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The tribological performance of lubricant is significantly affected by additive concentration. To realize optimization of additive concentrations, an eXtreme Gradient Boosting machine learning method was proposed to predict the tribological performance of a lubricant, reflected by wear volume, with data collected from four-ball friction experiments. The Shapley Additive exPlanation tool was used to explain the predictions of the model. Particle swarm optimization was used to optimize additive concentration proportions. The tribological properties of grease additives were verified through validation experiment. The chemical components of wear scars include MXenes, carbon films, iron oxides, and iron phosphides, which facilitate direct contact between friction surfaces. This study provides a novel data-driven approach for optimization of additive concentrations with effective and predictable tribological performance. [Display omitted] • A machine learning-based method was used for the optimal lubricant additive concentration selection. • SHAP explanation tool confirmed the importance of friction conditions as well as additive concentrations. • Particle swarm optimization was used to realize optimality searching of additive concentration proportions. • Enhancement in synergistic effect among lubricant additives with optimal proportions predicted. [ABSTRACT FROM AUTHOR]

Cellulose is a kind of low-cost, widely-sourced and environmentally friendly material. In this paper, a cellulose acetate/cellulose fiber paper composite membrane was prepared through a phase inversion process. Combining the advantages of these two materials, the composite membrane has good antifouling performance and excellent wear resistance. [ABSTRACT FROM AUTHOR]

Surface modification with polydopamine (PDA)‐based coating is widely used to obtain high performance and build special functions for modified surfaces. Herein, a mussel‐inspired nanohybrid coating (PDA/SiO2) was first co‐deposited onto the polytetrafluoroethylene (PTFE)/polyimide (PI) fabric surfaces via simultaneous polymerization of dopamine and hydrolysis of the tetraethoxysilane (TEOS) in a simple one‐pot method. This nanohybrid coating could afford the hybrid‐fabric sufficient active groups, improved surface roughness, and wettability without compromising fiber intrinsic strength. As a result, the interfacial bonding strength between fabric and PI resin matrix presented a significant increase as measured by the peeling tests. In addition, aramid pulp and aramid fiber powder were incorporated into the fabric composites to construct synergistic enhancement effects with PI fibers on bearing capacity and wear resistance. Results showed that the fabric@PDA‐TEOS/micro‐powder composites presented the best high‐temperature anti‐wear property resulting from the improved interfacial adhesion strength and carrying capacity of lubricant films. [ABSTRACT FROM AUTHOR]

Thick diamond‐like carbon (DLC) coatings with different silicon (Si) transition layer thickness are deposited by hollow cathode plasma immersion coating technology. The results show that the internal stress of the coating can be tuned by changing the deposition time of Si transition layer, thereby obtaining good adhesion strength. Friction and wear results show that all coatings have good tribological properties. The coating with 8 min Si transition layer (Si‐8) demonstrates the lowest friction coefficient (μ ≈ 0.03), even achieves ultralow friction (μ ≈ 0.008) for a short time. However, the wear rate of Si‐8 coating is found to be the largest (2.1 × 10−16 m3 (N m)−1. The low friction coefficient of Si‐8 coating is related to its high degree of graphitization, complete transfer film and fine wear debris. In contrast, the Si‐16 coating has the lowest wear rate of about 5.6 × 10−17 m3 (N m)−1 with a relatively high friction coefficient (μ ≈ 0.1). This is due to its high hardness and the formation of a nano‐twisted double helix carbon debris during the friction process. This nano‐twisted double helix structure can consume additional plastic deformation energy, while reducing the interface contact area and increasing the interface bearing capacity, thereby improving the wear resistance of the thick DLC coating. [ABSTRACT FROM AUTHOR]

Si3N4 as a structural ceramic is desirable for applications in spacecraft, transportation, and energy, but its poor high‐temperature properties still do not satisfy the actual requirements. Here, a TiC0.3N0.7 reinforced Si3N4 ceramic is successfully designed and fabricated via the high‐temperature nitridation of TiCx. It is found that TiC0.3N0.7 grains with the size of 1‐2 μm are uniformly dispersed in the Si3N4 matrix and show a firm bond with substrate. Compared with pure Si3N4, the doping of harder TiCN phase can effectively improve ceramic's hardness and fracture toughness at a certain temperature. Importantly, the ceramic material displays extraordinary wear resistance across a wide temperature range (eg, the wear rate of TiC0.3N0.7 containing Si3N4 over 63 times and 178 times better than pure Si3N4 at 600 and 900°C, respectively). More broadly, a correlation between wear mechanism and temperature is established, and the result shows that the mechanical strength and tribochemical oxidation as two key factors determine the wear behavior of the material. These results developed here can provide a springboard for preparation and optimization of multiphase ceramics that serve under high‐temperature conditions. [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]

In this article, the dry-sliding tribological behaviors of TiAl-based composites reinforced with 20 and 40 vol% in situ synthesized TiB produced by a hot-press sintering process were investigated from room temperature (RT) to 800 °C. The results show that the high-temperature wear resistance of the TiAl alloy is improved by adding the TiB particles under all the testing temperatures, and the more the TiB reinforcement, the better the wear resistance is. This improvement is more significant at 600 °C and above, especially for the composite with 40 vol% TiB, whose wear rate is 4-10 times lower than TiAl at 600 and 800 °C. Accordingly, the wear mechanisms transfer from abrasion wear at low and moderate temperature (RT, 200 and 400 °C) to oxidation wear at high temperature (600 and 800 °C). In addition to the brittle-to-ductile transition of the materials and oxide layer formation, the phase transition of AlO and TiO may be partly responsible for the promising wear resistance at high temperatures. [ABSTRACT FROM AUTHOR]

This article presents a new solution for the lubrication and wear problem of TiAl alloy in vacuum by coating Ti3AlC2 layer. Ti3AlC2 coating and Ti‐46Al‐2Cr‐2Nb alloy substrate are simultaneously consolidated by hot‐pressed approach. The coating demonstrates superior self‐lubricity, CoF of 0.2 and negligible wear, in the vacuum of 2.0 × 104 Pa. A transition layer is formed in the interface, resulting in very strong coating adhesion. [ABSTRACT FROM AUTHOR]

In this paper, Cu/AlMgB composites with by weight percent, 5, 10 and 20 % of the AlMgB (referred to CA-5, CA-10 and CA-20) were fabricated by hot-press sintering method. The mechanical and dry-sliding tribological properties of the three composites were investigated. The results indicated that the densities of the Cu/AlMgB composites were lower than copper, whereas the hardness higher. The friction and wear behaviors of the composites were strongly dependent on the AlMgB content. The friction coefficient was in the range of 0.73-1.0 for CA-5, but it was always steady at about 0.2 for CA-10 and CA-20. Accordingly, the increase in the AlMgB concentration can improve the wear resistance of the composites. [ABSTRACT FROM AUTHOR]

To improve the antiwear property and load carrying capacity of hybrid PTFE/Nomex fabric/phenolic composites, graphene and graphene oxide (GO) had been synthesized and were employed as fillers, together with graphite. Sliding wear tests show that the wear rates of filler-reinforced PTFE/Nomex fabric composites were reduced greatly when compared to unfilled fabric composite. Besides, it was found that the 2 wt% GO filled PTFE/Nomex fabric composites exhibited the optimal tribological properties. It was proposed that the self-lubrication of GO, the favorable interface stability of the composite, and the uniform transfer film on the counterpart pin contributed together to the reinforced tribological property of GO filled PTFE/Nomex fabric composite. We also investigated the influence of filler content, applied load, sliding speed, and tensile and bonding strength on the tribological properties of PTFE/Nomex fabric composites. [ABSTRACT FROM AUTHOR]

Purpose – In order to develop novel high EP S-containing additives and to meet the need of formulating GL-5 gear oil or other high EP lubricating oils, aims to investigate the tribological behaviors and mechanism of a di(iso-butyl)polysulfide (DIBPS), which was synthesized from some cheap materials at low temperature and under normal atmospheric pressure, as an additive in some mineral base oils compared with the traditional sulfurized olefin (SO) additive. Design/methodology/approach – The DIBPS additive was designed and synthesized, of which the main composition is the di(iso-butyl)trisulfide. Its load-carrying capacity, anti-wear and friction reduction properties as additive in some mineral base oils, compared with the traditional SO additive, were investigated using a four-ball machine and a Timken tester according to relative testing standards. The tribological mechanism was discussed according to the SEM and XPS analytical data. Findings – The results indicate that the four-ball PD value and the Timken OK value of the prepared DIBPS in VHVIS500 is clearly better than that of the traditional SO; the anti-wear property of DIBPS is equivalent to the traditional SO and the friction reduction effect of DIBPS is better than that of the traditional SO. The SEM and XPS data show that the DIBPS additive experiences different tribochemical reaction during tribological process compared with the traditional SO. The S active element of DIBPS reacted with surface metal mainly to form FeSO4 and/or Fe2(SO4)3 inorganic film, but the S active element of the traditional SO reacted with the surface metal mainly to form FeS inorganic film. This may be the chief reason why the prepared DIBPS possesses better EP properties than the SO. Research limitations/implications – The results show that the polysulfide additive (DIBPS) possesses better extreme pressure property than the traditional SO. However, more experimental study such as the synergic effect with other additives must be performed, from which it will be clearly shown whether the novel polysulfide can be applied in industrial oils. Practical implications – These results may be useful for the researchers to formulate some high EP industrial oils. Originality/value – This paper proves that the designed polysulfide additive, of which the main composition is the trisulfide, possesses better extreme pressure property than the traditional SO, and its tribological mechanicsm is also different with that of SO. It is noticed that the preparative method of this novel polysulfide additive has some superiorities, such as: low-experimental temperature, low-experimental pressure and cheap materials. [ABSTRACT FROM AUTHOR]

Ga‐based liquid metal (GLM) can be used as a current‐carrying lubricant, due to its combination of excellent electrical conductivity and good lubricity. However, the influence of electric field parameters on the lubrication mechanism of GLM is still unclear. This paper attempts to investigate the influence of current magnitude, voltage magnitude, current direction, and load on the lubrication behaviors of GLM at atmosphere and room temperature (≈26 °C). It is found that the interface action mechanism induced by an electric field is mainly reflected in four aspects, namely, Joule heating effect, electric field force, electrochemical effect, and electromigration effect. These interfacial physical and chemical effects are governed by the current magnitude, voltage magnitude, current direction, and load, bringing about distinct frictional products and thereby influencing the lubrication behaviors. Briefly, FeGa3 can only be formed when the current reaches 6 A and the load is above 40 N, and it has obvious friction‐reducing properties, but increases the wear due to its low content. When the frictional product is just the Ga‐rich film, the increase of oxidation degree is detrimental to the wear resistance. [ABSTRACT FROM AUTHOR]

[Display omitted] Traditional high strength engineering alloys suffer from serious surface brittleness and inferior wear performance when servicing under sliding contact at cryogenic temperature. Here, we report that the recently emerging CoCrNi multi-principal element alloy defies this trend and presents dramatically enhanced wear resistance when temperature decreases from 273 to 153 K, surpassing those of cryogenic austenitic steels. The temperature-dependent structure characteristics and deformation mechanisms influencing the cryogenic wear resistance of CoCrNi are clarified through microscopic observation and atomistic simulation. It is found that sliding-induced subsurface structures show distinct scenarios at different deformation temperatures. At cryogenic condition, significant grain refinement and a deep plastic zone give rise to an extended microstructural gradient below the surface, which can accommodate massive sliding deformation, in direct contrast to the strain localization and delamination at 273 K. Meanwhile, the temperature-dependent cryogenic deformation mechanisms (stacking fault networks and phase transformation) also provide additional strengthening and toughening of the subsurface material. These features make the CoCrNi alloy particularly wear resistant at cryogenic conditions and an excellent candidate for safety–critical applications. [ABSTRACT FROM AUTHOR]

Revealing the frictional behavior through the lens of structural and chemical evolution is crucial for comprehending the exceptional wear-resistance of alloys with complex composition. Here, we propose that superior wear resistance can be achieved via dynamic surface segregation during sliding at room temperature. This strategy was demonstrated in CrCoNi multi-principal element alloy (MPEA) films with nano-grain structure, which exhibit a remarkably low wear rate that is <50 % of that for their VCoNi counterpart. Such distinct wear behavior is attributed to the specific friction-driven Ni segregation on the CrCoNi surface, which facilitates the preferential oxidation and formation of a nanocomposite protective layer with equiaxed nanograins uniformly embedded in an amorphous matrix. This wear-induced unique microstructure accommodates sliding-induced plastic deformation against damage and is responsible for the superior wear-resistance. Having revealed these fundamental mechanisms by experiment and simulation, this study provides a brand-new perception for designing self-adaptive MPEA surfaces. This involves adjusting the evolution of deformation layers with specific structure and chemistry, precisely engineered for tribological applications. [Display omitted] [ABSTRACT FROM AUTHOR]

The unsatisfactory wear resistance and lubrication performance of CoCrNi multi-principal elements alloys (MPEAs) have emerged as critical challenges, impeding their extensive utilization as advanced engineering materials, despite their desirable mechanical and physical properties. Incorporating graphite to obtain MPEAs-based self-lubricating composites is believed to improve the wear resistance. However, it is challenging to prepare composites with high strength, large plasticity, and excellent anti-friction performance simultaneously. The present study reports the fabrication of novel CoCrNi MPEA-based self-lubricating composites, consisting of in-situ graphite and high-hardness silicides/carbides as reinforcement, prepared by powder metallurgy and reactive sintering. The 20.6 vol% Gr@CoCrNi–SiC composite exhibits an optimal trade-off between strength and ductility, along with anti-friction and wear resistance which is superior to the reported composites with different solid lubricants. The wear mechanism is attributed to the coordinated deformation mechanism between the CoCrNi FCC matrix and silicides/carbides, and the stabile lubrication effect supported by the structural transformation from the original polycrystalline lattice structure to core-shell nanocomposite structure (similar to diamond-like carbon) of the in-situ graphite. This simple, economical and practical strategy contributes to the development of MPEA self-lubricating composites with excellent comprehensive properties. [Display omitted] [ABSTRACT FROM AUTHOR]

The expected excellent tribological performance of high-entropy alloys (HEAs) is rarely achieved due to the absence of self-lubricating ability on the worn surface. In particular, the situation is more challenging in HEAs with face-centered cubic structure because of the inferior yield strength when used in dry sliding conditions. Unlike conventional soft-solid lubricants, which deteriorate the mechanical properties of HEA matrix, in this study we demonstrate in a protocol model alloy that the proper incorporation of few-layer graphene as reinforcement in CoCrFeNiMn can lead to both surface strengthening and lubrication. This is achieved by a partially chemical interface reaction between graphene and HEA via a tunable fabrication process, resulting in a reduction of wear rate and friction coefficient of 86.03% and 23.87%, respectively. As a result of the interfacial in-situ carbide strengthening together with the self-lubrication of graphene, this tailored composite structure also exhibits superior tribological properties over most HEA-based self-lubrication composites. Besides, the subsurface structure evolution and deformation mechanisms that influence the wear resistance are systematically clarified through microscopic exploration and atomistic simulation. The present study presents an effective strategy for the development of innovative HEA composites suitable for safety-critical applications, which overcomes the inherent compromise and achieves exceptional tribological performance, i.e., self-lubricating and anti-wear. [Display omitted] • The self-lubricating graphene reduces wear rate to an order of magnitude. • The wear rate of Gr/HEA composite surpasses most FCC-structured HEAs. • The in-situ carbides alter the plastic deformation mode from planar to wavy slips. • The graphene significantly alters the plowing and adhesion mechanisms during wear. [ABSTRACT FROM AUTHOR]

High-entropy bulk metallic glasses (HE-BMGs) with desired thermal stability often exhibit limited plasticity due to the occurrence of shear localization avalanches. The present study reports the fabrication of a novel composite TiZrHfNb 0.5 Cu 0.5 Be 0.5 , consisting of a high entropy crystalline phase (TiZrHfNb) and an amorphous matrix (TiZrHfCuBe). The composite exhibits a distinctive combination of strength and ductility, surpassing that of traditional BMG composites, along with a notable capacity for work-hardening. Furthermore, it demonstrates exceptional wear resistance under varying normal loads or frequencies. The deformation and wear mechanisms are attributed to the solid-solution strengthening and stress-induced β → α " martensitic transformation in the high entropy crystalline phase, as well as the deformation-induced crystallization in HE-BMG matrix. These findings would provide a new strategy for preparing advanced HE-BMGs composite with unique properties. • A composite TiZrHfNb 0.5 Cu 0.5 Be 0.5 , consisting of a high-entropy phase TiZrHfNb and an amorphous matrix TiZrHfCuBe is fabricated. • The composite has excellent strength-ductility combination, along with a notable work-hardening capacity. • The composite demonstrates exceptional wear resistance under varying normal loads or frequencies. • Deformation-induced crystallization nearby the crystal/amorphous interface is found during the deformation or wear process. [ABSTRACT FROM AUTHOR]

Sodium dodecyl sulfate (SDS) and 8-Hydroxyquinoline (8-HQ) intercalated layered double hydroxides (LDH) sheets were in-situ formed in MAO layer to prepare a composite coating (CI@LDH-MAO) on AZ31 magnesium alloy. This composite coating demonstrates commendable anti-corrosion performance, primarily attributed to the formation of LDH sheets and insoluble Mg(HQ) 2 compounds. The electrochemical impedance modulus of the composite coating surpasses that of the MAO coating by three orders of magnitude after immersion of 360 h. Concurrently, the CI@LDH-MAO composite coating exhibits exemplary tribological properties, characterized by a friction coefficient of approximately 0.19 and a wear rate of (11.5 ± 1.5)× 10−6 mm3/(N·m). This outstanding tribological performance can be ascribed to enhanced interaction of lubricants with the friction interface by 8-HQ and SDS anions. • 8-HQ and SDS anions intercalated LDH was in-situ formed in MAO coating. • The composite coating has excellent tribological and anti-corrosion performance. • The COF was reduced by > 80% and the wear rate was reduced by > 50%. • 8-HQ and SDS anions facilitated the interaction of lubricants with friction interface. [ABSTRACT FROM AUTHOR]

In this study, two-dimensional transition metal carbides and carbon nitride (MXene) and mesoporous silica nanoparticles (SiO 2) loaded with corrosion inhibitor 1-(3-((N-n-butyl) aminecarboxamido) propyl)-3-hexadecyl imidazolidin bromide (M16) were used to prepare a M16@MXene-SiO 2 nanocomposite with good anti-corrosion and wear resistance. The structure and composition of the nanocomposites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The synthesized M16@MXene-SiO 2 nanocomposite was then added to an epoxy coating on Q235 carbon steel. The uniform distribution of M16@MXene-SiO 2 in the coating was confirmed by SEM and atomic force microscopy (AFM). The electrochemical impedance spectroscopy (EIS) test showed that the corrosion resistance of epoxy coating was the best when the addition amount of M16@MXene-SiO 2 was 5 wt%, and its electrochemical impedance could reach 5.98 × 109 Ω∙cm2. After 144 h immersion, the coating resistance (R c) of the epoxy coating decreased to 3.88 × 103 Ω∙cm2, and that of the epoxy coating with M16@MXene-SiO 2 increased to 1.01 × 104 Ω∙cm2. The corrosion inhibition efficiency of M16@MXene-SiO 2 was tested by potentiodynamic polarization. After immersion for 24 h, the corrosion current density (I corr) of the epoxy coating was 2.23 × 10−7 A∙cm−2, which reduced to 4.38 × 10−8 A∙cm−2 after adding M16@MXene-SiO 2 and the corrosion inhibition efficiency increased by 80.36 %. In addition, the wear resistance of the epoxy coating was tested by reciprocating friction experiment. The friction coefficient of the epoxy coating decreased from 0.44 to 0.12 after adding 5 wt% M16@MXene-SiO 2. The results showed that the composite coating had excellent corrosion resistance, self-healing properties and wear resistance. The improvement in corrosion could be explained by the filling of coating defects with MXene-SiO 2 and the formation of corrosion inhibitor films. The improvement of friction performance was mainly attributed to the friction transfer film formed by MXene-SiO 2 and M16. [Display omitted] • A anti-corrosion and wear-resistant self-healing coating was developed. • The inhibitor 1-(3-((N-n-butyl) aminecarboxamido) propyl) -3-Hexadecyl imidazolidin bromide (M16) was adopted. • Two-dimensional carbon nitride and mesoporous silica composite nanomaterials (MXene-SiO 2) were prepared. • The film of M16 corrosion inhibitor improved the self-healing properties of the coating. • M16@MXene-SiO 2 had good dispersion in the coating and defects in coating were filled. [ABSTRACT FROM AUTHOR]

Solid-liquid lubricating technology is a quite effective approach to achieve long life for sliding components in space. Herein, the WS 2 -Ti films with porous and dense structures were prepared. The tribological performances of WS 2 -Ti films lubricated in two kinds of space liquid lubricants (P201 and PFPE) were mainly investigated in vacuum compared to the films in dry friction condition. The dense film exhibits the low friction coefficient of 0.02 and ultra-low wear rate of 2.3 × 10−8 mm3·N−1·m−1 in the dry friction condition. The dense film/oil coatings also show a very long wear life over 4.5 × 105 r, and their wear rates obviously decrease about 79 % and 67 % under harsh test condition compared to the porous film lubricated in P201 and PFPE, respectively. The related analyses indicate that nonpolar P201 molecule is found to have far better compatibility to WS 2 -Ti crystal surfaces than polar PFPE molecule. It contributes to forming compact tribolayer consisting of numerous ultrathin nanosheets, significantly extending wear life of the coating. Noteworthily, for the solid-liquid coatings, there is a new find that formation of transfer film firstly underwent amorphization and then occurred recrystallization. This reveals lubricating mechanism of the WS 2 -Ti/oil coating. • Dense WS 2 -Ti film exhibits ultra-low wear rate of 2.3 × 10−8 mm3·N−1·m−1. • WS 2 -Ti/P201 coatings significantly prolong the wear life due to formation of compact tribolayer inside wear track. • Nonpolar P201 molecule has better compatibility on WS 2 -Ti crystal surface than polar PFPE molecule. • There is a find that transfer film in the solid-liquid coating was formed via amorphization and then recrystallization. [ABSTRACT FROM AUTHOR]

Abstract Characteristic porous microstructure causes poor wear resistances of sputtered transition metal dichalcogenides (TMDs) films that have important applications in space technology. TMDs/metal multilayer films exhibit improved microstructural and tribological properties, but which are unreliable due to the mismatch in thermal/mechanical properties between them as well as the metal sensibility to atomic oxygen (AO). In this study, MoS 2 /WS 2 nano-scale multilayer films were fabricated to improve the microstructural, mechanical, tribological and environment-adaptive properties of TMDs films. Results revealed that as compared with MoS 2 or WS 2 single-layer film, the multilayer film exhibited a dense microstructure, strong (002) texture and high hardness. Correspondingly, it showed a significantly improved wear resistance in vacuum, whose wear life was ~one order longer than those of single-layer films. Simulation tests revealed that even drastic thermal shock could not cause the delamination of multilayer film, which was observed from TMDs/metal multilayer system; and the oxidation from AO irradiation was restricted into film surface layer (≤10 nm). These results indicated that the microstructural, mechanical and tribological properties of TMDs films were significantly improved by the nano-scale multilayer design, and the fabricated multilayer film had potential applications in space technology. Graphical abstract Unlabelled Image Highlights • WS 2 /MoS 2 nano-scale multilayer film was designed and fabricated. • Porous microstructure was significantly restrained by multilayer fabrication. • Multilayered film exhibited better mechanical, wear-resistant and space-environment-resistant properties. [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]

The guanidinium ionic liquids (GILs) are synthesized and have better thermal stability than perfluoropolyether (PFPE) and 1-hexyl-3-methylimidazolium bis(trifluoromethyl sulfony)imide (LF106) according to thermogravimetric analysis. GILs possess better antifriction and antiwear performance in wide temperature range (from RT to 300 °C) than PFPE and LF106. Meanwhile, GILs have the smaller weight loss and still perform good lubricating property after the treatment of high-temperature. Then, energy dispersive spectrometer (EDS), corrosion, electrochemical and quartz crystal monitor tests are carried out to investigate the influence of adsorbability of cations to the lubricating property of GILs and LF106 under different temperature conditions. [ABSTRACT FROM AUTHOR]

High temperature solid lubricating materials show important demands in applications for moving machine assemblies under extreme operating conditions. In this study, the tribological behavior of a nickel-alloy based self-lubricating composite (82.5%nickel-alloy–12.5%Ag–5%BaF 2 /CaF 2 ) against Si 3 N 4 ball was evaluated under various temperatures and sliding speeds. Results showed that the friction coefficient and wear rate of the composite were greatly dependent on testing temperature and sliding speed. The composite exhibited favorable lubricity in the wide temperature range from 25 °C to 800 °C. The friction and wear mechanisms were explored by observing and analyzing the worn surfaces. [ABSTRACT FROM AUTHOR]

Effect of Si addition on the high temperature tribological properties of TiZrV 0.5 Nb 0.5 refractory high entropy alloy was systematically studied. The results demonstrate that Si-microalloying affects the tribological properties by modulating the evolution of tribo-layer. Si-microalloying produces local tribo-layer with strong wear resistance by increasing the sintering rate of wear debris below 600 ℃, ultimately significantly reducing the coefficient of friction and wear rate. At 600 °C, Si-microalloying deteriorates the wear resistance due to the stress concentration at hard particles leading to accelerated fracture of the tribo-layer which hinders the formation of continuous protective tribo-layer. The enhanced tribological properties at 800 °C are attributed to the synergistic effect of suppressed oxide volatilization and rapid oxidation behavior ensuring continuous dense tribo-layer formation. • The high temperature tribological properties of TiZrV 0.5 Nb 0.5 Si x RHEA was studied. • The evolution of the tribo-layer plays a crucial role in the wear process. • The sintering rate of debris determines the formation of tribo-layer below 600 ℃. • A continuous and dense tribo-layer was formed for the Si0.3 alloy at 800 °C. [ABSTRACT FROM AUTHOR]

This study firstly reports a series of novel functional polyhedral oligomeric silsesquioxane-based ionic liquids (POSS-ILs) with remarkable lubrication performance as well as resistance to space atomic oxygen (AO) irradiation. The enhancement in both anti-irradiation properties and the lubrication performance can be attributed to the synergistic effect produced by POSS group along with the tribochemical reactions. The approximate cube-octameric POSS framework as a significant contributor converts the original sliding friction into a rolling mode. The key benefit of POSS-ILs derives from the active elements N and P present in ILs and corresponding tribochemical reaction film formed. These ILs are bound to have substantial applicability in the aviation lubrication field. [Display omitted] • Oligomeric silsesquioxane-based ionic liquids (POSS ILs) were synthesized. • These POSS ILs have resistance to space AO irradiation. • These POSS ILs convert the original sliding friction into a rolling mode. • These POSS ILs has good antifriction and wear resistance. [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]

Inheriting the advantages of bulk metallic glasses (BMGs) and high entropy alloys (HEAs), high entropy bulk metallic glasses (HE-BMGs) have sparked great interest in recent years. In this work, the evolutions of structural heterogeneity, thermal stability and mechanical property of the TiZrHfCuBe HE-BMG with minor Sn addition were characterized, and the corresponding tribological properties under different normal loads and frequencies were investigated. The results showed that minor Sn addition can significantly enhance wear resistance of the HE-BMG by improving its structural heterogeneity and mechanical properties in a rather limited composition range. When excessive Sn is added, plentiful crystal particles are precipitated in the amorphous matrix, and the wear mechanism of the HE-BMG changes from slight abrasive and oxidation wear to severe fatigue and oxidation wear, leading to dramatically declined wear resistance. These findings would provide guidance for the development of advanced HE-BMGs with unique properties. • A rather limited Sn addition could enhance mechanical properties and wear resistances of (TiZrHfCuBe) 1- x Sn x HE-BMGs. • Declined wear resistance of the (TiZrHfCuBe) 0.97 Sn 0.03 was caused by the excessive Sn addition. • The wear mechanisms of (TiZrHfCuBe) 1- x Sn x HE-BMGs change from abrasive and oxidation wear to fatigue and oxidation wear. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a series of ZrO2 matrix high-temperature self-lubricating composites were prepared by hot-press technique. The effect of Mo and Ag on the friction and wear behavior of the ZrO2(Y2O3)–Ag–CaF2–Mo composites in a wide temperature range was investigated. The XRD results showed that CaMoO4 formed on the worn surface above 400°C. The excellent lubrication performance of CaMoO4 endowed the low coefficient of friction of the ZrO2(Y2O3)–Ag–CaF2–Mo composites at high temperatures. The ZrO2(Y2O3)–10Ag–10CaF2–10Mo composites showed favorable wear resistance at all the tested temperatures which was attributed to the combined action of hardness and phase transformation. [Copyright &y& Elsevier]

Abstract: The tribological behavior of a Ni3Al alloy prepared by hot-pressed sintering was investigated at dry friction and sea water condition against AISI 52100 steel ball in ambient environment and at varying loads. The tribological results suggested that the Ni3Al alloy has the better wear resistance properties compared to Ti–6Al–4V alloy at dry friction and sea water conditions, and the Ni3Al alloy possesses the excellent wear resistance properties under sea water environment. Sea water plays a significant role in the improvement of tribological properties of the Ni3Al alloy, which has lubricating, cooling, and corrosive effects on the friction pairs. [Copyright &y& Elsevier]

Highlights: [•] Pure WS2 and WS2-Al composite films with different structures were prepared. [•] The compactness of WS2 film was significantly improved due to incorporation of Al. [•] Different mechanisms of atomic oxygen resistance of both the films were discussed. [•] Films before and after AO irradiation kept the unchanged tribological properties. [•] The composite films showed much better wear resistance than pure WS2 film. [Copyright &y& Elsevier]

The WS2–Ag composite films were prepared by radio frequency co-sputtering method. The effects of alloying Ag content on composition, microstructure, mechanical properties and friction behaviors have been analyzed by X-ray photoelectron spectroscopy (XPS), grazing incidence X-ray diffraction (GIXRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS) and high resolution transmission electron microscope (HRTEM), scratch tester, nano-indentation tester and ball-on-disk tribo-tester. The Ag addition was in present of nanocrystalline phase in the boundary of the crystalline WS2 matrix and induced morphology change, but could not completely prevent the columnar platelets. The columnar platelet was composed of a great deal of nanocrystalline and a small amount of amorphous WS2 phase. There were no substantial variations in the hardness of the composite films when the Ag content was in the range of 0–20.3at.%. The suitable amount of Ag content was benefited for improving the film adhesive strength and wear resistance both in vacuum and humid air environment. Particularly, the composite film with 9.0at.% Ag exhibited the longest wear life (about 7.6×105 cycles in vacuum, 6.7×105 cycles in humid air) under high Hertzian contact pressure (as high as 1.0GPa). The wear mechanism was discussed in terms of the rearrangement of wear track and formation of transfer film. [ABSTRACT FROM AUTHOR]

Si 3 N 4 ceramics with 0 vol% and 5 vol% tungsten particles were fabricated by gas pressure sintering. Commercial Si 3 N 4 ceramic balls were used as the tribo-pair to test the influence of the tungsten particles on the wear resistance of Si 3 N 4 ceramics. The tungsten particles in the samples were exfoliated and oxidized during the rubbing process. The tungsten oxide was uniformly doped into the wear debris, which turned the harmful exfoliated abrasives into a useful tribo-film. Compared with the monolithic Si 3 N 4 ceramic, the abrasive wear of Si 3 N 4 ceramics with introducing tungsten particles was almost eliminated, and the oxidative wear and surface fatigue were also reduced. The specific wear rate was reduced by more than an order of magnitude, from 4.70 × 10−6 mm3 N−1·m−1 to 3.78 × 10−7 mm3 N−1·m−1. • Tungsten particles were first introduced into Si 3 N 4 ceramic to adjust their tribological properties. • Harmful exfoliated abrasives were transformed into a useful tribo-film by tungsten induced tribochemical wear. • Specific wear rate of Si 3 N 4 ceramic was reduced by one order of magnitude after introducing 5 vol% tungsten particles. [ABSTRACT FROM AUTHOR]

Abstract: The dry-sliding tribological behaviors of Ti–46Al–2Cr–2Nb intermetallics and its composites with 20 and 40vol% in situ formed TiB2 produced by hot press sintering process were investigated. Also, the microstructures and mechanical properties of the three materials were examined. With the increase of TiB2 amount, the hardness and wear resistance ascended. The enhanced wear resistance can be attributed to the higher hardness and the load-carrying role of TiB2. The friction coefficient was irrespective of TiB2 content. The wear mechanism of the materials was dominated by fatigue wear and delamination. [Copyright &y& Elsevier]

Abstract: The high-temperature tribological behaviour of Fe–28Al–5Cr alloy and its composites containing TiC was investigated against a Si3N4 ceramic from 25 to 800°C. The high-temperature wear resistance of the materials was significantly improved by the addition of TiC, which was attributed to the high hardness of the composites, as well as the support role of hard TiC. The oxidation played an important role to friction and wear. [Copyright &y& Elsevier]

Abstract: It is of great significance to find ways to control the high-temperature friction and wear of ceramic materials. In this paper, a ZrO2 matrix high temperature self-lubricating composite with addition of MoS2 and CaF2 as lubricants were prepared using hot pressing method by tailoring the composition of CaF2. The wear and friction behavior of the composites was investigated from room temperature to 1000°C. The ZrO2–MoS2–CaF2 composites against SiC ceramic exhibited excellent self-lubricating and anti-wear properties at a wide temperature range. At 1000°C, the ZrO2–10MoS2–10CaF2 (wt.%) composite has a very low coefficient of friction of about 0.27 and wear rate of 1.54×10−5 mm3/(Nm). The low friction and wear were attributed to a new lubricant CaMoO4 which formed on the worn surfaces at high temperatures. [Copyright &y& Elsevier]

Abstract: Hydrogenated amorphous carbon films containing Si and Al (a-C:H/(Si, Al)) were deposited on Si(100) substrates at different negative bias voltages, by radio frequency (RF, 13.56MHz) magnetron sputtering. The chemical composition and structure were detected by means of X-ray photoelectron spectroscopy (XPS) and Raman spectra, respectively. It was found from the results of Raman spectra that the film deposited at zero negative bias voltage was highly hydrogenated, but significant graphitization happened to the films when high bias voltages were applied. The results of atomic force microscope (AFM) showed that the films deposited at moderate negative bias voltage had ultra-smooth surface. The mechanical and tribological properties of the films were measured by nano-indentation test and tribo-meter in ball-on-disk mode, respectively. It was revealed that the negative bias voltage had great impacts on the mechanical properties of the films. The tribological properties of the films were significantly improved when bias voltages were applied on substrates. Particularly, the film deposited at −200V performed a super-low friction behavior (0.0085) and long wear life (>105 revolutions) in ambient air under high Hertz contact stress (as high as 1.6GPa) though it showed a relatively low hardness. [Copyright &y& Elsevier]

Abstract: A Ni3Si–Cr7C3 composite coating was fabricated on AISI 1020 steel substrate by self-propagating high-temperature synthesis (SHS) casting route. Phase composition, microhardness and dry sliding wear behavior of the coating were studied. The results indicated that the coating was mainly consisted of Ni3Si and Cr7C3. The microhardness of coating is about 900HV. The friction and wear tests showed that although the friction coefficient had no obvious change, the wear resistance of the AISI 1020 steel matrix was improved greatly. Also, the corrosion test result showed that the coating had an excellent corrosion resistance. [Copyright &y& Elsevier]

• 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]

To improve the adaptability of GLC coatings in aqueous environment, a dense structure for GLC coatings was designed and constructed by nitrogen doping via PVD technique. The nitrogen content was tailored via tuning the nitrogen flow rate to optimize the tribological performances of the N-doped GLC coatings in water as well as to investigate the effects of different nitrogen contents. And the optimal nitrogen flow rate was 5 sccm. The results implied the nitrogen doping favored the increase of adhesion strength. The dense structure built by nitrogen doping entitled the N-GLC coatings to improved wear resistance in water and enhanced aqueous-adaptability, because the corrosion by water can be effectively inhibited compared with the column-structured nitrogen-free GLC coatings via PVD. [Display omitted] • The nitrogen modified GLC coatings with dense structure and better adhesion strength were constructed via PVD technique. • The nitrogen contents in the N-doped GLC coatings can be tailored by tuning the nitrogen flow rate in the PVD process. • The nitrogen-free GLC coating was failed in water environment, while the N-GLC coating with 5 sccm flow rate showed a lowest wear rate of 2.47 × 10-8 mm3/Nm. • The nitrogen doping contributed to the densification of the coatings and thus improved their aqueous-adaptability. [ABSTRACT FROM AUTHOR]

A novel and simple method for the preparation of two-component gel lubricant and some evaluation of its physicochemical and lubricating properties are reported. The addition of two-component gelator including bis(2-ethylhexyl) sulfosuccinate and cholesterol to white oil can result in self-assembly to form a gel. The gelation mechanism was characterized by the combination of atomistic molecular dynamics simulation and experiment. It not only has excellent thermal stability, but also possesses thermal reversibility, creep recovery and thixotropic properties. Noticeably, the gel can significantly enhance lubricous and AW performances of base oil. Obtained by FIB-TEM, EDS, XPS and QCM characterization, we speculate that the gelator forms an effective adsorption and tribochemical reaction film, so it can protect the contact surface from being worn. Image 1 • The manuscript reports a novel, simple and low cost method for the preparation of two-component gel lubricant. • The AOT and cholesterol added to food grade white oil can result in self-assembly to form a gel. • The obtained gel lubricants have excellent lubricity, wear resistance and higher load carrying capacity. • The gel lubricants are green and non-toxic, provide potential application in the field of food or drug processing. [ABSTRACT FROM AUTHOR]

High entropy alloys (HEAs) are an important candidate for high temperature mechanical systems. Here, effects of atmosphere, temperature and counterparts on the vacuum tribological behaviors of CoCrFeNi HEA fabricated by spark plasma sintering were systematically studied. Comparison of tribological behaviors in vacuum and air indicated that tribo-oxidation is detrimental to the wear resistance of CoCrFeNi HEA within temperature range 25–400 °C, but positive at 600 and 800 °C. The CoCrFeNi HEA obtains relatively low wear in vacuum when low testing temperatures and heterogeneous counterface are selected. The wear resistance of CoCrFeNi HEA in vacuum is superior or comparable to the steel and intermetallics. • The high-temperature tribological behaviors of CoCrFeNi HEA were studied. • Tribological properties of HEA depend on atmosphere, temperature and counterparts. • Tribo-oxidation is negative for the wear resistance below 600 °C but positive above. • In vacuum, surface oxidation, adhesive and mechanical properties determine the wear. [ABSTRACT FROM AUTHOR]