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A special "hard‐soft" MXene/Halloysite nanotube (HNTs)/ poly(amidoamine) (PAMAM) structure was constructed to improve the interfacial and tribological performances of fabric liner (FL) materials. Thereinto, the MXene/HNTs coating were successfully grafted onto fabric surface by electrostatic self‐assembly strategy, and a novel PAMAM dendrimer polymer terminated by amino groups was prepared via condensation reaction. The mechanical and tribological performances of MXene/HNTs/PAMAM@FL as well as wear mechanism were systematically evaluated. Specifically, the incorporation of MXene/HNTs/PAMAM coating enhanced the bonding strength by 62.4%, and declined the wear rate by 27.7% in comparison with pure FL. The splendid performance was ascribed to the synergistic effect of "soft" toughening PAMAM polymer and "hard" lubricating MXene/HNTs hybrids. The introduction of MXene/HNTs hybrids could enhance mechanical interlocking and bearing capacity. Then PAMAM polymer ameliorated interfacial adhesion and compatibility with resin via forming chemical bonds, which further reducing stress concentration through increased crack deflections due to the steric hindrance. Highlights: MXene/HNTs/PAMAM coating was prepared via electrostatic self‐assembly and condensation reaction.Interfacial adhesion of fabric liner achieved effective promotion.High‐quality tribofilm was constructed by the synergistic enhancement effect between MXene/HNTs particles and PAMAM polymer.The tribo‐chemical reactions participate in improving the lubricity and durability of tribofilm. [ABSTRACT FROM AUTHOR]

It is a substantial challenge to obtain single-phase ceramics with self-lubricating properties. Most conventional lubricated ceramics benefit from the addition of solid lubricants, which largely deteriorate theirs mechanical properties. Here, we report a single-phase (HfMoNbTaTi)C system high-entropy ceramic with self-lubricity inspired by the novel high-entropy design concept and regulation of high-temperature lubrication components (with different Mo contents). The formation mechanism of the single-phase structure is ascribed to the increasing of carbon vacancies with the increasing of Mo content. Meanwhile, the tribological performances are greatly enhanced at high temperature. Especially for (Hf 0.149 Mo 0.404 Nb 0.149 Ta 0.149 Ti 0.149)C 0.745 ceramic (with 20 wt% Mo) against Al 2 O 3 ball at 900 °C, the average friction coefficient is as low as 0.6, and its wear rate is reduced an order of magnitude. The results show that the self-lubrication mechanisms are tribo-chemical reactions to generate lubricating tribo-films. • Single-phase (Hf-Mo-Nb-Ta-Ti)C system ceramic with self-lubricity was prepared. • The formation mechanism of the single-phase structure was investigated. • Regulation of Mo content has a significant effect on tribological properties. • Tribo-films with lubricity have a vital impact on friction reduction and anti-wear. [ABSTRACT FROM AUTHOR]

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

In this work, the Cr-Ti-Mo ternary o -MAX ceramics based on the Cr 2 TiAlC 2 phase are synthesized, and their tribological performance at elevated temperatures up to 800 ºC in the air is evaluated. With Si 3 N 4 as a tribocouple, an unexpected ultra-low wear rate reaching 6.1 × 10−8 mm3 N−1 m−1 is observed in Cr 1.9 Ti 0.9 Mo 0.2 AlC 2 at 800 ºC, accompanied by a stable coefficient of friction (COF) around 0.33 in a wide temperature range. X-ray photoelectron spectroscopy (XPS) depth profiling confirms a tribofilm with gradient composition, which simultaneously offers fluid lubricating at elevated temperatures and self-healing after cooling. Particularly, confirmed by the theoretical simulations, the doping of Mo improves the interlayer binding as well as alters the oxidation behaviors of Cr 2 TiAlC 2. With an optimal interlayer binding strength and oxidation rate, the Cr 1.9 Ti 0.9 Mo 0.2 AlC 2 can generate a tribofilm possessing ideal composition, which simultaneously promotes lubrication and anti-wear performance at elevated temperatures. [ABSTRACT FROM AUTHOR]

Gallium-based liquid metal (GLM) has excellent extreme-pressure properties, but at low sliding speeds, it is typically in a boundary or mixed lubrication, causing poorer properties compared to traditional lubricants. In this paper, GLM/P composite lubricants composed of GLM particles and polydimethylsiloxane are prepared. Under a maximum-Hertz-stress of 0.69 GPa, GLM/P2–30% (viscosity of 1260 mPa∙s) can enter the elastohydrodynamic lubrication (EHL) regime at 0.2 m/s, has good EHL properties (friction coefficient of 0.06, wear rate in the order of 10−9 mm3/N·m). Meanwhile, it has high extreme-pressure properties (P B of 2300 N). The EHL film is formed mainly by polydimethylsiloxane, while GLM particles increase the thermal conductivity of lubricant and can be adsorbed on the frictional interfaces, thereby improving the EHL properties. [Display omitted] • GLM/P composite lubricant can enter the elastohydrodynamic lubrication regime under conventional load and low sliding speed. • Lubrication regimes and transition laws of GLM/P are determined by combining Stribeck curve with lubrication film thickness. • The lubrication mechanisms of GLM/P in elastohydrodynamic lubrication regime are revealed in detail. [ABSTRACT FROM AUTHOR]

MXene has tremendous potential for enhancing thermal and tribological properties of fabric composites. Yet, its susceptibility to stacking and weak interfacial adhesion in organic matrix impedes practical application. Herein, MXene-h-BN hybrids were successfully achieved utilizing facile thiol-ene click reaction to introduce hexagonal boron nitride onto the surface of MXene to construct unique hierarchical structure. h-BN is grafted onto MXene through covalent bonding, effectively boosting interfacial adhesion and dispersion in the resin matrix. The layered MXene-h-BN possesses good lubrication behavior, and h-BN can increase strength and thermal conductivity of the MXene support skeleton. The results demonstrate that the thermal conductivity, tensile and bonding strength of reinforced fabric composites are elevated by 43.28%, 34.25% and 43.75% compared with pure fabric composites, respectively. Additionally, the wear rate of reinforced fabric composites is significantly decreased by 63.44%. This paper will contribute a novel and prospective reinforcement design strategy for click reaction constructed nano-materials in tribology. • h-BN was efficiently and promptly grafted onto the surface of MXene through the thiol-ene click reaction. • The structure of 3D point plane network was constructed. • The thermal conductivity, tensile and bonding strength of fabric composites are enhanced by 43.28%, 34.25% and 43.75%. • The reinforced fabric composites create robust tribofilm and wear rate is reduced by 30%. [ABSTRACT FROM AUTHOR]

To supply wear-resistant coatings on AISI 310 austenitic stainless steel for harsh industry applications, Ni3Al intermetallic compound coatings were prepared by high-velocity oxygen fuel (HVOF) spraying. Ni3Al coatings were deposited under different oxygen/fuel ratios of 4.45, 4.89 and 5.34. The phase structure, microstructure, mechanical and tribological properties of the coatings at 25 °C were investigated firstly. As a result, the HVOF oxygen/fuel ratio of 4.89 was chosen to get the best physical properties of an average porosity 1.0 vol.%, thickness 290 μm, hardness 527 ± 16 HV, friction coefficient 0.75 and wear rate 1.74 × 10− 5 mm3/(N·m). Then tribological tests across a wide temperature range from 25 to 800 °C were carried out on the optimized coating: the coating presented the highest anti-friction and wear resistance at 600 °C, a continuous and dense oxide layer comprised of NiO, Ni2O3, Al2O3 and NiAl2O4 was formed and acted as a solid lubricant, and contributed a relatively low friction coefficient of 0.57 and wear rate of 8.91 × 10− 5 mm3/(N·m). The wear mechanisms were mainly tribo-oxidation wear and slight abrasive wear. [ABSTRACT FROM AUTHOR]

Ceramic design based on reducing friction and wear-related failures in moving mechanical systems has gained tremendous attention due to increased demands for durability, reliability and energy conservation. However, only few materials can meet these requirements at high temperatures. Here, we designed and prepared a Sn-containing Si 3 N 4 -based composite, which displayed excellent tribological properties at high temperatures. The results showed that the friction coefficient and wear rate of the composites were reduced to 0.27 and 4.88 × 10−6 mm3 N−1 m−1 in air at 800 °C. The wear mechanism of the sliding pairs at different temperatures was revealed via detailed analyses of the worn surfaces. In addition, the tribo-driven graphitization was detected on the wear surfaces and in the wear debris, and the carbon phase was identified by SEM, TEM, and Raman spectrum. [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]

[Display omitted] • The ultra-low friction is achieved by using the inorganic salts and the proton-based ionic liquid. • The addition of the proton-based ionic liquid and the inorganic salts can enhance the P B value to 3090 N. • The system is suitable for a wide range of applications, including load ranges, sliding speed range and different alcohol types. • The proton ionic liquid not only can be adsorbed on the surface of the friction pairs, but also can form a triple film to get ultra-low friction. • The addition of inorganic salts that can form hydrated molecular layer to withstand high normal loads is the key factor. Macroscale facilitated lubrication is a forward-looking strategy in modern tribology that can significantly reduce friction and wear in mechanical equipment. However, it has been studied experimentally mainly for special friction pairs or point-to-surface contact. In the present work, we have achieved the ultra-low friction for point-to-point contact at the steel/steel interfaces by using the inorganic salts (NaCl and KCl) and the proton-based ionic liquid possessing a simple synthesis step and good solubility stability in aqueous 1,3-propylene glycol (PDO aq). Besides, the addition of the proton-based ionic liquid (PIL) can enhance the maximum non-seizure load (P B value) in PDO aq to 3090 N and the addition of inorganic salts don't lower the P B value. Results show: (1) The proton ionic liquid can be adsorbed on the surface of the friction pairs through electrostatic interactions, and undergo a friction chemical reaction to form a triple film that can effectively cushion the direct contact and collision of the microgrooves. (2) The addition of inorganic salts can form hydrated ions, which can shape a hydrated molecular layer to withstand high normal loads and balance the van der Waals attraction by hydration repulsion, which is a key factor in realizing the ultra-low friction. This discovery greatly expands the application of facilitated lubrication for point-to-point contact on steel surfaces in engineering applications. [ABSTRACT FROM AUTHOR]

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

Ga-based liquid metals have promising applications as coolants and lubricants in the computer science, medical, and nuclear industries. In this paper, soft metal Cu was used as an additive to improve the lubricating performance of Ga-In-Sn. CuGa 2 phases were in-situ generated. At room temperature (RT, 25 °C) and 150 °C, GC0.2 and GC0.5 (Ga-In-Sn doped with 2 wt% and 5 wt% Cu) exhibited significantly better lubricating properties than Ga-In-Sn. At 150 °C, the wear rate of T91 steel lubricated by GC0.2 was 72.95% lower than that lubricated by Ga-In-Sn. At 300 °C, GC0.2 maintained a similar lubricating performance to that of Ga-In-Sn. The lubrication mechanism showed that the change in lubricant characteristics and friction film were the main factors to improve the lubricity. • Novel Cu-doped gallium-based liquid metals were successfully prepared. • CuGa2 phases could be in-situ generated in Cu-doped liquid metal. • GC0.2 exhibited outstanding lubrication performance at RT∼300 °C. • The change of lubricant characteristics and friction film improved the lubricity. [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]

The effects of proton radiation (PR) irradiation on the components, friction and wear of Ti:WS 2 /P201 composite lubricating system were mainly investigated. PR irradiation has a great effect on the physicochemical properties of P201 oil, which can not only decompose oil into small molecular but also make it cross-linking and polymerization. More seriously, oil layer with good wettability transfers to a solid-like organic film on sample surfaces after PR irradiation. In addition, PR irradiation has a slight effect on the microstructure of Ti:WS 2 film due to coverage of oil layer. Meanwhile, Ti:WS 2 /P201 system obviously increases the friction coefficient and wear rate, especially extremely shortened life at high irradiation dose. It attributes to P201 oil occurred degradation when suffers from high PR energy, forming polymer with higher molecular weight. The polymer has poor replenishment on sliding contact interface, so destroying endurance of transfer film, which deteriorates the component and property of the system. At the high irradiation dose, the oil nearly loss fluidity, causing severe abrasive wear and tribo-oxidation, further accelerating the failure of the solid-oil materials. [Display omitted] • PR irradiation generates a great influence on the tribological properties of Ti:WS 2 /P201 system constructed by Ti:WS 2 film and P201 oil. • After PR irradiation, P201 oil layer with good wettability transfers to a solid-like organic film on sample surfaces. • PR irradiation degraded P201 oil to form small volatile molecular compound and polymer with higher molecular weight. • The replenishment capacity of oil become poor on contact area, further destroying wear resistance of transfer film. [ABSTRACT FROM AUTHOR]

Abstract: Novel ionic liquid materials based on 1-alkyl-4-[5-(alkylsulfanyl)-1,3,4-oxadiazol-2-yl] pyridinium tetrafluoroborate derivatives were synthesized. Ultra-thin ionic liquid films were prepared on silicon wafers by means of spin-coating and their tribological properties were investigated. The wear life increases when the chain length decreases. Under low load, they show good tribological properties which are closely related to the interaction between ionic liquid and substrate surface, especially the film of 1-ethyl-4-[5-(ethylsulfanyl)-1,3,4-oxadiazol-2-yl] pyridinium tetrafluoroborate, it has low friction coefficient and long wear life. So, this kind of ionic liquid can be potentially applied as ultra-thin lubricating coating. [Copyright &y& Elsevier]

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]

In this work, the friction and wear properties of layered MoAlB ceramics sliding against Al 2 O 3 and Inconel 718 alloy (Inc718) from room temperature (RT) to 800 °C were studied. The tribological behaviors of MoAlB ceramics are found to be greatly influenced by the test temperature and the counterpart. From RT to 800 °C, the MoAlB/Al 2 O 3 tribo-pairs exhibit a higher friction coefficient and wear rate compared with those of the MoAlB/Inc718 tribo-pairs. Irrespective of the laminate structure, the tribological properties of MoAlB ceramics are associated with the oxides that are induced by tribo-oxidation reactions. For the MoAlB/Al 2 O 3 tribo-pairs, abrasive wear and adhesive wear are responsible for the poor friction and wear behaviors. However, the tribo-film, which consists of oxides of Ni, Cr and Fe, can provide a good lubrication effect when MoAlB slides against Inc718. [ABSTRACT FROM AUTHOR]

Developing high-performance fabric composites with comprehensive properties is of paramount importance to broaden their application areas. In this work, a novel technique was studied to enhance interfacial adhesion via the adsorption of the complex amphiphilic biopolymer protein onto the surface of PPS/PTFE fabrics. Additionally, WS 2 @Ti 3 C 2 nanohybrids with heterostructures were synthesized, and the distinctive hierarchical microstructure facilitated the multiple reinforcement of the fabric composites. The results suggest that the decoration of BSA offers reaction sites with the phenolic resin and enhances the interfacial performance. Compared to the pure hybrid fabric composites, the tensile and bonding strength of the reinforced hybrid fabric composites are increased by 35.91% and 68.51%. Moreover, the wear rate of the reinforced hybrid fabric composites is decreased by 59.3%. [Display omitted] • The WS 2 @Ti 3 C 2 nanohybrids with heterostructures were synthesized. • The complex amphiphilic biopolymer protein BSA adsorbed onto the surface of fabrics, which enhanced interfacial adhesion. • The tensile and bonding strength of the reinforced hybrid fabric composites increased by 35.91% and 68.51%. • The wear rate of the reinforced hybrid fabric composites was decreased by 59.3%. • The synergistic effects of bioprotein decoration and WS 2 @Ti 3 C 2 could create robust tribofilm on the steel counterpart. [ABSTRACT FROM AUTHOR]

Abstract Extreme pressure lubrication is a great challenge for many mechanical systems like bearings and gears. Here, an novel functional material based on Ga-based liquid metal has been applied to successfully lubricate the steel-ceramic sliding pairs at extreme high load (1500 N), which significantly outperforms other liquid lubricants like oil and ionic liquid. Ga-based liquid metal provides a low friction coefficient (0.11–0.23) and wear rate (10−8-10−7 mm3/Nm) of AISI 52100 steel disc (C 0.98-1.10 Mn 0.25-0.45 P ≤0.025 S ≤0.025 Si 0.15-0.30 Cr 1.30-1.60 Fe 96.5-97.32 , mass %; American Iron and Steel Institute standard) when it slides against Si 3 N 4 balls over a load range 100–1500 N. To elucidating these interesting results, the lubrication mechanisms of Ga-based liquid metal are studied by tribo-surface analysis. Highlights • Liquid metal (LM) provides a new strategy for lubricating the steel-ceramic pairs. • LM displays good lubricity and extraordinary load-bearing for steel-ceramic pairs. • This good property is due to boundary lubrication of LM and nano-scale Ga tribo-film. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a “green” way of in situ forming ionic liquids (ILs) as high‐temperature lubricants by dissolving high content of lithium bis(trifluoromethylsulfonyl)imide in lard oil (LO). Nuclear magnetic resonance spectroscopy result indicated that lithium bis(trifluoromethylsulfonyl)imide could have a reaction with triacylglycerols, which are the major component of LO and formed the IL (Li[triacylglycerol])bis(trifluoromethylsulfonyl)imide. Differential scanning calorimetry result shown that ILs could effectively enhance the thermal‐oxidation stability of LO. Tribological behaviours of lubricant application in steel/steel contacts were evaluated on an Optimol SRV‐IV oscillating reciprocating friction and wear tester at 250°C. It was found that the in situ formed ILs possessed excellent friction‐reducing and antiwear properties in LO compared with perfluoropolyether (as a reference lubricant) under the same conditions. The wear mechanisms are tentatively discussed according to the morphology observation of worn surfaces of steel discs by scanning electron microscope and the surface composition analysis by X‐ray photoelectron spectroscopy. [ABSTRACT FROM AUTHOR]

CoCrFeNiMn high entropy alloy (HEA) owns prominent strain hardening capacity and high tensile elongation but poor wear resistance. In present work, in-situ carbide/CoCrFeNiMn composites with excellent anti-wear properties were fabricated by a flake powder metallurgy route using graphene oxide (GO) and CoCrFeNiMn as original powders. As a result, the hard carbide phase, Cr 7 C 3 , is formed in the soft matrix via in-situ reaction at the GO/HEA interface, which leads to a dense distribution of small-sized Cr 7 C 3 and strong interfacial bonding of the composites. With the addition of 5 wt% GO, the microhardness is improved by 66.7% and the macroscopic wear rate is decreased by 78.3% as compared with CoCrFeNiMn HEA. Increased nano-scratch resistance indicates that the dense distribution of hard Cr 7 C 3 carbide and the strong Cr 7 C 3 -CoCrFeNiMn interfacial bonding play key roles to resist the plastic flow of the HEA matrix during friction and wear. This study may provide a pathway to improve the wear resistance of HEA for engineering applications. [ABSTRACT FROM AUTHOR]

The wear behavior of nanostructured hypoeutectic FeB alloy was investigated in comparison with coarse grained counterpart. The friction coefficient of the FeB alloy changed slightly with grain size. While the wear rate decreased as the grain size decreased to nano scale. Both Fe2O3 and Fe2SiO4 oxides were found on the worn surfaces in the nanostructured FeB alloy, but only a few oxide films were observed for the coarse grained counterpart. These results suggested that the nanostructured eutectic was conducive to forming oxide films on the worn surface of the FeB alloy, and improved the wear resistance. [ABSTRACT FROM AUTHOR]

In recent years, the development of high-performance fabric composites has attracted widespread interest, but the frictional heat accumulation of fabric composites under high-speed has resulted in frictional failure, which has hindered the application of fabric composites. To remedy this deficiency, inspired by multilayer structure of fish scales, biomimetic MXene derivative DOPO-HQ-IPTS@Ti 3 C 2 T x was manufactured in situ, which boosted interfacial compatibility with MXene and provided remarkable enhancement in terms of mechanical performances and tribological properties of fabric composites. The tensile strength of reinforced fabric composites is enlarged by 45%. In addition, the wear rate of the reinforced fabric composites is reduced by 77%. Hence, the biomimetic nanomaterial DOPO-HQ-IPTS@Ti 3 C 2 T x offers a simple and dependable method for obtaining fabric composites with superior overall properties. [Display omitted] • The plywood-like biomimetic MXene derivatives (DOPO-HQ-IPTS@Ti 3 C 2 T x) were successfully fabricated. • The scale-spine like DOPO-HQ-IPTS was embedded on Ti 3 C 2 T x , which boosted the compatibility of Ti 3 C 2 T x. • The tensile strength of the reinforced fabric composites was enlarged by 45% compared to the pure fabric composites. • The wear rate of the reinforced fabric composites was reduced by 77%. • The incorporation of DOPO-HQ-IPTS@Ti 3 C 2 T x could create a homogeneous and firm tribofilm on the steel counterpart. [ABSTRACT FROM AUTHOR]

Herein, a bioinspired molecule-dopamine n-butenylamide-was self-assembled on Gallium-based liquid metal (GLM) nanodroplets to introduce vinyl group, and the zwitterionic poly (2-methylacryloxyethyl phosphocholine) (PMPC) was grafted onto GLM nanodroplets via surface-initiated free radical polymerization to obtain hybrid PMPC-GLM microgel. The as-prepared PMPC-GLM microgel has good dispersion stability in aqueous solution (chemical stability > 2 months), and shows excellent antibacterial properties due to the hydration of PMPC and antibacterial effect of Ga3+. Moreover, the hydration layer endows PMPC-GLM microgel with satisfactory tribological properties as an aqueous lubricant additive, with the COF and wear rate reduced by 65% and 62%. In addition to hydration lubrication, the improved tribological performance is attributed to the formation of protective film on the worn surface. [Display omitted] • Gallium-based liquid-metal Nanodroplets hybrid microgel (PMPC-GLM) was successfully prepared. • PMPC-GLM microgel exhibits good chemical stability in water (more than two months). • PMPC-GLM microgel shows excellent lubrication performance as an aqueous additive. [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]

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

The study aims to explore the physicochemical and tribological properties of perfluorooctane sulfonate ionic liquids (PSILs) CFSON and CFSOP. The results showed that CFSOP exhibited excellent friction-reducing and anti-wear properties at both room and high temperatures, and CFSON presented excellent tribological properties at high temperature when they were used as lubricants for steel/steel, steel/copper, and steel/aluminum friction pairs. As compared with traditional fluorine-containing ionic liquid (IL) 1-butyl-3-methylimidazolium bis(trifluoromethyl-sulfonyl) imide (L-F104), increasing the fluorocarbon chain length of the anion is proven to be an effective way to improve the performance of the PSILs in terms of hydrophobicity, corrosion resistance, and tolerance to extreme pressure, thereby making them more suitable to be used as lubricants under harsh conditions. The X-ray photoelectron spectroscopy analysis indicated that physical adsorption and tribochemical reactions occurred and generated protective films on the sliding surface during the rubbing process, which reduced the friction and elevated the anti-wear efficiency of the PSILs. [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 order to lubricate ZrO2 ceramic, a series of ZrO2 matrix high-temperature self-lubricating composites were designed and prepared by hot-press technique. It was found that the ZrO2(Y2O3)–CaF2–Mo–graphite system showed a good tribological behavior at both low and high temperatures. The wear mechanism of the composite was investigated in detail. [Copyright &y& Elsevier]

Thick multilayered DLC coatings were deposited on the inner surface of pipes with different draw ratios by hollow cathode plasma immersion ion processing (PIIP). By tuning the acetylene (C 2 H 2) flow rate, the change of plasma density caused by different draw ratios can be compensated to fulfill the uniform deposition of thick DLC coatings along the pipes. The influence of C 2 H 2 flow rate on the mechanical and tribological properties of the DLC coatings were investigated. With the increase of draw ratio, the deposition temperature and gas pressure declined, and the plasma density became more asymmetrical in the axial direction. Increasing the flow rate can timely replenish the plasma inside the pipe and resolve the mass depletion problem, resulting in better thickness and structure uniformity of the DLC coatings. The greatest deposition rate of 28.6 μm/h was obtained at the 250 sccm C 2 H 2 flow with a draw ratio of 5:1. The results of Raman spectrum and XPS indicated that the content of sp2-carbon bonds decreased with the increasing draw ratio for lower impact energies of ions. The higher sp3 carbon bonds content contributed to the formation of carbonaceous transfer layers, which resulted in the lower friction coefficient and wear rate. • Uniform deposition of thick DLC coatings inside of pipes with different aspect ratio. • The greatest deposition rate of 28.6 μm/h was obtained. • Increasing the C 2 H 2 flow rate can improve the coating uniformity and cover the mass depletion. • The higher sp3 carbon bonds content contributed to the lower friction coefficient and wear rate. [ABSTRACT FROM AUTHOR]

High-temperature self-lubricating nickel-alloy based composites with Ag and three amounts of BaF2/CaF2 eutectic were prepared by hot press sintering technique. Both the composites with 5wt% and 10wt% BaF2/CaF2 eutectic exhibited markedly higher strength than 15wt% composite. The friction coefficient of the three composites was comparable. All three composites showed the highest wear rate at 600°C, but very lower at 800 and 900°C. The friction coefficient of the three composites was slightly lower as sliding against Si3N4 than Inconel 718. The friction and wear mechanism was proposed. [ABSTRACT FROM AUTHOR]

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

Abstract: The anti-wear and antioxidant behaviors of 2,2,6,6-tetramethyl-1-piperidinooxy (TEMPO) and its derivatives were studied. The tribological properties of lubrication oils with or without the addition of TEMPOs were investigated on an Optimol SRV IV oscillating friction wear tester and the oxidative stability was evaluated by RBOT test using SH/T-0193 and ASTM D2272 procedures. The results showed that the addition of TEMPOs can improve the antiwear and antioxidant behaviors of lubrication oils remarkably. Moreover, the addition of TEMPOs can improve the performance of lubrication oil under atomic oxygen radiation. [Copyright &y& Elsevier]

An onion-like carbon material was prepared from candle soot, and its tribological properties as an additive were investigated in water. The material assumed a spherical shape with a layered nanostructure based on high-resolution transmission electron microscopic analysis and had considerable sp hybrid carbon as revealed by Raman spectroscopy. The tribological properties were determined on an optimal SRV-IV oscillating reciprocating friction and wear tester. The results indicate that these candle soots as additives are able to effectively reduce both the friction and wear of sliding pairs in water. In addition, the chemical reactivity, physical stability, surface charge, and size of candle soot had a key impact on their lubrication properties. Based on our characterization of the wear scars by scanning electron microscopy and in situ Raman spectroscopy, we suggest a rolling and sliding lubrication mechanism. [ABSTRACT FROM AUTHOR]

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

• 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]

Abstract: Bronze matrix composites were prepared by the powder metallurgy technology (P/M). The tribological properties of composites sliding against AISI321 stainless steel pins were studied under sea water condition. The alumina had a strengthened effect on the hardness and wear resistance of composites, but it increased the friction coefficient of bronze material. The nickel coated graphite improved the interfacial bonding between the bronze and graphite. The graphite was an effective solid lubricant in sea water. Sample with 3wt% Al2O3 and 3wt% nickel coated graphite showed good tribological properties in sea water. The composites showed different wear mechanisms. Sea water showed lubricating effect and corrosive effect during the sliding process. [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: The bronze–alumina–silver composites were prepared by powder metallurgy technique (P/M). The tribological properties of composites sliding against AISI321 stainless steel pin were studied by using a pin-on-disk test machine under sea water condition. The silver showed the good lubricating effect in sea water. The addition of alumina improved the hardness and wear resistance of composites. The friction coefficient of bronze–alumina–silver composites increased with the increase of Al2O3. However, the specific wear rate of composites decreased with increasing Al2O3. Bronze–2wt% Al2O3–7wt% Ag showed the best tribological properties under sea water condition, especially, at the high loads and sliding speeds. The composites showed different wear mechanisms during the sliding process. Sea water showed the lubricating effect due to the presence of corrosion products on the worn surfaces. [Copyright &y& Elsevier]

Abstract: In this study, we report that a layered Ti3AlC2 ceramic exhibited three distinct tribological behaviors at different vacuum degrees. It is firstly found that the layered Ti3AlC2 exhibited intrinsic self-lubricity under vacuum degree from 2.0×104 to 5Pa with the coefficient of friction (CoF) as low as 0.2 and nearly no wear. Under lower 0.1Pa and air atmosphere, however, it showed lubrication failure. Under lower 0.1Pa, The CoF abruptly rose after transitory low friction in initial duration and deteriorated wear occurred in the Ti3AlC2. The CoF sluggishly ascended to stable value from 0.2 to 0.7 in air. The lubricating mechanism of Ti3AlC2 ceramic was proposed. [Copyright &y& Elsevier]

Abstract: Bronze–graphite composites containing 8.4∼15wt% of Ni-coated graphite were fabricated by P/M method. The tribological properties were investigated under sea water condition. The friction coefficient of composites decreased with increasing graphite content. The wear resistance was improved by the addition of Ni-coated graphite but degraded at high graphite content. The results indicated that bronze–nickel coated graphite composites showed much better tribological properties in comparison with bronze and bronze–uncoated graphite composites. The composite with 11.7wt% nickel coated graphite showed the best tribological properties. The addition of nickel coated graphite not only increased the mechanical properties, but improved tribological properties. [Copyright &y& Elsevier]

Abstract: The paper reports the dry-sliding tribological behavior of Fe100−x –Ni x (x=20,23,25,30) alloys with various martensite fractions. For all the alloys, the friction coefficient decreased with increasing applied load and increased with increasing sliding speed, but there was nearly no difference between the different alloys. The wear rate of the alloys increased with increasing applied load and decreased slightly with increasing sliding speed. Microstructures had great influence on the wear behavior of these alloys. The Fe77Ni23 alloy with well-proportioned martensite exhibited the best wear resistance. [Copyright &y& Elsevier]

Abstract: The Ni3Si–Cr7C3 composite coatings with various contents of Cr7C3 were deposited on the AISI 1020 steel substrate by self-propagating high temperature synthesis casting and their tribological performances were studied under water and acid environments. The results demonstrated that all the Ni3Si–Cr7C3 composite coatings showed excellent friction-reduction, and wear resistance performances compared to the substrate and the AISI 321 stainless steel. While it is worth noting that the coating containing 37.2wt.% of Cr7C3 exhibited the best tribological performances. In addition, the friction reduction and wear resistant mechanism was also discussed and considered to be microploughing under both water and acid environments. [Copyright &y& Elsevier]

Abstract: The mechanical properties and wear behavior of an Fe70Ni30 alloy with twinned martensite structure obtained by deep cryogenic treatment at −196°c (DCT) were evaluated in comparison with that of coarse-grained (CG) Fe70Ni30 alloy (single austenite phase). The results showed that after the introduction of martensite with nano-scale twins, the Vickers hardness of Fe70Ni30 increased from 145 to 248Hv. The friction coefficient of both samples was almost the same, and it decreased with increasing applied load and increased with increasing sliding speed. The XPS results indicated that oxide protecting film was formed on the worn surface, which may dominate the friction coefficient. The wear rate for both samples increased with increasing applied load and decreased slightly with increasing sliding speed. The wear resistance of DCT-Fe70Ni30 alloy was obviously enhanced. The wear mechanisms were investigated by SEM accordingly. [Copyright &y& Elsevier]

Abstract: High temperature self-lubricating composites Ni3Al–BaF2–CaF2–Ag–Cr were fabricated by powder metallurgy technique. In this paper the effect of Cr content on tribological properties at a wide temperature range starting from room temperature to 1000°C was investigated. It was found that Ni3Al matrix composite with 20wt% Cr exhibited low friction coefficient of 0.24–0.37 and a wear rate of 0.52–2.32×10−4 mm3 N−1 m−1. Especially at 800°C it showed the lowest friction coefficient of 0.24 and a favorable wear rate of 0.71×10−4 mm3 N−1 m−1. This implied that 20wt% Cr was the optimal Cr content and its excellent tribological performance could be attributed to the balance between strength and lubricity. [Copyright &y& Elsevier]

Abstract: The tribological behaviors of Babbitt alloy 16-16-2 sliding against aluminum bronze ZCuAl9Mn2 lubricated by sea water were systematically investigated in this paper. The results indicated that the friction coefficient decreased as the load increased to 30N and then remained at a steady level at high loads, but decreased with increase in sliding speed. The wear rate increased with load, but decreased with sliding speed. The formation of basic lead carbonate Pb3(OH)2(CO3)2 during the sliding process played a critical role in the remaining low friction coefficient in sea water. [Copyright &y& Elsevier]

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

Abstract: The tribological properties of a Fe3Al material in an aqueous solution of 1mol/l H2SO4 corrosive environment sliding against a Si3N4 ceramic ball are studied using an Optimol SRV oscillating friction and wear tester in a ball-on-disc contact configuration. We investigate the effects of load and sliding speed on tribological properties of the Fe3Al material. The worn surfaces of the Fe3Al material are examined by a scanning electron microscope (SEM) and an X-ray photoelectron spectroscope (XPS). It is found that the Fe3Al material exhibits better wear resistance than 1Cr18Ni9Ti stainless steel in the sulfuric acid corrosive environment. The wear rate of the Fe3Al material is on the order of 10−13 m3/m and increases with increasing load, but does not vary below the sliding speed of 0.08m/s then dramatically increases with increasing sliding speed. The friction coefficient of the Fe3Al material is in the range of 0.1–0.28, and slightly increases with increasing load, and does not vary with the increase of sliding speed. The Fe3Al material occurs tribochemical reaction with the H2SO4 aqueous solution in the friction process. Wear mechanism of the Fe3Al material is dominated by microploughing and corrosive wear. [Copyright &y& Elsevier]

Ionic liquids of the alkylimidazolium hexafluorophosphate type were prepared and evaluated as lubricants for the contact of steel/steel. Their tribological properties of the synthetic ionic liquid as the lubricants were investigated on an Optimol SRV oscillating friction and wear tester in ambient condition and on a CZM vacuum friction tester at 1×10−3 Pa. These synthetic ionic liquids show excellent tribological performance and are superior to the conventional lubricant of liquid paraffin containing 2 wt.% of zinc dialkyldithiophosphate (ZDDP) in terms of the friction-reduction ability and load-carrying capacity. The elemental composition and chemical nature of the boundary films generated on the steel surface were analyzed on a scanning electron microscope with a Kevex energy dispersive X-ray analyzer attachment (SEM/EDS) and X-ray photoelectron spectrometer (XPS). The SEM results showed light abrasion and phosphorus on the worn surface after lubrication with the ionic liquids of alkylimidazolium hexafluorophosphates, and the XPS results indicated the occurrence of the tribochemical reaction of ionic liquid with iron during the sliding process, with the formation of FePO4 and FeF2. [Copyright &y& Elsevier]

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]