Nano additive CeO2 without sulfur and phosphorus was used in combination with molybdenum dithiocarbamate (MoDTC) to solve the problems of low load-bearing capacity and unsatisfactory ...friction-reducing property of organic molybdenum in lubricating grease. By using quartz crystal microbalance (QCM) to analyze the adsorption behavior of the composite additive, it was found that the viscoelastic co-adsorption behavior of MoDTC and CeO2 nanoparticles significantly improved the adsorption rate and equilibrium adsorption mass, which made the PB value of the composite additive increased by 77.6 % and 12.6 % compared with CeO2 and MoDTC, respectively. In the tribofilm formed by composite additive, CeO2 nanoparticles that do not undergo frictional chemical reactions with MoDTC form a flat and hard intermediate layer in the tribofilm, which improves the bearing capacity and effectively suppresses the fluctuation and accumulation of layered MoS2 on the surface. The layered structure is concentrated on the surface of the tribofilm and parallel to the friction direction, significantly reducing the sliding resistance between layers. Therefore, a thinner MoS2 layer with appropriate orientation is more conducive to improving the friction reduction performance of the grease. This results in a 33.9 % decrease in the friction coefficient of organic molybdenum, while its load-bearing capacity increases from 900 N to 1400 N, enabling lithium complex grease to achieve low friction, low wear, and high load simultaneously.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A clever way to accomplish low friction in sliding contacts is to use materials that combine high hardness with low shear strength. Such seemingly paradoxical combination of high resistance and low ...resistance to plastic deformation can only be realized by combining a hard substrate material with a thin easy-shear coating. Some prominent such coating candidates are sulfides and selenides of mainly molybdenum and tungsten. This paper focuses on tungsten disulfide, WS2, and explores the many routes to formation and regeneration of such low-friction tribofilms. The initial surfaces involve various types of coatings, materials and fluids, including W and S in different states, but none of which include crystalline WS2. All formation routes result in remarkably similar, pure crystalline WS2 tribofilms.
•This paper focuses on tungsten disulfide, WS2, and explores the many routes to formation and regeneration of such low-friction tribofilms.•The initial surfaces involve various types of coatings, materials and fluids, including W and S in different states, but none of which include crystalline WS2.•All formation routes result in remarkably similar, pure crystalline WS2 tribofilms.•These tribofilms constitute beautiful and extremely efficient examples of the classical low-friction combination: low shear strength and small area of real contact.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The poor dispersibility, strong interlayer interaction, and inferior crack resistance ability restrict the employment of graphene as a lubricant additive. Herein, we prepared fluorinated graphene ...with different F/C ratios by direct fluorination of multilayer graphene utilizing F2. Among them, highly fluorinated graphene (HFG) with an F/C ratio of about 1.0 presented prominent thermal stability and excellent tribological performance as an oil-based lubricant additive, whose friction coefficient and wear rate had a 51.4 and 90.9% decrease compared to that of pristine graphene, respectively. It was confirmed that C–F bonds perpendicular to the graphene plane contributed to increasing the interlayer distance and tribological performance of fluorinated graphene, while the randomly oriented CF2 and CF3 groups did not count as influential, as demonstrated via X-ray diffraction, X-ray photoelectron spectroscopy, and polarized attenuated total reflection-Fourier transform infrared spectroscopy. Meanwhile, Raman measurements traced the formation process of integrated and stable HFG tribofilm during friction process, and the corresponding stability was attributed to the physical and chemical interactions between HFG and friction pairs. More interestingly, the outstanding crack resistance ability of HFG preserved the sheet structure from destruction due to decreased in-plane stiffness and out-plane stress, thus constructing the tough tribofilm. The simple and feasible preparation makes HFG a promising candidate as advanced lubricant in industrial fabrication.
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IJS, KILJ, NUK, PNG, UL, UM
•Black phosphorus dotted with Ag nanoparticles is synthesized by a facial and in-suit chemical reduction approach.•The nanocomposite of Ag/BP is an excellent lubricant additive achieving ultralow ...friction and excellent wear resistance.•Ag/BP can act as a catalyst to decompose the base PAO oil forming a carbon-based tribofilm during rubbing process.•The formed tribofilm consisting of BP and amorphous carbon corresponds to the superior lubricating ability of Ag/BP.
Black phosphorus (BP) is a new two-dimensional (2D) material with attractive nanoscale chemical and physical properties. Herein, black phosphorus dotted with silver nanoparticles (Ag/BP) was synthesized via a facile and in-suit chemical reduction approach without reductant. The tribological properties of as-prepared Ag/BP nanocomposite as lubricant additive in poly-alpha-olefin (PAO6) based oil were investigated by a ball-on-disc tribometer. The results demonstrate that the oil dispersed with trace amount of Ag/BP nanoadditives shows excellent lubricating performance for the steel/steel contact. The friction coefficient and wear rate of the oil dispersed with 0.075 wt% Ag/BP nanoadditives are reduced by 73.4% and 92.0% respectively, as compared to the based PAO6 oil. The possible friction-reducing and anti-wear mechanisms of Ag/BP nanoadditives in oil are illustrated by analyzing the wear scar surfaces. During scratching, the Ag/BP nanomaterials serves not only as a friction-reducing and anti-wear additive, but also as a catalyst to decompose the based PAO oil for forming a carbon-based tribofilm under ambient condition that further reduces the friction and wear. The findings here provide a novel insight into the design of lubricant additive incorporated in base oil and suggests a new potential application of black phosphorus in lubrication and tribology.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Diamond-like carbon (DLC) films are capable of offering low friction coefficient and high wear resistance when rubbed in both dry and lubricated interfaces. However, the inherent mechanisms governing ...fretting wear in DLC films with temperature are still not well comprehended. Herein, atomic-scale analysis was conducted to unveil the relationship between interfacial tribofilms and the fretting wear behaviors. The results emphasize the determining role of the interaction between the tribo-sintered tribofilms and the transferred carbon tribofilms, as well as the structural evolution in the DLC film with temperature. The room temperature (RT) fretting experiment establishes a bilayer nanostructured tribofilm with a C-rich transfer layer on a Fe-rich tribo-sintered layer. As the fretting temperature elevates the graphitization degree of the tribofilms exacerbates, surface oxidation and hydrogen effusion arise in the DLC film, resulting in higher friction coefficients and wear rates. Chromium outward diffusion at 500 °C establishes a Cr-rich interlayer in the tribofilm, which forms interfacial chromium-carbon bonds, promotes adhesive carbon transfer, and leads to the sharp increase of the friction force and wear rate. These findings provide new insights into the fretting wear mechanisms, and provide guidance for the application of DLC films in elevated-temperature fretting scenarios such as aero-engines tenon and spline connections.
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•Carbon transfer layer established on Fe-rich tribo-sintered layer in fretting.•Chromium out-diffusion at high temperature generates Cr-rich interlayer.•Cr-rich layer boosts carbon transfer and forms sandwich structured tribofilm.•Cr–C interaction, graphitization, and hydrogen loss deteriorate fretting wear.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
MXenes induce excellent wear resistance under solid lubrication due to their distinctive surface chemistry, easy-to-shear ability, and capability to form low-friction and wear-resistant tribofilms. ...However, beyond the extensively studied Ti3C2Tx, other promising members of the MXene family remain largely underexplored. Therefore, we spray-coated multi-layer vanadium carbide (V2CTx) coatings (thickness ∼10.8 μm) on steel substrates and studied their tribological performance for prolonged times (10,000 cycles) using a reciprocating ball-on-disk tribometer with acting contact pressure of 445 MPa in ambient conditions. Results show that V2CTx-coated substrates demonstrate an 8-fold reduction in friction (COF of 0.11) and a 10-fold wear rate reduction (1.405 × 10−6 mm3 N−1 m−1). High-resolution materials characterization confirmed that the remarkable tribological performance of these coatings can be traced back to the formation of protective films on the substrate (tribofilm) and counterbody (transferfilm) consisting of contact pressure and frictional heat-induced degraded, deformed, exfoliated V2CTx nanosheets, nanocrystalline oxides, and amorphous carbon debris. This work fully elucidates the tribological potential of V2CTx, which is of utmost relevance for designing high-performance lubricating materials. Our work has assessed the performance of multi-layer V2CTx (M2XTx) due to its remarkable thermal stability, low molecular weight, good mechanical properties, and high interlayer spacing, thus serving as an entry point into diverse MXene compositions, including M4X3Tx (V4C3Tx).
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•First experimental study of 2D black phosphorus (BP) coatings as solid lubricant.•Tribological tests on 2D BP coatings under linear-reciprocating conditions.•Assessment of the ...frictional performance of BP coatings for two thicknesses.•Notable friction reduction observed for thicker BP coatings.•Verification of the overall solid lubrication potential of BP coatings.
Black phosphorus (BP), a rather new 2D material, features excellent electronic, optical, and tribological properties, but its potential for solid lubrication is completely unexplored. Therefore, our paper aims at experimentally evaluating the solid lubrication performance of 2D black phosphorus (BP) in dependence of the coating thickness by performing tribological tests under ball-on-disc linear-reciprocating sliding in dry conditions. BP was spray-coated onto bearing steel discs, while the effect of the thickness was evaluated by fabricating two BP coatings, BP-thin and BP-thick. Our results demonstrate that BP coatings reduced friction compared to uncoated reference samples. However, only thicker BP coatings are capable to induce a stable, long-lasting four-fold friction reduction, which was mainly traced back to the formation of a stable tribofilm in the contact zone. Therefore, our study proves the potential of BP for solid lubrication purposes with the overall aim to kick-start and boost more research endeavours in this newly emerging field.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Since the first mechanical exfoliation of graphene in 2004, the interest in 2D materials has significantly risen due to their outstanding property combination. Multiple 2D materials have been ...synthesized until today, while black phosphorus (BP) resembles one of their latest additions. The unique properties of BP, especially for electronic and optical devices (i.e., high carrier mobility and electrical conduction, field-effect transistor, layer-dependent bandgap, anisotropic transport), have gained notable attention. However, its layered structure, similar to those of graphene and MoS2, is also advantageous to optimize the friction and wear performance. Moreover, the strong in-plane covalent bonds and weak interlayer van-der-Waals forces favour the formation of low-friction and wear-resistant films. Although BP holds a great tribological potential, the literature to date on this topic is rather scarce. Therefore, it is a timely moment to holistically summarize the synthesis approaches and properties of BP thus guiding interested researchers to use it in mechanical/tribological applications. The existing state-of-the-art regarding tribological research is critically discussed and compared to other 2D materials thus highlighting existing research gaps and paving the way for future research activities.
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•Synthesis approaches of 2D black phosphorus (BP) is historically discussed.•Structure-property relationship of BP is holistically analysed.•Existing state-of-the-art related to BP tribology is critically analysed.•Existing challenges and future research directions for BP tribology are outlined.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In pursuit of energy efficiency and durability throughout human history, advances in lubricants have always played important roles. Ionic liquids (ILs) are room-temperature molten salts that possess ...unique physicochemical properties and have shown great potential in many applications with lubrication as one of the latest. While earlier work (2001–2011) primarily explored the feasibility of using ILs as neat or base lubricants, using ILs as lubricant additives has become the new focal research topic since the breakthrough in ILs’ miscibility in nonpolar hydrocarbon oils in early 2012. This work reviews the recent advances in developing ILs as additives for lubrication with an attempt to correlate among the cationic and anionic structures, oil-solubility, and other relevant physicochemical properties, and lubricating behavior. Effects of the concentration of ILs in lubricants and the compatibility between ILs and other additives in the lubricant formulation on the tribological performance are described followed by a discussion of wear protection mechanism based on tribofilm characterization. Future research directions are suggested at the end.
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IJS, KILJ, NUK, PNG, UL, UM
Nanomaterials have garnered significant interests owing to their attractive tribological potentials. Although numerous investigations pertaining to nano-reinforced composites have been conducted, the ...critical interactions between multidimensional nanoadditives and tribofilms are yet to be reviewed comprehensively. This review critically examines the current state of multidimensional nanomaterials that serve as functional additives in tribology. After brief discussion on major characteristics of multidimensional nanoadditives, the formation mechanisms of a tribofilm under the solid/liquid lubrication states are elaborated, and the functions of multidimensional nanoadditives are discussed. Additionally, concise conclusions regarding the formation mechanism and influencing factors of nano-tribofilms under solid/liquid lubrications are provided. The current challenges and prospects are presented such that the understanding of nano-tribology can be further intensified and their practical applications diversified.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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