Synergistic Lubricating Effect Research Articles

The Synthesis of Cu-Coated Ti2SnC Ceramic and Its Tribological Behaviors as a Lubricant Additive

Lubricant additive plays an important role in reducing the friction and wear for base oil. MAX phase ceramics may have superior advantages for additive application due to their unique nanolayered structure. In this paper, Ti2SnC ceramic is prepared by sintering the elemental mixtures at 1250 °C. In addition, Cu-coated Ti2SnC ceramic is successfully prepared using a chemical plating method for the first time. It is confirmed that the Ti2SnC ceramic has good self-catalytic activity, and a layer of stacking Cu nano-particles can be deposited on the Ti2SnC surface without pretreatment. When the Cu-coated Ti2SnC ceramic powder is doped into PAO10 base oil, the oil can exhibit excellent lubrication properties, where the friction coefficient is as low as 0.095. A layer of tribo-film can be formed during the sliding process when the Cu-coated Ti2SnC ceramic is incorporated into PAO10 base oil, which can reduce the friction coefficient. The superior lubrication properties can be attributed to the synergistic lubrication effect of Ti2SnC ceramic and Cu nano-particles.

Preparation and tribological properties of NiCr–Mo–Ag–O/Mo–V–Ag–O bilayer film at RT-1000 °C

The primary objective of this research is to investigate the structure and tribological properties of NiCr–Mo–Ag–O/Mo–V–Ag–O bilayer films in a wide temperature range (RT-1000 °C). The bilayer films were prepared by pulsed laser deposition (PLD) technology, so as to provide the theoretical basis and experimental guidance for the study of the synergistic lubricating effect of Mo and V bimetallic lubricating oxides. The NiCr–Mo–Ag–O composite target was fabricated by the hot-press sintering technique. Subsequently, a NiCr–Mo–Ag–O/Mo–V–Ag–O bilayer film was deposited on Inconel 718 by pulsed laser deposition (PLD). The tribological properties of the film were evaluated by HRT-1000 high-temperature ball-on-disc configuration at RT-1000 °C. The obtained results reveal that the NiCr–Mo–Ag–O target is marked by a compact structure and homogeneous composition. Furthermore, the composite film exhibits a smooth surface and dense structure, comprised of polycrystalline and amorphous phases. The measured hardness and elastic modulus of the film approximated 4.9 GPa and 153.5 GPa, respectively. Additionally, the lowest friction coefficient of the film is about 0.28 at 800 °C. Upon reaching this temperature, the cooperative lubrication resulting from NiMoO4, Ag2Mo2O7, and AgVO3 contributed effectively towards reducing the film's friction coefficient.

Superlow friction and wear enabled by nanodiamond and hexagonal boron nitride on a-C:H films surfaces in dry nitrogen

Hydrogen-deficient amorphous carbon (a-C:H) is subjected to abnormally high friction in an inert environment, and the possibility of maintaining ultra-low friction is still a great challenge. Here, nanodiamond and hexagonal boron nitride are used to improve the tribological properties of a-C:H films. Particularly, an excellent synergistic lubrication effect was obtained after surface treatment using a solution droplet of nanodiamond + h-BN mixture with a mass ratio of 1:1 and a concentration of 0.1 mg/mL, and concurrently vacuum heated at 80 °C. The COF also decreased sharply to be below 0.001, about two orders of magnitude lower than the case without surface treatment. Correspondingly, the wear rate of steel ball was also decreased by ∼97%. The dominant factor to obtain ultra-low friction is the incommensurate contact between the tribolayer formed by nanodiamond + hexagonal boron nitride and the hydrogen passivation layer. Meanwhile, the incommensurate contact of mismatched h-BN nanoflakes promotes the formation of ultra-low friction. Besides, low shear slip at the interface formed by the in-situ growth of h-BN layered shear band and ND + h-BN nano-composited shear band, respectively, rubbing against the upper ND + h-BN mixed tribolayer also makes a contribution. The ultra-low friction is achieved under the joint action of these factors. These findings can enrich the understanding of the surface modification of a-C:H films by low-dimensional nano-lubricants. It is helpful to develop solid carbon films with more adaptability and robustness under extreme working conditions and provide important scientific and technical guidance.

Preparation and tribological performance of corncob-shaped nanospherical-Ni-BTC MOFs@HNTs nanocomposite towards friction improvement

The improvement of interface compatibility of nanomaterials as nanoadditives was conductive to raise the friction performances in oil. Herein, we successfully constructed a corncob-shaped Ni-BTC MOFs@HNTs nanocomposite through the controllable growth of nanospherical Ni-BTC MOFs on the external surface of HNTs nanotubes. The composition and structure of Ni-BTC MOFs@HNTs were determined by a catalog of characterization. Due to being the better interface compatibility of MOFs in organic compound, the existence of Ni-BTC MOFs on the external surface of HNTs evidently promoted the dispersibility of HNTs nanotubes in oil. The tribological behaviors of Ni-BTC MOFs@HNTs as nanoadditives in base oils were deeply studied by ball-on-ball contact friction. The experimental results showed that the average friction coefficient and wear scar diameter of Ni-BTC MOFs@HNTs -base oil were decreased by 39.7% and 29.4% at 0.04 wt% adding content relative to base oil, respectively. Meanwhile, the carrying capacity of Ni-BTC MOFs@HNTs-base oil was increased by 16.3%. Finally, the worn surfaces lubricated by Ni-BTC MOFs@HNTs-base oil were deeply characterized by a series of spectra analysis, thus revealing the synergistic lubrication effect of Ni-BTC MOFs and HNTs.

Synthesis, characterization and tribological performances of nano-CeO2/biodiesel carbon soot composites as a novel lubricant additive in polyalphaolefin

This study fabricated nano-CeO2/biodiesel carbon soot (BCS) composites using the raw material BCS, which is the byproduct of biodiesel combustion and cerium salt and used as a novel lubricant additive to PAO6 for steel/steel contact. Oleylamine modified nano-CeO2/BCS composites comprise abundant lipophilic groups, and thus nano-CeO2/BCS composites exhibit good dispersion in PAO6. The tribological results showed that nano-CeO2/BCS composites significantly improved the lubricating performances of PAO6. In case of 0.1 wt% nano-CeO2/BCS composites dispersed in PAO6, the friction coefficient and wear volume were reduced by 17.3 and 35.2%, respectively. The improved tribological properties were attributed to the composites rolling and forming of a lubricating film on the friction surface and the presence of BCS and CeO2 in composites exerting a synergistic lubricating effect, which simultaneously improved the tribological properties of PAO6. This discovery contributes to the conversion of BCS into valuables and promotes the high value utilization of BCS as a lubricating additive.

Fabrication of MXene@Fe3O4@PNA composite with photothermal effect as water-based lubricant additive

Improving the tribological performance of water via designing nanomaterials as lubricant additive has garnered mounting interest. In this work, the poly-(N-isopropylacrylamide) microgel is grafted onto Fe3O4 nanoparticles surface (Fe3O4@PNA) via free radical polymerization. Then, the Fe3O4@PNA can self-anchored on the MXene nanosheets via hydrogen bonding interaction to obtain MXene@Fe3O4@PNA composite. The as-prepared MXene@Fe3O4@PNA can effectively reduce friction and wear when used as a water-based lubricant additive. Compared with pure water, the average coefficient of friction (COF) and wear volume decrease by 61% and 78.7%, respectively. The lubrication mechanism was analyzed by focused ion beam technique-TEM (FIB-TEM) and X-ray photoelectron spectroscopy (XPS). The outstanding tribological performance of MXene@Fe3O4@PNA is attributed to the synergistic lubrication effect of MXene and Fe3O4@PNA. Interlayer shear of MXene and spherical Fe3O4@PNA can make MXene@Fe3O4@PNA play a full role of sliding friction and rolling friction mechanism, which can induce tribo-chemical reactions to form a protective film on the contact area of the friction pair. In addition, the hydrophilic groups of the MXene@Fe3O4@PNA can adsorb a large number of water molecules and form a hydration layer, reducing the agglomeration of nanosheets and acting as a boundary lubrication film. Moreover, the as-prepared MXene@Fe3O4@PNA exhibit excellent photothermal conversion performance in both underwater environment and dry state. Based on this characteristic, infrared light can be collected efficiently and stored quickly. Then, convert and utilize it. Therefore, the multifunctional MXene@Fe3O4@PNA has a broad application prospect as a water-based intelligent lubrication additive.

Effect of Cr3C2 content on microstructure, mechanical and tribological properties of Ni3Al-based coatings

To broaden the applicability of Cr3C2 -reinforced Ni3Al-based coatings, which possess exceptional high-temperature strength and anti-friction properties for high-temperature solid lubrication, this study examined the influence of varying Cr3C2 concentrations (0 wt%, 10 wt%, 15 wt%, and 20 wt%) on the phase composition, microstructure, mechanical performance, and friction and wear behaviors of Ni3Al-based coatings from 25 °C to 800 °C. The findings indicated that decarburization of Cr3C2 took place during HVOF spraying, forming Cr7C3. The remarkable high-temperature lubricity of all coatings can be attributed to the synergistic lubrication effect resulting from the precipitation of soft metal Ag, the brittle-plastic transformation of MoO3, and high-temperature solid lubricants such as NiCr2O4 and Ag2MoO4, which are induced by high-temperature friction. The second phase strengthening of Cr3C2 and the solute effect in the Ni3Al matrix phase significantly improved the hardness and toughness of the coatings, thereby enhancing their wear resistance. Notably, the coating containing 15 wt% Cr3C2 exhibited the lowest coefficients of friction (COFs) and wear rates (WRs) (10−5 mm3·(N·m)−1), ranging from 0.60 to 0.26 and 14.48 to 2.01 at 25 °C to 800 °C, which can be ascribed to the coordination between lubricity and mechanical strength.

Synergism lubrication of graphene and carbon nanotube in polymeric composites under drying sliding condition

The internal lubrication of polyimide (PI) with added graphene oxides (GOs) and carbon nanotubes (MWCNTs), as well as their binary hybrid nano-additives (GCNTs), were contrastively investigated under dry sliding conditions. The friction coefficient of neat PI or its nanocomposites decreases as a stepwise increase of the load fitting a negative exponential equation while growing linearly as a stepwise increase of the velocity. Micromorphological and physicochemical variations occurring at friction interfaces have been analyzed using X-ray photoelectron spectroscopy, Raman spectroscopy, and high-resolution transmission electron microscopy results. Given the structural discrepancy between GOs and MWCNTs, the obtaining results showed that the different microcosmic tribological mechanisms for GCNTs enable to produce a synergistic lubricating effect, resulting in facilitating the complicating interface sliding between nanocomposites and steel balls.

Microstructure and tribological properties evolution of Ni–Mo–SrSO4 composites as a function of Mo contents at different temperatures

Ni–Mo–SrSO4 composites with different Mo amount were prepared by hot pressing in a vacuum. The oxygen-deficient environment derived from the degradation of SrSO4 during fabrication process led to the formation of SrMoO4, Sr2NiMoO6, and SrO in the sintered composites. With the increment in the contents of Mo, excessive dissolved Mo atoms accelerated the oxidation of Ni in the oxygen-deficient environment, which eradicated SrMoO4 phase. As compared to sintered material containing Sr2NiMoO6 and SrO, the appearance of SrMoO4 led to a distinct decrease in the density and microhardness. To reveal the effect of SrMoO4 on the wear mechanism, the tribological properties of the sintered composites against Al2O3 ball were investigated at different temperatures. The result indicated that the in-situ composite consisting of 80.75 wt.% Ni, 14.25 wt.% Mo, and 5 wt.% SrSO4 exhibited good friction and wear properties at room temperature (RT) and 800 °C, which was attributed to the development of the intact tribofilm with grooves consisting of SrMoO4, Sr2NiMoO6, NiO, and h-MoO3 at RT and the synergistic lubricating effect of SrMoO4, Sr2NiMoO6, and oxides (NiO, α-MoO3, SrMoO4, α-NiMoO4, and β-NiMoO4) at 800 °C.

Tribological performance analysis of nano-FeS films deposited on the surface of bearing steel

The wear and adhesion of bearing surface under boundary lubrication is the key to the development and application of bearing technology. For improving the antifriction and antiadhesion properties of the bearing materials, the sulfur rich nano self-lubricating thin layers were prepared on the bearing surface by low-temperature sulfide permeation technology. The morphology and composition of the sulfurized layer were characterized microscopically, and the tribological properties of the sulfurized layer were analyzed to reveal the anti-friction and anti-adhesion mechanism of the sulfurized layer on the surface of bearing steel. The results show that the sulfurized layer is flatter and does not contain nanostructures when the formulation does not contain thiourea, and the content of element S is lower. After the addition of thiourea, the surface of the sulfurized layer is formed by the accumulation of nanosheet-like structures. The nano sulfurized layer has higher S-element content and better tribological properties. When thiourea and tartaric acid are added to the sulfurizing formula at the same time, the nano-sheet structure of the sulfurized layer is more dense and uniform. Moreover, the number of microcracks in the sulfurized layer is small, and the tribological properties are further improved. At the same time, the sulfide in the self-lubricating thin layer and the lubricating oil stored in the gaps can make the bearing surface have a typical "liquid-solid synergistic lubrication effect". That is conducive to the formation of the self-lubricating film and the transfer to the dual parts. All these factors improve the antifriction and antiadhesion properties of the bearing materials effectively.

Tribological Properties of Nanoparticles in the Presence of MoDTC

Nanoparticles can reduce the friction coefficient and present a self-restorative effect and MoDTC is important as a friction-reducing additive. Both are important for improving lubricating performance. In this study, the tribological performances of nanoparticles in the presence of MoDTC were studied. The chemical synthetic and ball-milled nanoparticles were selected as test samples, and tribological performances were evaluated by a block-ring friction test rig. Experimental results show that the synthetic serpentine particle with a 200–800 nm diameter exhibits the lowest friction coefficient and wear, while the ball-milled kaolin particle shows the highest friction and wear. A synergistic lubricating effect has been shown when mixing the synthetic nano serpentine particle and MoDTC. The friction coefficient of “BD + synthetic serpentine” reduced from 0.011 to 0.055 after the compound with MoDTC. At 150 °C, the “BD + synthetic serpentine + MoDTC” improves the production of MoS2 on the friction surface, which further reduced the friction coefficient and wear, while the ball-milled kaolin reduced the production of MoS2, which leads to a high friction coefficient. The synthetic serpentine shows a round surface without any sharp edge, which shows the minimal ploughing effect on the friction surface. Based on the experimental results, the synthetic nanoparticles have the best antiwear and friction reduction performance when compounded with MoDTC.

Tribological performance and failure mechanism of Ti:WS2/P201 hybrid lubrication system under atomic oxygen irradiation

Ti:WS2 films with duplex-layer structure were deposited by magnetron sputtering. The mechanical properties and tribological performance of Ti:WS2 film were improved after Ti incorporation. Ti:WS2/P201 hybrid system constructed by combination of Ti:WS2 film and P201 oil displays a synergistic lubricating effect, significantly prolonging lubricating lifetime compared to the single film. It is attributed to the effectively repairing function in some wear areas owing to the debris acted as an additive in oil. However, the AO irradiation can decrease the tribological performance of Ti:WS2/P201 hybrid system to different extent, depending on dose of irradiation. The high-dose AO irradiation rapidly deteriorates the tribological properties of the hybrid system, dramatically shortening the lubricating lifetime. It is found that the AO irradiated oil caused the severe tribo-oxidation reaction with the increase of sliding distance, resulting in forming numerous W oxides and carbide. Finally, failure mechanism of Ti:WS2/P201 hybrid system under AO irradiation were revealed.

Tribological properties of NiMo matrix composite containing in-situ formed Sr2NiMoO6 and SrO at elevated temperatures

NiMo alloy and NiMo–5SrSO4 composite were fabricated to reveal the effect mechanism of Sr2NiMoO6 and SrO derived from the decomposition characteristics of SrSO4 in vacuum on the microstructure, density, microhardness, and tribological properties against Al2O3 ball at different temperatures. The formation of Sr2NiMoO6 and SrO led to a negligible increase in the density and microhardness of the sintered composite. Below 400 °C, compared to NiMo alloy, the poor tribological properties were observed in NiMo–5SrSO4 composite, which was responsible for the appearance of Sr2NiMoO6 and SrO on the worn surface. However, with the further increase in the temperature, the friction coefficient and wear rate of NiMo–5SrSO4 composite reached as low around 0.26 and 1.32 × 10−5 mm3/Nm at 800 °C respectively, which was attributed to the synergistic lubricating effect of SrMoO4 generated from the tribochemical reaction between SrO and MoO3, Sr2NiMoO6, and oxides (MoO3, NiO, and NiMoO4) on the rubbing surface.

Synergistic effect and long-term lubricating mechanism of WS2/oil combinations determined via oil molecule structures in vacuum

WS2 film with excellent lubricating property was combined with lubricating oils (PAO, PFPE and MACs) with different molecule structures to construct WS2/oil composite lubricating systems, respectively. The influences of the molecule structures and properties of oils on tribological properties of the systems were investigated systematically in vacuum. The result indicated that the WS2/PAO and WS2/MACs systems exhibited the obvious synergistic lubricating effect under relatively harsh testing condition, markedly prolonging the lubricating life and decreasing the wear rate. There is a new discovery that numerous ultrasmall WS2 nanosheets were generated and uniformly adhered to friction contact area, further in-situ forming the tribolayer that significantly enhanced the lubricating life. The lubricating mechanism of the long lifetime for WS2/oil systems is finally revealed.

Synergistic Lubrication Effect between Oxidized Black Phosphorus and Oil Molecules Triggers Superlubricity.

Oxidized black phosphorus (BP) has been demonstrated as a promising oil-based nanoadditive because of its superior friction-reducing capability. However, the synergistic lubrication effect between oxidized BP and oil at the molecular level dominating the friction properties remains unclear. In this Letter, the synergistic lubrication effect between oxidized BP and two typical oil molecules (nonane and nonanoic acid) was explored with an atomic force microscope. The superlubricity of oxidized BP with an ultralow friction coefficient of 0.006 was achieved in the nonanoic acid environment, exhibiting a 96% reduction compared with that in the nonane environment. There was a confined nonanoic acid layer in the contact zone with a tilt angle of 35° because of the hydrogen bonding interaction, contributing to the superlubricity. This observation sheds light on the exploration of the lubrication mechanism of oxidized BP as a nanoadditive in oil, which reveals the considerable implications for the design of high-performance lubrication system.

Enhancement of frictional properties of Ni-MoS2 self-lubricating composite coatings by microgroove arrays

The self-lubricating Ni-MoS2 composite coating deposited on a stainless-steel (SS) surface with microgroove arrays are prepared and detailed characterized in this paper. Laser surface texturing (LST) and electrochemical deposition (ECD) are carried out successively to fabricate such composite coating. Compared with the Ni-MoS2 coating deposited directly on the non-LST substrate, the coefficient of friction (COF) of the Ni-MoS2 coating on the microtextured substrate is reduced from 0.17 to 0.14, the wear volume is decreased by 21%, the average depth of wear track is decreased by 61%, the running-in time is significantly minimized to 1/11, and the lifetime is remarkable increased. The excellent frictional properties can be attributed to the influence of the microtexture on the growth pattern of Ni-MoS2 coating, as well as the synergistic lubrication effect between texture and the Ni-MoS2 structure.

Enhanced superlubricity on a-C films by lubrication with 3-hydroxypropionic acid

In this work, the macroscopic superlubricity with an extremely low coefficient of friction (COF) of 0.004 was achieved on the friction pair of the steel/amorphous carbon (a-C) film with the lubrication of 3-hydroxypropionic acid aqueous solution (3HPA(aq)). The excellent lubrication performance was ascribed to the solid-liquid synergistic lubrication effect between the a-C film and the 3HPA. The triboreaction occurred on the friction pair, resulting in the chemisorption of 3HPA molecules on the a-C film and the steel surface. The hydrated water layer was formed on the chemisorption layer through the hydrogen bonding with water, which contributed to the reduction of COF. Moreover, the feasible graphitization of the a-C film also played an important role on the achievement of superlubricity. This work presented a novel approach for achieving superlubricity on the diamond-like carbon (DLC) and provided support on the development of DLC lubrication in industrial applications.

Alkyl-functionalized black phosphorus nanosheets triggers macroscale superlubricity on diamond-like carbon film

The mechanical components’ friction and wear are the main factors to reduce the lifetime and cause the energy loss of machine. In this work, the alkyl-functionalized black phosphorus (BP) nanosheets were synthetized and used as lubricating additives in poly alpha olefins (PAO), which could trigger macroscale superlubricity on the silicon doped diamond-like carbon (Si-DLC) film deposited on the engineering steel surfaces. The COF of the PAO with the alkyl-functionalized BP additives could reduce down to 0.006, which reduced by more than 90% in comparison to that in the absence of functionalized BP. It shows that the high contact pressure and shear action in the running-in process make PAO and functionalized BP recombine to form a composite tribofilm. This composite tribofilm mainly contained the phosphorus oxides and silicon oxides, providing an extremely low shear strength and thereby resulting in a superlubricity state. These findings provide a novel method to achieve oil-based superlubricity on the engineering steel surfaces through the synergistic lubrication effect between the BP and Si-DLC.

Friction and Wear Characteristics of Aqueous ZrO2/GO Hybrid Nanolubricants

Aqueous nanolubricants containing ZrO2 nanoparticles, graphene oxide (GO) nanosheets, or hybrid nanoparticles of ZrO2 and GO were formulated using a cost-effective ultrasonication de-agglomeration method. The friction and wear characteristics of these water-based nanolubricants were systematically investigated using a block-on-ring testing configuration with a stainless- and alloy steel contact pair. The concentrations and mass ratios of nanoadditives were varied from 0.02 to 0.10 wt.% and 1:5 to 5:1, respectively, to obtain optimal lubrication performance. The application of a 0.06 wt.% 1:1 ZrO2/GO hybrid nanolubricant resulted in a 57% reduction in COF and a 77% decrease in wear volume compared to water. The optimised ZrO2/GO hybrid nanolubricant was found to perform better than pure ZrO2 and GO nanolubricant in terms of tribological performance due to its synergistic lubrication effect, which showed up to 54% and 41% reductions in friction as well as 42% and 20% decreases in wear compared with 0.06 wt.% ZrO2 and 0.06 wt.% GO nanolubricants. The analysis of wear scars revealed that using such a ZrO2/GO hybrid nanolubricant yielded a smooth worn surface, with 87%, 45%, and 33% reductions in Sa compared to water and 0.06 wt.% ZrO2 and 0.06 wt.% GO nanolubricants. The superior tribological performance can be ascribed to the combination of the rolling effect of ZrO2 nanoparticles and the slipping effect of GO nanosheets.

Synergy of phospholipid and hyaluronan based super-lubricated hydrogels

Synthetic hydrogels have been widely studied for the application of artificial joints and other biomedicals. In this work, the synergy of phospholipid and hyaluronan (HA) based super-lubricated hydrogel was synthesized with zwitterionic polymers through free-radical polymerization. The coefficient of friction could reduce down to 0.004, reaching a super-lubricated state, which exhibited a remarkable reduction of friction (approximately 85%) in comparison to that of the original hydrogel in the absence of lipids and HA. The friction reduction was observed under a wide range of sliding velocities, normal loads, and different upper friction materials (including steel, glass, polytetrafluoroethylene, and silicon nitride). The enhanced lubrication performance was mainly attributed to the formation of a robust lipid-based hydration boundary layer at the hydrogel interface with the synergistic lubrication effect between lipids and HA arising from electrostatic interaction. Our approach may provide the potential application for cartilage replacement and artificial joints and help us develop hydrogels with good lubrication characteristics.