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The present study aims to investigate the lubrication potential of the combination of Nickel-doped reduced graphene oxide (rGO-Ni; 0.5, 1.0, 1.5 and 2.0 wt pct) and Ag (10 wt pct) in Spark Plasma Sintered (SPS) Ni-alloy based composites by carrying out tests at 5N load and 0.5 m/s from room temperature (RT) to 800 °C for realizing low friction and low wear which is hitherto unexplored. The doping of rGO with Nickel has been done to improve its wettability with the matrix. Field emission scanning electron microscopy, 3D optical profilometry and X-ray diffraction analysis have been carried out on the worn surfaces to reveal the operating mechanisms of wear. The results indicate that the coefficient of friction (CoF) and wear rate decreased with increasing amount of rGO in the composites and the one having 2.0 wt pct rGO-Ni exhibited the lowest CoF (~ 0.42–0.47) and wear rate (~ 2.84–73.49 × 10−5 mm3/Nm) from RT to 600 °C due to cooperative synergy between the solid lubricants. However, both CoF and wear rate increased from 600 to 800 °C for the composites containing Ag and rGO-Ni due to the probable loss of assistive action between rGO and other lubricating species (silver molybdates or oxides). [ABSTRACT FROM AUTHOR]

Yttria-stabilized zirconia and flake graphite c omposite (C/YSZ) coatings were successfully prepared on a TC4 substrate by electrophoretic co-deposition and sintering at 1100 °C using YSZ nanopowder and flake graphite. The effects of the graphite content on the microstructure and friction-wear properties were investigated. The results indicated that flake graphite agglomerated in the C/YSZ coating. The YSZ coating with 0.6wt.% graphite exhibited the highest toughness with the plastic resistance index (H/E) of 0.0172, which was 6.8 % higher than that of the YSZ coating, and effectively inhibited the formation of coating cracks. However, an increase or a decrease in the graphite content led to a decrease in the toughness of the C/YSZ composite coating. The agglomerated graphite in the C/YSZ composite coating acted as a solid lubricant and affected friction and wear properties. The coefficient of friction (COF) of the 0.6C/YSZ sample was 0.45, which was 40 % lower than that of the YSZ sample. The reason for this was that graphite effectively inhibited the falling-off of debris from the coating surface and reduced abrasive wear. However, an excessive amount of graphite, i.e., in case of the 0.8C/YSZ coating, decreased the roughness of the wear surface, leading to a reduction in the H/E and COF by 24.4 % and 29.7 %, respectively. [ABSTRACT FROM AUTHOR]

During shearer operation, the piston rod is susceptible to wear from the invasion of pollutants, thus ruining the sealing ring in the hydraulic cylinder. This work attempts to conduct a systematic investigation of Cu-doped diamond-like carbon (Cu-DLC) film to improve the seal performance. The failure process of the cylinder was analyzed, and relevant parameters were determined. Several Cu-DLC films were deposited on the substrate of the piston rod in a multi-ion beam-assisted system, and their structures and combined tribological performances were investigated. The hardness of the film ranges from 27.6 GPa to 14.8 GPa, and the internal stress ranges from 3500 MPa to 1750 MPa. The steady-state frictional coefficient of the film ranges from 0.04 to 0.15; the wear rate decreases first and then increases, and it reaches its lowest (5.0 × 10−9 mm3/N·m) at 9.2 at.% content. a:C-Cu9.2% film presents optimal combined tribological performances in this experiment. The modification mechanism of Cu-DLC film for the seal performance may come from the synergistic effects of (i) the contact force and friction-heat-induced film graphitization, (ii) Cu doping improves the toughness of the film and acts as a solid lubricant, and (iii) the transfer layer plays a role in self-lubrication. [ABSTRACT FROM AUTHOR]

This paper presents possible modifications to the properties of grey cast iron by laser heat treatment. These modifications are analyzed especially with regard to wear properties as a result of graphite content, which is a well-known solid lubricant. Examples of applications of grey cast iron in cases where good wear resistance is required are presented. Laser hardening from the solid state, laser remelting, and laser alloying are characterized. In this study, changes in the surface layer caused by these treatments were analyzed (especially the influence on the microstructure—including graphite content—and wear properties). It was shown that all of these treatments enable the wear resistance of the surface layer to be enhanced, mostly due to the increase in the hardness and microstructure homogeneity. It was also proven that it is possible to retain the graphite phase (at least partially) in the modified surface layer, which is crucial in the case of friction wear resistance. In particular, laser hardening from the solid state does not eliminate graphite. Laser remelting and alloying cause the dilution of carbon from the graphite phase to the melted metal matrix, but, in the case of nodular cast iron, it is possible that not all of the valuable graphite in the surface layer is lost. [ABSTRACT FROM AUTHOR]

Highlights In the present work, the tribological as well as thermo‐mechanical properties of glass‐filled and carbon‐filled PTFE composites are investigated. Solid lubricants like molybdenum disulfide (MoS2) and graphite are also incorporated in such composites in order to achieve better friction and wear properties. When compared to virgin PTFE, both carbon‐filled PTFE and glass‐filled PTFE composites showed the lowest wear rate. Again, the specific wear rate of glass‐filled PTFE composite was lower as compared to carbon‐filled PTFE composite sample under all test speed. A novel combination of a reinforcing filler (glass fibers) and a solid lubricant (MoS2) incorporated PTFE composite sample [PTFE (90 wt%) + glass fibers (5 wt%) + MoS2(5 wt%)] exhibited the lowest wear rate of the order of 10−9 mm3/Nm which was reduced to around 100‐fold as compared to virgin PTFE under sliding speed of 6.28 m/s. The wear rate was reduced due to the reinforcement of fibers but fibers support the load preferentially, whereas MoS2 and graphite offers a good lubricating effect. The morphological, thermo‐physical and thermo‐mechanical characterization of such composite materials were also carried out using various techniques such as SEM, TGA, DSC, TMA, and DMTA. Such PTFE composites having very good thermo‐mechanical as well as tribological properties have potential to be used as seals, gears, bearings etc. in dynamic aerospace applications. This investigation relates to the PTFE composites to obtain good thermo‐mechanical as well as tribological properties Incorporation of a novel combination of glass fibers and MoS2 exhibited lowest wear rate of the order of 10−9 mm3/Nm The wear property was around 100‐fold lower as compared to virgin PTFE. Such PTFE composites could be used as seals, gears, bearings etc. in dynamic aerospace applications. [ABSTRACT FROM AUTHOR]

As an excellent solid lubricant in vacuum and inert gas environment, molybdenum disulfide (MoS2) is easy to be oxidized in high temperature, which leads to serious deterioration or even failure of lubricating performance. The introduction of doped phase or composite can improve the high temperature lubricating performance of MoS2-based lubricating coating to some extent. In this work, the effect of nano-particles zinc oxide (ZnO) and layered graphene oxide (GO) on the high temperature (400, 450 and 500 °C) tribological properties of MoS2-based composite lubricating coatings were studied. It was found that the tribological performance of MoS2-ZnO composite coating were the best for almost all test conditions, and the average friction coefficient and wear rate were about 0.25 ~ 0.27 and 4 ~ 6 × 10−5 mm3/Nm, respectively. The promising tribological performance of MoS2-ZnO composite coating was attributed to the ZnO that mitigated the oxidation of MoS2, and the formation of ZnS. It is the formed ZnS, nano-ZnO and a small amount of MoS2 that provided synergistic lubrication. However, the introduction of layered GO deteriorated the tribological properties of the MoS2-based composite coating, due to the high-temperature decomposition of GO and the formation of hard abrasive particles. The results can provide reference for the design and preparation of MoS2-based composite lubricating coating. [ABSTRACT FROM AUTHOR]

Polytetrafluoroethylene (PTFE) is widely used in tribological applications. However, it faces challenges due to its high wear rate. Reinforcement of additives in PTFE reduces its wear rate by up to 10,000 times in dry conditions. Infusing metallic filler materials like Al, Cu, and Pb improves PTFE wear performance but increases the coefficient of friction (COF). However, it may not be suitable for corrosive environments due to potential metal reactivity. Reinforcing PTFE composites with carbon‐based materials reduces weight, improves wear properties, and lowers COF. Pre‐treated materials enhance bonding for improved anti‐friction and anti‐wear properties. PTFE and its composites are widely used in journal bearings, bearing pads, and ball bearings due to their excellent low‐speed, low‐load lubrication properties. They outperform Babbitt alloy in bearing pads, except in heat conductivity. PTFE can also be used as a solid lubricant and can be combined with additives for improved performance. Apart from it, achieving an optimal combination of properties for all forms of reinforcement can be challenging due to the difficulty in determining exact values for multiple properties with specific types of reinforcement. This article provides a comprehensive review that delves into the significant findings pertaining to reinforcement and its application in bearing technology. Highlights: Metals and carbon‐based fillers improve tribo‐properties.Polytetrafluoroethylene (PTFE) provides lubrication and thermal stability to the polymeric materials.Estimation of tribo‐thermal properties in combination is a challenge.Testing conditions greatly impact PTFE composites performance.PTFE as a solid lubricant suitable for low‐speed/load applications. [ABSTRACT FROM AUTHOR]

ABSTRACT The study investigated the potential of waste plastic oil (PO) as an alternative to petroleum‐based lubricants, specifically mineral oil. The rheological properties, dispersion stability, friction, and wear performance of PO were examined and compared with mineral oil. Results showed that PO demonstrated similar lubrication performance to mineral oil. To enhance the lubrication performance of PO, the study incorporated various concentrations of nano CuO solid lubricant additives, resulting in the formation of CuO nano lubricants. These lubricants showed an improvement in friction and wear by 20% and 44% compared with PO. Furthermore, the CuO solid lubricant additives were functionalized and incorporated in the same concentrations into PO, resulting in the formation of functionalized nano lubricants, which further lowered the friction and wear by 28% and 91% compared with PO. The novelty of the paper is that a simple chemical functionalization process that not only helped in improving its dispersion stability of additives in the PO, but also enhanced the wear performance. The mechanisms behind the enhancement of friction and wear performance were discussed. Based on these findings, it can be concluded that incorporating functionalized nano additives in PO improve friction and wear performance in mechanical components, promoting wider utilisation of PO. [ABSTRACT FROM AUTHOR]

This study highlights the impact of low amounts of MoS2 quantities on composite performance by examining the effects of ultrasonication exfoliated MoS2 at different loadings (0.1–0.5 wt%) on the mechanical and tribological parameters of epoxy composites. Even at low concentrations, the ultrasonication and exfoliation procedures greatly improve the dispersion of MoS2 in the epoxy matrix, enabling its efficient incorporation into the tribofilm during sliding. Optimum mechanical properties were demonstrated by the MoS2/epoxy composite at 0.3 wt%, including a modulus of elasticity of 0.86 GPa, an ultimate tensile strength of 61.88 MPa, and a hardness of 88.0 Shore D, representing improvements of 61.5%, 35.45%, and 16.21%, respectively. Corresponding tribological tests revealed that high sliding velocity (10 N load, 0.2 m/s) resulted in a 44.07% reduction in the coefficient of friction and an 86.29% reduction in wear rate compared to neat epoxy. The enhanced tribological performance is attributed to the efficient removal and incorporation of MoS2 into the tribofilm, where it acts as a solid lubricant that significantly reduces friction and wear. Even though an ultra-low amount of filler concentration was added to the composite, a unique finding was the high MoS2 content in the tribofilm at higher sliding speeds, enhancing lubrication and wear protection. This study establishes that even ultralow MoS2 content, when uniformly dispersed, can profoundly improve the mechanical and tribological properties of epoxy composites, offering a novel approach to enhancing wear resistance. [ABSTRACT FROM AUTHOR]

Rapid developments in aerospace and nuclear industries pushed forward the search for high-performance self-lubricating materials with low friction and wear characteristics under severe environment. In this paper, we investigated the influence of the Mo element on the tribological performance of nickel alloy matrix composites from room temperature to 800 °C under atmospheric conditions. The results demonstrated that composites exhibited excellent lubricating (with low friction coefficients of 0.19–0.37) and wear resistance properties (with low wear rates of 2.5–28.1 × 10−5 mm3/Nm), especially at a content of elemental Mo of 8 wt. % and 12 wt. %. The presence of soft metal Ag on the sliding surface as solid lubricant resulted in low friction and wear rate in a temperature range from 25 to 400 °C, while at elevated temperatures (600 and 800 °C), the effective lubricant contributed to the formation of a glazed layer rich in NiCr2O4, BaF2/CaF2, and Ag2MoO4. SEM, EDS, and the Raman spectrum indicated that abrasive and fatigue wear were the main wear mechanisms for the studied composites during sliding against the Si3N4 ceramic ball. The obtained results provide an insightful suggestion for future designing and fabricating solid lubricant composites with low friction and wear properties. [ABSTRACT FROM AUTHOR]

Highlights In polymer‐based dental composites, wear is a three‐body wear system mainly abrasive, because of the food particles and wear products suspended in the oral cavity, which are transferred to the microcavities of the surface of the replacements. Due to this fact, the incorporation of nanodiamond as reinforcement in these polymer–matrix composites, which promotes the creation of a solid lubricant tribofilm surface could be advantageous. With the reinforcement of nanodiamonds, BisGMA/TEGDMA‐based composites increase their microhardness by 95%–420%. A maximum hardness exceeding 65 HV is achieved with a reinforcement of 3.2 wt%. The specific wear rate of neat BisGMA/TEGDMA is near 10−4 mm3/Nm and the Archard's coefficient is 2.6 × 105. The incorporation of a content of 1.6 wt% ND is enough to cause a diminution of ~78% in the friction coefficient and a reduction of the specific wear rate and Archard's coefficient of ~50%. Nevertheless, the addition of relatively high contents reduces the effectiveness of photoinitiation and photocuring, which is related to the scattering and absorption of light radiation by ND. This causes a significant decline in elastic properties starting at 50 μm from the surface. Photocuring polymer resin was successfully reinforced with nanodiamonds. Microhardness increases from 95% up to 420%, close to commercial composites. Friction coefficient and wear rate are reduced with 1.6 wt% nanodiamonds. High levels of reinforcement reduce the effectiveness of photocuring. [ABSTRACT FROM AUTHOR]

The present work epitomises extracting the graphite (Gr) solid lubricant from the corn stover. The extracted Gr was incorporated as reinforcement in the A356 alloy (Al-7Si), and the effect of the Gr particles on the mechanical and tribological properties was investigated. In spite of this, the input process parameters for the dry sliding wear test at room temperature against the EN31 steel disc were optimised through ANOVA analysis. The fabricated A359—X wt% (X = 0, 2.5, 5, 7.5) composite through bottom pouring stir casting techniques was analysed microstructurally by using XRD and FESEM analysis. The micro Brinell hardness and tensile strength were investigated per ASTME10 and ASTME8M standards. A wear test was performed for the composite pins against the EN31 steel disc according to ASTM G99 specifications. The XRD analysis results depict the presence of carbon (C), aluminium (Al), and silicon (Si) in all the wt% of the Gr reinforcement. However, along with the elements, the Al2Mg peak was confirmed for the A356—7.5 wt% Gr composite and the corresponding cluster element was confirmed in FESEM analysis. The maximum micro Brinell hardness of 92 BHN and U.T.S of 123 MPa and % elongation of 7.11 was attained at 5 wt% Gr reinforcement due to uniform Gr dispersion in the A356 alloy. Based on the ANOVA analysis, the optimal process parameters were obtained at 20 N applied load, 1 m/s sliding velocity, and 1000 m sliding distance for the optimal wear rate of 0.0052386 g/km and 0.364 COF. [ABSTRACT FROM AUTHOR]

Wind power gears will be excessively worn due to lubrication failure during operation. Herein, the tribological properties of rubbing pairs are improved by filling solid lubricants into surface texture. In texture design, three types of topological textures (Circle (C), Hexagon (H) and Circle/Hexagon (CH)) were obtained by cell topology optimization, and then three cases with 20%, 30%, and 40% density were designed for each texture. Next, SnAgCu and TiC were deposited in texture of AISI 4140 steel (AS) to obtain 9 kinds of self-lubricating surfaces. Among them, AS with 30% CH density (AS-CH30) exhibits excellent mechanical and tribological properties. Compared with AS-C and AS-H, the maximum equivalent stress of AS-CH was decreased by 10.86% and 5.37%, respectively. Friction coefficient and wear rate of AS-CH30 were 79.68% and 78% lower than those of AS. The excellent tribological performances of AS-CH30 can be attributed to the synergistic effect of topological surface and solid lubricants. Topological surface can not only reduce fluctuation of equivalent stress, but also promote the stored lubricants to be easily transferred at the contact interface to form a 200 nm lubricating film containing solid lubricants (mainly), oxides and wear debris. [ABSTRACT FROM AUTHOR]

This investigation delves into the behavior of copper oxide (CuO) as a solid lubricant inside zirconia toughened alumina (ZTA) ceramic composites. The investigation starts with the preparation of ZTA through co-precipitation followed by powder metallurgy to develop CuO (1.5 wt. %)/ZTA composites. In all cases, hot isotactic pressing is applied for densification. The fully densified samples are thoroughly mirror-polished to investigate the mechanical and tribological properties. A 1.8% reduction in micro-hardness and 6% improvement in fracture toughness are observed with incorporation of CuO into the ZTA matrices. The analysis reveals that the presence of ionic copper at the grain boundary leads to the formation of copper-rich phases, causing a decrease in hardness. However, the softer CuO particles contribute to crack bridging and crack deflection, enhancing fracture toughness. Subsequent investigation into the tribological properties highlights the positive influence of the softer CuO phases acting as a secondary component within the ZTA matrix. A significant enhancement of 39.34% in the Coefficient of Friction (COF) is achieved by incorporating CuO into the ZTA matrix. This improvement can be attributed to the formation of a patchy layer through smearing and squeezing actions on wear debris during sliding. The uniform patchy layer results in smoother and more polished surfaces, leading to an improvement in both the COF and specific wear rate. Further wear analysis reveals various phenomena contributing to surface wear, including pullout of grain particles, micro-fracture, high abrasions, and laminar removal of grains. Overall, the introduction of CuO proves to be beneficial, showcasing improved mechanical and tribological properties in the developed composites, with application in dies, inserts, sparkplugs, etc. [ABSTRACT FROM AUTHOR]

Herein, MoS2 solid lubricant is introduced in the form of Mo‐coated MoS2 powder, to enhance the antifriction properties of sintered ferrous antifriction materials (FAMs). The microstructure, phase composition, and tribological properties of Fe–15Cu–0.8C–3.75 (Mo‐coated MoS2) (MC1) are investigated and compared with Fe–15Cu–0.8C (M0) samples, with a discussion on the wear mechanism at a wide temperature range of room temperature to 600 °C. The study reveals that the addition of Mo‐coated MoS2 powders effectively prevents the decomposition of MoS2 during sintering, enhances the bonding strength between MoS2 and the substrate, and significantly improves the hardness of the sintered Fe–15Cu–0.8C samples. In comparison with the sintered Fe–15Cu–0.8C samples, the sintered Fe–15Cu–0.8C–3.75 (Mo‐coated MoS2) samples exhibit good antifriction properties with a frictional coefficient of 0.23 at 600 °C and a wear rate of 6.3 × 10−7mm3 N m−1 at 300 °C. Introducing Mo‐coated MoS2 significantly reduces the average friction coefficient and wear rate of the sintered FAMs at elevated temperatures, attributed to the formation of FeMoO4. The antifriction performance of MC1 samples notably decreases with increasing test temperatures. The main wear mechanism is oxidative wear above 300 °C. [ABSTRACT FROM AUTHOR]

A solid-liquid composite lubrication coating capable of controlling friction and wear has received widespread attention among researchers. Here, a novel self-lubricating ceramic coating was created through a combination of thermal spraying, hydrothermal reactions, and vacuum impregnation. Its mechanical properties, tribological performance, and self-lubrication mechanism were thoroughly analyzed. The results indicate that the thermally sprayed ceramic coating contained carbon spheres and perfluoropolyether. As a result of the in-situ synthesis of carbon spheres, the coating exhibited enhanced mechanical properties. Compared to the single solid lubricant coating, the solid-liquid composite coating decreased the coefficient of friction by 46.7% to 0.112 and decreased the wear rate from 1.25 × 10−6 mm3/m N to 3.70 × 10−7 mm3/m N. It is proposed in this work that solid-liquid composite coatings can be prepared by utilizing the defects such as pores and microcracks inherent in thermal spray coatings for introducing solid lubricating phases and liquid lubricating phases. This strategy addresses the issue of degradation of the mechanical properties of conventional ceramic-based self-lubricating coatings due to their tribological design. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Polyimide (PI) has good mechanical properties and thermal stability, while high coefficient (COF) and wear rate limit its wide application. In order to endow PI with better friction and wear resistance, Mo2Ti2C3 MXene was used as solid lubricant to prepare Mo2Ti2C3/PI nanocomposites with different content of Mo2Ti2C3. The effect of the amount of Mo2Ti2C3 on the tribological behavior of PI was explored and the tribological mechanism was also analyzed Tribological tests showed that at 1.2 wt% of Mo2Ti2C3 addition, the composite material demonstrated superior friction and wear resistance, exhibiting a 19.9% decrease in the COF and a 79.7% decrease in the wear rate compared to single PI due to the good self‐lubricating properties of Mo2Ti2C3 MXene. Moreover, Mo2Ti2C3 can also effectively assist PI to form sleek transfer films without interruption or gaps on the steel balls, resulting in a reduced friction COF and wear rate of the material. This work demonstrates that Mo2Ti2C3 MXene is an aussichtsreich additive for polymers to improve the tribological properties and broadens the applications of Mo2Ti2C3/PI composites in friction material area. Highlights: Mo2Ti2C3 significantly improves the tribological performance of polyimide.The thermal properties of Mo2Ti2C3/polyimide are enhanced by the introduction of Mo2Ti2C3.The minimum coefficient of Mo2Ti2C3/PI composites was only 0.246 at the 1.2 wt% content of Mo2Ti2C3.The wear rate of Mo2Ti2C3/PI composites was decreased by 79.7% at the 1.2 wt% addition of Mo2Ti2C3.Mo2Ti2C3 promotes the establishment of tribo‐film to protect the Mo2Ti2C3/PI composites from friction. [ABSTRACT FROM AUTHOR]

In this present investigation, novel hybrid magnesium composites were synthesized by the inclusion of self-lubricating (BN/MoS 2) and ceramic (ZrO 2) particulates with the help of the powder metallurgy technique. ZE41 magnesium (Mg–4Zn-1RE-0.7Zr) was applied for a broad range of components, including the gearbox casing, the framework of the door, and transmission in aircraft like the Sikorsky UH-60 and the Boeing 727. Apart from its structural application, its usage was limited because of its deficient wear and mechanical properties. This research focuses on enhancing the potential applications of the ZE41 magnesium alloy by improving its mechanical and tribological characteristics. The design of the experiment scheme was applied to explore the effect of individual reinforcements and their synergistic effects on various properties of prepared composites. Microstructural inspection was employed to inspect the morphological characteristics of prepared specimens through scanning electron microscope (SEM) and Energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction analysis (XRD). By analysing SEM, EDS, and X-ray diffraction patterns, the microstructural evaluation reveals uniform phase dispersion and the existence of reinforcements with some minor defects. As a result of the inclusion of reinforcements in composites, the hardness of the reinforced specimen improved to 39.65%, while the wear rate of the reinforced specimen decreased to 40.90% compared with monolithic alloy. A multi-objective grey relational analysis (GRA) optimization method was used to perform a detailed tribological analysis on Specimen G (ZE41 mg + 3% ZrO 2 + 3% MoS 2). According to the results of GRA, the optimized rate of wear and frictional coefficient were achieved on sliding velocity (4 ms−1), sliding distance (2000 m), and load (10 N). The worn surface micrograph reveals that the reinforced composite underwent abrasion and delamination wear, while the unreinforced alloy experienced plastic deformation. [ABSTRACT FROM AUTHOR]

(AlCrNbSiTiMoW)N high-entropy alloy (HEA) coatings with various nitrogen-to-argon gas flow ratios (RN = N2/Ar) in the range of RN0 to RN1.25 were deposited on WC and Si substrates using a radio-frequency magnetron sputtering system. The as-sputtered coatings were then annealed at 950 °C for 1 hour in a vacuum. The effects of the nitrogen flow ratio on the composition, microstructure, mechanical properties, tribological properties, and corrosion resistance of the various coatings were systematically explored. The as-deposited RN0, RN1.0, and RN1.25 coatings exhibited FCC structures, while the RN0.5 and RN0.75 coatings had amorphous structures. Following the annealing process, all of the coatings showed an FCC structure. The annealing process had no significant effect on the hardness of the coatings. Thus, they were inferred to have excellent thermal stability. Among the coatings, the HRN1.0 coating showed the highest hardness (37.4 GPa), adhesion strength, and tribological properties, with a wear depth and wear rate of 0.07 μm and 0.41 × 10-6 mm3/Nm, respectively. The wear depth and wear rate of the HWC substrate were 0.28 μm and 1.67 × 10-6 mm3/Nm, respectively. Thus, compared with the HWC substrate, the HRN1.0 coating improved the wear depth and wear rate by 75.0 and 75.4%, respectively. The tribological performance of the annealed HRN1.0 coating was enhanced as a result of the formation of a greater amount of MoO3 and WO3 solid lubricant phases and a higher hardness and hardness-to-elastic modulus ratio. The RN1.0 coating exhibited the best corrosion resistance among all the coatings. The corrosion current density of the RN1.0 coating was 1.8 × 10-7 A/cm2, while that of the WC substrate was 2.2 × 10-7 A/cm2. In other words, the RN1.0 coating improved the corrosion resistance by 18.1%. However, the corrosion resistance reduced following the annealing process due to a greater surface roughness. [ABSTRACT FROM AUTHOR]

Present investigation attempted to explore the tribological properties of atmospheric plasma sprayed coatings. In order to assess the role of solid lubricants, different weight percentages (5, 10, and 15 wt.%) of silver (Ag) were taken, whilst MoS2 concentration remained fixed. Dry sliding wear tests were conducted for different specimens namely, Ni-Al-MoS2-5 wt.% Ag (NA5), Ni-Al-MoS2-10 wt.% Ag (NA10) and Ni-Al-MoS2-15 wt.% Ag (NA15) at different loads of 4, 9, 14 & 19 N, and slid speed of 0.3 m/s under room temperature (RT) conditions. It was observed that coefficient of friction (COF) and wear rate of specimens decreased as the load increased till 14 N, and beyond that increasing trend was noticed. However, the NA10 specimen has revealed the best tribological properties in terms of minimum COF (0.48) and wear rate (4.7 × 10−5 mm3/Nm) at 14 N and 0.3 m/s. The synergy of Ag and MoS2 on the frictional properties of specimens have been well explained with the help of worn surface morphologies and some useful conclusions were made. [ABSTRACT FROM AUTHOR]

Lighter and more powerful next generation vehicles and other rotary machinery demand bearings to operate in harsher conditions for higher efficiency, and the continuous development of advanced low-wear and friction materials is thus becoming even more important to meet these requirements. New aluminium composites reinforced with high performance lubricate phases such as graphene nanoplatelets (GNPs) are very promising and have been vigorously investigated. By maintaining a low coefficient of friction (COF) and offering great strength against wear due to their self-lubricating capability, the solid lubricant like GNPs protect the bearing surface from wear damage and prevent change in metallurgical properties during temperature fluctuations. This paper first studies the high-temperature tribological performance of aluminium matrix composites reinforced with GNP, consolidated via powder metallurgy, then elucidates their tribological mechanism. We report that the best tribological performance is achieved by the composite containing 2.0 wt% GNP, with an extraordinarily low COF of 0.09 and a specific wear rate of 3.5×10−2 mm3·N−1·m−1, which represent 75% and 40% reduction respectively, against the plain aluminium consolidated under identical conditions. The in-track and out-of-track Raman analysis have confirmed the role of GNPs in creating a tribofilm on the counterpart surface which contributed to the excellent performance. [ABSTRACT FROM AUTHOR]

This study introduces a low-friction composite based on PEEK to improve its friction and wear properties. The composite incorporates PTFE as a solid lubricant and utilizes PPTA as a reinforcing material within the PEEK matrix. These components were prepared utilizing a compression molding method, followed by a series of exploratory experiments to identify the optimal preparation conditions for PEEK. This research assesses how the PTFE/PPTA/PEEK composites perform in terms of friction and wear under dry and oil-lubricated conditions. By examining wear tracks using scanning electron microscopy and white light interference microscopy, this study aims to uncover the wear mechanisms of PEEK and its composites under different lubrication scenarios. Results show that the main wear mechanisms for the PTFE/PPTA/PEEK composites and bearing steel are ploughing and adhesive wear. The presence of PPTA helps reduce wear by leveraging its strong fibers and thermal stability, while the coefficient of friction decreases as PTFE creates a smooth, solid lubricating film on the surface. Notably, PEEK composites containing 25 wt% PTFE and 6 wt% PPTA demonstrate the lowest wear rates and reduced coefficient of friction in both dry and oil-lubricated conditions. [ABSTRACT FROM AUTHOR]

This research aims to create a composite that is inexpensive and can be used in mechanical applications. The main aim is to improve the tribological performance of PA66 by reinforcements. Two fillers were utilised in the experimentation because MoS2 is a remarkably effective solid lubricant in dry conditions, but the results are not the same in high humidity. H-BN is utilised here to get the benefit in both dry and humid environments and to reduce the negative impact of humidity on the tribological performance of composite. Tensile and hardness tests were performed to identify the mechanical properties, while tribological tests on pin-on-disc were performed to analyse the COF and wear rates of materials. SEM, XRD, and DSC characterisations were utilised to analyse the tensile fracture mechanism, crystallinity, and glass-transition temperature of materials, respectively. The result shows that the strength and hardness of the composite increased in a reasonable amount compared to virgin PA66. Wear and COF tests were conducted with three different parameters, and the results showed an improvement in wear rates of composites compared to virgin PA66. [ABSTRACT FROM AUTHOR]

This study explored the effect of pre-corrosion damage on the tribology behavior of the austenitized and the different tempered conditions of 13 wt.% Cr martensitic stainless steel under dry sliding conditions using a "ball on plate" configuration. Corrosion immersion experiments were performed in 5 wt.% HNO3 solution at room temperature for 30 min. The austenitized and the tempered at 300 °C (T300) specimens displayed the attack along the prior austenitic grain boundaries, whereas the specimens tempered at 550 (T550) and 700 °C (T700) showed intergranular plus interlath corrosion and uniform corrosion, respectively. Subjecting this corrosion-damaged specimens to dry sliding revealed non-monotonic friction and wear behavior with tempering temperature. The microstructure and the type of corrosion attack together determined the overall wear performance of the tempered conditions. The specific wear rate (k) decreased in the order kT700 > kT550 > kT300 ~ kaustenitized. The k value of the austenitized and the T300 specimens (~ 32 − 35 × 10−6 mm3/Nm) is observed to be 12 and 15 times lower than the k value of T550 (~ 408 × 10−6 mm3/Nm) and T700 (~ 495 × 10−6 mm3/Nm) specimens, respectively. The reason for the lower k value is due to the continuous, thick (~ 4 μm thickness) Cr-rich tribo-film that formed on the wear track and acted as solid lubricant. The T550 and T700 specimens had a discontinuous Fe-rich tribo-film on the wear tracks; therefore, rubbing in the presence of harder and loose Fe-rich oxides particles led to severe adhesion plus galling in T550 and smearing plus plastic deformation in T700 specimens. It was also found that the wear rate and surface damage are reduced for pre-corroded austenitized and T300 specimens compared to the respective unattacked pristine specimens; however, the opposite effect was observed in T550 and T700 specimens. [ABSTRACT FROM AUTHOR]

Self-replenishable ways of applying solid lubrication in tribological systems are limited to the use of sintered self-lubricating composites. These are obtained by mixing solid lubricants with metallic powders or by the in situ precipitation of the lubricating phase. Both techniques can produce self-lubricating composites able to promote low friction coefficients in dry sliding conditions. However, the combination of solid lubricant and matrix is limited by the thermodynamic interactions during sintering. Filling the pores of sintered parts with solid lubricants by vacuum impregnation is a versatile way to promote solid lubrication, allowing any combination of solid lubricant and matrix to be used, avoiding deleterious phases and other sintering problems typical in sintered self-lubricating composites. In this work, low alloy sintered steel was produced by mixing Astaloy CRL powders with 0.6 wt% C, the sintered specimens were impregnated with graphite (1.10 μm), and the durability and wear rates of the resulting composites were studied using ball-on-flat reciprocating tests. The results show that the impregnation technique is able to fill the surface pores with graphite, producing friction coefficients down to 0.06 in dry-sliding conditions and wear rates ranging from 10−4 to 10−7 (mm3/N-m). The main wear mechanism of the impregnated specimens was plastic deformation on the surface, which causes sealing of pores, while the wear of the counter-bodies was mainly abrasive. The durability of the lubricity regime is directly proportional to the amount of lubricant available as pores get sealed by the sliding action of the counter-body, so is proportional to the porosity. [ABSTRACT FROM AUTHOR]

In recent years, there has been significant attention on the application potential of medium and high-temperature self-lubricating composites as sliding parts in extreme environments. This study examines the effects of different Mo and Ag content on the composition and wear resistance of Ni60-cladded coatings at room temperature, 300 °C and 600 °C, while also analyzing their wear mechanism by studying the tribofilm. The results indicate that with an appropriate weight addition of Mo and Ag, one typical lubricant called Ag2MoO4 emerges. At room temperature, the cladding layer containing 5 wt.% Mo and 5 wt.% Ag exhibits a wear rate of 2.08 × 10−6 mm3/Nm, and an average coefficient of friction (COF) of 0.3410. These two are 85% and 11% lower than those of the Ni60 cladding layer, respectively. At 300 °C, MoO3 and Cr2MoO6 act as solid lubricants. Furthermore, at 600 °C, a MoSi2 and SiO2 film forms on the worn surface to prevent further oxidation of MoSi2 and enhance oxidation resistance. The main wear mechanism is adhesion wear. Under higher temperatures, the newly formed Ag2MoO4 in the composite cladding layer adopts a layered cubic spinel structure where low-energy Ag-O bonds preferentially break during friction processes, demonstrating excellent lubrication performance. [ABSTRACT FROM AUTHOR]

A series of polyimide (PI)/V2CTx MXene composites was synthesized via polyamide acids (PAA) and two‐dimensional (2D) V2CTx MXene obtained by etching precursor V2AlC. PI/V2CTx MXene composites with different mass ratios were obtained by blending and heating with PAA. The results showed that V2CTx MXene has excellent dispersion in PI. In particular, V2CTx MXene exhibited excellent friction reduction and anti‐wear properties as a solid lubricant additive, and the wear rate (WR) was reduced by 43.2% by incorporating only 0.8 wt% of V2CTx MXene in the pristine PI and 71.9% by incorporating 1.2 wt%. Scanning electron microscopy (SEM) and x‐ray photoelectron spectroscopy (XPS) analyses showed that the continuous transfer film consisting of a high proportion of tribo‐chemical products formed on the contact surface is significant to improve the lubrication performances of the PI composites. This work broadens the application of MXene in the field of tribology and contributes to energy conservation and sustainable development of human society. Highlights: The tribological properties could be tuned by changing the ratio of PI to V2CTx MXene.The WR of PI composites was reduced by 71.9% with incorporating 1.2 wt% of V2CTx MXene.The formation of transfer films on the contact surface is significant for improving anti‐wear of PI. [ABSTRACT FROM AUTHOR]

Polyamide polymers are widely used in tribological areas in a wide range of industries. The purpose of this study is to extend the tribological life of this material. For this purpose, composite materials were produced by adding solid lubricants such as graphite and wax to the polyamide 6 (PA6) matrix at different rates, and the synergistic effect of these composites on tribological behavior was investigated. Tribological experiments were carried out under dry sliding conditions and on themselves. The polyamide 6/graphite/wax composites were first produced in the form of granules in a twin‐screw extruder, and then test samples were molded using the injection molding technique. Wear tests were performed using a pin‐on‐disc wear device. Tribological tests were carried out at a sliding speed of 0.5 m s−1 and under loads ranging from 10 N to 250 N. Following the experiments, the friction coefficient, specific wear rate, and surface wear were determined under the condition of the materials working on each other. The results showed that the lowest specific wear rate and friction coefficient were obtained for the polyamide 6 composites containing 6 % wax and 15 % glass fiber working on each other. [ABSTRACT FROM AUTHOR]

It is a substantial challenge to obtain single-phase ceramics with self-lubricating properties. Most conventional lubricated ceramics benefit from the addition of solid lubricants, which largely deteriorate theirs mechanical properties. Here, we report a single-phase (HfMoNbTaTi)C system high-entropy ceramic with self-lubricity inspired by the novel high-entropy design concept and regulation of high-temperature lubrication components (with different Mo contents). The formation mechanism of the single-phase structure is ascribed to the increasing of carbon vacancies with the increasing of Mo content. Meanwhile, the tribological performances are greatly enhanced at high temperature. Especially for (Hf 0.149 Mo 0.404 Nb 0.149 Ta 0.149 Ti 0.149)C 0.745 ceramic (with 20 wt% Mo) against Al 2 O 3 ball at 900 °C, the average friction coefficient is as low as 0.6, and its wear rate is reduced an order of magnitude. The results show that the self-lubrication mechanisms are tribo-chemical reactions to generate lubricating tribo-films. • Single-phase (Hf-Mo-Nb-Ta-Ti)C system ceramic with self-lubricity was prepared. • The formation mechanism of the single-phase structure was investigated. • Regulation of Mo content has a significant effect on tribological properties. • Tribo-films with lubricity have a vital impact on friction reduction and anti-wear. [ABSTRACT FROM AUTHOR]

The synergistic effects of carbon fiber (CF) and polytetrafluoroethylene (PTFE) on the friction and wear behavior of polyarylene ether nitrile (PEN) under dry lubrication condition were studied. According to the scanning electron microscopy (SEM) on the composites' surface after wear, the wear mechanism of the composites under dry sliding condition was analyzed. The research results show that the addition of solid lubricants PTFE and carbon fibers to PEN helps to enhance the properties of friction and wear. The specific wear rate is decreased to 5.7 × 10−7 mm3/N m at a PTFE composition of 5 wt%, which is optimized by 33.4% more than PEN/CF composites. In addition, wear mechanisms are mainly abrasive wear, accompanied by adhesive wear and plowing of the friction ring. [ABSTRACT FROM AUTHOR]

This research investigates the tribological characteristics and sustainability of WS2 deposited Al 6061-T6 surface under dry sliding conditions and optimizes the wear parameters to enhance the tribological behaviour and discuss its sustainability. The experiment used the Box–Behnken design, which examines the effective interaction between dry sliding parameters and specific wear rate (SWR) and friction coefficient (COF). By varying the load (L), sliding velocity (V) and distance (D), the wear behaviour of WS2 deposition against EN 31 steel was examined through the pin-on-disc experiment. Grooving, debris formation, polishing, tribolayer, ploughing, transfer material, smearing, delamination and pitting are observed through scanning electron microscope (SEM) analysis. For optimum conditions, SEM with energy dispersive spectroscopy was utilized to characterize the worn surface, and X-Ray diffraction (XRD) patterns confirmed the phases of W, WO3, WS2, Al, AlO, Al2S3 and Al4C3. [ABSTRACT FROM AUTHOR]

Purpose: The CL60 steel wheels of subway vehicles operating on specific lines require frequent refurbishment due to rapid wear and tear. Considering this issue, MoS2-based and graphite-based solid lubricants are used to reduce the wear rate of subway wheels and extend their service life. Design/methodology/approach: Under laboratory conditions, the effect of MoS2-based and graphite-based solid lubricants on the friction and wear performance of subway wheels and rails was evaluated using a modified GPM-60 wear testing machine. Findings: Under laboratory conditions, MoS2-based solid lubricants have the best effect in reducing wheel/rail wear, compared to the control group without lubrication, at 2 × 105 revolutions, the total wheel-rail wear decreased by 95.07%. However, when three types of solid lubricants are used separately, the hardness evolution of the wheel-rail contact surface exhibits different characteristics. Practical implications: The research results provide important support for improving the lifespan of wheel and rail, extending the service cycle of wheel and rail, reducing the operating costs of subway systems, improving the safety of subway systems and providing wear reduction maintenance for other high wear mechanical components. Originality/value: The experiment was conducted through the design and modification of a GPM-60 testing machine for wear testing. The experiment simulated the wheel-rail contact situation under actual subway operation and evaluated the effects of three different solid lubricants, MoS2-based and graphite-based, on the wear performance and surface hardening evolution of subway wheel-rail. [ABSTRACT FROM AUTHOR]

Dry, MQL and cryogenic machining have largely been superseded by the use of solid lubricants that possess a lamellar crystal structure with low shear strength, which reduces friction and prevents surface damage. Also, it is perceived that conventional liquid-based lubricants can be omitted. The present paper is intended to provide an experimental investigation of the impact of hexagonally structured molybdenum disulfide (H-MoS2) solid lubricant on Inconel 718 in terms of temperature, surface roughness, chip thickness, chip morphology, tool wear and micro-hardness. Dry and MQSL were selected for evaluating the performance of the hexagonally structured molybdenum disulfide (H-MoS2). Drilling experiments were carried out using TiN-coated solid carbide drills at a cutting speed of 40–60 m/min and feed rate of 0.08—0.1 mm/rev. The results revealed that H-MoS2 showed comparable performance under dry, MQSL conditions. The H-MoS2 cooling reduces the average roughness by about 59–67% over dry and 29–42% over MQSL conditions. Flank tool wear was reduced by 35–53% and 12–34% in comparison with dry, MQSL cooling, due to H-MoS2 wan der Waal forces experienced between the cutting interfaces. H-MoS2 increased the micro-hardness by 20% over dry machining, and 12% over MQSL. H-MoS2 outperformed MQSL and dry conditions in terms of chip morphology, and micro-hardness. [ABSTRACT FROM AUTHOR]

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Solid lubricant materials could be used in various extreme conditions owing to the excellent anti‐friction and ‐wear with the low friction coefficient and wear rate. Polyurethane (PU)‐based solid lubricants as one of the widely utilized composite materials had been well‐known by researchers all over the world. PU‐based composite lubricants were commonly segmented into single‐phase lubricants and multi‐phase lubricants via inorganic or organic lubricant additives. What is more, the modified PU by solid lubricants would endow higher tribological performances than that of single‐phase PU‐based lubricants. Based on the multi‐component synergy, the multi‐phase lubricants could significantly improve the PU matrix's lubrication and wear resistance and enhance the comprehensive performance such as corrosion resistance. This paper mainly discussed and summarized the recent development in tribological performances of PU‐based composite lubricants, and explored their prospective research directions. [ABSTRACT FROM AUTHOR]

Electrically as well as thermally conductive lubricants have drawn considerable attention and are an emerging research topic because they have unique advantages and advanced lubrication performance over traditional lubricants such as corrosion protection and efficient heat dissipation. For instance, some components of electric vehicles (EVs) such as bearings, seals, pads and gears require conductive lubricants to avoid premature failure and electromagnetic interference (EMI) problems due to induced shaft voltages and currents. This review provides a comprehensive overview of the recent developments in conductive lubricants. The review focuses on the important aspects to enhance the thermal and electrical conductivities as well as the tribological behavior (COF, and wear rate) of conductive solid, semisolid, and liquid lubricants. The lubricants that are electrically and thermally conductive with superior tribological performances have been identified through extensive literature review and presented in tabular form. This review summarizes the effect of various additives used to improve the conductive properties of the lubricants, such as polyalphaolefin oil, hydraulic oil, paraffin oil, and mineral oil. Furthermore, the review discusses the lubricating mechanism of conductive solid and liquid lubricants to facilitate a deeper understanding. Finally, the future perspectives and the research directions for conductive lubricants are also addressed. [ABSTRACT FROM AUTHOR]

Introducing self-lubricating composites in various industries is a method for reducing the use of externally harmful petroleum-based lubricants in sliding contacts as well as reducing energy dissipation in industries, both of which are environmentally conscious aspects. An attempt has been made to fabricate the self-lubricating composites of aluminum (Al) matrix and solid lubricant molybdenum disulfide (MoS2) of different weight fractions (1.5 wt.%, 3.5 wt.%, 5.5 wt.%, 7.5 wt.% and 9.5 wt.%) as reinforcement using stir-casting. Mechanical properties such as hardness, tensile behavior and fracture response have been evaluated and rationalized regarding clustering of reinforced particles, generation of porosity and interfacial bonding strength. The tribological response was determined based on evaluation of dry sliding wear rate, coefficient of friction and mass abrasion rate at constant applied load (20 N) and sliding velocity (2.5 m/s). The SEM micrographs revealed the degree of wear response evaluated in terms of delamination, formation of groves and presence of metal debris at the worn pin surface for varying wt.% of fabricated Al/MoS2. The 5.5 wt.% MoS2 reinforced composite exhibited the optimized outcomes in terms of strength and wear properties. MoS2 could be considered a competent solid lubricant as well as a reinforcing particle as obtained through the present investigations. [ABSTRACT FROM AUTHOR]

The aim of this research was to study the tribological behavior and properties of antifriction polyetheretherketone (PEEK) based composites loaded with solid lubricant particles as well as carbon fibers under both dry friction and water lubrication conditions. The investigated tribological properties varied due to a change in the pattern of the formation and adherence of a transfer film (TF) on the steel counterpart surface. Under the water lubrication conditions, a wear rate increased for the composite loaded with both polytetrafluoroethylene (PTFE) and carbon fibers (CF) due to the suppression of the adherence of a transfer film on the steel counterpart by protruding carbon fibers above the sliding surface, followed by abrasive damage to both rubbed bodies. Therefore, they were not recommended for use in water lubrication bearings. Another composite, loaded with both PTFE and molybdenum disulfide (MoS2) was suggested for using in such bearings according to the 'ball-on-disk' scheme under mixed dry friction/water lubrication conditions. [ABSTRACT FROM AUTHOR]

In this study, dry sliding wear behaviour of a copper alloyed austempered ductile iron (ADI) consisting of very fine ausferrite, small high carbon austenite blocks, was investigated against 100Cr6 ball using ball-on-disc tribometer. Tribotests were conducted at different loads of 10, 30, 50, and 100 N and speeds between 0.39 to 0.79 m/s. Worn-out surfaces and wear debris revealed tribe-oxidation and abrasive wear as the primary mechanism for material removal at lower loads and low speed (0.39 m/s). With an increase in load and speed, fragmented graphite nodules acted as solid lubricants. Additionally, partial transfer of tribo-oxide onto the counter-body ball, and plastic deformation and strain hardening of ADI matrix lowered the friction coefficient and wear rate at higher loads and speed, to nearly 1/3 and 1/10 as compared with those at lower loads and speed. The superior wear resistance of present ADI is worthy of consideration for transmission parts. [ABSTRACT FROM AUTHOR]

Plastic recycling in the automotive industry is a priority. In this study, the effect of adding recycled polyvinyl butyral (rPVB) from automotive windshields on the coefficient of friction (CoF) and specific wear rate (k) of a glass–fiber reinforced polyamide (PAGF) is investigated. It was found that, at 15 and 20 wt.% of rPVB, it acts as a solid lubricant, reducing CoF and k up to 27% and 70%, respectively. Microscopical analysis of the wear tracks showed that rPVB spreads over the worn tracks, forming a lubricant layer, which protects the fibers from damage. However, at lower rPVB content, fiber damage cannot be prevented as the protective lubricant layer is not formed. [ABSTRACT FROM AUTHOR]

Dimple texturing is the emerging practice to minimize friction and wear in frictional contact pairs. The tribological properties of the frictional contact pairs can be enhanced by optimizing the dimple-texture shape, dimple pitch and area density ratio. In this investigation, the frictional properties of dimple-textured tungsten carbide discs with hardened AISI H-13 steel pins was investigated using a pin on disc wear tester. Laser marking technology was employed to fabricate the polar arrays of honeycomb texture (HT) and spherical dimple-textures (ST) with 25% and 35% area density ratios. The sliding wear test was conducted for the dry and MoS2 (molybdenum disulphide) solid lubricant conditions to investigate the effect of coefficient of friction and wear rate of dimple structures with variation in disc rotational speeds in the range of 1000 rpm, 1250 rpm and 1500 rpm. The results indicate that, ST surface with MoS2 coating with 35% of area density at 1500 rpm exhibited best results in comparison to nontextured (NT) and HT with and without aid of MoS2 coating. The friction coefficient and wear rate for ST surface with MoS2 coating were 13.5% and 24% lower in comparison with HT at operating conditions of 35% of area density at 1500 rpm, respectively. Similarly, in comparison with NT the ST surface with an operating condition of 35% of area density at 1500 rpm exhibited 39.1% and 48.2% reduction in friction coefficient and wear rate, respectively. [ABSTRACT FROM AUTHOR]

Aluminium metal matrix composites (AMMC) are now a group of new advanced materials preferred for its lightweight, high strength, low coefficient of thermal expansion, and high wear resistance properties. Although many processes are used for the development of particulate reinforced aluminium composites, stir casting is proved to be one of the prominent and economical routes for the processing of metal matrix composites. The present work is focused on the effect of hybrid ceramic particle reinforcements on the mechanical and tribological properties of AMMC. Three different volume fractions of Al2O3 particulates namely 2, 4 and 6 weight percent along with 4 common weight percent of SiC reinforcements in all the samples in the average particles size range of 35–40µm were added to the liquid melt of AA7075 and stirred at 500 rpm for 15min. The micro-structures of the composites were examined using a metallurgical and scanning electron microscope. The reinforcements are found to be distributed uniformly within the matrix. The effects of hybrid reinforcement on mechanical properties were investigated. The wear rate of composite material decreased significantly with increase in reinforcements. The mechanical properties increased significantly due to the high load bearing capacity of the SiC and Al2O3 particulates. The coefficient of friction was found to reduce due to the increased weight percent of Al2O3 particles, which acted as the solid lubricants during sliding. [ABSTRACT FROM AUTHOR]

The dispersion stability of carbon-based solid lubricants/lubricating oils remains a challenge to overcome. Recently, novel processing routes were developed to obtain 2D turbostratic graphite particles via solid-state reactions between B4C and Cr3C2 (GBC) and between SiC and Fe (GSF) that present outstanding tribological properties in a dry scenario, as well as functionalized graphene (GNH). This work investigated the suspension stability of GBC and GSF particles (0.05 wt.%) dispersed in a low-viscosity polyol ester lubricating oil and their tribological performance. Ammonia-functionalized graphene (GNH) particles were also used as a reference. In order to evaluate the dispersion stability, in addition to the classical digital image technique, a much more assertive, reliable, quantitative and rarely reported in the literature technique was used, i.e., the STEPTM (Space and Time-resolved Extinction Profiles) technology. Reciprocating sphere-on-flat tribological tests were carried out, in which before contact, 0.2 μL of pure oil and suspension (POE + 0.05 wt.% of solid lubricant) was applied on a flat surface. The results showed that the GBC particles remained remarkably stable and reduced the sphere wear rate by 61.8%. From the tribosystem point of view, the presence of GBC and GSF reduced the wear rate by 18.4% and 2.2%, respectively, with respect to the pure oil, while the GNH particles increased the wear rate by 4.2%. Furthermore, the wear rate was improved due to the highly disordered carbon tribolayer formation identified on both surfaces. [ABSTRACT FROM AUTHOR]

The hydrogenated amorphous carbon (a-C:H) film, which is widely used in the engineering field, has attracted more and more researchers' attention. A-C:H films exhibit super-low friction coefficient and low wear in inert atmospheres but high friction coefficient and wear in ambient air. In this study, 3D graphene and h-BN were used as solid lubricants to reduce the friction and wear of steel-a-C:H film contact conditions under different loads. When 0.01 wt% of 3D graphene and 0.1 wt% h-BN were mixed at a volume ratio of 1:1, the lubricating effect is optimum. Compared with a-C:H films, not only the friction coefficient is reduced, but also the wear rate is further reduced. This is mainly due to the formation of an ordered and dense transfer film on the sliding interface, which effectively prevents the direct contact between the surfaces of the friction pair. [ABSTRACT FROM AUTHOR]

Copper-based solid lubrication inlay technology is widely used in industrial production, especially in low-speed and heavy load conditions, and the structure and distribution of the filling pore have a significant influence on the friction performance due to the distribution of contact stress. In this paper, based on the operating conditions of the bottom pivot of the Three Gorges gate, graphite is used as a solid filled lubricant. The effects of filling pore diameter, filling pore depth, and area distribution rate on the friction and wear properties were studied by orthogonal equivalent test on MMW-1A tester with grease. Combining the three-dimensional morphology test and ferrography analysis, the results show that: 1) the influence of three parameters on the test results are: filling pore diameter > area distribution rate > filling pore depth; 2) when the filling pore diameter is 3 mm, the area distribution rate is 12%, and the filling pore depth is 0.5 mm, which is the equivalent the optimal structure of the filling pore size under working conditions. According to this conclusion, the actual filling structure can be obtained based on the similarity theory. As Coulomb friction is material and contact stress related, the calculation of the stress distribution during dynamic operation is difficult and therefore the analysis is carried out experimentally. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate the structural, mechanical and tribological behaviours of thermally oxidized MoS2 films. MoS2 coatings were deposited on D2 tool steel substrates using the closed field unbalanced magnetron sputtering method (CFUBMS). The thermal oxidation process was carried out at four different temperatures. Tribological properties were determined by pin‐on‐disc wear tests in the atmospheric environment. It was determined that thermal oxidation temperatures affected the chemical composition of MoS2 films, but did not cause any change in film thickness. The wear rates of the samples differed depending on the oxidation temperature and the applied load. The lowest wear rate was determined as 1.97 × 10−8 mm3/Nm in the oxidized film at 350°C. In addition, the highest hardness value was obtained as 655 HV in the film oxidized at 400°C, and the lowest coefficient of friction was obtained as 0.01 in the film oxidized at 350°C. [ABSTRACT FROM AUTHOR]

Refractory high/medium entropy nitrides (HENs/MENs) exhibit comprehensive application prospects as protective films on mechanical parts, particularly those subjected to sliding contacts at elevated temperatures. In this study, a new MEN system TiNbWN, forming a single fcc solution, is designed and its wear performance at temperatures ranging from 25 to 750 °C is explored. The wear mechanisms can be rationalized by examining the subsurface microstructural evolutions using the transmission electron microscopy as well as calculating the phase diagrams and interfacial adhesion behavior employing calculation of phase diagram (CALPHAD) and density functional theory (DFT). To be specific, increased wear losses occur in a temperature range of 25–600 °C, being predominantly caused by the thermally-induced hardness degradation; whereas at the ultimate temperature (750 °C), the wear loss is refrained due to the formation of nanocrystalline oxides (WnO3n−2, TiO2, and γTiOx), as synergistically revealed by microscopy and CALPHAD, which not only enhance the mechanical properties of the pristine nitride film, but also act as solid lubricants, reducing the interfacial adhesion. Thus, our work delineates the role of the in situ formed nanocrystalline oxides in the wear mechanism transition of TiNbWN thin films, which could shed light on the high-temperature wear behavior of refractory HEN/MEN films. [ABSTRACT FROM AUTHOR]