Solid Lubricant Research Articles

Solid lubrication performance of Ti2CTx coatings with reduced friction and extended durability

MXene research in tribology has predominantly focused on Ti3C2Tx, overlooking the untapped potential of other promising MXenes with equally intriguing properties. Thus, to enhance tribological reliability in industrial applications, Ti2CTx coatings were applied to 316 stainless steel as a solid lubricant. Using a linear ball-on-disk tribometer under 460 MPa pressure, we found that Ti2CTx coatings reduced friction by 82% and wear rate by 70% compared to uncoated steel. Advanced characterizations showed that this improved tribology is linked to nanostructured carbon-rich protective tribofilms resulting from the contact pressure-induced graphitization of Ti2CTx MXenes sheets. Our research comprehensively elucidates the tribological effectiveness of multi-layer Ti2CTx, which is pivotal to design advanced lubricants for contemporary mechanical applications.

Synergistic lubrication effects of Sn–Ag–Cu and MXene–Ti3C2 to improve tribological properties of M50 bearing steel with microporous channels

Purpose This paper aims to study the synergistic lubrication effects of Sn–Ag–Cu and MXene–Ti3C2 to improve the tribological properties of M50 bearing steel with microporous channels. Design/methodology/approach M50 matrix self-lubricating composites (MMSC) were designed and prepared by filling Sn–Ag–Cu and MXene–Ti3C2 in the microporous channels of M50 bearing steel. The tribology performance testing of as-prepared samples was executed with a multifunction tribometer. The optimum hole size and lubricant content, as well as self-lubricating mechanism of MMSC, were studied. Findings The tribological properties of MMSC are strongly dependent on the synergistic lubrication effect of MXene–Ti3C2 and Sn–Ag–Cu. When the hole size of microchannel is 1 mm and the content of MXene–Ti3C2 in mixed lubricant is 4 wt.%, MMSC shows the lowest friction coefficient and wear rate. The Sn–Ag–Cu and MXene–Ti3C2 are extruded from the microporous channels and spread to the friction interface, and a relatively complete lubricating film is formed at the friction interface. Meanwhile, the synergistic lubrication of Sn–Ag–Cu and MXene–Ti3C2 can improve the stability of the lubricating film, thus the excellent tribological property of MMSC is obtained. Originality/value The results help in deep understanding of the synergistic lubrication effects of Sn–Ag–Cu and MXene–Ti3C2 on the tribological properties of M50 bearing steel. This work also provides a useful reference for the tribological design of mechanical components by combining surface texture with solid lubrication. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-12-2023-0381/

Carbon nanotubes used to enhance the wear properties of AlSi10Mg/CNTs nanocomposites prepared through additive manufacturing

In this work, varying weight percentages of carbon nanotubes (CNTs) were reinforced in the AlSi10Mg alloy, and prepared nanocomposites through additive manufacturing. The distribution of CNTs in the metal matrix were achieved through functionalization and ball milling. The dispersion of CNTs were investigated through FESEM, TEM, and Raman spectroscopy. To study the wear properties, the prepared samples underwent wear tests at various loads and speeds. The wear properties, worn surfaces, and microhardness were thoroughly investigated. The results unveiled that the incorporation of CNTs led to a decrease in the wear rate and a reduction in the coefficient of friction. It was observed that CNTs functioned as a solid lubricant, resulting in a significant reduction in both the coefficient of friction and wear rate. The microstructures of the worn surfaces and wear channels became smaller and smoother after the addition of CNTs, and smaller-sized debris was produced.

Electrodeposited MoxSyOz/Ni Tribological Coatings.

Deposition of molybdenum disulfide (MoS2) coatings using physical vapor deposition (PVD) and mechanical burnishing has been widely assessed for solid lubricants in space applications but still suffers from line-of-sight constraints on complex geometries. Here, we highlight one of the first demonstrations of electrodeposited MoxSyOz and MoxSyOz/Ni thin-film coatings from aqueous solutions of ammonium tetrathiomolybdate for solid lubricant applications and their remarkable ability to provide low coefficients of friction and high wear resistance. Characterization of the coating morphology shows amorphous microstructures with a high oxygen content and cracking upon drying. Even so, electrodeposited MoxSyOz can achieve low steady-state coefficients of friction (μ ∼ 0.05-0.06) and wear rates (2.6 × 10-7 mm3/(N m)) approaching those of physical vapor deposited coatings (2.3 × 10-7 mm3/(N m)). Additionally, we show that adding dopants such as nickel increased the wear rate (7.5 × 10-7 mm3/(N m)) and initial coefficient of friction (μi = 0.23) due to compositional modifications such as dramatic sub-stoichiometry (S/Mo ∼ 1) and expression of a NiOx surface layer, although doping did reduce the degree of cracking upon drying.

Tribological performance and composition optimization of semi-metallic friction materials applied for carbon ceramic brake disc

The tribological performance of C/C–SiC paired semi-metallic brake pads suitable for automobiles was investigated in this study. Factors on tribological properties of semi-metallic brake pads such as the contents of phenolic resin, copper fibers, steel fibers and MoS2 were tested by the orthogonal experimental. According to the SAE-J2522 test procedure, an optimized compositional formulation was derived based on the brake test results combined with fuzzy comprehensive evaluation. The wear mechanism of brake pairs was discussed, and the compositional formulation of the brake pad was further optimized after the analysis of the friction surface morphology before and after braking. The results showed that copper fibers had the greatest effect on the friction performance of brake pads. Copper fibers contributed to stabilization of the coefficient of friction (COF) and effectively improved the wear resistance. However, at higher braking speeds (≥120 km/h), the copper fibers were converted from fibrous to flaky and softened, acting as a solid lubricant on the friction surface, resulting in a low COF of brake pads. The tribological performance of brake pads could be improved by reducing the content of copper fiber and increasing the content of hard particles.

Influence of GNPs solid lubricant on the fabrication of Cu/SS304L composite micro channels

The different solution-processed concentrations of graphene solid lubricant (0 – 30 mg/mL) were applied on the surface of copper/stainless steel 304 L composite foils. A variable trend of rolling force occurs, with a first falling and then rising trend and the lowest rolling force was obtained at 25 mg/mL for 3.82 kN. Besides, the height of ridges and aspect ratio were improved with an increased solution-processed concentration. On the valley surfaces, the GNPs filled up the cracks, flattened the grooves and eliminated the micro scratches. This indicates the self-repairing and self-polishing mechanisms of GNPs in the micro rolling process. The sliding and exfoliation of GNPs also contributed to the reduced roughness and improved quality of the sample surfaces.

Highly Interfacial Active Gemini Surfactants as Simple and Versatile Emulsifiers for Stabilizing, Lubricating and Structuring Liquids

AbstractTo date, locking the shape of liquids into non‐equilibrium states usually relies on jamming nanoparticle surfactants at an oil/water interface. Here we show that a synthetic water‐soluble zwitterionic Gemini surfactant can serve as an alternative to nanoparticle surfactants for stabilizing, structuring and additionally lubricating liquids. By having a high binding energy comparable to amphiphilic nanoparticles at the paraffin oil/water interface, the surfactant can attain near‐zero interfacial tensions and ultrahigh surface coverages after spontaneous adsorption. Owing to the strong association between neighboring surfactant molecules, closely packed monolayers with high mechanical elasticity can be generated at the oil/water interface, thus allowing the surfactant to produce not only ultra‐stable emulsions but also structured liquids with various geometries by using extrusion printing and 3D printing techniques. By undergoing tribochemical reactions at its sulfonic terminus, the surfactant can endow the resultant emulsions with favorable lubricity even under high load‐bearing conditions. Our study may provide new insights into creating complex liquid devices and new‐generation lubricants capable of combining the characteristics of both liquid and solid lubricants.

Highly Interfacial Active Gemini Surfactants as Simple and Versatile Emulsifiers for Stabilizing, Lubricating and Structuring Liquids.

To date, locking the shape of liquids into non-equilibrium states usually relies on jamming nanoparticle surfactants at an oil/water interface. Here we show that a synthetic water-soluble zwitterionic Gemini surfactant can serve as an alternative to nanoparticle surfactants for stabilizing, structuring and additionally lubricating liquids. By having a high binding energy comparable to amphiphilic nanoparticles at the paraffin oil/water interface, the surfactant can attain near-zero interfacial tensions and ultrahigh surface coverages after spontaneous adsorption. Owing to the strong association between neighboring surfactant molecules, closely packed monolayers with high mechanical elasticity can be generated at the oil/water interface, thus allowing the surfactant to produce not only ultra-stable emulsions but also structured liquids with various geometries by using extrusion printing and 3D printing techniques. By undergoing tribochemical reactions at its sulfonic terminus, the surfactant can endow the resultant emulsions with favorable lubricity even under high load-bearing conditions. Our study may provide new insights into creating complex liquid devices and new-generation lubricants capable of combining the characteristics of both liquid and solid lubricants.

Design of ternary solid lubricants SiO2/Ti3C2/PTFE for wear-resistant, self-lubricating polyimide composites

BackgroundPolyimide is widely used in aerospace, electronics and electrical appliances, automotive, chemical and other fields due to its high temperature stability, excellent mechanical properties. However, polymer materials are often subjected to severe wear and tear under complex operating conditions due to their poor lubrication performance. Therefore, the improvement of lubrication performance is a key strategy to extend the service life of polyimide. MethodsHerein, a ternary solid lubricant SiO2/Ti3C2/PTFE (STP) is innovatively prepared by solution dispersion for reducing the friction of polyimide to increase the lubricity. Specifically, SiO2 and PTFE are intercalated accordion-like Ti3C2 nanosheets, thereby causing the nanosheets to slide relative to each other under external frictional stress. Then, STP was introduced into polyimide to prepare the ultra-wear-resistant and self-lubricating composites by blending. Significant findingsThe results of the study showed that the STP significantly enhanced the lubrication properties of the composites, the lowest coefficient of friction (0.29) of the composites is 22.81 % lower than that of the polyimide. In addition, the inclusion of hybrids helps to form a transfer film, which effectively improves the abrasion performance of polyimide, and the lowest wear rate (0.18 × 10−5 mm3/(N·m)) was 93.35 % lower than that of polyimide.

Recycling Automotive Plastic Waste: Residual Polyvinyl Butyral (rPVB) as Solid Lubricant in Polyoxymethylene (POM) Blends

Polyoxymethylene (POM) is an engineering thermoplastic commonly used in tribological applications due to its low friction and auto-lubrication properties. To improve its performance further and broaden its applications to higher sliding speeds and loads, it is commonly reinforced with different particles, fibers, or solid lubricants. In this study, the effect of adding residual polyvinyl butyral (rPVB) from automotive windshields production lines on the tribological performance of POM during pin-on-disk wear tests at different loads (12, 15, and 18 N) and sliding speeds (0.25, 0.50, and 0.75 m/s) is investigated. It was found that rPVB acts as a solid lubricant, reducing the coefficient of friction (CoF) up to 50%. It is suggested that the formation of a protective layer of adhered material on the wear track is the mechanism behind CoF reduction. Melt flow index, Shore D hardness and elastic properties decrease linearly with rPVB content. However, the reduction in tensile strength, and thus shear strength of the blends, seems to be more significant on their CoF behavior than the reduction in hardness. No trend was found for wear resistance. Under certain sliding conditions rPVB decreased volume loss, but in other cases it increased it. It is suggested that, for the conditions analyzed in this study, adding 10 wt% of rPVB to a POM matrix results in the best balance of tribological performance, with an overall CoF reduction of 36%, and an average volume loss increase of only 1%.

Large‐Scale Numerical Simulation of the Solid Lubricant Behavior in the Leg Joints of Insects

AbstractSemi‐solid lubricant in the leg joints of insects is represented by tiny cylindrical fragments. The dynamics of lubricant behavior between contact surfaces at the joint scale are investigated using numerical simulation. Results of modeling show that lubricant fragments tend to stick together and form clots of varying shapes and sizes under the influence of shear motion. Formation of such clots, accompanied by constant loss and reproduction of the lubricant, allows maintaining of fluctuating clearance between contact surfaces and helps to reduce friction. Foreign contaminant particles penetrating an open insect joint are removed by the lubricant, to which they stick, reducing abrasive wear.

Understanding the effect of solid lubricants on scratch behavior in epoxy resins: An experimental and statistical approach

AbstractEpoxy resins inherently have low resistance to scratching. To increase the scratch resistance of epoxy resins, reinforcing solid lubricants into the resin is an option. For this purpose, in this study, polytetrafluoroethylene (PTFE) and graphite were reinforced in two different epoxy resins (rigid and toughened) at different reinforcement ratios (5, 10, and 15 wt%). The effects of solid lubricant reinforcement on the scratch behavior of rigid and toughened epoxy resins were examined both experimentally and statistically. Scratch tests were performed throughout a distance of 10 mm using a test apparatus under a load of 15 N and a scratch speed of 30 mm/min. Following the scratch tests, the COF (Coefficient of Friction) values, scratch hardness, scratch width, and depth of all samples were determined and compared to neat epoxy for each resin. In general, it has been determined that solid lubricant reinforcement at higher reinforcement ratios has a positive effect on the COF value (15 wt%). In the case of 15 wt% graphite reinforced rigid and toughened epoxy, a decrease of 15.90% and 17.77%, respectively, was obtained in the COF value compared to the neat epoxy. After the scratch tests, statistical analysis was performed according to RSM to support the experimental results, and ANOVA tables were obtained.Highlights Epoxy adhesives exhibit low scratch resistance. Examining the impact of PTFE and graphite reinforcement on scratch behavior. Two types of epoxy and varied reinforcement ratios (5, 10, and 15 wt%) were studied. Solid lubricant reinforcement to epoxy positively affected scratch behavior.

STUDY ON MECHANICAL PROPERTIES OF DEVELOPED ECO-FRIENDLY BRAKE PADS USING GRAY RELATIONAL ANALYSIS IN BOX BEHNKEN DESIGN OF EXPERIMENT

Over the years, asbestos has been a leading material for developing automobile brake pads. However, due to its hazardous nature to human health, many researchers have found that organic materials possess the potential for replacement. The organic materials used in this research were the hybrid of coconut fruit fibre CFF and oyster sea shell OSS. These materials were gathered from the river bank, dried, crushed, washed, ground, sieved, and moulded with different additives: CuO (abrasive), graphite (friction modifier or solid Lubricant), epoxy resin (binder), hardener (catalyst) by Box Behnken design BBD of L27 experiment. Therefore, an experimental test on mechanical properties was performed to check the developed brake pad's characterization. Then, grey relational analysis was used to analyze grey relational grade GRG to convert a multiple response process optimization problem into a single response optimization using maximization of maximum GRG. The optimum parameter values producing the highest value of grey relational grade were chosen as rank one, pertained to the factors setup for experiment number S3232 having moulding pressure of 11.25MPa, moulding temperature of 180oC, and heat treatment time of 180min. The optimized response values obtained from the experiment sample S3232 give the highest values on all the responses, i.e., density of 3.483g/cm3, hardness of 52.91BHN, compressive strength of 2.78MPa, ultimate tensile strength of 3.92MPa, impact energy of 17.87N, cold water absorption of 0.2863%, hot water absorption of 0.4785%, and oil absorption of 0.4402%. After that, the optimized brake pad sample (S3232) was applied to the automobile and was suitable for braking owing to its high mechanical properties.

Enhancing oil pressure dynamics in a high-performance racing engine with innovative lubrication system tuning

This work focuses on fine-tuning the oil pressure dynamics of a single-seater formula car, a participant in international engineering competition organized by the Society of Automotive Engineers (SAE). Adhering to competition guidelines, the Honda CBR600RR 05-06® motorcycle engine, renowned for its 600 c.c. displacement and exceptional power-to-weight ratio, emerges as a popular choice. However, as this engine is originally equipped with a wet sump lubrication system (featuring deep wet sumps to prevent oil starvation during turns), this presents challenges when adapted to Formula Society of Automotive Engineers (FSAE) cars. Cornering leads to significant pressure drops, as sloshing exposes the pickup port, causing consequential engine issues. To tackle sloshing-related challenges and pressure loss during lateral and longitudinal g-forces, a dry sump lubrication system was introduced in the Formula car. The dry sump system also lowers the engine’s center of gravity, by reducing sump height. However, transitioning to the dry sump system and integrating it with the existing engine demanded extensive design modifications to various components, including the oil reservoir, lubrication lines, scavenging pump, and oil ports. These adjustments were essential to achieve the targeted elevation in oil pressures at higher engine RPMs. A relationship between the engine oil pressure and the engine RPM was developed as part of the study.

Comparison of conventional hydrothermal and microwave‐assisted synthesized g‐C3N4/MoS2 nanocomposite coated steel substrate by tribological measurement

AbstractMolybdenum disulfide is an effective solid lubricant, but it suffers from oxidation and moisture absorption issues, resulting in insufficient wear resistance and a shortened lifespan. This study introduces an innovative approach, integrating graphitic carbon nitride with molybdenum disulfide via advanced microwave‐assisted synthesis, offering precise control over synthesis parameters. The research assesses the tribological performance, comparing it with conventional hydrothermal synthesis. The study extensively investigates the morphology, microstructure, and tribology of a g‐C3N4/MoS2 nanocomposite created through novel microwave (g‐C3N4/MoS2‐MW) and hydrothermal techniques (g‐C3N4/MoS2‐HT). MoS2 exhibits a flower‐like structure, while graphitic carbon nitride has a layered structure, as confirmed by elemental analysis via energy‐dispersive X‐ray spectroscopy. X‐ray diffraction identifies g‐C3N4 peaks at 13.0° (100) and 27.5° (002) and hexagonal MoS2 peaks at 14° (002), 32.7° (100), 35.8° (102), and 58.3° (110). The Fourier‐transform infrared spectrum reveals peaks at 1237.4 and 808 cm−1 (aromatic and triazine ring breathing modes in g‐C3N4), 1407.1 and 1638.9 cm−1 (C=N and C−C heterocyclic structures), and 3432 cm−1 (vibrations due to −NH and −OH). The coefficients of friction for microwave‐assisted and traditional hydrothermal synthesized nanocomposites are 0.22 and 0.34, respectively. The wear depths are 98 microns and 141 microns, with a wear scar diameter of 2.87 mm for g‐C3N4/MoS2‐MW and 3.45 mm for g‐C3N4/MoS2‐HT, indicating superior lubrication with the microwave‐assisted coating.

Tool wear analysis in AISI 52100 steel machining with sustainable approach

ABSTRACT Manufacturing industries work towards the development of low toxic, eco-friendly, and sustainable alternatives to save the ecosystem from the harmful effects of traditional cutting fluids used for machining from long decades. The utilization of solid lubricants in machining is an advance alternative aimed at regulating the temperature in the machining zone without causing environmental pollution. The present study illustrates the machining performance of AISI 52100 steel employing solid lubricant-assisted machining (SLAM). The study evaluates the machining performance of SLAM with respect to cutting forces, vibration acceleration, tool wear, chip morphology, and surface roughness against dry machining (DM). The experimental findings indicate that utilizing SLAM leads to a notable decrease in cutting forces, ranging between 45% to 60%, a reduction in vibration acceleration by 14% to 29%, a decrease in tool wear by 11% to 17%, and a substantial improvement in surface finish ranging from 47% to 66% compared to DM.

The role of epoxidation process on improving the oxidative, thermal stability, and tribological performance of mustard oil nano lubricants

This study investigated the potential of inedible mustard oil (MO) (Brassica juncea) as a suitable bio-lubricant for enhanced thermal, oxidative stability, and tribological performance. To improve the MO's oxidative stability, it was subjected to a chemical epoxidation reaction, forming epoxidized mustard oil (EMO). The MO and EMO were evaluated for viscosity, functional groups, wettability, oxidative stability, thermal stability, friction, and wear performance. The epoxidation process resulted in nearly doubling the oxidative stability, as well as improving the thermal stability of the MO. Results showed that the EMO exhibited better lubricating properties than the MO, including lower friction and wear. To further improve the lubrication performance of the EMO, solid lubricant additives (SLAs) were incorporated in various concentrations. These SLAs were graphene nanoplatelets (GNP) and hexagonal boron nitride (hBN). The GNP and hBN nano lubricants reduced friction by 31% and 13% compared to the EMO. The same nano lubricants also lowered wear by 73% and 51% relative to the EMO. The underlying mechanisms behind the improvement in the friction and wear performance were discussed. The EMO can be considered as a suitable base stock for renewable and sustainable energy applications.

TRIBOLOGICAL PROPERTIES OF MATERIALS DESIGNED FORCONTACT WIRE / CURRENT COLLECTOR SLIDER CONTACTS

The article describes basics of production as well as a structure and tribological properties of a compositewith a B101 bronze matrix and glassy carbon acting as a solid lubricant. The composite is intended foruse as a sliding cover of a current collector in a rail transport. It is intended to replace the previously usedcarbon-copper composites, which have insufficient mechanical properties for high-speed rail. The results ofcomparative tribological tests of the matrix and composite material in contact with a traction copper (Cu-ETP)confirmed lower wear of the composite than that of the matrix under friction in air, without current load. Theaddition of 10% of a large-cell glassy carbon foam (90% porosity) reduced the wear of the contact (by 28%and 10%) but did not significantly reduce (by 8.4–5.8%) the friction forces. In the tested contacts abrasive andadhesive wear, caused by the presence of copper, dominated. Self-mated materials tend to develop adhesivebonds. Therefore, the next stage of the research optimising a composite production process, e.g. by using aglassy carbon foam with smaller elementary structure or glassy carbon microparticles will be used.

Correlation of Fabrication Methods and Enhanced Wear Performance in Nanoporous Anodic Aluminum Oxide with Incorporated Molybdenum Disulfide (MoS2) Nanomaterials.

Wear performance is integral to component longevity, minimizing industrial waste and excess energy costs in a wide variety of applications. Anodized aluminum oxide (AAO) has many beneficial properties leading to its wide use across industries as a surface treatment for many aluminum components, but the wear properties of the coating could be improved significantly. Here, we used an electrochemical method to incorporate molybdenum disulfide (MoS2), a nanomaterial used as a dry lubricant, to modify alloys of aluminum during AAO preparation. Using Raman spectroscopy and tribological scratch measurements, we thoroughly characterized the structure and wear behavior of the films. The MoS2 deposition procedure was optimal on aluminum 5052 anodized in higher acid concentrations, with friction coefficients at around 0.05 (~10× better than unmodified AAO). Changing anodization conditions to produce harder films with smaller pores led to worsened wear properties, likely because of lower MoS2 content. Studying a commercial MoS2/AAO film of a different Al alloy (7075) showed that a heat treatment step intended to fully convert all deposited MoSx species to MoS2 can adversely affect wear in some alloys. While Al 6061 and 1100 produced films with worse wear performance compared to Al 5052 or 7075, our results show evidence that acid cleaning after initial anodization likely removes residual alloying elements, affecting MoS2 incorporation. This study demonstrates a nanomaterial modified AAO film with superior wear characteristics to unmodified AAO and relates fabrication procedure, film structure, and practical performance.

Tribological properties of graphene-reinforced polyurethane bearing material

For water-lubricated stern tube bearing in ships, bearing material with low friction can prevent severe damage on the shaft surface when lubrication failure occurs, and hence improve operation reliability of the whole propeller system. In this work, 0.25–5 wt% of solid lubricant graphene platelets were blended with commonly used bearing matrix thermoplastic polyurethane (TPU) via melting injection, and tribological performance of TPU composites were investigated at a set of applied loads and sliding speeds which mimics the actual operating conditions. Graphene inclusion at a low content (< 0.5 wt%) reduced friction and wear compared to neat TPU, while maintaining mechanical properties. Graphene-induced tribofilm is formed and it is believed to offer low shear strength at the sliding surfaces while also regulating the size of wear particles. Since more platelets are exfoliated due to the greater extent of surface damage under high loads, it presents a pressure-dependent anti-friction ability. Higher concentration of graphene led to further friction reduction but deteriorated both the strength and ductility of materials due to the agglomeration. Results from Raman spectroscopies show that graphene-reinforced TPU composites underwent no chemical changes but mechanical deformation during rubbing, and this resulted in wear particles and tribofilm, containing graphene platelets with modified structure.