically active V-Ag-N solid solution coating by magnetron sputtering and realized high hardness, high toughness, and excellent self-lubricating performance under dry friction and oil lubrication conditions. Through detailed experimental investigations, we explain the enhanced mechanism of both hardness and toughness because of solute Ag; moreover, the solute Ag can trigger the appearance of lubricating silver vanadate phase in dry friction and result in a low coefficient of friction. Besides, it was confirmed that the solute Ag atom would induce effectively catalytic ability for in situ formation of self-lubricating onion-like-carbon structures (OLCs) scrolls from base oil at the sliding interface. The novel strategy would be to open a window for more efficiently catalyzing the in situ formation of silver vanadate and OLCs scrolls activated by solute Ag atoms and more significantly improving the hardness and toughness, thereby further improving self-lubricating behavior under dry friction and oil lubrication conditions. Unlabelled Image • Solid solution V-Ag-N coatings were formed by co-sputtering at Ag content ≤ ~5 at.%. • The self-lubricating behavior under dry friction and oil lubrication was achieved catalyzed by solute Ag. • The self-lubricating behavior under dry friction is ascribed to silver vanadate. • The oil lubrication ability is attributed to onion-like carbon tribofilm activated by solute Ag. [ABSTRACT FROM AUTHOR]

Tribological studies have shown that polytetrafluoroethylene @ phenolic resin core/shell (PTFE@PR) composite maintained excellent tribological properties under harsh working conditions (120 °C, 0.1 m/s, 100 N, friction pair with roughness of 2.528 μm), suggesting the core/shell composite would be a candidate lubricating material with multi-environmental adaptability. The friction-induced transfer film with long-range ordered crystal structure and fiber-like morphology was observed by scanning electron microscope, while the strong chemical bonding between the PTFE-PR transfer film and friction pair was confirmed by X-ray photoelectron spectroscopy. The crystallinity of the long-range ordered transfer film and wear debris under the shear force is higher than that of the original specimens by attenuated total reflection Fourier transform infrared spectroscopy. Besides, the wear life of the PTFE@PR transfer film was six times higher than that of PTFE, reflecting its long durability. Image 1 • Core/shell PTFE@PR composite with multi-environmental adaptability presents good tribological properties. • PTFE-based polymer transfer films exhibit fibrous morphology and high crystallinity under shear force induction. • The crystallinity of long-range ordered transfer film and wear debris is higher than that of original specimens. • Strong chemical bonding exists between the PTFE@PR transfer film and the steel friction pair. • Wear life of transfer film for core/shell PTFE@PR composite is 6 times higher than that of PTFE. [ABSTRACT FROM AUTHOR]

To decrease coefficient of friction (CoF) of the 6063 aluminum alloy modified by microarc oxidation (MAO) treatment, a MoS 2 lubricating layer was synthesized on the MAO coating by hydrothermal reaction. The as-synthetized MoS 2 powders demonstrated high purity and interesting micro-spheres structure assembled by many nano-lamellae. The prepared MoS 2 layer was ~11 ± 3.3 μm thick, and padded the surface porosity of MAO ceramic coatings. These composite coatings were slidden against GCr15 steel counterparts in air at variable applied loads. According to the results of tribological test, the CoF of MAO/MoS 2 composite coatings reduced by ~31.4%, 45.5% and 42.1% compared to single MAO coatings at 2, 4 and 6 N loads, respectively, due to the low shear strength of MoS 2. The wear track of MAO/MoS 2 composite coatings also displayed more uniform and smoother, causing more stable sliding process. Additionally, the existence of MoS 2 layer significantly decreased the wear rate of both coatings and related counterpart balls, implying the enhanced anti-wear properties. Scanning electron microscopy (SEM) and Raman spectrometer revealed that the primary wear mechanism of single MAO coating was a combination of adhesive wear, abrasive wear and oxidation, while the MAO/MoS 2 self-lubricating composite coating only showed slight abrasive wear combined with oxidation occurrence. Unlabelled Image • MAO/MoS 2 composite coating was prepared by MAO treatment and hydrothermal reaction. • MoS 2 powers padded the surface porosity of MAO ceramic coatings. • The plane orientation evolution of MoS 2 crystals was confirmed by Raman spectroscopy. • MAO/MoS 2 composite coating has lower CoF and better anti-wear ability. [ABSTRACT FROM AUTHOR]

The poor self-lubricating behavior and antibacterial activity of Ti-6Al-4V alloy hinder its medical applications in surgical instruments. And thus, Ag-based transition metal nitrides nanocomposite films on Ti-6Al-4V substrate where Ag existed in the form of nanoparticles have been commonly employed to improve the above properties. In this work, two kinds of Ag-based TaN films (~3 at.% Ag) with solute Ag atoms and Ag nanoparticles are respectively fabricated on the surface of Ti-6Al-4V alloy by magnetron sputtering, aiming to insight into their self-lubricating behavior and antibacterial activity. It is revealed that as Ag resides in form of solute atoms rather than nanoparticles in Ta-Ag-N films, the enhanced antibacterial activity, lower coefficient of friction (CoF) coupled with raised hardness (~39 GPa) and enhanced toughness can be achieved. Compared with the Ag nanoparticles, solute Ag atoms are considerably easier to form Ag 2 O in the atmosphere and to produce self-lubricating silver tantalate (AgTaO 3) phase during the sliding, respectively contributed to the enhanced antibacterial activity and the drop in CoF. It suggests that the new strategy of incorporating solute Ag atoms into TaN can improve its self-lubricating ability and antibacterial activity for possibly extending the surgical instruments service life and reducing healthcare costs. • TaN films with solute Ag or Ag nanoparticles are prepared by magnetron sputtering. • Enhanced antibacterial activity and self-lubricating were obtained for Ta-Ag-N film. • Antibacterial activity depends on interfacial charge transfer induced by solute Ag. • Self-lubricating behavior is ascribed to the formation of the silver tantalate phase. [ABSTRACT FROM AUTHOR]

High entropy alloy nitride coatings (HEAN), showing superior mechanical strength, high oxidation resistance, and thermal stability, have often been used in protective hard coatings field. However, the high temperature tribological field of novel HEA nitride films has not yet been well studied. The correlations among tribological properties, compressive residual stress, mechanical properties, and self-lubricating oxide are still limited. In this research, the novel (AlCrNbSiTiMo)N coatings were fabricated on both Inconel-718 and Si (100) substrate by radio frequency (RF) magnetron sputtering via tuning both substrate bias at 300 °C deposition temperature. The (AlCrNbSiTiMo)N coatings with a specific substrate bias exhibit an outstanding hardness of 34.5±0.8 GPa. In the wear test at 700 °C, the films deposited at −100 V revealed the lowest wear rate around 1.2 × 10−6 mm3N−1 m−1. With Molybdenum doping, the MoO 3 Magnéli phase was observed on the surface at elevated temperature wearing process, and the friction coefficient at high temperature decreased significantly due to a lubricating surface. The coating exhibited the average friction coefficient value of 0.48 in the wear test of 700 °C. The high temperature tribological performance was addressed and related to the mechanical properties, the plastic deformation resistance H3/E2, and the excess residual stress of the films. This study provides a new design for hard coatings applied to severe wearing conditions. By tuning substrate bias, the (AlCrNbSiTiMo)N coatings exhibit outstanding mechanical and tribological characteristics, which will be a promising candidate for high temperature tribological protective film. • The high entropy alloy nitride coating (AlCrNbSiTiMo)N revealed favorable hardness of 34.5±0.8 GPa. • The (AlCrNbSiTiMo)N coatings exhibited low friction coefficient of 0.48±0.08 at 700°C owing to the Magnéli phase MoO 3. • The optimal wear rate of 1.2×10−1 mm3 N−1m−1 was demonstrated by controlling residual stress via substrate bias tuning. [ABSTRACT FROM AUTHOR]

TiN and WS2 + hBN reinforced Ni-based alloy self-lubricating composite coatings were fabricated on TC4 alloy by laser cladding using TiN, NiCrBSi, WS2, and hBN powder mixtures. Energy-dispersive spectroscopy (EDS), scanning electron microscopy (SEM), X-ray diffractometry (XRD), and optical microscopy (OM) were adopted to investigate the microstructure. The wear behaviors of the self-lubricating composite coatings were evaluated under large contact load in room temperature, dry-sliding wear-test conditions. Results indicated that the phases of the coatings mainly include γ-Ni, TiN, TiNi, TiW, WS2, and TiS mixtures. The average microhardness of the composite coating is 2.3–2.7 times that of the TC4 matrix. Laser cladding TiN/WS2 + hBN/NiCrBSi self-lubricating composite coatings revealed a higher wear resistance and lower friction coefficient than those of the TC4 alloy substrate. The friction coefficient (COF) of the coatings was oscillating around approximately 0.3458 due to the addition of self-lubricant WS2 + hBN and hard reinforcement TiN. The wear behaviors testing showed that the wear resistance of the as-received TC4 was significantly improved by a laser cladding TiN/WS2 + hBN/NiCrBSi self-lubricating composite coating. [ABSTRACT FROM AUTHOR]

YSZ/Ag self-lubricating coatings were prepared on 316 L stainless steel substrates via thermal spraying technology, vacuum impregnation and in-situ synthesis for the first time. Silver is filled into the pores and voids, and evenly distributed on the surface. Owing to the formation of lubricating film during the sliding process in vacuum, the friction coefficient of the coating is reduced by about 2 times after the introduction of silver. Since the lubricating film can be continuously replenished and repaired, the YSZ/Ag self-lubricating coating has a relatively long service life (>100,000 sliding cycles). • YSZ/Ag coatings were prepared via in-situ synthesis of silver. • YSZ/Ag coatings exhibit favorable mechanical properties. • YSZ/Ag coatings exhibit excellent vacuum tribological properties. • The coating can provide nano-sized silver particles to the lubricating film, constantly repairing it to maintain stability. The friction coefficient of thermal sprayed ceramic coatings is relatively high, and the traditional introduction of lubricants will result in the decline of mechanical properties of coatings, which severely limits their applications. Herein, YSZ/Ag self-lubricating coatings were prepared on 316 L stainless steel substrates via thermal spraying technology, vacuum impregnation and in-situ synthesis for the first time. The morphologies, mechanical properties and vacuum tribological performance of composite coatings were studied in detail by comparing with YSZ coatings. Results show that silver particles distribute in the pores, cracks of YSZ coatings, and the filling of defects by silver improves the micro-hardness, fracture toughness and cohesive strength of the coatings. In addition, owing to the formation of lubricating film during the sliding process in vacuum, the friction coefficient of the coating is reduced by about 2 times and the wear rate is reduced by about 600 times after the introduction of silver. At the same time, the addition of the silver lubricant makes the wear of the coupling ball significantly reduced. Since the lubricating film can be continuously replenished and repaired, the YSZ/Ag self-lubricating coating has a relatively long service life (>100,000 sliding cycles). [ABSTRACT FROM AUTHOR]

Polyurethane/graphene oxide (PU/GO) hybrid wall microcapsules were prepared by interfacial polymerization and electrostatic adsorption method. 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm]BF 4)-loaded PU microcapsules were first fabricated in lignin-stable Pickering emulsion system. These PU microcapsules were treated with poly(ethyleneimine) (PEI) cross-linked polydopamine (PDA) to positively charge their outer surface, and then GO with negative charge was successfully attracted to the PDA-PEI modified PU microcapsules by electrostatic force. [BMIm]BF 4 -loaded PU/GO hybrid wall microcapsules with mean size of 82±26 μm were successfully prepared. Synthesized microcapsules have excellent permeability resistance and thermal stability, and the core content of microcapsules was 56.5±4.3wt.%. Epoxy composites containing microcapsules were fabricated and their tribological properties were investigated. GO can effectively improve the friction resistance of epoxy composites. The friction coefficient decreased from 0.610 (pure epoxy) to 0.265 (epoxy containing 15wt.% PU microcapsules) and 0.150 (epoxy containing 15wt.% PU/GO microcapsules). The wear rate decreased from 86.0×10−14 to 3.1×10−14 and 1.2×10−14 m3/Nm, respectively. The self-lubricating mechanism was described in detail. The GO and [BMIm]BF 4 ionic liquid have the synergistic contribution to good self-lubricating performance of epoxy composites. [ABSTRACT FROM AUTHOR]

• MAX (Ti 3 SiC 2) and Ti 5 Si 3 silicide composite coatings were successfully prepared by in-situ synthesis laser cladding. • Excellent self-lubricating properties of the coatings are attributed to Ti 3 SiC 2 , Ti 5 Si 3 and TiC. • Laser-clad Ti 3 SiC 2 /Ti 5 Si 3 /TiC/Ni-based composite coatings exhibit small amount of adhesive wear, plastic deformation. In the work the in-situ synthesis of Ti 3 SiC 2 (MAX) phase and silicide reinforced Ni-based composite self-lubricating coatings from Ti-Si-C system and NiCrBSi powders were carried and initiated by laser cladding with use of 5 kW fiber laser beam with 3 mm spot. The microstructures of the laser-clad in situ synthetic self-lubricating coatings were analyzed by a scanning electron microscope (SEM) equipped with an X-ray energy dispersive spectrometer (EDS). An X-ray diffraction (XRD) spectrometer and an electron back-scattered diffraction (EBSD) were used for determination of the reaction products in the composite coatings. The friction and abrasion behavior of the coatings were evaluated at room temperature by a dry sliding friction tester. The results indicate that in-situ chemical reactions took place between elements Ti, Si and C in the laser molten pool, and the reaction products included Ti 3 SiC 2 , Ti 5 Si 3 , and TiC ceramics as well as TiNi x compound. Finally, three laser-clad Ti 3 SiC 2 /Ti 5 Si 3 /TiC/Ni-based composite coatings with the total thickness about 1 mm were fabricated on Ti6Al4V alloy. The average microhardness of the three coatings was 703.2 HV 0.2 , 751.9 HV 0.2 and 850.6 HV 0.2 respectively, which has been significantly improved, compared with the hardness of Ti6Al4V substrate (about 360 HV 0.2). The average friction coefficient of the Ti 3 SiC 2 /Ti 5 Si 3 /TiC/Ni-based composite coating (50 wt% Ni25/50 wt% Ti-Si-C) reduced to 0.33 at room temperature, and it exhibited the wear rate of 13.5 × 10−5 mm3 N−1 m−1. The laser cladding Ti 3 SiC 2 /Ti 5 Si 3 /TiC/Ni-based composite coatings characterized by small amount of adhesive wear, plastic deformation and relatively smooth wear surface could be observed. [ABSTRACT FROM AUTHOR]

In this study, magnesium matrix composites reinforced with 5 wt% WS 2 and 15–20 wt% SiC particles were sintered via powder processing. The friction and wear behaviour were studied using a ball-on-disc tribometer against Al 2 O 3 ball, subjected to normal loads of 1–4 N, room temperature and 110 °C, sliding speed of 22.5 mm/s, and lubricant of PAO base oil. The wear track and tribo-layer generated were investigated by optical profilometry and scanning electron microscopy. The average friction coefficient for Mg metal matrix composites (MMCs) was found to be 0.1–0.2 compared with 0.16–0.46 for pure Mg. Under all testing conditions, the Mg MMCs exhibited much lower friction coefficient and outstanding anti-wear property compared with unreinforced Mg and the Mg alloy AZ31. • Lightweight magnesium matrix reinforced with SiC and WS 2 (Mg MMCs) were sintered via powder processing. • Friction and wear tests were conducted under both room and elevated temperature. • Mg MMCs exhibited outstanding anti-wear and self-lubricating properties in addition to enhanced mechanical strength. • Mg MMCs provide a competitive advantage as greener components operating in tribological applications. [ABSTRACT FROM AUTHOR]

Porous ultra-high-molecular-weight polyethylene (UHMWPE) self-lubricating materials were designed and fabricated by a rotary sintering method, and the microstructure and properties were evaluated. Results showed that the rotary molding could not only significantly improve the molding efficiency but also formed uniform internal microstructures with high porosity, excellent mechanical properties, and low friction coefficient. Under oil lubricating conditions, the friction curve of samples quickly reached a steady state, the friction coefficient was reduced by 50%, and the repeat utilization was up to 99%. The following optimum sintering conditions were shown: Sintering temperature of 180 °C or 190 °C, sintering time determined as 10 min, and loading capacity of between 3.6 g and 3.8 g. Therefore, it is expected that this work will open a convenient and compatible strategy for fabricating porous materials with good self-lubricating performance. [ABSTRACT FROM AUTHOR]

In this work, laser cladding has been employed for the preparation of nickel-based self-lubricating coating NiCrAlY/Ag 2 O/Ta 2 O 5 on Inconel 625 alloy substrate. In order to study the evolution of Ag 2 O and Ta 2 O 5 in the coating and its effect on the microstructure, three coatings of NiCrAlY/Ag 2 O, NiCrAlY/Ta 2 O 5 and NiCrAlY were prepared for comparison. The composition and microstructure of the powders and the corresponding composite coatings were studied by SEM-EDS and XRD. The average hardness of Coating (A, B, C, D) and substrate is 369.5 HV, 300.7 HV, 306.5 HV, 332.1 HV, and 246.8 HV, respectively. The friction and wear properties of the self-lubricating coating were studied by MFT-5000 multifunctional friction and wear tester at RT (room temperature) ~750 °C. In order to compare with the self-lubricating coating, the same friction and wear test was done on the substrate under the same condition. It can be seen that the friction coefficient of the self-lubricating coating from RT to 750 °C is 0.64, 0.23, 0.62 and 1.5 times lower than that of the substrate, and its wear rate is 2.03, 2.11, 2.82 and 1.04 times lower than that of the substrate, respectively. SEM-EDS and XRD were used to analyze the morphology and composition of the worn surface. It can be seen from the results that Ag is the main lubrication phase at room temperature, and NiO and Ag work together to lubricate at 350 °C. When the temperature reaches 550 °C, Ag loses its effective lubrication, while the wear-resistant glaze layer composed of NiO and CrO 2 provides the main lubrication. At 750 °C, AgTaO 3 and Ag 2 Ta 4 O 11 formed by in-situ reaction will act as a synergistic lubrication with the wear resistant glaze layer composed of oxide. The synergistic lubrication of Ag, NiO, CrO 2 , AgTaO 3 and Ag 2 Ta 4 O 11 enables self-lubrication of the composite coating in a wide temperature range. • NiCrAlY/Ag 2 O/Ta 2 O 5 self-lubricating composite coating was prepared by laser cladding. • The addition of Ta 2 O 5 contributed to the refinement of grain structure of the coating. • AgTaO 3 and Ag 2 Ta 4 O 11 are formed by in situ synthesis at high temperature, and they exhibit excellent wear reduction • The synergistic lubrication of Ag, NiO, CrO 2 , AgTaO 3 and Ag 2 Ta 4 O 11 achieves wide temperature range self-lubrication. [ABSTRACT FROM AUTHOR]

In this study, micro-arc oxidation (MAO) of aluminum 6061 alloy was carried out within a silicate base electrolyte containing 0.75 g/L of cellulose, and the tribological properties of the coating were investigated. The as-prepared coating was detected by Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), a scanning electron microscope (SEM) and an energy-dispersive spectrometer (EDS), respectively. The results suggested that cellulose filled in the microcracks and micropores, or it existed by cross-linking with Al3+. In addition, it was found that the cellulose had little effect on the coating hardness. However, the thickness and roughness of the coating were improved with the increase in cellulose concentration. Moreover, the ball-on-disk test showed that the friction coefficient, weight loss and wear rate of the MAO coating decreased with the increase in cellulose concentration. Further, the performances of the coatings obtained in the same electrolyte, under different preserved storage periods, were compared, revealing that the cellulose was uniformly dispersed in the electrolyte and improved the tribological properties of the MAO coating within 30 days. [ABSTRACT FROM AUTHOR]

Self-lubricating micro impregnated diamond bits (IDBs) were manufactured for the first time via hot-pressing powder metallurgy to investigate the effectiveness of two promising solid lubricant additives, WS 2 and CaF 2 , in improving IDBs' self-lubricating and drilling performances through laboratory drilling test and micro analyses. It was found that, with increase in lubricant concentration, the rate of penetration (ROP) of WS 2 IDBs increased exponentially, while that of the CaF 2 IDBs decreased monotonically from its maximum value at 6 vol% CaF 2 concentration. For WS 2 IDBs, the increase in ROP was at the sacrifice of substantial deterioration of IDBs' service life, while the service life of CaF 2 IDBs gradually increased to surpass that of lubricant-free IDBs at 8 vol% CaF 2 addition and continued to grow. Micro analyses, including measurement of diamond protrusion height and micro morphological analysis of IDBs' worn surface, were conducted using a confocal laser scanning microscopy (CLSM). The 10 vol% CaF 2 IDBs were found under good protection from either matrix or diamond wear. By contrast, the surface of the 6 vol% WS 2 IDBs suffered severe wear. Based on CLSM images, it was inferred that the high ROP and low service life of WS 2 IDBs were a result of enhanced three-body abrasive wear by breakaway diamond grits. In general, self-lubricating IDBs with 10 vol% CaF 2 addition acquired best overall performances in that they achieved longest service life while having higher ROP than lubricant-free IDBs. • Self-lubricating impregnated diamond bits (IDBs) were designed and produced. • The rate of penetration of WS 2 self-lubricating IDBs is enhanced. • The service life of CaF 2 self-lubricating IDBs is prolonged. • The mechanism behind the phenomena is revealed by micro analyses. [ABSTRACT FROM AUTHOR]

1Cr13MoS is a kind of material with excellent corrosion resistance and good mechanical properties. Meanwhile, it also has good self-lubricating properties due to the presence of molybdenum disulfide phase inside the material and can be used as friction pair material in the pump. In this paper, the hardness, microstructure, distribution of the self-lubricating phase, friction and wear properties of 1Cr13MoS after heat treatment were studied. After quenching at 1000 °C and tempering at 520 °C, the hardness of 1Cr13MoS prepared by pyrometallurgy is higher than that of HB 350. The tempering sorbite structure is evenly distributed, and the self-lubricating phase MoS2 is discretely distributed on the substrate with the average size is about 6 μm, which leads to good friction and wear properties. It is worth noting that the 1Cr13MoS is actually operated as friction pair material on the water pump and has a significant wear improvement effect compared to the conventional 12% chrome steel series. [ABSTRACT FROM AUTHOR]

An organic coating is commonly used to protect metal from corrosion, but it is prone to failure due to microcracks generated by internal stress and external mechanical action. The self-healing and self-lubricating achieved in the coating is novel, which allows an extension of life by providing resistance to damage and repair after damage. In this study, a new approach to microencapsulating bifunctional linseed oil with polyurethane shell by interfacial polymerization. Moreover, the self-healing and self-lubricating coatings with different concentrations of microcapsules were developed. The well-dispersed microcapsules showed a regular spherical morphology with an average diameter of ~64.9 μm and a core content of 74.0 wt.%. The results of the salt spray test demonstrated that coatings containing microcapsules still possess anticorrosion, which is improved with the increase of microcapsules content, after being scratched. The results of electrochemical impedance spectroscopy showed a |Z|f=0.01Hz value of 104 Ω·cm2 for pure epoxy coating after being immersed for 3 days, whereas the coating with 20 wt.% microcapsules was the highest, 1010 Ω·cm2. The results of friction wear showed that the tribological performance of the coating was enhanced greatly as microcapsule concentration reached 10 wt.% or more, which showed a 86.8% or more reduction in the friction coefficient compared to the pure epoxy coating. These results indicated that the coatings containing microcapsules exhibited excellent self-healing and self-lubricating properties, which are positively correlated with microcapsules content. [ABSTRACT FROM AUTHOR]

Multilayer wall microcapsules efficiently loaded with a lubricant (ionic liquid [BMIm]PF6) are successfully synthesized via a combination of interfacial and in situ polymerization reactions based on lignin nanoparticle–stabilized Pickering emulsion templates. The resulting microcapsules are spherical in shape, with an ideal structure of a rough outer surface and a smooth inner surface. The mean diameter and wall thickness of the resultant microcapsules are 52 ± 18 µm and 3–6 µm. The core fraction is ≈71.29 wt%. Compared with the pure epoxy resin, the friction coefficient of self‐lubricating composites decreases by 83.6% (from 0.55 to 0.09) and the wear rate decreases by 218 times (from 76.8 × 10−14 to 0.352 × 10−14 m3 N−1 m−1) by incorporating 20 wt% of the resultant microcapsules into the epoxy resin. It is demonstrated that [BMIm]PF6, a more efficient lubricant, release from the microcapsules during the friction process produced a boundary lubricating film. The bipolar property of [BMIm]PF6 makes the lubricating film firmer, which can efficiently prevent direct contact between the resin matrix and counterface. Furthermore, the rough poly(urea‐formaldehyde) outer surface of multilayer microcapsules brings in an improved interface property between the microcapsules and resin matrix. Multilayer wall microcapsules efficiently loaded with [BMIm]PF6 ionic liquid are successfully synthesized. The friction coefficient of self‐lubricating composites decreases by 83.6% and the wear rate decreases by 218 times by incorporating 20 wt% of the resultant microcapsules into the epoxy resin. Three reasons that contribute to the ultralow friction properties are elaborated. [ABSTRACT FROM AUTHOR]

A self-lubricating plasma electrolytic oxidation–polytetrafluoroethylene (PEO–PTFE) composite coating was successfully fabricated on the surface of commercially pure titanium by a multiple-step method of plasma electrolytic oxidation, dipping and sintering treatment. The microstructure and tribological properties of the PEO–PTFE composite coating were investigated and compared with the PEO TiO2 coating and the PTFE coating on titanium. Results show that most of the micro-pores of the PEO TiO2 coating were filled by PTFE and the surface roughness of PEO–PTFE composite coating was lower than that of the PEO TiO2 coating. Furthermore, the PEO–PTFE composite coating shows excellent tribological properties with low friction coefficient and low wear rate. This study provides an insight for guiding the design of self-lubricating and wear-resistant PEO composite coatings. [ABSTRACT FROM AUTHOR]

Smart nanocontainers with stimuli-responsive property can be used to fabricate a new kind of self-lubricating nanocomposite, while the practical potential of the metal-organic frameworks (MOFs) as nanocontainers for lubricants has not been realized. In this work, mesoporous Cu-BTC MOFs storing oleylamine nanocomposites were explored from synthesis and microstructure to self-lubricating characterization. The stress stimuli-responsiveness behavior of the Cu-BTC storing oleylamine (Cu-BTCO) for lubrication has been investigated by subjecting it to macroscopic ball-on-disc friction tests. The steady-state coefficients of friction (COFs) of the Cu-BTC nanocomposites without lubricants were ca. 0.5. In contrast, after oleylamine as the lubricant was incorporated into the Cu-BTC container in the nanocomposite, ultralow friction (COF, ca. 0.03) was achieved. It has been demonstrated that the improved lubricating performance was associated with the lubricating film which was in situ produced by the chemical reaction between the oleylamine released from the nanocontainer and the friction pairs. Therefore, the nanocomposite with smart Cu-BTC container holds the promise of realizing extraordinary self-lubricating properties under stress stimuli.

It is known that smooth, hydrophobic solid surfaces exhibit low ice adhesion values, which have been shown to approach a lower ice adhesion strength limit (∼150 kPa) defined by the water receding contact angle. To overcome this limit, we have designed self-lubricating icephobic coatings by blending polydimethylsiloxane (PDMS)-poly(ethylene glycol) (PEG) amphiphilic copolymers into a polymer matrix. Such coatings provide low ice adhesion strength values (∼50 kPa) that can substantially reduce the lower bound of the ice adhesion strength achieved previously on smooth, hydrophobic solid surfaces. Different molecular mechanisms are responsible for the low ice adhesion strength attained by these two approaches. For the smooth hydrophobic surfaces, an increased water depletion layer thickness at the interface weakens the van der Waals' interactions between the ice and the polymeric substrate. For the self-lubricating icephobic coatings, the PEG component of the amphiphilic copolymer is capable of strongly hydrogen bonding with water molecules. The surface hydrogen-bonded water molecules do not freeze, even at substantial levels of subcooling, and therefore serve as a self-lubricating interfacial liquid-like layer that helps to reduce the adhesion strength of ice to the surface. The existence of nonfrozen water molecules at the ice-solid interface is confirmed by solid-state nuclear magnetic resonance (NMR) spectroscopy.