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Abstract: The friction and wear behavior of a steel-on-steel contact lubricated by phosphazene-type additive tetrakis(3-trifluoromethylphenoxy)-bis(4-fluorophenoxy)-cyclotriphosphazene (X-1P) and novel synthetic bridged cyclotriphosphazenes was investigated on a oscillating friction and wear tester. The thermal stability of the lubricants was investigated by means of thermogravimetric analysis. It was found that bridged cyclotriphosphazenes give lower wear volume loss and higher thermal stability than X-1P. In particular, the bridged cyclotriphosphazene with aromatic-ring side branch structures has the best antiwear ability and thermal stability among the investigated lubricants. The worn surfaces were analyzed by means of scanning electron microscopy, and X-ray photoelectron spectroscopy (XPS). It was found that tribochemical reaction was involved in the sliding of steel against steel under the lubrication of the synthetic lubricants, with the generation of a protective layer composed of inorganic fluoride FeF2 and organic compounds consisting of C, F, O, N and P, which contributed to improve the friction and wear behavior. [Copyright &y& Elsevier]

TiO2 thin films were grown on a glass substrate by sol–gel and dip-coating processes from specially formulated sols, followed by annealing at 460 °C. Thermogravimetric analysis (TGA) and differential scanning calorimetric analysis (DSC) of dried sols were performed to explore the thermal events occurring during the annealing process of the sol–gel TiO2 films. The chemical states of some typical elements in the target films were detected by means of X-ray photoelectron spectroscopy (XPS). The morphologies of the original and worn surfaces of the samples were analyzed by means of atomic force microscopy (AFM) and scanning electron microscopy (SEM). The tribological properties of TiO2 thin films sliding against AISI52100 steel and Si3N4 ball were evaluated on a reciprocating friction and wear tester. As the results, the target film was obtained and reaction may have taken place between the film and the glass substrate. TiO2 films are superior in reducing friction and resisting wear compared with the glass substrate. SEM observation of the morphologies of worn surfaces indicates that the wear of glass is characteristic of brittle fracture and severe abrasion. Differently, abrasion, plastic deformation and micro-crack dominate the wear of TiO2 films. The superior friction reduction and wear resistance of TiO2 films are attributed to slight plastic deformation as well as good adhesion of the film to the substrate. [Copyright &y& Elsevier]

Cyclotriphosphazene lubricants were synthesized and the relationship between their structures and tribological properties was investigated using an optimol SRV oscillating friction and wear tester and one-way reciprocating friction tester. The elemental composition and chemical nature of the antiwear films generated on 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). It was found that aryloxyphosphazene with polar substituent as a lubricant of steel–steel and steel–aluminum pair gave low wear, while aryloxyphosphazene with nonpolar group on the phenyl pendant led to high wear. Phosphazene provides poor lubricity for the steel–aluminum system under low load (0.5–3 N). The XPS analytical results of the antiwear films generated on the steel and aluminum surface indicate that phosphazene reacted with steel or aluminum counterface and formed a surface protecting film consisting of fluoride and organic compounds containing O, C, F, N, and P during friction. This contributes to reduce the friction and wear of steel–aluminum system. [Copyright &y& Elsevier]

Abstract: SiO2, TiO2, and hydroxyapatite (HA) thin films with good biocompatibility were grown on Ti–6Al–4V (coded as TC4) substrate by sol–gel and dip-coating processes from specially formulated sols, followed by annealing at 500°C The chemical states of some typical elements in the target films were detected by means of X-ray photoelectron spectroscopy (XPS). Atomic force microscopy (AFM) and high-resolution scanning electron microscopy (SEM) are applied to characterize the original unworn films. The tribological properties of thin films sliding against an AISI52100 steel ball were evaluated on a reciprocating friction and wear tester. As the result, the target films composed of nano-particles ranging from 30nm to 100nm around were obtained. All the sol–gel ceramic films are superior in resisting wear compared with the TC4 substrate. Among all, HA film shows the best resistance while SiO2 film shows the worst wear resistance both under higher (3N) and lower load (1N). TiO2 shows good wear resistance under lower load (1N). SEM observation of the morphologies of worn surfaces indicates that the wear of TC4 is characteristic of abrasive wear. Differently, abrasion, plastic deformation and micro-fracture dominate the wear of ceramic films. The superior friction reduction and wear resistance of HA film is greatly due to the slight plastic deformation of the film. It is supposed that the deformation of the HA film is closely related to the special arrangement of the nano-particles and microstructure. HA film is recommended for clinical application from the point of wear resistance view. [Copyright &y& Elsevier]

The tribological properties of FeAl intermetallics under dry sliding against AISI52100 steel at ambient conditions were studied on an Optimol SRV oscillating friction and wear tester in a ball-on-disc contact configuration. Effects of load and sliding speed on tribological properties of the FeAl intermetallics were investigated. The worn surfaces of the FeAl intermetallics were examined with a scanning electron microscopy (SEM) and an X-ray photoelectron spectroscopy (XPS). It was found that the FeAl intermetallics had better wear resistance than the AISI52100 steel. An adhered oxide debris layer was formed on the worn surface in friction. Area and thickness of the friction layer varied with variety of sliding speed but did not vary with load. The oxide layer contributed to decreased wear but increased friction. Wear rate of the material increased with the load, but dramatically decreased at first and then slightly decreased with the sliding speed. The friction coefficient of the material was 0.45–0.60, and did not change with the load, but increased with sliding speed at first, and then tended to be a constant value. Wear mechanism of the material was transformed from microfracture to surface fatigue with increase of sliding speed. [Copyright &y& Elsevier]

The tribological behavior of nanocrystalline Fe 88 Si 12 alloy in vacuum environment has been investigated compared with coarse grained counterpart. The results demonstrated that the friction coefficient of the Fe 88 Si 12 alloy reduced with the decrease of both grain size and oxygen partial pressure. The wear resistance of the Fe 88 Si 12 alloy improved more effective in vacuum than in air as the grain size decreased. As the hardness and oxidation activity of the Fe 88 Si 12 alloy decreased, the wear mechanism changed from adhesion and oxidation to plastic deformation and adhesion when the grain size and oxygen partial pressure decreased. [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: 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: NiAl, NiAl–Cr–Mo alloy and NiAl matrix composites with addition of oxides (ZnO/CuO) were fabricated by powder metallurgy route. It was found that some new phases (such as NiZn3, Cu0.81Ni0.19 and Al2O3) are formed during the fabrication process due to a high-temperature solid state reaction. Tribological behavior was studied from room temperature to 1000°C on an HT-1000 ball-on-disk high temperature tribometer. The results indicated that NiAl had high friction coefficient and wear rate at elevated temperatures, while incorporation of Cr(Mo) not only enhanced mechanical properties evidently but also improved high temperature tribological properties. Among the sintered materials, NiAl matrix composite with addition of ZnO showed the lowest wear rate at 1000°C, while CuO addition into NiAl matrix composite exhibited the self-lubricating performance and the best tribological properties at 800°C. [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: Dry-sliding tribological performance of the Fe–28Al–5Cr and its composites containing 15, 25, 35, 50wt.% TiC, produced by hot-pressing process, was investigated against an AISI 52100 steel ball in ambient environment at varying applied load and sliding speed. It can be found that the coefficient of friction (COF) is irrespective of TiC content and applied load, but increases from 0.46 to 0.60 with increasing sliding speed at the given testing conditions. The wear-resistance increases with an increase of TiC contents. Impressively when TiC amount reaches 50wt.%, the wear-resistance improves about 4–30 times compared to the pure Fe–28Al–5Cr at different sliding parameters. The wear rates of all the materials increase mildly with an increase in applied load, but are nearly independent of the sliding speed at an applied load of 20N. The wear rates of the all materials are on the order of 10−3–10−4 mm3 m−1. In a word, the addition of the TiC can improve significantly the dry-sliding wear-resistance of the Fe–28Al–5Cr intermetallics at room temperature. The enhanced wear-resistance is attributed to the high hardness of the composites and as well hard TiC phase play a role of load-carrying. Worn surface features of all the materials were examined using a scanning electron microscopy (SEM). The dominant wear mechanism of Fe–28Al–5Cr and 15% composite was flaking-off, but those of 25–50% composites was flaking-off and plowing. [Copyright &y& Elsevier]

Abstract: The tribological properties of the nano-eutectic Fe1.87C0.13 alloy are investigated under dry-sliding against AISI52100 steel ball in ambient environment with varying applied load and sliding speed. As comparison, the tribological properties of the same alloy after annealing treatment, which is with coarse-grained microstructure, also are examined at the same testing condition. The worn surfaces of the alloys are analyzed by a scanning electron microscope (SEM). The wear resistance of the nano-eutectic Fe1.87C0.13 alloy is about 2–6 times higher than that of the annealed coarse-grained Fe1.87C0.13 alloy, and the wear rates increase with increasing applied load and sliding speed. Friction coefficients of the two alloys are almost same. These results demonstrate that the wear resistance of the Fe1.87C0.13 alloy is improved by forming nanostructure to obtain enhanced mechanical properties, but the friction coefficient is not significantly affected owing to almost the same friction surface states. The wear mechanism of the two alloys shows slight difference. [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]

Abstract: A series of asymmetrical tetraalkylphosphonium ionic liquids were synthesized and evaluated as a new kind of lubricant for the contacts of steel/Al using an Optimol SRV oscillating friction and wear tester in ambient condition. The phosphonium ionic liquid shows excellent tribological performance and is superior to the conventional ionic liquids 1-ethy-3-hexylimidazolium hexafluorophosphate (P206) in terms of anti-wear performance and load-carrying capacity. The chemical compositions of the boundary film generated on different contact surfaces 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 friction-reduction and anti-wear mechanism were proposed to originate from the layered structure of ionic liquid under boundary lubrication and the tribochemical reaction of anions with the fresh surface, respectively. [Copyright &y& Elsevier]

A series of S, P-containing triazine derivatives, 2,4-bis-(diethylamino)-6-(O,O′-dialkyl dithiophosphate)-s-1,3,5-triazine, which are potential environmentally friendly lubricating oil additives, were synthesized. The tribological properties as lubricating oil additives in vegetable oil were evaluated using a four-ball tester. The results show that the series of triazine derivatives possess good antiwear performance, excellent load-carrying capacity. These compounds also show good friction-reducing properties. The action mechanism was estimated through analysis of the worn surface with X-ray photoelectron spectroscopy (XPS) and scanning electron microscope (SEM). [Copyright &y& Elsevier]

Three novel ashless triazine–dithiocarbamate derivatives, which are potential environmentally friendly oil additives, were synthesized. Their tribological properties as additives in rapeseed oil (RSO) were evaluated using a four-ball tester. Their anticorrosive properties and thermal stabilities were also investigated. The results indicate that the three novel triazine–dithiocarbamate compounds possess excellent load-carrying capacity, good corrosion inhibiting performance and high thermal stability. Although these additives show friction-reducing property at high additive concentration (5 wt.%), they have friction increase and wear promote natures in most cases. The elemental composition and chemical state of the antiwear films generated on steel counterface were investigated with scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis and X-ray photoelectron spectroscopy (XPS). It was found that the synthetic additives reacted with the counterface metal and generated a surface protective film consisting of sulfate, FeS and absorbed compounds containing organic-N. [Copyright &y& Elsevier]

Three S-(1H-benzotriazole-1-yl) methyl N,N-dialkyldithiocarbamates were synthesized and their tribological behaviors as additives in rapeseed oil (RSO) were evaluated using a four-ball tester. Thermal degradation tests were conducted to identify their thermal stabilities using thermogravimetric analyzer (TGA). The worn surface of the steel ball was investigated by X-ray photoelectron spectroscopy (XPS). The results indicate that the additives possess excellent load-carrying abilities and high thermal stabilities, but have no antiwear and friction-reducing properties. Based on the results of XPS analysis, it can be seen that tribochemical reactions occur between the synthesized compounds and metal surfaces during the sliding process. [Copyright &y& Elsevier]