Lubrication In Vacuum Research Articles

Effect of cation nature on vacuum tribo-degradation and lubrication performances of two tetrafluoroborate ionic liquids

Vacuum lubrication and tribo-degradation performance investigations of two imidazolium tetrafluoroborate ionic liquids (ILs, LAB103 and LB104), were systematically conducted by the VFBT-4000 vacuum four-ball tribometer equipped with a quadrupole mass spectrometer. They both have quite wide liquid range with high thermostability and good fluidity at low temperature. Results of vacuum tribological tests show that LAB103 present better lubricity and lower corrosivity as compared with that of LB104, due to its strong adsorption layers and robust tribofilms on worn surfaces. Tribo-degradation test results exhibit that the decomposition of ILs is mainly caused by frictional stimulus. The decomposition products partially diffuse to vacuum chamber, being captured by mass spectrometer detector and others participate in the tribochemical reactions.

Temperature Resistance of Russian Vacuum Lubricants

The temperature resistance of Russian vacuum lubricants is studied. The antifrictional properties of lubricants based on perfluoropolyethers are found to be similar: they ensure a low frictional coefficient at 30–300°C. The thermal stability is best for Amethyst and Nika lubricants.

Probing carbon-based composite coatings toward high vacuum lubrication application

Abstract For challenges in minimizing friction and wear of spatial mechanical systems, synergetic lubrication coatings were prepared by spinning liquid lubricants and hybrid greases on the diamond-like carbon (DLC) films, and were evaluated whether they could achieve a long-term safe and reliable operation under high vacuum. Under high vacuum conditions, liquid lubricants significantly reduce the friction and wear of DLC films. Hybrid greases not only show excellent lubrication performance, but also greatly enhance the tribological behavior of DLC films, especially the grease with optimal proportion. Such excellent tribological performance of DLC-based composite coatings at low applied loads depends on the synergy of DLC and fluid film, in reverse the tribo-chemical reaction film under harsh working conditions.

Computational investigation of the lubrication behaviors of dioxides and disulfides of molybdenum and tungsten in vacuum

Lamellar compounds such as the disulfides of molybdenum and tungsten are widely used as additives in lubricant oils or as solid lubricants in aerospace industries. The dioxides of these two transition metals have identical microstructures with those of the disulfides. The differences in the lubrication behaviors of disulfide and dioxides were investigated theoretically. Tungsten dioxide and molybdenum dioxide exhibit higher bond strengths at the interface and lower interlayer interactions than those of the disulfides which indicates their superlubricity. Furthermore, the topography of the electron density of the single layer nanostructure determined their sliding potential barrier; the dioxides showed a weaker electronic cloud distribution between the two neighboring oxygen atoms, which facilitated the oxygen atoms of the counterpart to go through. For commensurate friction, the dioxides exhibited nearly the same value of friction work, and same was the case for the disulfides. The lower positive value of friction work for the dioxides confirmed their improved lubricity than the disulfides and the higher mechanical strength of the bulk dioxides demonstrated that they are excellent solid lubricants in vacuum.

Fluorine and sulfur co-doped amorphous carbon films to achieve ultra-low friction under high vacuum

Fluorine and sulfur co-doped amorphous carbon (a-C:S:F) films were synthesized from C2H2 and SF6 plasma mixture, and the bonding states of S and F in films were scrutinized. The a-C:S:F films exhibited a more ordered carbon structure than hydrogenated films. The friction behavior of films was tested against GCr15 bearing steel balls under high vacuum (HV) conditions. Ultra-low steady-state friction coefficient (0.01–0.02) was achieved for a-C:S:F films containing about 2.0 at.% H, depending on the concentrations of S and F in films. Graphite-like transfer layer on the ball surface provided a low-adhesive sliding surface terminated by –CF2- and –CF3 groups. The electrostatic repulsive interaction between the F-terminated transfer layer and the S- and F-terminated carbon structure was probably responsible for the ultra-low friction behavior. Intriguingly, the sp2-C clusters containing ‘thiophene-S’ (–C–S–C–) structure in films might contribute to the low friction when sliding against an highly fluorinated surface. These results demonstrate that the lubricating properties of a-C films in vacuum can be achieved through the S and F co-doping, which is of great significance for developing a-C films as vacuum lubricants.

In Vacuo Tribological Behavior of Polytetrafluoroethylene (PTFE) and Alumina Nanocomposites: The Importance of Water for Ultralow Wear

Polytetrafluoroethylene (PTFE) is widely regarded as an excellent candidate for solid lubrication in vacuum. However, it is often precluded from many prac- tical applications due to its intrinsically high wear rate. Over the past decade, it has been discovered that small loading fractions of alumina nanofillers can increase the wear resistance of PTFE by three to four orders of mag- nitude. This dramatic increase in wear resistance has in turn prompted numerous tribological studies to examine the robustness of this performance. In this study, the wear and friction behavior of unfilled PTFE and PTFE and alumina nanocomposites were evaluated under a broad range of vacuum environments from 760 to 4 9 10 -6 Torr. The nanocomposites of PTFE/alumina showed a dramatic increase in wear of over two orders of magnitude at the highest vacuum conditions. There appears to be an optimal vacuum environment around 1-10 Torr, in which these samples achieved the lowest wear rates of approximately 2.5 9 10 -7 mm 3 /(Nm).

Morphological effect of MoS 2 nanoparticles on catalytic oxidation and vacuum lubrication

The closed layered MoS 2 nano-balls and the opened layered MoS 2 nano-slices were prepared by decomposing MoS 3 in hydrogen atmosphere. The obtained MoS 2 nanoparticles were respectively used as catalysts for S 2− oxidation into SO 4 2− and lubricating fillers in polyoxymethylene (POM) plastic. Only basal surface could be found in the closed layered MoS 2 nano-balls, which represented very low catalytic efficiency for S 2− oxidation into SO 4 2−. However, the opened layered MoS 2 nano-slices were of both basal surface and rim-edge surface and showed excellent catalytic properties. Moreover, it was shown that MoS 2 nano-balls could improve the self-lubrication of POM plastic in vacuum. However, MoS 2 nano-slices led to the obvious degradation of POM, implying it is not a proper additive for POM. The high activity of MoS 2 nano-slices for catalyzing S 2−oxidation and degrading POM was ascribed to their small sizes and partly wedge-like shapes, which led to a considerable increase in the rim sites. The weak catalysis and excellent lubrication of MoS 2 nano-balls were resulted from its closed structure and chemical inertness.

Ultra Starvation Studied in the Spiral Orbit Tribometer

Spiral orbit tribometry has been used to study the coefficient of friction and electrical contact resistance of two vacuum lubricants in both the flooded system and the regime in which only a few nanoliters (μ g) of the lubricant are present, and the latter regime is designated here as ultrastarved. The experiment was supported by the extension to the ultrastarved regime of the recent analysis by Cann and coworkers of contact film thickness as a function of the lubricant volume in the heavily starved regime. The coefficients of friction in the ultrastarved regime were found to be the same as for the flooded system. The contact resistance was found to be zero at the beginning of the tests in the ultrastarved regime. The analysis by Cann and coworkers predicts the absence of a mobile liquid film at the contact in the ultrastarved regime. It is speculated that this persistence of lubrication into the ultrastarved regime is due to the retention of adherent lubricant molecules on the contacting surfaces and the sliding of these molecules over each other. An incomplete coverage of these molecules permits zero contact resistance at the start of the test. The results indicate that ball bearings can operate normally in the ultrastarved regime until the lubricant is consumed by tribochemical reaction.

Frictional properties of diamond and fullerene nanoparticles sprayed by a high-velocity argon gas on stainless steel substrate

Lubricating abilities of diamond nanoparticles with size between 50 nm and 200 nm were studied in vacuum and in air to clarify the effective use of diamond fine powders for tribological purposes. Spraying of powders with a high-velocity argon gas jet was performed to form deposits on stainless steel (SUS304) substrates. For sliding in vacuum against SiC and Al2O3 balls under a 0.5 N applied load and 3.5 mm/s sliding speed, the deposits of microcrystalline diamond powders with a mean particle size of 50 nm and detonation nanodiamond with a mean aggregate size of around 75 nm demonstrated friction coefficients of less than 0.01 and 0.03, respectively, and ball wear rates of less than 2·10− 6 mm3/(Nm). This means that diamond fine powders smaller than 100 nm can be considered as good solid lubricants in vacuum, because they demonstrate not only a low friction coefficient, but also wear rate of SiC ball lower than non-lubricated SUS304 does. A C60 deposit, formed by the same method on the SUS304, was readily scratched from the substrate in vacuum; however, under open-air conditions, a friction coefficient of around 0.1 and a SiC ball wear rate of about 2·10− 6 mm3/(Nm) were observed. This fact calls attention to the influence of the deposition method on C60 frictional properties.

Spiral Orbit Tribometry — Part II: Evaluation of Three Liquid Lubricants in Vacuum

The coefficients of friction and relative degradation rates of three lubricants run in the boundary regime in vacuum are evaluated in a Spiral Orbit Tribometer. This tribometer subjected the lubricants to rolling contact conditions similar to those found in angular contact ball bearings. A multiply alkylated cyclopentane (MAC) hydrocarbon lubricant suffered degradation at a rate almost two orders of magnitude less than the degradation rate of two perfluoropolyalkylether (PFPE) lubricants.

Effect of additives on friction, wear, and iron fluoride formation under perfluoropolyether fluid lubrication in vacuum and various atmospheres containing oxygen

The performance of two kinds of perfluoropolyether (PFPE) lubricant additives was evaluated for reducing friction, wear, and iron fluoride formation in the frictional system of iron sliding on iron in vacuum, in dry air, in O 2, and in room air atmospheres. The additives used were PFPE having (A) an end carboxyl group and (B) a bis (aminophenyl)sulfone sector in the middle of the PFPE molecule. The carboxyl type additive reduces both the friction and wear in vacuum, reduces the friction but accelerates the wear in dry air and in O 2, and reduces both the friction and wear in moist room air. The aminophenylsulphone type additive reduces the friction, but accelerates the wear in vacuum and ail the spectra showed that the additives A and B have a markedly good and a poor ability, respectively, to reduce iron fluoride formation in vacuum. Both the additives, however, failed to prevent iron fluoride formation in atmospheres containing oxygen. This paper discusses the friction and wear characteristics of the additives based on WDX surface analysis and observations.

A remotely controlled positioning system for the ALT-II limiter blades

The limiter module positioning system for ALT-II is described, with emphasis on the components which operate in the high vacuum, high temperature TEXTOR environment. The design constraints imposed by the environment are discussed, including material compatibility and vacuum lubrication. The development of each component operating inside TEXTOR is described. Problems with the system's universal joints are reported, and the current status of system performance is given.

Adhesion, Friction, Wear and Lubrication in Vacuum

Adhesion, friction, wear and lubrication studies conducted in a vacuum environment have provided insight into the influence of the basic properties of materials on the aforementioned characteristics. With metals, crystal structure, orientation, order-disorder reactions, ductile to brittle transitions, texturing and segregation of alloy constituents to surfaces have all been found to affect adhesion, friction and wear. Strong chemical interactions at the interface have been observed with clean metal surface in contact with polymers and ceramics. These interactions result in strong adhesive bonding. Nearly any material when adsorbed on or reacted chemically with a clean surface in vacuum will reduce adhesion, friction and wear. Even fractions of monolayers will accomplish a reduction in adhesion, friction and wear from that observed for materials in the atomically clean state.

A low temperature indium seal

An indium seal is described which operates reliably without vacuum lubrication in superfluid helium due to the tightening of the screws after single cooling with liquid nitrogen. (auth)

Paper 10: A Short Survey of European Work on Lubrication in Vacuum

Paper 10: A Short Survey of European Work on Lubrication in Vacuum

Vapor-deposited, thin gold films as lubricants in vacuum (10 −11 mm Hg) : T. Spalvins and D. H. Buckley, NASA TN-D-3040, (1965) 13 pp

Abstract : Thin gold films were vapor deposited on nickel, nickel-chromium, and nickel rhenium surfaces to be used for lubrication purposes. The durability of the film was determined by friction characteristics. Durability and strong bonding (adhesion) between the film and the substrate are essential when thin films are used as lubricants. Two methods of substrate preparation for vapor deposition were investigated: (1) mechanical polishing and (2) electron bombardment. Friction experiments were conducted with a hemispherical niobium rider sliding on the deposited gold film on a rotating disk. Results of this investigation indicated that the film endurance life during friction experiments was increased when the substrate was electron bombarded and thermally etched prior to vapor deposition on the etched surface at an elevated temperature of 800 deg F. A diffusion-type interface was believed to be formed between the film and the substrate.

1768. Vapour deposited gold films as lubricants in vacuum (10 −11 torr) : T Spalvins and D H Buckley, J Vac Sci Technol, 3(3), 1966, 107–113

1768. Vapour deposited gold films as lubricants in vacuum (10 −11 torr) : T Spalvins and D H Buckley, J Vac Sci Technol, 3(3), 1966, 107–113

1185. Vapour-deposited thin gold films as lubricants in vacuum −10−11 torr

1185. Vapour-deposited thin gold films as lubricants in vacuum −10−11 torr

Vapor Deposited Gold Thin Films as Lubricants in Vacuum (10−11 mm Hg)

Gold thin films of 1800 Å to be used as lubricants were vapor deposited on Ni, Ni-Cr, and Ni-Re substrates. Strong bonding (adhesion) and durability between the film and substrate were found to be essential when thin films are used as a lubricant. Factors that were investigated included the selection of the film and substrate material. Strong durability of the thin film is directly related to the type and structure of the interfacial region. Two methods of substrate preparation prior to vapor deposition were investigated: (1) mechanically polished surface and (2) electron bombarded surface. Gold was vapor deposited on the mechanically polished surface at room temperature and on the thermally etched surface at an elevated temperature approximately (800 °F). Strength and durability of the films were investigated in sliding friction experiments with a hemispherical niobium rider sliding on the films at a velocity of 5 ft/min. Results obtained in these friction experiments indicated that the film endurance life was considerably better on the thermally etched surface. This increased film durability with the thermally etched surface is believed to be owing to the formation of a diffusion type interface between the film and the substrate. Because of the disregistry at grain boundaries, a higher rate of diffusion and preferential trapping in and around the grain boundaries occurs, with these regions acting as lubricant reservoirs during the friction experiments.

40. Vapour deposited thin gold films as lubricants in vacuum (10 −1 mm Hg) : H R Kaufman,NASA TN/D3040, Oct 1965, 1–13

40. Vapour deposited thin gold films as lubricants in vacuum (10 −1 mm Hg) : H R Kaufman,NASA TN/D3040, Oct 1965, 1–13