Solid Lubricant Coatings Research Articles

Frictional properties and environmental adaptability of Ti-MoS2/WC multilayer films

Magnetron-sputtered molybdenum disulfide films are extensively utilized as solid lubricating coatings in space applications as a result of their low friction coefficient and minimal contamination. However, MoS2-based films are sensitive to hygrothermal and oxidation environment, and are easily oxidized to form MoO3, which results in high friction and wear of the films, significantly reducing their operational lifespan. Especially when the spacecraft adopts the launching mode of coastal launch or ocean platform, the performance deterioration caused by oxidation of MoS2 films during transportation, storage and launch is more serious. Therefore, to enhance the frictional performance and oxidation resistance of the films in humid and salt spray environments, the Ti-MoS2/WC multilayer films with preferred (002) crystal plane orientation were prepared, achieving a friction coefficient of 0.009 in a vacuum environment and a wear rate of 1.1×10-7 mm3/N∗m. In particular, the film can maintain this extremely low coefficient of friction even after exposure to moisture or salt spray. These findings demonstrate that the dual doping of Ti and WC and the design of multilayer structures enable MoS2 films to achieve outstanding frictional performance and oxidation resistance. This is crucial for designing MoS2 films with excellent environmental adaptability.

Strengthening mechanism of different morphologies of nano-sized MSH on tribological performance of phosphate/MoS2 bonded solid lubricating coatings

Magnesium silicate hydroxides (MSHs) with granular, schistose, and tubular morphologies were separately incorporated to enhance the tribological properties of phosphate/MoS2 composite coatings. The nano-schistose MSH demonstrated superior tribological performance due to its effective interactions with the worn surface and frictional synergies with solid lubricants. Incorporation of nano-schistose MSH decreased the friction coefficient of composite coatings by about 34.7% and increased the anti-wear performance of composite coatings by about thirteen times. Nano-schistose MSH facilitated the formation of a friction-induced multi-layer heterogenous slipping structure with layered solid lubricants at the friction interface. Moreover, tribo-chemical reactions between nano-schistose MSH and worn surface promoted the in-situ formation of a cermet supporting film, and this also induced the gradual in-situ formation of a lubrication film on the top of worn surface. Consequently, the contact state between tribo-pairs was timely regulated and the invalidation of the nanocomposite slipping structure was effectively restrained during the friction process. As a result, the service life of the phosphate composite coatings was significantly extended and further abrasion on the worn surface was notably reduced.

Tribological behavior of MoS2–Sb2O3-annealed nanodiamond coating on PEO-LST treated Ti6Al4V

MoS2–Sb2O3 coating is commonly used as solid lubricant for titanium alloys, but the wear-resistance performance is still limited. Core-shell annealed nanodiamond (AND) particle is used as reinforcement for MoS2–Sb2O3 coating on Ti6Al4V substrate treated by plasma electrolytic oxidation (PEO) and laser surface texturing (LST). The incorporation of AND particles into the MoS2–Sb2O3 coating results in a 39 % decrease in friction and significantly reduces wear on the composite coating. Structural transformation of AND particles to amorphous carbon and graphitic structure promotes the densification of top-layer coating, enhancing lubrication and wear-resistance. Change of contact stress by PEO-LST promotes the formation of dense tribofilm and re-orientation of MoS2. This study has implications for the development of solid lubrication coatings for aerospace applications through functional nanomaterials and targeted designed surfaces.

Cold Spray Deposition of MoS2- and WS2-Based Solid Lubricant Coatings

The cold spray deposition technique has been used to produce a new class of solid lubricant coatings using powder feedstocks of the metal disulfides WS2 or MoS2, either pure or mixed with Cu and Ni metal powders. Friction and cycle lives were obtained using ball-on-flat reciprocating tribometry of coated 304 SS flats in dry nitrogen and vacuum at higher Hertzian contact stresses (Smax = 1386 MPa (201 ksi)). The measured friction and thickness of the coatings were much lower than for previous studies (COF = 0.03 ± 0.01 and ≤1 µm, respectively), which is due to their high metal disulfide:metal ratios. Cu-containing metal sulfide coatings exhibited somewhat higher cycle lifetimes than the pure metal sulfide coatings, even though the Cu content was only ~1 wt%. Profiling of wear tracks for coatings tested to 3000 cycles (i.e., pre-failure) yielded specific wear rates in the range 3–7 × 10−6 mm3N−1m−1, similar to other solid lubricant coatings. When compared to other coating techniques, the cold spray method represents a niche that has heretofore been vacant. In particular, it will be useful in many precision ball-bearing applications that require higher throughput and lower costs than sputter-deposited MoS2-based coatings.

Synthesis and tribological characterization of cold-sprayed Ni-based composite coatings containing Ag, MoS2 and h-BN

The tribo components often fail to perform in a desired way due to absence of adequate lubrication in severe conditions and may cause loss of material. Even under room temperature (RT), it is desirable to maintain the proper lubrication for efficient functioning. In recent years, many efforts have been made to develop a coating material which can facilitate low friction and wear properties in diverse working conditions. The proper use of the solid lubricants can deliver utmost lubricity and, therefore, minimize the loss of materials. Solid lubricating coatings have found various industrial applications in harsh environmental conditions, such as in internal combustion engine, gas turbine and aircraft. As far as development of coating is concerned, cold spray (CS) technology has been observed to develop the coatings at relatively low temperature (avoids decomposition) as compared to conventional thermal spray technologies (plasma spray & high velocity oxy fuel). In the current investigation, synergistic response of the participating solid lubricants viz. silver (Ag), molybdenum disulfide (MoS2) and hexagonal boron nitride (h-BN) on the tribological properties of the developed coatings were studied in various working regime of loads. The tribological characteristics of different composite coatings, such as NiAl-MoS2-Ag (NB0), NiAl-MoS2-Ag-5 wt. % hBN (NB5), NiAl-MoS2-Ag-7.5 wt % hBN (NB7.5) and NiAl-MoS2-Ag-10 wt % hBN (NB10) against alumina ball were explored at various loads (6, 11, 16 and 21 N) and at a fixed speed of 0.3 m/s under room temperature (RT). The fixed concentration of Ag and MoS2 with varying weight percentage of h-BN (0, 5, 7.5 and 10 wt %) were introduced as solid lubricants for evaluating the lubricating potential of h-BN. During the tests, coefficient of friction (COF) and wear rate were observed to lessen as the load increased from 6 to 16 N. However, increased COF and wear rate were noticed for all the participating coatings at higher load (21 N). The ideal content of hBN in the deposited coatings was ascertained in order to get the utmost favourable lubricating conditions. It was observed that NB7.5 coating exhibited the enhanced tribological characteristics under the aforesaid operating conditions. Coating NB7.5 shows the best friction and wear characteristics during each testing load and reached a COF (0.19) and wear rate (2.1 × 10−5 mm3/Nm) at 16 N load. The observed wear mechanisms were analysed on the basis of the synergy shown by Ag, MoS2, and hBN as well as the optimal hBN level in the coating (NB7.5) which helped in attaining the improved tribological properties.

Research on Friction and Wear Behaviors of Different Solid Lubricant Coatings on Aluminum-Based Piston Skirts

Abstract Stringent requirements in emissions drive the application of low-carbon fuel engines, which result in prominent friction and lubrication problems in the cylinder. Solid coating technology is an effective way to enhance the tribological performance of tribo-pairs and has great potential to solve friction and lubricant problems. In this work, graphite, molybdenum disulfide (MoS2), and tungsten disulfide (WS2) solid lubricant coatings were prepared on aluminum-based piston skirts, respectively. The friction and wear behaviors of three coatings were investigated using a self-designed piston skirt friction and wear apparatus. The chemical products generated on the worn surfaces were analyzed, and the combined effect of lubricating oil and solid lubricant coatings was confirmed. The results show that the solid coatings can effectively enhance the friction and wear characteristics of piston skirt-cylinder liner tribosystem, and WS2 coating has the best anti-friction and wear-resistant performance among the three coatings.

Efficiency of Antifriction Solid Lubricant Coatings for Metal–Polymer Friction Pairs

Efficiency of Antifriction Solid Lubricant Coatings for Metal–Polymer Friction Pairs

Combining Carbon Nanoparticle Coatings and Laser Surface Texturing for Enhanced Lubricity Under High Loads

Developing new lubrication concepts greatly contributes to improving the energy efficiency of mechanical systems. Nanoparticles such as those based on carbon allotropes or 2D materials have received widespread attention due to their outstanding mechanical and tribological performance. However, these systems are limited by a short wear life. Combining nanoparticle coatings with laser surface texturing has been demonstrated to substantially improve their durability due to the reservoir effect which prevents immediate particle removal from the contact. In this study, we investigate the high-load (20 N) tribological performance of AISI 304 austenitic stainless-steel substrates, which are line-patterned by laser interference patterning and subsequently coated with different carbon nanoparticle coatings (carbon nanotubes, carbon onions, carbon nanohorns) against alumina and 100Cr6 counter bodies. In addition to that, benchmark testing is performed with conventional solid lubricant coatings (graphite, MoS2, WS2). Electrophoretic deposition is used as the main coating technique along with air spraying (for WS2). All coatings substantially improve friction compared to the purely laser-patterned reference. Among all coating materials, carbon nanotubes demonstrate superior lubricity and the longest wear life against 100Cr6 and alumina counter bodies. Detailed characterization of the resulting wear tracks by energy-dispersive X-ray spectroscopy, scanning electron microscopy, and confocal laser scanning microscopy provides insights into the friction mechanisms of the various solid lubricant particles. Further, material transfer is identified as an important aspect for effective and long-lasting lubrication.

Evolution of the structure and tribological behavior of the organic coatings under gamma-ray irradiation

More reliable and long-term irradiation stability is essential for lubrication protection materials that served in nuclear energy equipment. In this paper, three typical commercially organic bonded solid lubricating coatings were chosen to investigate the influence of gamma (γ)-ray irradiation on microstructure and tribological behaviors. The evolution of microstructure and the changes of tribological properties for these coatings after irradiation were comparatively studied in detail. The results revealed that the crystallinity of the molybdenum disulfide (MoS2) lubricating phase was improved and were partial oxidized in the coatings after γ-ray irradiation, resulting in the surface roughness of the coating with MoS2 as the solid lubricating phase decreased significantly. The polytetrafluoroethylene (PTFE) lubricating phase was degraded from the long chains structure to smaller molecules after γ-ray irradiation. The results of tribological properties of the three coatings after γ-ray irradiation indicated that, for polyamide-imide-based lubricating coatings, the friction coefficient is decreased and the wear rate is increased after irradiation. For phenolic epoxy-based lubricating coating, the cross-linking effect of γ-ray irradiation predominated to improve the wear resistance and prolong the wear life of the coating. But overall, the influence of irradiation on tribological properties of three polymer-based coatings could almost be neglected duo to the changes of the microstructure in nanoscale. This work provides path and direction for design and preparation of the lubricating coatings that served in a nuclear reactor.

Synthesis and characterization of low-friction W-V-N alloy coatings using reactive magnetron sputtering technique for tribological applications

In recent years, self-lubricating hard coatings have garnered significant interest across various industries such as cutting tools, molds, and manufacturing because of their ability to reduce friction and wear at high temperatures in dry-cutting applications. The present study focuses on synthesis of tungsten-vanadium-nitride (W-V-N) coatings using the reactive magnetron cosputtering technique in an Ar + N2 plasma gas environment. The coating microstructure, surface morphology, wetting behavior, and mechanical properties were characterized by grazing incidence x-ray diffraction, field-emission scanning electron microscopy, atomic force microscopy, energy-dispersive spectroscopy, and nanoindentation. Wear resistance properties of the prepared W-V-N alloy coatings were investigated using a ball-on-disk tribometer at two different temperatures. The findings indicate that all W-V-N coatings, regardless of the vanadium content, exhibit a face-centered cubic structure and form a solid solution of W-V-N. Among the coatings studied, W0.68V0.32N exhibited the highest hardness (14.25 GPa) and Young's modulus (257.53 GPa), as well as an excellent wear resistance. Increasing the vanadium content in the W-V-N coating led to a notable reduction in both the specific wear rate and friction coefficient. Moreover, this reduction was more pronounced with an increase in temperature during the wear test. Improvement in the wear properties can be attributed to the formation of Magnéli phases of vanadium oxides on the surface of the coatings. The ability of the W-V-N coating to reduce friction and wear, combined with its improved mechanical properties, makes it a promising candidate for solid lubricating coatings in tribological applications.

Elevated temperature tribological assessment of Ni-based cermet self-lubricating coatings deposited by cold spray

Solid lubricant coatings provide reduced friction and wear resistance and hence finding widespread application in harsh environmental conditions, such as gas turbine, aircraft, and internal combustion engines. It is apparent that single lubricant fails to offer effective lubrication over wide temperature range. Hence, two or more solid lubricants are mutually incorporated to achieve the appropriate lubrication by their synergy under harsh service conditions. The current investigation is being carried out to evaluate the synergistic impact of different solid lubricants viz. silver (Ag), molybdenum disulfide (MoS2), hexagonal boron nitride (h-BN) and chromium oxide (Cr2O3) on the frictional properties of coatings from room temperature (RT) to 800 °C. Cold spraying process has gathered extensive acceptance for the development of metallic and metallic-ceramic coatings. The current study elucidated the tribological characteristics of cold sprayed nickel-based high temperature lubrication coatings, namely, Ni-Al-MoS2-Ag (NB0), Ni-Al-MoS2-Ag-5 wt% h-BN (NB5), Ni-Al-MoS2-Ag-7.5 wt% h-BN (NB7.5), Ni-Al-MoS2-Ag-10 wt% h-BN (NB10) and Ni-Al-MoS2-Ag-Cr2O3–7.5 wt% h-BN (NB7.5 + 7 wt% Cr2O3) against Al2O3 ball in an operative testing regime from (RT-800 °C) using ball-on-disc tribometer. Results indicated that NB7.5+ 7 wt% Cr2O3 coating exhibited remarkable self-lubricating and wear resistance properties as compared to other coatings. However, NB7.5+ 7 wt% Cr2O3 revealed slightly higher coefficient of friction (COF) in compare to NB7.5 coating till 400 °C, and beyond that it showed a decreasing trend and lesser COF in compare to other coatings. The observed wear mechanisms at different temperatures were discussed in detail after analyzing the morphologies of worn surface. The pivotal role played by the participating solid lubricants were also discussed in detail which help in to provide the continuous compacted layers at the worn surfaces at elevated temperature.

Influence of 1-Ethyl-3-methylimidazolium Diethylphosphate Ionic Liquid on the Performance of Eu- and Gd-Doped Diamond-like Carbon Coatings

A composite lubricating system that combines solid and liquid lubrication can create a synergistic effect by leveraging the strengths of both types of lubricants. Solid lubrication coatings possess advantageous load-bearing abilities and exhibit low volatility. By adopting this approach, the system retains the merits of solid lubrication while simultaneously harnessing the advantages of liquid lubrication. The unique properties of diamond-like carbon coatings (DLCs) offer the potential to create binding locations for lubricant additives by introducing dopant elements that have a high affinity with additives. In the present work, the combined use of europium-doped diamond-like carbon (Eu-doped DLC) with varying atomic concentrations of the dopant element (1.7 at. % and 2.4 at. %) and gadolinium-doped diamond-like carbon (Gd-doped DLC) with different atomic concentrations of the dopant element (1.7 at. % and 2.3 at. %) was studied alongside a pure DLC coating and the incorporation of an ionic liquid (IL) additive in a tribological block-on-ring system. The focus was on the 1-Ethyl-3-methylimidazolium diethylphosphate ionic liquid with a concentration of 1 wt. % in polyalphaolefin (PAO) 8. Among the investigated pairs, the coefficient of friction (CoF) of 1.7 at. % Eu-doped DLC coupled with the IL was the smallest in boundary, mixed, and elastohydrodynamic lubrication regimes. Quantification of wear was challenging due to minimal and localized wear on the DLC coating surfaces. The decrease in friction within the boundary lubrication regime underscores the promise of mechanical systems that integrate 1.7 atomic percent Europium-doped diamond-like carbon coatings with ionic liquids (IL). This study presents a compelling avenue for future scholarly exploration and research efforts focused on reducing friction and improving the efficiency of moving components, particularly in situations where tribological properties exert a substantial influence

Анализ технологий восстановления коленчатых валов автотракторной техники

Characteristic defects of internal combustion engine crankshafts of automotive vehicles include wear of friction surfaces - journals, faces, grooves and threads, - as well as residual deformations and fatigue cracks. To eliminate defects, crankshafts are repaired using technological operations to restore the shape and location, linear and angular dimensions, as well as roughness, wear resistance and fatigue resistance of elements and surfaces. To analyze the restoration techniques of crankshafts of automotive vehicles the operating conditions, the authors considered the main defects and types of surfacing and spraying applied by means of electric arc, gas-flame, detonation, and plasma (induction and plasma-arc) methods. The authors note that to meet reliability requirements, the restored parts should have a ratio of hardness (НRСв /НRСн) and fatigue strength (G-1B/G-1H) higher than one as compared to new parts. However, no crankshaft restoration technique fully meets this requirement, because the wear resistance of new crankshafts in most cases is higher than that of restored parts. Based on the analysis of crankshaft restoration techniques, the authors determined the following effective ones: the finishing antifriction non-abrasive treatment (FANT) with the use of antifriction, wear-resistant and solid lubricant coatings applied to the parts using various methods. This technique increases wear and corrosion resistance, resistance to fatigue wear, and improves the running-in of the rubbing machine parts.

Nanoscale friction of high entropy alloy sulfide thin films in comparison with molybdenum disulfide

We present nanoscale friction measurements performed on sputter-deposited high entropy alloy (HEA) sulfide thin films [(VNbTaMoW)S2] via atomic force microscopy. The results reveal (i) the influence of deposition time on the film morphology and (ii) the presence of isolated areas of low friction on film surfaces. We compare the friction results on HEA sulfide thin films with those on a prototypical solid lubricant, sputter-deposited molybdenum disulfide (MoS2), and find that they are superior in terms of lubricative performance. Variable temperature x-ray diffraction, performed up to 973 K, reveals that HEA sulfide thin films exhibit improved oxidation resistance when compared with MoS2 films. Combined, our results show that HEA sulfide thin films have considerable potential as oxidation-resistant solid lubricant coatings.

The effects of Ti content on tribological and corrosion performances of MoS2–Ti composite films

The easy shear of the MoS2 film and thus the low coefficient of friction makes it one of the excellent candidates for solid lubricant coatings. In this paper, the Ti content in MoS2–Ti composite films was controlled by varying the power of the titanium target using magnetron sputtering. The structure, components and properties of the MoS2–Ti composite films with different Ti contents were systematically investigated. The results showed that MoS2–Ti composite films were dense and uniform with no obvious defects. Besides, the titanium oxides were formed in the MoS2–Ti composite films, which would have a suppressive effect on the oxidation of MoS2. The hardness and elastic modulus increased with the Ti content of MoS2–Ti composite films. As Ti content increased, the friction coefficients of MoS2–Ti composite films first decreased and then increased. At the Ti target power of 0.28 kW, the average friction coefficient of the composite film reached a minimum value of about 0.048. However, when the Ti target power was 0.32 kW, the composite film had the best wear resistance and corrosion resistance.

Solid Lubrication System and Its Plasma Surface Engineering: A Review

In aerospace, aviation, nuclear power, and other high-tech fields, some essential moving parts must operate under high vacuum, high load, intense radiation, and other conditions. Under such extreme conditions, only solid lubricating materials can meet the lubrication requirements. Traditional material modification methods have problems such as high energy consumption, severe pollution, and narrow scope of application. Plasma modification technology can overcome these shortcomings. This paper focuses on several commonly used plasma preparation techniques for solid lubricating coatings, including plasma chemical heat treatment, physical vapor deposition, plasma immersion ion implantation and deposition, plasma spraying, and plasma electrolytic oxidation. Subsequently, the material systems of metal-based solid lubrication coatings are reviewed: soft metals, oxides, sulfides, nitrides, and carbon-based materials. Finally, found that the development of new solid lubricants, the improvement of existing preparation technology, and the development of new processes are the key development directions in the future.

Assessment of the Wear Intensity of Friction Pairs with Solid Lubricant Coatings during Sliding and Reversing Movements

Assessment of the Wear Intensity of Friction Pairs with Solid Lubricant Coatings during Sliding and Reversing Movements

In situ tribological regulation behavior induced by MSH@LaF3 in phosphate/MoS2 bonded solid lubricating coatings

Composite powders consisted of tubular MSH and LaF3 NPs were incorporated to improve the tribological performance of phosphate/MoS2 composite coatings. It suggested that tribological performance of composite coatings can be greatly promoted by MSH@LaF3, and at the same time, the enhancement effect can be further facilitated by high-temperature treatment on MSH@LaF3. The concrete reason was attributed to that LaF3 stimulated dehydration of structural water and stripping of silicon-oxygen tetrahedra sheet from MSH matrix, through which MSH@LaF3 can easily undergo tribo-chemical reactions with the worn surface and initiated in-situ formation of cermet tribo-film. What’s more, MSH@LaF3 that transferred into the tribo-film also induced the formation of MoS2 lubrication film on the top worn surface.

Synergistic effect of ceria-zirconia nanoparticles and hBN nanosheets incorporation on the corrosion resistance of MoS2 solid lubricant coatings

Molybdenum disulphide is a conventional solid lubricant material due to their layered crystal structure enabling easy shearing resulting in low coefficient of friction. Even though MoS2 is highly lubricating, the corrosive nature of this dry solid lubricant limits its application, especially in oxidizing and humid environment. The present work focuses on the improvement of corrosion resistance properties of MoS2 nanosheets coatings, while maintaining its excellent anti-friction properties by incorporating hexagonal boron nitride (hBN) nanosheets and ceria-zirconia nanoparticles (CZ NPs). A hybrid structure consisting of MoS2, hBN and CZ NPs was prepared as a composite and multilayer coating. The coatings were characterized by FE-SEM, XRD, Raman spectroscopy and XPS. The inclusion of hBN and CZ NPs did not significantly alter the coefficient of friction (CoF) and wear for the composite and multilayer coatings, as determined by the tribological investigations conducted using high frequency reciprocating rig (HFRR). The MH30-CZ composite coatings showed higher CoF compared to MH30-CZ multilayer coatings, with only 7.75 % increase as compared to pure MoS2 coating. The composite structure and multilayer structure showed high long-term corrosion resistance while the latter had the highest resistance to corrosion and oxidation. The hybrid multilayer structure had the lowest corrosion current density and corrosion rate with 167 % enhancement in total impedance. In the hybrid coating, hBN acts as a physical and insulating barrier to the flow of corrosive ions and charge transfer while CZ NPs forms insoluble precipitates which further impedes the corrosion. The galvanic cell formation of MoS2 with steel was suppressed due to the presence of insulating CZ NPs layers. The synergic effect of hBN and CZ NPs resulted in high long-term corrosion resistance of the coating.

Synthesis, properties and solid lubrication performance of MoAlB-based MBene

Efficient lubrication under harsh conditions is essential for aerospace, automotive, and electrical systems. Novel two-dimensional (2D) materials can serve for this purpose by providing materials with low friction and excellent wear-resistance under these conditions. Therefore, we studied the solid lubrication performance of a novel boridene phase (MoAlB etched into layered 2D Mo2B2 MBene) spray-coated onto stainless-steel substrates. Studies on elemental and phase composition demonstrated the preferential etching of Al over Mo from the parental phase, while infrared spectroscopy confirmed OH and BO groups. The MBene demonstrated adequate colloidal stability, which is essential for the generation of homogeneous solid lubricant coatings. The solid lubrication performance of MBene was tested using ball-on-disk tribometry, revealing a promising reduction in friction and wear by 50%, even under a load of 400 mN (contact pressure of 0.8 GPa). Raman spectroscopy confirmed the formation of a beneficial tribo-layer, comprising both the initial MBene and its oxidation products, which played a cruical role in reducing observed friction and wear. Furthermore, calculated mechanical parameters demonstrated its elastic stability, meeting Born–Huang criteria. Mo2B2's elastic constants fall between other 2D materials such as MXenes, graphene, and MoS2, with surface functionalization impacting its mechanical properties. Altogether, our study provides cutting-edge knowledge about the promising solid lubrication performance of MBenes.