The sliding behavior of an amorphous silica sample between two rigid surfaces is in the focus of the present paper. Molecular Dynamics using a classical Tersoff’s potential and a recently developed ...ReaxFF potential was applied for simulating sliding within a thin film corresponding to a tribofilm formed from silica nanoparticles. The simulations were performed at different temperatures corresponding to moderate and severe tribological stressing conditions. Simulations with both potentials revealed the need of considering different temperatures in order to obtain a sound interpretation of experimental findings. The results show the striking differences between the two potentials not only in terms of magnitude of the resistance stress (about one order of magnitude) but also in terms of friction mechanisms. The expected smooth sliding regime under high temperature conditions was predicted by both simulations, although with Tersoff’s potential smooth sliding was obtained only at the highest temperature. On the other hand, at room temperature Tersoff-style calculations demonstrate stick-slip behavior, which corresponds qualitatively with our experimental findings. Nevertheless, comparison with a macroscopic coefficient of friction is not possible because simulated resistance stresses do not depend on the applied normal pressure.
► Long term stability and friction as low as 0.15, could be obtained against ball bearing steel during 70,000 revolutions. ► Generally, the coatings with high carbon content showed the best ...tribological behaviour. ► All nanocomposites showed low dynamic contact resistance. ► The dynamic contact resistance followed the coating resistivity. ► Differences between static and dynamic contact resistance are due to oxides on the coating surfaces that brake during sliding.
Ceramic nanocomposite coatings in the Ti–Ni–C were deposited using PVD and studied with respect to tribological properties and contact resistance. It was shown that coatings could be deposited combining of a low contact resistance and a low friction coefficient against silver, making them suitable for use in high performance electrical contacts.
Nine coatings with different amounts of C and Ni were deposited. Coatings on flat Ni plated copper substrates were tested in a tribological ball-on-disc setup against ball bearing steel balls. Depending on primarily the amount of carbon the coatings showed very different friction coefficient and wear rate. The coatings were also deposited on cylindrical Ni plated copper substrates. Using geometrically identical silver plated cylinders as counter surface these were evaluated in a test setup better resembling a real life electrical contact. For most coatings a low electrical contact resistance was measured. The evolution of friction coefficient and contact resistance was correlated to wear marks and contact tracks, with their generated tribofilms, as examined after testing using electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Tribochemically active Ti
–
C
–
S coatings are nanocomposite coatings containing a S-doped titanium carbide, from which S can be released in a tribological contact. This work studies tribochemical ...reactions between a Ti
–
C
–
S coating and various counter surface materials, and their effect on the tribological performance. Tribological tests were performed in a ball-on-disc set-up, using balls of five different materials as sliding partners for the coating: 100Cr6 steel, pure W, WC, 316-L steel and Al
2
O
3
. For W balls, a WS
2
tribofilm was formed, leading to low friction (down to
µ
= 0.06). Furthermore, increasing normal load on the W balls was found to lead to a strong decrease in
µ
and earlier formation of the low-friction WS
2
tribofilm. Similar WS
2
and MoS
2
tribofilms were, however, not formed from WC- and Mo-containing 316-L balls. The performance when using WC and Al
2
O
3
balls was significantly worse than for the two steel balls. It is suggested that this is due to sulphide formation from Fe, analogous to formation of anti-seizure tribofilms from S-containing extreme pressure additives and steel surfaces. The tribochemical activity of Ti
–
C
–
S coatings, with the possibility of S release, is thus beneficial not only for pure W counter surfaces, but also for Fe-based sliding partners.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The beneficiary effects of tungsten disulphide (WS2) inorganic fullerene-like nanoparticles (IFLNPs) in the lubrication industry were shown in recent years. However, their successful incorporation ...into lubricants (oils, greases) is not straightforward. In practice, the lubricant contains several components for different purposes, e.g. reducing the oxidization of the oil (antioxidant), minimizing the wear rate (anti-wear additive), dispersants, etc. These additives can contain chemically active compounds, which under the lubrication process (where locally extreme conditions can develop: high pressure and flash temperatures) can change the chemistry in the contact zone and block the beneficial effects of the inorganic nanoparticles. In this investigation, poly-alpha-olefin (PAO) is being used as base oil in which the WS2 nanoparticles and different additives are mixed. A ball-on-disc sliding test revealed that certain additives inhibit the nanoparticles to reduce friction (less than 5 % decrease in friction coefficient), while in other cases, the friction reduction was above 50 %. The comparison is being made between PAO + additive and PAO + additive + IFLNPs. Scanning electron microscope and energy dispersive X-ray spectroscopy were used to investigate the elemental composition of the tribofilms formed on the wear marks. Further analysis was made in order to reveal correlations between elemental compositions of the tribofilms and external parameters such as the friction coefficient and wear rate. For instance, a strong correlation between tungsten content of the tribofilm and the friction coefficient was found.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Purpose
Surface roughness has been proved to be influencing the running-in wear of machined components under dry and lubricated sliding conditions. Zinc dialkyl dithiophosphate (ZDDP) is widely used ...as an anti-wear additive, which reduces the wear by the formation of a tribofilm on the surface (Spikes, 2004). Factors such as temperature, sliding distance, etc. influence the formation of the film. A significant reduction in the power loss due to friction and wear is possible if a synergy is attained between surface roughness effects and the effectiveness of the tribofilm. The present work aims to study the influence of surface roughness and ZDDP addition on the formation and removal of the tribofilm under high contact pressures.
Design/methodology/approach
Samples were prepared by machining. Surface roughness was varied by varying the milling parameters. A reciprocating friction and wear test machine with a ball-on-flat geometry was used for the study. Tests were performed with mineral base oil and base oil added with 1 per cent by weight ZDDP under different operating parameters. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) with energy dispersive X-Ray spectroscopy (EDS) analysis were conducted to study the surface morphology of the tribofilm.
Findings
A quasi-steady-state analysis conducted showed that the wear rate was much lower when tested with base oil containing ZDDP after about 65 min. AFM analysis confirmed the presence of chemically reacted films on the surface. SEM analysis revealed agglomeration of crystal like glassy phosphates. However, high contact pressures at the interface caused the removal of the films resulting in variations in the coefficient of friction. A comparison of the wear rates among the samples of different roughness values tested at 100°C showed that the anti-wear performance of ZDDP was not effective due to high contact pressures.
Originality/value
The findings in this study regarding the tribofilm formation with ZDDP additive and its failure due to high contact pressures will be beneficial for further investigation on wear resistant boundary films developed under such extreme conditions.
Purpose
The phosphorus and zinc contained in zinc dialkyl dithiophosphate (ZDDP) caused severe environment pollution and catalyst poison. Thus, the phosphorus-free additive, such as borate esters, ...has become one of studying hot topics in the area of oil additive. However, the stability of hydrolysis greatly limited the use of borate esters. The purpose of this paper is to improve the stability of hydrolysis by synthesizing a new kind of N-containing heterocyclic borate ester (MTTDB) as a lubricant additive.
Design/methodology/approach
The tribological properties of novel borate ester (MTTDB) as an additive in the base oil were studied by a four-ball machine. The element composition and chemical state of the tribofilm were investigated by scanning electron microscopy, energy dispersive spectrometer and X-ray photoelectron spectroscopy.
Findings
The results showed that the base oil lubricated by MTTDB exhibited high hydrolytic stability, good anti-wear property and excellent extreme pressure performance. When 2.5 per cent MTTDB was added into the 100N base oil, the smallest wear scar diameter (0.46 mm) was obtained. Furthermore, the decomposed borate ester, organic sulfide adsorbed on the worn surface was detected, and S element reacted with the steel surface and generated FeSO4, both of which contributed to the formation of the tribofilm.
Originality/value
Based on N-containing heterocyclic compounds, for instance, thiadiazole derivatives, introducing nitrogen and sulfur elements into borate ester, a new kind of N-containing heterocyclic borate ester (MTTDB) exhibited excellent property in hydrolysis stability, friction-reducing, anti-wear and extreme pressure. This synthesized method would be helpful for the borate ester used as additive in engine oil, gear oil and other industrial lubricants.
Two recent trends in engine oil formulation are a progressive reduction in phosphorus concentration so as to reduce its impact on the de-NO
x
catalyst, and an increase in dispersant concentration to ...control the level of lubricant viscosity increase over extended drain intervals. Unfortunately, both of these trends make it more difficult to generate and retain effective antiwear films on lubricated surfaces and both thus strengthen the need to understand the processes by which antiwear films are formed, and removed, during rubbing. This article and its companion outline a study of the kinetics of antiwear film growth and removal. In Part I, a test method for monitoring antiwear film thickness during rolling/sliding is described and employed to explore how various factors, including operating temperature, antiwear additive type and concentration, and the presence of dispersant, influence both the formation and removal of the tribofilms formed by the antiwear additive zinc dialkyldithiophosphate (ZDDP). Part II then analyzes the obtained results to derive a kinetic model of ZDDP film formation and removal (Fujita, et al.
1
.
Presented at the STLE Annual Meeting in Toronto, Ontario, Canada May 17-20, 2005
Review led by Elaine Yamaguchi
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
The microstructure and oxidation kinetics of the surface layers of AlN-(TiCr)B
2
coating produced by magnetron RF sputtering have been studied in the course of the coating formation and use in tools ...of cBN-based polycrystalline superhard materials in machining ShKh 15 hardened steel. The coating is formed with the liquid phase present. After cutting the formation of two-layer tribofilm with a nanosized external layer has been revealed on the surface of the cutting insert. The tribofilm phase composition has been defined by a layer-by-layer Auger analysis. The film external nanosized layer is a glassy phase as solid solutions of Fe
2
O
3
-Al
2
O
3
oxides that acts as a solid lubricant. As the cutting speed increases, the wear rate of a tool with a coating has been found to decrease as compared with tools without a coating.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Plasma nitriding is applied to many industrial parts running in the boundary (or mixed) regime. It is necessary to understand the synergistic effect on tribological behavior between the nitrided ...steel surface and lubricant additive to achieve an effective performance. However, there has been very little work concerning the effect of plasma-nitrided steel on the tribochemical interactions of zinc dialkyldithiophosphate (ZDDP) additive and the composition of ZDDP tribofilm. In this work, the interactions and synergistic tribological effects between the plasma-nitrided AISI 52100 steel surface and ZDDP additive under boundary lubrication were investigated. The tribological behavior of plasma-nitrided and untreated steels under lubrication with different ZDDP concentrations was examined on a four-ball friction and wear tester. The chemical characteristics of the tribofilms generated on the worn surfaces were analyzed by X-ray photoelectron spectroscopy (XPS). The results showed that the obvious synergistic effects of better friction reduction and wear resistance between plasma-nitrided steel and ZDDP were attributed to the hard nitrided layer and the shorter chain phosphates tribofilm with greater carbon and phosphate contents.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
The beneficiary effects of tungsten disulphide (WS
2
) inorganic fullerene-like nanoparticles (IFLNPs) in the lubrication industry were shown in recent years. However, their successful incorporation ...into lubricants (oils, greases) is not straightforward. In practice, the lubricant contains several components for different purposes, e.g. reducing the oxidization of the oil (antioxidant), minimizing the wear rate (anti-wear additive), dispersants, etc. These additives can contain chemically active compounds, which under the lubrication process (where locally extreme conditions can develop: high pressure and flash temperatures) can change the chemistry in the contact zone and block the beneficial effects of the inorganic nanoparticles. In this investigation, poly-alpha-olefin (PAO) is being used as base oil in which the WS
2
nanoparticles and different additives are mixed. A ball-on-disc sliding test revealed that certain additives inhibit the nanoparticles to reduce friction (less than 5 % decrease in friction coefficient), while in other cases, the friction reduction was above 50 %. The comparison is being made between PAO + additive and PAO + additive + IFLNPs. Scanning electron microscope and energy dispersive X-ray spectroscopy were used to investigate the elemental composition of the tribofilms formed on the wear marks. Further analysis was made in order to reveal correlations between elemental compositions of the tribofilms and external parameters such as the friction coefficient and wear rate. For instance, a strong correlation between tungsten content of the tribofilm and the friction coefficient was found.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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