Synergistic Lubricating Effect Research Articles

Synergistic lubrication mechanisms of AISI 4140 steel in dual lubrication systems of multi-solid coating and oil lubrication

In order to improve tribological properties of AISI 4140 steel (AS) for dry/starved lubrication, AS biomimetic self-lubricating material (AS-SACT) was prepared by filling SnAgCu-TiC into biomimetic microtextures. Compared with AS, the friction coefficient of AS-SACT was reduced by 5.34% and wear depth was reduced by 62.39% in starved lubrication. Tribological properties of AS-SACT in starved oil are close to those of full oil lubrication. Under starved lubrication, the precipitated lubricant spreads into a 2.2 µm solid film on contact surface. In addition, the lubricant precipitation area forms a 'storage area' for storing lubricating oil and wear debris. The synergistic lubrication effect of multi-solid coating and oil lubrication makes AS-SACT have excellent anti-friction and wear-resisting effect.

Tribological behavior of graphene oxide-Fe3O4 nanocomposites for additives in water-based lubricants

Graphene oxide-Fe3O4 (GO-Fe3O4) nanocomposites were synthesized via the solvothermal method and used as lubricant additives. The tribological tests and a series of characterization techniques were conducted to understand the lubrication mechanism of GO-Fe3O4 nanocomposite. The GO-Fe3O4 nanocomposites exhibited excellent tribological properties due to high dispersion stability in water. Friction results indicated that the GO-Fe3O4 can significantly improve the tribological properties and the friction coefficient and wear scar diameter had been reduced by 33.6% and 32.3% compared with base fluid, respectively. Raman results showed that the GO nanosheets formed a protective film on the contact interfaces, which facilitated shear, reduced the wear and inhibited the tribo-corrosion. The lubrication mechanism was attributed to the synergistic lubrication effect between the Fe3O4 nanospheres and the GO nanosheets.

Inhibition of cold‐welding and adhesive wear occurring on surface of the 6061 aluminum alloy by graphene oxide/polyethylene glycol composite water‐based lubricant

In this paper, graphene oxide/polyethylene glycol (GO/PEG) composite water‐based lubricant was prepared by an ultrasonic dispersion method, and characterized and analyzed by Fourier transform infrared (FT‐IR), Raman spectroscopy, X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). The suspension performance of GO/PEG composite water‐based lubricant in water was verified by static sedimentation and centrifugation, and then, the prepared GO/PEG composite water‐based lubricant was added into 304 stainless steel and 6061 aluminum alloy, and the coefficient of friction (COF) curve, average COF value, average wear rate, corresponding photomicrographs of balls and disks after wear, and energy‐dispersive spectrometer (EDS) elemental analysis were used to illustrate the lubrication effect and lubrication mechanism. The results show that the GO/PEG composite water‐based lubricant possesses excellent suspension ability in water, and the average COF value and wear rate of GO/PEG composite water‐based lubricant are reduced by 78.8% and 88.8%, respectively, compared with water lubrication. The excellent lubrication effect of GO/PEG composite water‐based lubricant can effectively reduce the cold‐welding and adhesive wear phenomenon, mainly because GO/PEG composite water‐based lubricant first fills the uneven surface of friction mating to form a high‐quality lubricating film and then because of the special space structure of GO and the low shear between GO layers and the synergistic lubrication effect of GO/PEG.

Polydopamine-stabilized ZIF-8: Improved water stability and lubrication performance

ZIF-8, a novel lubricant additive, is considered to have great potential in reducing friction and wear due to large specific surface area, thermal stability and mechanical flexibility. However, ZIF-8 nanoparticles readily hydrolyze in aqueous solutions, transforming into large-sized lamellar and rod-like materials, which is a major bottleneck as a water-based lubricant additive. Herein, a strategy is proposed to functionalize ZIF-8 via mussel-inspired polydopamine (PDA) polymerization process to improve its lubrication stability in the water phase. The modified ZIF-8 (PDA@ZIF-8) can firmly “locked” water molecules on the surface of PDA to protect internal structure of ZIF-8, and improve its dispersion and stability of ZIF-8 in water. Moreover, ZIF-8@PDA tribofilm and iron oxide chemical protection film are formed during the friction process, and the low shear strength water layer between the contact surfaces contribute to achieving powerful synergistic lubricating effects, resulting in friction coefficient and wear track width reduce by 65% and 66%, respectively. Therefore, this work provides a promising alternative for expanding the practical application of ZIF-8 in aqueous environment and tribology.

Synergistic lubrication effect of antioxidant and low content ZDDP on PFPE grease

PurposeThe purpose of this study is to reduce the use of Zinc dialkyl dithiophosphates (ZDDP) and improve the frictional properties and thermal oxidation stability of Perfluoropolyether (PFPE) grease by adding antioxidant additives. The addition of antioxidants can reduce the consumption of ZDDP as an antioxidant, thus improving the anti-wear efficiency of ZDDP and reducing the excess phosphorus element in the grease.Design/methodology/approachIn this study, an antioxidant with good comprehensive performance was selected from several antioxidants by tribological tests and high-temperature tests. Then, the effect of its combination additive with ZDDP on PFPE grease was investigated. The anti-wear property, anti-friction property, thermal oxidation stability and extreme pressure property of greases containing different proportions of ZDDP and antioxidant were tested by four-ball tester and synchronous thermal analyzer (STA). The effects of additives on properties of grease were analyzed by SEM, EDS, LSCM, XPS and FT-IR.FindingsThe research shows that 2,6-Di-tert-butyl-4-methylphenol (BHT) can be used as an antioxidant in combined additives to reduce the antioxidant reactions of ZDDP, thus improving the anti-wear efficiency of ZDDP and further enhancing the anti-wear performance of the grease. Moreover, BHT and ZDDP have a synergistic effect on the high temperature performance of the PFPE grease due to their different antioxidant mechanisms.Social implicationsIn this paper, the problems related to PFPE grease are studied, which has a certain guiding effect on the industrial application of fluorine grease and the related formulation design.Originality/valueIn this paper, the properties of PFPE grease under different lubricating condition were studied. The synergistic lubrication effect of antioxidant and ZDDP are discussed. It provides experimental and theoretical support for reducing the content of ZDDP and improving the performance of additives.

Tribological behaviours of black phosphorus/MoS2 composites as water‐based lubrication additives

AbstractIn this investigation, a self‐assembly method was used to fabricate black phosphorus (BP)/MoS2 composites as water‐based lubrication additives. The tribological behaviours of the lubrication additives for GCr15 steel ball/TC4 titanium alloy disk contact under different mass ratios, loads and rotational speeds were also investigated. The experimental results showed that 0.01 wt.% BP and 0.04 wt.% MoS2 as water‐based lubrication additive have the best the synergistic lubrication effect. Compared with pure water, coefficient of friction (COF) and wear rate of the lubrication additive at the test conditions of 8 N and 150 r/min were reduced by 32.6% and 68.8%, respectively. As the loads increased, the COFs and wear rates of all the lubricants including pure water, BP as water‐based lubrication additive (BP‐WL), MoS2 as water‐based lubrication additive (MS‐WL) and BP/MoS2 composites as water‐based lubrication additive (BM‐WL) were all reduced. As the rational speeds increased from 100 to 250 r/min, all the lubricants were firstly decreased and then increased. Based on tribological tests and wear surface analysis, the lubrication mechanism of BM‐WL is proposed. The interlaminar shear and the adsorption of BP/MoS2 composites on the wear surface of the friction pairs are the key to reducing COFs sand wear rates. In addition, the tribo‐chemical reaction films consists of FeO/Fe2O3, Al2O3 and TiO2 were formed during the friction process, which can effectively protect the surface of the titanium alloy/steel contact from wear.

Synergistic lubrication effect of Al2O3 and MoS2 nanoparticles confined between iron surfaces: a molecular dynamics study

Synergistic lubrication effect of Al2O3 and MoS2 nanoparticles confined between iron surfaces: a molecular dynamics study

Macroscale superlubricity of Si-doped diamond-like carbon film enabled by graphene oxide as additives

Carbon-based materials including diamond-like carbon (DLC) and graphene have been demonstrated as extraordinary lubricating materials due to its specific structure and weakness of the interlayer interactions. In this work, the extreme coefficient of friction (COF = 0.002) was achieved on the silicon-doped hydrogenated amorphous carbon (a-C:H:Si) film by lubrication with graphene oxide (GO) nanosheets as additives in ethylene glycol. The tribochemical reactions occurred on the Si3N4 surface and a-C:H:Si film, leading to the formation of the silica colloid layer on both Si3N4 and a-C:H:Si surfaces. In the meantime, the physical adsorption of GO nanosheets on the friction surfaces makes the shear plane transfer from Si3N4/a-C:H:Si interface to GO/GO interface, which results in a further reduction of shear stress. The mechanism and modelling of a-C:H:Si and GO nanosheets synergistic lubrication effect was finally established to reveal the design principle of superlubricity at macroscale.

Long-Term Lubrication at 500 °C Using Continuously Replenishable Solid Lubricating Film Polymerized In Situ by Gasified Monomers PA and PPD

Through the introduction of gas-phase monomers phthalic anhydride (PA) and p-phenylenediamine (PPD), replenishment of lubricants during high-temperature friction processes could be realized. According to Fourier transform infrared spectroscopy (FTIR) and gas chromatography–mass spectrometry (GC-MS) analyses, in a 10-min ball–disc friction test at 500 °C, the introduced monomers contacted and polymerized in the gas phase to form solid products with the structure of imides or long carbon chains, which provided superior thermal stability. Solid lubricating films were generated on the disc surface by the physical deposition of these polymerized products and then fall off and attach to the contact position of the ball to form a transfer film. Compared to nonlubricated friction, the coefficient of friction (COF) was reduced from 0.54 to 0.24, and the wear rates of the balls and disc were reduced from 8.32 × 10−6 to 0.65 × 10−6 mm3·N−1·m−1 and from 2.62 × 10−4 to 7.48 × 10−6 mm3·N−1·m−1, respectively. With continued friction but no further introduction of monomers, the solid lubricating film generated in the initial 10 min could provide even more remarkable lubrication for at least the next 15 min, with a minimum COF of 0.01. This could be related to the reinforcing and synergistic lubricating effect of carbonized product powders that gradually formed a continuous phase on the polymerized products’ matrix. After the COF increased, low friction could be re-attained by reintroduction monomers, but lubrication would be limited by the previous wear. This novel lubricating film shows potential in high-temperature lubrication, because it has both the effectiveness and stability of solid lubrication and the replenishability of gas lubrication.

Synergistic lubricating effect of graphene/ionic liquid composite material used as an additive

We prepared a graphene/ionic liquid (G/IL) composite material by the hybridization of G and an IL for use as a lubricating oil additive. The friction coefficient and wear volume of a base oil containing 0.04 wt% of the G/IL composite was reduced by 45% and 90%, respectively. Furthermore, the base oil containing the G/IL composite exhibited better lubricating properties than the base oil containing G, IL, or a mixture of IL and G at the same mass fraction. A synergistic lubrication mechanism was also revealed. The G/IL composite was adsorbed and deposited on the wear surface, forming a more ordered protective film and a unique tribochemical reaction film during rubbing. Therefore, the G/IL composite exhibited the synergistic lubricating effects of G and IL, which significantly improved the lubricating performance of the base oil. This study also suggested a way to limit the out-of-plane puckering of G at the macroscale.

Tribological behaviors of polyelectrolyte capped carbon nanoparticles in polyethylene glycol

Polyethyleneimine (PEI) capped carbon nanoparticles (CNPs-PEI), gained by hydrothermal treatment of citric acid and PEI, were transformed into the polyelectrolyte capped CNPs (CNPs-PEI-NTf2) by HCl protonation process and anion exchange process between Cl− and bistrifluoromethanesulfonimide (NTf2 −). The CNPs-PEI-NTf2 exhibited superb comparability with polyethylene glycol (PEG200). Their tribological behaviors as the lubricant additives of PEG200 were evaluated under the four-ball mode and steel/steel contact. Amazingly, adding particularly low amount (0.05 wt%) of CNPs-PEI-NTf2 made the friction coefficient and wear volume of PEG200 reduce by 66.1% and 86.6%, respectively. The surface analysis results of wear scars demonstrated that the CNPs-PEI-NTf2 as additives not only directly participated in the formation of mixed boundary lubrication films through the synergistic lubrication effect between the PEI-NTf2 groups and CNPs of CNPs-PEI-NTf2, but also should play the rolling, mending and polishing effects on the rubbing surfaces, and hence exhibited the outstanding friction-reducing and anti-wear functions.

Preparation and tribological properties of PTFE/DE/ATF6 composites with self-contained solid-liquid synergetic lubricating performance

A new kind of PTFE composite with self-contained solid-liquid synergetic lubricating effect is prepared by the combination of PTFE, porous diatomite (DE), and immersed lubricating oil (ATF6). The tribological and mechanical properties of composites with different DE contents and varying cold-pressed pressures were investigated systematically. Due to the oil storage effect of DE particles, the maximum oil content of PTFE/DE composite is 16.4 wt%. With the increase of DE content, the surface hardness, elastic modulus and yield strength can be increased from 3.2 to 3.6 HV, 37.8–60.2 MPa and 8.7 MPa–12.8 MPa, respectively. With the addition of DE, the wear rate of PTFE decreases but the coefficient of friction (COF) increases. Meanwhile, with the addition of DE and ATF6, both the COF and wear rate of PTFE decrease. The COF can be reduced by 68% from 0.121 (specimen 0%-10 MPa-dry) to the minimum value of 0.039 (composite 10%-10 MPa-ATF6), and the wear rate can be reduced by 82% from 1.95 × 10−4 mm/Nm (0%-50 MPa-dry) to the minimum value of 0.35 × 10−4 mm/Nm (10%-50 MPa-ATF6). The enhanced antifriction performance of the composite PTFE/DE/ATF6 is contributed by the synergistic lubricating effect of self-contained liquid lubricant of ATF6 and the solid lubricant of PTFE. The prepared PTFE/DE/ATF6 composites exhibit excellent tribological performance as well as the mechanical properties, which can be used to fabricate a new kind of self-lubricating materials with high performance and long durability.

Extreme-Pressure Superlubricity of Polymer Solution Enhanced with Hydrated Salt Ions.

The development of new routes or materials to realize superlubricity under high contact pressure can result in energy-saving and reduction of emissions. In this study, superlubricity (μ = 0.0017) under extreme pressure (717 MPa, more than twice the previously reported liquid superlubricity) between the frictional pair of Si3N4/sapphire was achieved by prerunning-in with a H3PO4 (HP) solution followed by lubrication with an aqueous solution consisting of poly(vinyl alcohol) (PVA) and sodium chloride (NaCl). Under the same test condition, the aqueous PVA lubricant did not show superlubricity. Results of X-ray photoelectron spectroscopy and Raman spectroscopy indicate the formation of a PVA-adsorbed film at the frictional interface after lubrication with PVA but not after lubrication with PVA/NaCl, indicating competitive adsorption between hydrated Na+ ions and PVA molecules. The hydrated Na+ ions adsorbed preferentially to the solid surfaces, causing the transformation of the shear interface from a polymer film/polymer film to a solid/polymer film. Meanwhile, the hydrated Na+ ions also produced hydration repulsion force and induced low shear stress between the solid surfaces. Furthermore, NaCl increased the viscosity of the polymer lubricant, enhanced the hydrodynamic effect between interfaces, and decreased direct contact between the friction pair, causing a further reduction in friction. Thus, the superlubricity of the PVA/NaCl mixture is attributed to the combination of hydration and hydrodynamic effects. This study provides a novel route and mechanism for achieving extreme-pressure superlubricity at the macroscale, through the synergistic lubricating effect of hydrated ions and a polymer solution, propelling the industrial application of superlubricity.

High temperature tribological behaviors and wear mechanisms of NiAl-MoO3/CuO composite coatings

The MoO3/CuO binary oxides were selected as the potential high temperature lubricants in this work based on the ionic potential and cation polarizability approach correlated to the lubricity of solid oxides. The NiAl composite coatings with addition of 10, 30, and 50 wt% of MoO3/CuO (1:1) were fabricated via atmospheric plasma spraying (APS) technology. The tribological properties of these NiAl-MoO3/CuO composite coatings were evaluated from room temperature to 800 °C, and the basic wear mechanisms were investigated as well. The results show that, at 800 °C, the composite coating with 30 wt% of MoO3/CuO led to the lowest friction coefficient (approximately 0.16) and wear rate (3.7 × 10−5 mm3 N−1 m−1). These superior tribological outcomes were attributed to the synergistic lubricating effect of MoO3, CuO, NiO and NiMoO4 which formed on the worn surfaces via tribo-chemical reactions. Meanwhile, the decomposition of CuMoO4 formed by tribo-chemical reaction and worked synergistically to reduce the friction coefficient and wear rate at high temperatures. Meanwhile, the decomposition of CuMoO4 formed via tribo-chemical reaction of MoO3 and CuO at high temperature was observed at 800 °C sliding.

Preparation and tribological properties of solid-liquid synergetic self-lubricating PTFE/SiO2/PAO6 composites

Herein, 25 kinds of polytetrafluoroethylene (PTFE) composites with solid-liquid synergetic self-lubricating property were prepared by filling PTFE matrix with hollow SiO2 particles and lubricating oil (PAO6). Hollow SiO2 particles containing PAO6 acting as lubricating fillers were applied to enhance the tribological performances of PTFE matrix. The generated PTFE composites displayed solid-liquid synergetic self-lubricating property and could achieve ultralow friction. Factors such as the cold-pressed pressure and the SiO2 content that affect the tribological performance of the composites were investigated in detail. The compactness of the composites was enhanced when the cold-pressed pressure increased. The porosity of the composite with 25 wt% SiO2 decreased from 38.2% to 14.3% when the cold-pressed pressure was increased from 10 MPa to 50 MPa. As the cold-pressed pressure was increased, the antiwear performance of the composites was enhanced but their antifriction performance become worse. The composites containing PAO6 achieved lower coefficient of friction (COF) and smaller wear rates than composites without PAO6. The COF value decreased from 0.143 (pure PTFE) to an ultralow value of 0.037 (composite 5%-10 MPa-oil). The enhanced antifriction performance of the composite was associated with the synergistic lubricating effect of the liquid lubricant of PAO6 and the lubrication of the PTFE matrix. All the prepared PTFE/SiO2/PAO6 composites exhibited excellent antifriction performance and improved antiwear property and thus can be used to fabricate a new kind of self-lubricating materials.

Chemical- and Mechanical-Induced Lubrication Mechanisms during Hot Rolling of Titanium Alloys Using a Mixed Graphene-Incorporating Lubricant.

Hot rolling of titanium alloy currently is carried out without lubrication because of the surface defects. In order to explore an effective lubrication scheme to reduce friction and wear during hot rolling of titanium alloy, a mixed graphene-incorporating lubricant has been proposed to study its lubrication performance and mechanism. The tribological experiments were carried out by ball-disk friction and wear tester under hot-rolling parameters. Scanning electron microscopy (SEM), X-ray energy spectrum analyzer (EDS), X-ray powder diffractometer (XRD) and Raman analysis were used to analyse the surface and cross-section of the wear marks on the samples after the tribological experiments. The results show that the friction coefficient decreases up to about 35% compared with tests under dry and lubricated conditions. The surface quality of the wear marks is improved significantly after applying the proposed lubricant. The graphene which is embedded in the phosphate film can be effectively applied as a lubricating material to strengthen the lubricating film with less combustion loss at high temperatures. A chemical- and mechanical-induced lubrication mechanism for the hot rolling of titanium sheets has been proposed due to the synergistic lubrication effect of the graphene, ZrO2 nano particles and phosphate. It is of great significance and potential value to apply this proposed lubricant as an effective way to reduce the wear, friction and oxidation during the hot-rolling process of titanium alloy.

Microstructure, mechanical and tribological properties of Mo-V-N films by reactive magnetron sputtering

Vanadium and molybdenum can form the lubricating oxide films at high temperatures, which provided a foundation for the development of self-lubricating films. In this paper, the MoN, VN films and the Mo-V-N films with different molybdenum‑vanadium atom ratios have been prepared by reactive magnetron sputtering to study their tribological properties. The results showed that the Mo-V-N film with the vanadium content of 22 at.% has the highest hardness and the best wear resistance, as well as the average friction coefficient is as low as 0.27 at 700 °C. The results show that the Mo-V-N film with 22 at.% V content has the highest hardness, the best wear resistance and the average friction coefficient as low as 0.27 at 700 °C. The optimal molybdenum‑vanadium atom ratio in Mo-V-N film is favorable for the formation of lubricious glaze layers composed mainly of V2O5 and MoO3 on the worn surface at 700 °C, which has better synergistic lubrication effect.

Phosphonium-organophosphate modified graphene gel towards lubrication applications

Graphene oil as an emerging lubricant usually did not achieve the desired lubricity due to the poor interface compatibility of graphene and base oil, especially at harsh friction conditions. Herein, a simple mechanical grinding method was first carried out to fabricate trihexyltetradecylphosphonium bis(2-ethylhexyl) phosphate modified graphene gel ([P66614][DEHP]-G) for high-performance additive. The as-prepared [P66614][DEHP]-G gel shows the extraordinary thermostability, dispersity and tribological properties even at high load and temperature conditions. TOF-SIMS and Raman analysis on the friction interface reveal the existence of multi-film structure which presents good synergistic lubricating effect thereby improving the tribological behaviors. This paper provides a good strategy to fabricate high-performance oil-miscible graphene composites for reducing the friction and wear under harsh conditions.

Ultrastable Lubricating Properties of Robust Self-Repairing Tribofilms Enabled by in Situ-Assembled Polydopamine Nanoparticles.

Aqueous lubrication in nature is attracting increasing attention in the tribological fields for reducing friction energy consumption and improving anti-wear durability. Generally, adding nanolubricant additives is one of the most important strategies to effectively enhance the interface performance under boundary lubrication via the formation of a protective tribofilm on rubbing surfaces. However, the adsorbed tribofilms are unstable and are prone to failure during friction, and the interaction mechanism between the tribofilms and frictional interfaces is partly disclosed. In this study, inspired by mussels, an in situ-assembled polydopamine (PDA) tribofilm is achieved with PDA nanoparticles as aqueous lubricant additives, which shows excellent lubrication properties. The coefficient of friction is interface-independent and is reduced by as much as 83%. The results show that the PDA tribofilm can not only form chemical bonding with metal interfaces but also present a synergistic lubrication effect with the upper ceramic surface. Especially, a self-repairing effect of the PAD tribofilm is observed, by which the ultrastable lubricating properties can be achieved during friction, and thus, the friction and wear can be effectively controlled. This work provides an effective method for improving the interface stability of friction pairs under aqueous lubrication and also shows great meaning for industrial applications.

Research on synergistic lubrication effect of silver modified Cu–Ni-graphite composite

Cu–Ni-graphite composite is intended to be used as switch slide baseplates in the high-speed railways., The composite is modified by silver element to enhance the tribological properties. Pin-on-disk wear tests were conducted to evaluate the tribological properties. The synergistic lubrication effect generated when the silver-modified Cu–Ni-graphite composite slide against U75V steel. The results showed that the silver-modified Cu–Ni-graphite composite consists of α-Cu, graphite, and a silver phase. The higher graphite content in the composite corresponds to lower coefficient of friction and wear weight loss. Both the coefficient of friction and wear weight loss of the silver-modified composite are much lower than those of the unmodified Cu–Ni-graphite composite. The synergistic lubrication effect of graphite and silver in the composite decrease the friction coefficients and wear weight loss. Compared with the single graphite lubrication, the introduction of the silver phase efficiently enhances the lubricating property and decreases the microcutting and deformation effects. The wear mechanism of silver-modified Cu–Ni-graphite composite with 1–6 wt% graphite content consists of microcutting, oxidation wear, and adhesion wear. The delamination and fatigue wear are resisted at the higher graphite contents by the addition of the silver phase.