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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]

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]

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]

Purpose – To study some tribochemical properties of tetrazole derivatives, n-hexadecanyl (1H-tetrazol-1-yl) acetate (HTA) and 1-phenyl-5-(octylthio)-tetrazole (PCT) as lubricating oil additives in hydrogenised oil, and estimate the action mechanism.Design/methodology/approach – The two tetrazole compounds were synthesized, and added them in hydrogenised oil with different concentrations. Their anti-wear properties were evaluated with a four-ball machine, the wear scar was analyzed with a X-ray photoelectron spectroscopy (XPS).Findings – The novel compounds possess good anti-wear, friction reduction properties and good load-carrying capacity. According to the XPS results, the novel compounds were migrated onto the surface of the steel balls and adsorbed on the surface. The two additive compounds, themselves, and their decomposers contributed to the corresponding tribological performances. With S element contained in the compound PCT, the influence on the load-carrying capacity of the base oil was enhanced. It may be due to the formation of S2- and SO42- compounds on the worn surface which could form a protective film.Research limitations/implications – Their antioxidant, anticorrosion, anti-wear properties are not estimated.Practical implications – Two useful EP and AW lubricating oil additives were synthesized, and maybe it is the potential industrial applied lubricating oil additives.Originality/value – This paper provided a study way of some N-containing heterocyclic compounds as lubricating oil additives. [ABSTRACT FROM AUTHOR]

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

The reduction of the wear rate and friction coefficient of composites simultaneously has a great challenge. Herein, a unique phase change microcapsule is designed with n-docosane as the core, TiO 2 coated with sodium alginate as the shell, as well as surface-decorated Ti 3 C 2 T x nanosheets. In this microcapsule system, n-docosane absorbs part of the frictional heat via solid-liquid phase change and releases it continuously to achieve self-lubrication. The TiO 2 shell possesses excellent load-bearing capacity and Ti 3 C 2 T x is susceptible to interlayer slip, which reduces the friction and wear of fabric composites. The results indicate that an average wear rate and friction coefficient of fabric composites are decreased by 60.85 % and 11.83 % with the addition of microcapsules. A strong and continuous tribofilm is formed on the steel surface, and the tribofilm enhances the boundary lubrication of the steel counterpart. This paper is expected to provide a novel design thought for the application of core-shell structure in tribology. • The MXene decorated hierarchical phase change microcapsules are designed. • The phase change microcapsules exhibit excellent lubrication. • An average wear rate and friction coefficient of reinforced fabric composites are decreased by 60.85 % and 11.83 %. • The reinforced fabric composites generate strong tribofilm. [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]

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]

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]

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: 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 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]

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]

• 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]