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Composite coatings with solid lubricants can improve the tribological performance of aluminum alloy parts prepared by Laser Powder Bed Fusion (LPBF). In this study, Ni-MoS2 self-lubricating composite coatings were one-step prepared on additive manufactured aluminum alloy surface via jet electrodeposition. The properties and lubrication performance of the coatings prepared using composite electrolyte with different MoS2 particle diameters and concentrations were investigated. The lubrication mechanism of the composite coating was discussed. The results showed that 0.8 μm MoS2 had less agglomeration than 80 nm, resulting in a uniform surface. The lubrication performance of the composite coating was affected by MoS2 particles content and coating hardness. With the increase of MoS2 concentration in the composite electrolyte, the friction coefficient and wear rate decreased, and achieved the best lubrication performance of 0.12 friction coefficient and 0.11 mg/m wear rate when MoS2 composite electrolyte is 5 g/l and MoS2 is 0.8 μm. However, the addition of soft MoS2 decreased the coating hardness, lower hardness will cause lubrication failure. [ABSTRACT FROM AUTHOR]

The ball bearing market is mature where there is a massive range of products available with new ones being developed all the time due to technological advancements. Additive Manufacturing (AM) provides a promising approach for developing oil-impregnated ball bearings. Oil impregnated bearings are critical for applications requiring smooth and low-friction motion. This study explores the feasibility of utilizing laser powder bed fusion (LPBF) technology to fabricate 304 stainless steel (304SS) samples with open pores, which can then be impregnated with a lubricant. To achieve this, 304SS powder was used, and optimum selective laser melting (SLM) printing parameters were altered to induce intentional pores. Initial screening of samples involved Archimedes density measurements and computed tomography (CT) scanning was conducted on a selected samples to assess their porosity levels. CT scan foam analysis results indicated a correlation between hatch spacing and porosity. Results revealed trends in cell volume and solidified scanning tracks thickness, indicating greater connectedness with larger pores. Synthesis of these findings could help in the development of efficient and reliable open pores that may find use in oil-impregnated self-lubricating ball bearings. [ABSTRACT FROM AUTHOR]

MAX phase ceramics is a large family of nanolaminate carbides and nitrides, which integrates the advantages of both metals and ceramics, in general, the distinct chemical inertness of ceramics and excellent physical properties like metals. Meanwhile, the rich chemical and structural diversity of the MAXs endows them with broad space for property regulation. Especially, a much higher self‐lubricity, as well as wear resistance, than that of traditional alloys and ceramics, has been observed in MAXs at elevated temperatures in recent decades, which manifests a great application potential and sparks tremendous research interest. Aiming at establishing a correlation among structure, chemical composition, working conditions, and the tribological behaviors of MAXs, this work overviews the recent progress in their high‐temperature (HT) tribological properties, accompanied by advances in synthesis and structure analysis. HT tribological‐specific behaviors, including the stress responses and damage mechanism, oxidation mechanism, and wear mechanism, are discussed. Whereafter, the tribological behaviors along with factors related to the tribological working conditions are discussed. Accordingly, outlooks of MAX phase ceramics for future HT solid lubricants are given based on the optimization of present mechanical properties and processing technologies. [ABSTRACT FROM AUTHOR]

In engineering applications, it is crucial to extend service life by reducing the coefficient of friction (COF) and wear rate to improve dry wear resistance. This work investigates the tribological properties of NiCrAlY-Cr3C2-Ti2SnC coatings with different Ti2SnC additions over a wide temperature range. Composite coatings with varying Ti2SnC concentrations were deposited onto TC4 titanium alloy substrates using atmospheric plasma spraying. Pin-on-disk wear tests were utilized to evaluate the tribological performance of the coatings, including the friction coefficient and wear rate, from room temperature to 800 °C. The wear mechanism of the coating was determined using SEM and a 3D profiler. The results demonstrate that the coating containing 30 wt.% Ti2SnC (NC-30TSC) exhibits the lowest friction coefficient (0.29) and wear rate (4.89 × 10−5 mm3·N−1·m−1) at 800 °C. The composite coatings containing Ti2SnC exhibited a decreased coefficient of friction and wear rate due to the high-temperature decomposition products of Ti2SnC, such as TiO2 and TiC. The wear mechanisms of the NC-30TSC coating were adhesive and fatigue wear at 300 °C, adhesive and oxidation wear at 600 °C, and oxidation wear at 800 °C. Additionally, the prefabricated cracks on the surface of the NC-30TSC coating healed after isothermal treatment, demonstrating excellent self-healing performance. [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]

Incorporating graphene as ceramic additives can significantly enhance both the toughness and self-lubricating characteristics of ceramic matrices. However, due to the difficult dispersion and easy agglomeration of graphene, the preparation process of composite ceramics still faces many problems. In this study, a laminated laser-induced reduced graphene oxide/hexagonal boron nitride (L-rGO/h-BN) was introduced as an additive into a silicon nitride matrix, then a silicon nitride/reduced graphene oxide/hexagonal boron nitride (Si3N4/L-rGO/h-BN) ceramic composite was successfully synthesized using Spark Plasma Sintering technology. This approach led to enhancements in both the mechanical and self-lubricating properties of silicon nitride ceramics. This is due to the good monodispersity of the incorporating graphene in the silicon nitride matrix. The flexural strength and fracture toughness of the ceramic composite experienced notable increases of 30.4% and 34.4%, respectively. Tribological experiments demonstrate a significant enhancement in the self-lubricating performance of ceramic composites upon the incorporation of L-rGO/h-BN. The coefficient of friction and wear spot diameter experienced reductions of 26.6% and 21%, respectively. These improvements extend the potential industrial applications of Si3N4/L-rGO/h-BN ceramic composites. Throughout the friction process, the evenly exposed rGO and h-BN demonstrate an effective self-lubricating effect on the wear surface. This research paves the way for a novel approach to fabricating high-performance self-lubricating structural ceramics. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Aeronautical Materials is the property of Editorial Board of Journal of Aeronautical Materials and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The manuscript presents the synthesis and dry sliding wear performance of Al7075 alloy‐based composites. Five compositions namely Al7075 alloy, Al7075+3 vol % molybdenum disulfide, Al7075+3 vol % molybdenum disulfide+3 vol % zirconium diboride, Al7075+3 vol % molybdenum disulfide+6 vol % zirconium diboride and Al7075+3 vol % molybdenum disulfide+9 vol % zirconium diboride were stir cast and characterized for hardness, x‐ray diffraction, microstructure, and tribological properties. In‐situ formed zirconium diboride particles increase the hardness of Al7075 alloy whereas molybdenum disulfide shows the opposite trend due to its self‐lubricating nature. X‐ray diffraction analysis identifies subsequent phase particles in the matrix while microstructural images exhibit the dispersion and morphology of reinforcement particles. The wear tests and friction coefficient were analyzed with variations of sliding velocity, normal load, sliding distance, and compositions. Further, the obtained wear results were also correlated with microstructure and wear surface topography. Al7075+3 vol % molybdenum disulfide composite shows the lowest coefficient of friction because of its self‐lubricating nature. Al7075+3 vol % molybdenum disulfide+9 vol % zirconium diboride hybrid composite exhibits the lowest wear rate at high velocity as well as at high load and can be potentially used in manufacturing and tribological applications. Moreover, the use of this material may lead to the minimum requirement of external toxic lubricants that make it cost‐effective and environmentally sustainable. [ABSTRACT FROM AUTHOR]

This work reviews surface modification techniques for improving the wear and corrosion resistance of 42CrMo steel. The advantages and disadvantages of various methods, including thermal spraying, deposition, hardfacing, laser cladding, nitriding, and laser surface treatment, are discussed. The review elaborates on the materials commonly employed in laser cladding technology, including iron-based, cobalt-based, nickel-based, and high-entropy alloys and reinforced composite coatings. Furthermore, the mechanisms and methods of improving the wear and corrosion resistance of 42CrMo steel are summarized. Finally, this review presents research shortcomings and future opportunities of surface modification techniques. This review also provides a theoretical guide for the application of 42CrMo steel. [ABSTRACT FROM AUTHOR]

A CoCrFeNi-Ag-Mo self-lubricating composite was fabricated by spark plasma sintering. The effect of Ag and Mo addition on the microstructure, mechanical and tribological properties of CoCrFeNi high entropy alloy (HEA) was systematically investigated. Ag addition led to the formation of Ag-rich phase in CoCrFeNi HEA matrix. With the addition of Mo, part of Ag-rich phases were distributed inside the Mo-rich phase. There were clear diffusion regions between Mo and HEA matrix, residual Mo phases and dispersed Ag-rich phases in Mo-rich phases. The hardness and strength were decreased with the addition of Ag and increased with the addition of Ag and Mo. The ultimate plasticity strain of CoCrFeNi-Ag-Mo composite exceeded 45%. The coupling addition of Ag and Mo effectively improved the tribological properties from room temperature to 800 °C. This phenomenon could be ascribed to the low hardness and yield strength of CoCrFeNi-Ag composite, as well as the thermo-softening due to the friction-induced heat and high experimental temperature. At room temperature, Ag-rich phases acted as a lubricant, and Mo-rich phases improved the anti-wear property. At 400 °C, tiny Ag particles were uniformly distributed on the worn surface, which played roles in friction-reducing. At 800 °C, the Ag2MoO4 layers in-situ formed by tribo-chemistry reactions offered good lubricating and anti-wear functions. [ABSTRACT FROM AUTHOR]

Cured epoxy resins have poor abrasion resistance, which shortens the service life of the material. This work aims to improve the tribological properties of epoxy resins by coupling self‐lubrication and auto‐healing. In this study, linseed oil microcapsules with an average particle size of 38.57 μm and good thermal stability were successfully prepared by in situ polymerization. The effects of microcapsule content on the tribological, mechanical, and self‐healing properties of the composite coatings were studied. It was demonstrated that the composite coating has outstanding self‐lubricating properties. The coefficient of friction reduced from 0.634 (pure epoxy resin) to 0.0459 (epoxy resin with 10 wt.% linseed oil microcapsules). Wear rate reduced from 7.16 × 10−4 mm3/(N m) to 1.74 × 10−5 mm3/(N m). The self‐lubricating mechanism of the coating was investigated by SEM and EDS, which indicated that the formation of uniform and continuous lubricating film on the surface of the friction pairs was the key to improving the wear resistance of the material. In addition, the linseed oil released after the microcapsules rupture can repair the abrasion marks by reacting with oxygen during the friction process. The dual‐functional effect of linseed oil microcapsules prolongs the life of epoxy resin coating and expands its application range. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to investigate the effects of ball–material ratio on the properties of mixed powders and Cu-Bi self-lubricating alloy materials. Design/methodology/approach: Cu-Bi mixed powder was ball milled at different ball–material ratios, and the preparation of Cu-Bi alloy materials was achieved through powder metallurgy technology. Scanning electron microscopy, X-ray diffraction and Raman spectroscopy were conducted to study the microstructure and phase composition of the mixed powder. The apparent density and flow characteristics of mixed powders were investigated using a Hall flowmeter. Tests on the crushing strength, impact toughness and tribological properties of self-lubricating alloy materials were conducted using a universal electronic testing machine, 300 J pendulum impact testing machine and M200 ring-block tribometer, respectively. Findings: With the increase in ball–material ratio, the spherical copper matrix particles in the mixed powder became lamellar, the mechanical properties of the material gradually reduced, the friction coefficient of the material first decreased and then stabilized and the wear rate decreased initially and then increased. The increase in the ball–material ratio resulted in the fine network distribution of the Bi phase in the copper alloy matrix, which benefitted its enrichment on the worn surface for the formation a lubricating film and improvement of the material's tribological performance. However, a large ball–material ratio can excessively weaken the mechanical properties of the material and reduce its wear resistance. Originality/value: The effects of ball–material ratio on Cu-Bi mixed powder and material properties were clarified. This work provides a reference for the mechanical alloying process and its engineering applications. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Materials Engineering / Cailiao Gongcheng is the property of Journal of Materials Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

Copyright of Journal of Materials Engineering / Cailiao Gongcheng is the property of Journal of Materials Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A series of CoCrFeNiMn high-entropy alloy matrix self-lubricating composites were prepared by spark plasma sintering. The composites are composed of an FCC phase, Cr7C3, Ag, and eutectic fluoride BaF2/CaF2 phases. The microstructure of the composites is uniform. The additional phases distribute along the boundary of equiaxed grains of the FCC phase. The compressive yield strength and fracture toughness decrease with the increase of eutectic fluoride BaF2/CaF2. The composites are susceptible to brittle cleavage fracture. [ABSTRACT FROM AUTHOR]

To improve the service performance of diamond cutting tools under dry working conditions, three oxides (B2O3, TiO2, and ZnO) were innovatively used to prepare oxide self-lubricating diamond cutting-tool matrix. Rockwell hardness, three-point bending strength, and relative density tests were conducted to determine the effects of oxides on the mechanical properties of diamond cutting-tool matrix from the macroscale, whereas SEM, EDS, roughness test, physical, and molecular-dynamic-simulated dry-wear tests were used synthetically to explore the effects of oxides on the wear behavior of diamond cutting-tool matrix. Test results indicated that proper oxide addition improved the tribological properties of diamond cutting-tool matrix but decreased its mechanical properties to some degree. Furthermore, oxides more easily slid during the dry-wear process by changing its molecular-group morphologies. Consequently, self-lubricating films were generated and the wear resistance of the diamond cutting-tool matrix increased with the decrease in fatigue wear and fractured abrasive wear. [ABSTRACT FROM AUTHOR]

High-temperature ablation is a common failure phenomenon that limits the service life of the transmission parts on heavy-duty machines used in heavy load, high temperature, high shock conditions due to in-sufficient supply of lubricating oil and grease. Traditional self-lubricating coatings prepared by inorganic, organic or organic-inorganic hybrid methods are prone to be oxidated at high temperatures to lose their friction reducing function, so that it is difficult to meet the engineering requirements of high-temperature lubrication. We design viscoelastic polymer coatings by a high-temperature self-lubricating and wear-resistant strategy. Polytetrafluoroethylene (PTFE, Tm = 329 °C) and polyphenylene sulfide (PPS, Tg = 84 °C, Tm = 283 °C) are used to prepare a PTFE/PPS polymer alloy coating. As the temperature increases from 25 to 300 °C, the PTFE/PPS coating softens from glass state to viscoelastic state and viscous flow state, which is owing to the thermodynamic transformation characteristic of the PPS component. Additionally the friction coefficient (µ) decreased from 0.096 to 0.042 with the increasing of temperature from 25 to 300 °C. The mechanism of mechanical deformation and surface morphology evolution for the PTFE/PPS coating under the multi-field coupling action of temperature (T), temperature-centrifugal force (T-Fω), temperature-centrifugal force-shearing force (T-Fω-Fτ) were investigated. The physical model of "thermoviscoelasticity driven solid-liquid interface reducing friction" is proposed to clarify the self-lubricating mechanism determined by the high-temperature viscoelastic properties of polymers. The high-temperature adjusts the viscosity (η) of the coating, increases interface slipping and intensifies shear deformation (τ), reducing the friction coefficient. The result is expected to provide a new idea for designing anti-ablation coatings served in high temperature friction and wear conditions. [ABSTRACT FROM AUTHOR]

The service life of Inconel 718 (IN718) nickel-based superalloys under extreme working conditions is limited due to their poor tribological properties. In this study, IN718 cellular structure self-lubricating composites were fabricated by selective laser melting (SLM) and multi-soft metal (Sn-Pb-Ag) infiltration. Different cellular structures were verified by means of numerical simulation and experiment. The effects of pore diameter and temperature on tribological properties of the selective-laser-melted (SLMed) IN718 with Sn-Pb-Ag (INSPA) infiltration self-lubricating composites were investigated. Results show that INSPA samples of cellular structure with a pore diameter of 1.4 mm (INSPA3) exhibited excellent tribological properties compared to the two other pore diameters of 1.2 mm (INSPA2) and 1.0 mm (INSPA1). The tribological properties test results at different temperatures indicate that the coefficient of friction (COF) of INSPA3 was decreased from 0.29 to 0.13 as the temperature of 25 °C rose to 350 °C. The reason is that more Sn-Pb-Ag lubricant was stored in the Ф1.4-mm holes, which were heated and expanded to the worn surface during the friction process to realize self-compensation lubrication. At 350 °C, the friction product of Pb2O was decomposed into PbO and other multicomponent friction oxides were generated, which improves the wear resistance of the SLMed INSPA self-lubricating composites. This study demonstrates a potential approach to enhance the tribological properties and service life of IN718 superalloys used in harsh friction conditions. [ABSTRACT FROM AUTHOR]

Cu-based self-lubricating materials can effectively adapt to complex natural environments and ensure consistency in materials used for switch transitions. These materials were tested through interface reinforcement research, improving their mechanical and tribological properties and providing a theoretical basis for new switch slide baseplate materials. Results showed that the coefficient of friction and wear weight loss of Cu-based self-lubricating materials decreased with an increase in graphite content after Cu and Ni plating on the graphite surface, reaching a minimum value at a graphite content of 6 wt.%. The coefficient of friction and wear weight loss of the Ni-plated material were reduced 11.1% and 85.6%, respectively, whereas the coefficient of friction and wear weight loss of Cu-plated materials were reduced 7.2% and 78.4%, respectively. Compared to Cu plating, Ni plating substantially enhanced the friction and wear performance of Cu-based self-lubricating materials. Cu and Ni plating increased the adhesion of the materials on the pin surface and the adhesive materials' composition was consistent with the lubricating film, which changed the grinding mechanism between the pin and the disk. Ni plating had a stronger effect on the tribological performance of Cu-based self-lubricating materials than Cu plating. [ABSTRACT FROM AUTHOR]

This article aims to investigate the percolation and supply behavior of lubricant on the porous self-lubricating material. The numerical model is established to describe the infiltration-exudation response in the deformed porous material. It is found that the lubricant stored in the pores is forced to flow when the loaded porous matrix deforms. The flow drives the seepage stratification in the porous body and forms an interlayer flow zone. The fluid pressure gradient in the normal direction is the internal factor of the seepage stratification. The interlayer flow zone first appears in the middle of the vertical direction of the porous matrix. With the increase of loading time, the interlayer flow zone gradually moves from the middle to the bottom of the porous matrix, which means that the quantity of the lubricant stored in the porous surface decreases. In the whole process of the seepage response, the lubricant flows out from the inlet and continuously supplies lubricant to the contact area. Delaying the downward movement of the interlayer flow zone can ensure the continuous exudation of the lubricant, which is beneficial to maintain excellent lubrication characteristics. [ABSTRACT FROM AUTHOR]

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In this study, the MYB-500 high-frequency and high-load oscillatory tribotester was used to carry out life cycle tests to investigate the self-lubricating properties and damage behavior of Kevlar/PTFE fiber-reinforced composite. Wear debris and wear behavior of the frictional surface were analyzed to explore key factors affecting the self-lubricating stability and service life of materials. Results show that the life cycle of Kevlar/PTFE fiber-reinforced composite can be divided into three stages by the change of friction coefficient and wear depth, including running-in, stable and failure stage. The life stage and performance of materials can be evaluated by monitoring the friction temperature and friction coefficient in real time. When the friction coefficient reaches 0.16 or the friction temperature monitored exceeds 150 °C, it can be determined that the material life is terminated. From wear surface analysis and change of wear loss, it is indicated that the wear exhibits notable nonuniform characteristic. Based on the wear surface of material after failure, it is concluded that the initial nonuniformity of the material thickness has significant influence on wear damage as well as life cycle. Therefore, the self-lubricating behavior of material can be improved by modifying relevant process parameters to obtain the uniform material thickness, and meanwhile, the wear life was increased from 242 to 293 h. [ABSTRACT FROM AUTHOR]

This research aims to assess the mechanical characteristics of high-performance copper composites made utilizing powder metallurgy. The composites were produced by adding reinforcement elements (Al2O3-Cr3C2) at different rates (3-6–9 wt.%) into copper-graphite (Cu-5Gr) via hot pressing technique. The microstructure, hardness, three-point bending and wear performance were analysed. The results determined that hybrid reinforced composites exhibited higher density, hardness and bending strength compared to Cu-Gr composites. The highest hardness of 73.02 HB was found in the CG-4 (copper graphit-4) sample. The maximum bending stress of 151.06 MPa occurred in sample CG-2. In addition, it was observed that the wear resistance increased significantly with the addition of the hybrid reinforcements. The lowest specific wear rate of 7.961 × 10−7 mm3/N.m occurred in sample CG-6. As a result, 15.92%, 58.16% and 83.21% improvements were achieved in hardness, bending strength and wear performance, respectively. The current work indicates that certain mechanical properties of copper can be improved via the powder metallurgy process and the addition of reinforcements which could expand the applications and use of this metal in different industries. [ABSTRACT FROM AUTHOR]

Wear tends to shorten tool life, reduce component quality. To prevent or postpone the wear of tool steel forming tools, methods to increase wear resistance, such as increasing the material hardness, optimizing the carbide distribution and application of surface coatings, are often used. However, the formation of lubricating phases in steels leading to anti-attrition is less investigated. The friction behavior of three steels were investigated thoroughly by a tribo test with different normal loads. A Field-emission scanning electron microscope (FE-SEM) along with energy dispersive X-ray spectroscopy (EDS) were used to characterize the microstructure as well as the influence of the precipitated phases on the wear mechanisms. Results showed the friction coefficient decreased with increasing normal load, whereas the wear rate increased with increasing normal load. Compared with SKD11 and DC53 steels, the friction coefficient and wear volume of SLD-MAGIC steel were reduced by 0.1 to 0.3 and 10% to 30%, respectively. With the increase of normal load, the wear mechanism changed in order from abrasive wear, adhesive wear to oxidation wear. The more carbide contents, the rounder the carbide, the better the wear resistance of the tool steel. It can be shown that, under different normal loads, SLD-MAGIC exhibits better wear performance than SKD11 and DC53 tool steels, which is mainly due to the self-lubricating phenomenon of SLD-MAGIC steel. The self-lubricating mechanism was due to the fact that the exfoliated sulfide during wear formed a lubricating film to reduce wear. [ABSTRACT FROM AUTHOR]

The machinability and wear reduction mechanism of self-repairing and self-lubricating ceramic tools sintered by vacuum hot-pressing method in the dry turning of 40Cr hardened steel was studied. By comparing the cutting performance and wear morphology of AT (Al2O3/TiC) ceramic tools under different cutting parameters, it was found that AT10B@5 (Al2O3/TiC/10 vol% TiB2/5 vol% h-BN@Al2O3) tool has a longer service life and better machining quality. Owing to the precipitation of solid lubricant during the cutting of AT10B@5 ceramic tool, the friction force during the cutting is reduced, thus decreasing the cutting force and cutting temperature of AT10B@5 ceramic tool during the cutting. The main cutting force decreased by 20.8%; the cutting temperature decreased by 22.2%; and the friction coefficient of front tool face decreased by 11.6% compared with AT tool. This effectively improved the surface quality of working parts, reduced the tool wear, increased the processing quality of work piece, and prolonged the tool life. [ABSTRACT FROM AUTHOR]

Metal matrix self-lubricating composites exhibit outstanding performance in various environments, reaching the required properties by modifying the reinforcement–matrix ratio and the production method. The present research investigated the effects on tribological performance and electrical properties of different pressure loads, maintaining pressing time, and sintering temperatures during the production of copper–10 wt% tungsten disulfide (Cu–WS2) composite via powder metallurgy. Moreover, additional thermo-mechanical treatments were evaluated, namely second pressing and second sintering steps. The density and the hardness of the produced composites were measured, as well as the electrical resistivity, considering sliding electrical contacts as possible employment. The outputs of the wear tests were considered together with the analysis of the wear track via scanning electron microscopy and confocal laser scanning microscopy to understand wear mechanisms. Different production routes were compared in terms of electrical resistivity, wear coefficient, and specific wear rate, calculated by the confocal laser scanning microscopy, and friction coefficient, measured during the wear test. The main results highlighted that the increase in sintering temperature was detrimental to the hardness and tribological properties; higher load and additional pressing step determined a general improvement in the tested properties. [ABSTRACT FROM AUTHOR]

Due to the excellent properties of titanium alloys, they are widely used in various fields. However, the poor tribological performance limits the further development of titanium alloys. In this paper, TC4 with microporous channels was manufactured by laser additive manufacturing technology. On this basis, TC4-Sn-Ag-Cu (TSAC) and TC4-Sn-Ag-Cu-Nb2C (TSACN) self-lubricating materials were prepared. The friction and wear tests were carried out under dry friction conditions, and tribological behaviors and friction-induced noise were analyzed. The results show that TSACN self-lubricating composite has outstanding tribological properties and noise suppression performance. Compared with TC4, the friction coefficient and equivalent sound pressure level of TSACN are reduced by 20.1 and 6.7%, respectively. The excellent tribological properties are mainly attributed to the synergistic effect of microporous channel and Sn-Ag-Cu-Nb2C. Microporous channel can promote the diffusing of lubricants and accelerate the formation rate of lubricating film; Nb2C can enhance soft metal lubricant Sn-Ag-Cu to make the lubricating film more dense. The lubricating film can repair wear pits, furrows and other defects on the worn surface and avoid the direct contact between the counterpart ball and the sample, thereby improving the tribological properties of TC4 and reducing the friction-induced vibration and noise. [ABSTRACT FROM AUTHOR]

Although flame-sprayed Ni60 coatings are widely used for the surface wear protection of mechanical parts, they have intrinsic shortcomings such as the high porosity and the lack of self-lubricating performance. In this work, MoS2 was introduced into the flame-sprayed Ni60 coating via hydrothermal synthesis, and the microstructure and tribological properties of the fabricated Ni60/MoS2 composite coating were studied. Microstructure observation of coatings shows that MoS2 in situ grew in the flame-sprayed Ni60 coating, both along the wall of internal pores/gaps and on the coating surface, leading to the significantly decreased coating porosity. The friction and wear tests show that the steady friction coefficient of the Ni60/MoS2 composite coating was about 0.22, which is 75% lower than that of the Ni60 coating (about 0.88). The wear rate of the Ni60/MoS2 composite coating after the 1 h wear test was about 1.22 × 10–7 mm3N−1 m−1, reducing significantly compared to that of the Ni60 coating (2.16 × 10–7 mm3N−1 m−1). The superior tribological performance of the Ni60/MoS2 composite coating was attributed to the synergistic action of the self-lubricating MoS2 and the wear-resistant Ni60. [ABSTRACT FROM AUTHOR]

Copyright of Precious Metals / Guijinshu is the property of Precious Metals Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Hot forging dies play an important role in metallurgy, automotive, aerospace and weapons industries. However, due to the high temperature and high pressure of hot forging die and the working environment of cyclic load, the friction and wear performance of hot forging die is poor and the service life is low. The use of traditional lubricants can prolong the life of the mold, but it will cause environmental pollution, harm to workers' health and other problems. In this paper, 35Ni15Cr Fe-based self-lubricating die material was prepared by high energy ball milling and vacuum sintering. The wear properties of the materials were studied under ball-to-disc wear conditions at 600 °C. The results show that when CaF2 content is 8 wt%, the friction coefficient and wear rate of the material are the lowest, which are 0.3 and 0.9166 × 10−5 mm2 min−1, respectively. When the load increases, the friction coefficient first increases and then decreases, but the wear rate continues to increase. The wear mechanism mainly includes abrasive wear, adhesive wear, oxidation wear and fatigue wear. The friction reduction mechanism is that CaF2 is precipitated from the self-lubricating mold material and Fe and Ni are oxidized to the boss on the wear surface. The broken boss and lubricant form a lubricating film and accumulate into a glaze layer. The material can be used in high temperature forging environment without additional lubricant. [ABSTRACT FROM AUTHOR]

In this study, highly stable aluminium silicate (Al2SiO5) particles were spatially dispersed with tungsten disulphide (WS2) particles, making aluminium alloy (AA7075) composites suitable for tribological applications. The composite fabrication was done through the squeeze casting technique by dispersing aluminium silicate (Al2SiO5) particles with 5–15% weight percentages and WS2 particles with weight percentages of 5% in the aluminium alloy. Optical microscopy and X-ray diffraction (XRD) techniques were employed to study the distribution of particles and phase analysis. Hardness and tensile strength tests were conducted to assess the mechanical strength of composites. Dry sliding wear behaviour of aluminium alloy and composites was studied using a pin-on-disc tribometer. Wear performance was evaluated over a load range of (20, 40, 60, and 80 N) at a sliding velocity of 2.0 m/s with a sliding distance of 3000 m. SEM, XRD, and Energy Dispersive Spectroscopy (EDS) were used to investigate the particles' effects on the wear mechanism. The 3D surface topography was used to characterise the worn surface map, and wear depth has been analysed. The experimental results revealed that both particle dispersed conditions show a synergetic effect on reducing wear rate and friction coefficient better than alloy and monodispersed particle composite. The higher wear resistance on the AA7075/10 wt.% Al2SiO5/5 wt.% WS2 coordinate was shown by the combined effect of reinforcement particles through the formation of a stable and compacted tribo lubricating layer consisting of mixed SiO2 and WO3, which retains wear resistance properties of the composites. [ABSTRACT FROM AUTHOR]

Hybrids of fluorinated graphite/MoS2 (FGr@MoS2) were prepared via a hydrothermal method and used as lubricating additives to take full advantage of the synergy between FGr and MoS2 in carbon-fiber-reinforced polymer (CFRP). The results show a 21.6% reduction in the friction coefficient compared to the neat sample when the CFRP was filled with 1.2 wt.% FGr@MoS2 hybrids. The addition of 1.5 wt.% FGr@MoS2 resulted in a 60.9% reduction in the wear rate compared to neat CFRP. For the 1.2 wt.% FGr@MoS2-reinforced CFRP, the friction coefficient maintained a relatively steady value of approximately 0.46 at various temperatures, indicating frictional stability. However, the wear rate increased by 13.95% at 60 °C compared to that at room temperature. The interfacial bonding force between the FGr@MoS2 hybrid and the matrix, as well as the adhesive force with the surface of the counterpart ball, is improved, caused by the heterostructure of FGr@MoS2, resulting in enhanced mechanical properties and formation efficiency as well as the transfer film on the surface of the counterpart ball. The results suggest that an FGr@MoS2 micro-nano structure is a promising additive to be applied in polymer tribology. [ABSTRACT FROM AUTHOR]

In this work, we showed that the mesoporous molecular sieve SBA‐15 could be used as an oil storage smart microcontainer to adsorb PAO6 oils and is prepared as an oil‐containing molecular sieve SBA‐15O, the compositing of SBA‐15O with unsaturated polyester resins (UPR) can significantly improve the lubrication properties of UPR. The oil‐containing molecular sieve SBA‐15O was prepared by vacuum impregnation and compounded into the UPR. The lubricating effect of different SBA‐15O contents on the UPR was investigated. As compared with the UPR, the coefficient of friction (COF) of the 10%SBA‐15O/UPR could be reduced to 10% of that without SBA‐15O, and the wear rate by three orders of magnitude. The results show that the improvement of lubricating performance is related to the release of lubricating oil from the microcontainer to the surface to produce a lubricating oil film during friction, thereby enhancing the self‐lubricating performance of the composite material. [ABSTRACT FROM AUTHOR]

A silicon nitride ceramic bearing has good self-lubricating characteristics. It still has a good operational status under the condition of a lack of oil. However, the temperature distribution of a silicon nitride ceramic bearing during its operation is unclear. To clarify the thermal distribution of a full-ceramic ball silicon nitride ceramic bearing under self-lubricating conditions, the changing trend of the rolling friction temperature between the rolling elements and channels with different accuracies is analyzed using the friction testing machine. The bearing heat generation model based on the silicon nitride material coefficient is established, and the life test machine measures the temperature of the bearing to verify the accuracy of the simulation model. The results show that the friction temperature between the ceramic ball and channel decreases with the increase in ceramic ball level. With an increase in the ceramic ball pressure and temperature, the friction temperature rises. Under self-lubrication, when the bearing bears a heavy load, the influence of the rotating speed on temperature rise tends to decrease. Under the condition of high speed, with the increase in load, the change range of temperature rise shows an upward trend. The important relationship between the bearing's heat and bearing's load and speed is revealed. It provides some theoretical guidance for the thermal analysis of a silicon nitride ceramic ball bearing under the self-lubricating condition to improve the service life and reliability of full-ceramic ball bearings. [ABSTRACT FROM AUTHOR]

In Kaplan turbines, the most critical components are the self-lubricating polymer composite bearings used to control the guide vanes and the turbine blades. Reducing the sliding wear and friction of these bearings can benefit both the economy and the environment, including longer useful life, lower operational costs, and higher efficiency. In this study, the influence of stainless-steel counter surface roughness and lay on the tribological behaviour of three bearing materials used in hydropower applications were investigated using a linear reciprocating flat-on-flat configuration under high contact pressure and low sliding speed. The surface roughness was measured using white light interferometry. SEM and EDS analysis were used to investigate the worn surfaces. Results from this study show that overly smooth surfaces result in higher friction and wear of the counter surface, while rougher surfaces have a negative effect on the wear of the polymers. Highest surface coverage using protective transfer layers is found on the steel surfaces with the perpendicular lay and is accompanied with a lower coefficient of friction compared to the parallel lay. The dominant wear mechanism of the bearing materials changes from delamination wear to abrasive wear between the lowest and the intermediate roughness for steel surfaces with the parallel lay. It can be concluded that counter surface topography has a significant influence on the tribological behaviour of these bearing materials and that the effect differs between the self-lubricating polymer composites. [ABSTRACT FROM AUTHOR]

The results of a study of the friction and wear characteristics of the developed nanostructured glass-composite self-lubricating detonation coatings with the composition SiC–Ni–Cu–Al–Si–C additionally containing a SiO2–Al2O3–B2O3 aluminoborosilicate glass phase and structurally free MgC2, which forms α‑graphite during thermal decomposition are presented. It is indicated that their synergistic effect promotes the creation of an antifriction surface layer that minimizes contact parameters. An increase in the adhesion strength of the coatings is achieved by preliminarily applying a sublayer of glass-like sodium silicate Na2O(SiO2)2 onto the working surface. It is noted that the intercalation of the graphite layer by the particles of the subsurface zone does not affect the tribotechnical characteristics of the coatings. The developed coatings show high performance properties; here, the way of wear stabilization is the presence of a thin-film antifriction layer based on α-graphite, which shields unacceptable processes of molecular adhesion interaction. [ABSTRACT FROM AUTHOR]

Ni35 + 20% SiC + 20% Ni/MoS2 self-lubricating coatings were fabricated on a grade 45 steel surface by laser cladding to obtain better comprehensive performance of wear resistance and corrosion resistance. The macroscopic morphology, microstructure, microhardness, phase composition, corrosion resistance and wear resistance of the coatings were investigated. The results show that the microstructure of the cladding layer is dense, mainly composed of cellular crystal and equiaxed crystal; The average microhardness of the coating is about 700 HV; The phase composition of the coating mainly includes Ni-Cr-Fe solid solution and metal sulfide, such as MoS2, NiS, Cr2S3, and CrMo3S4; Under the simulated seawater environment of 3.5% NaCl, the self-corrosion potential is 0.052 V and the self-corrosion current density is 1.69 × 10−5 A∙cm2. Compared with grade 45 steel, the corrosion resistance is greatly improved; After 20 min of wear, the weight loss of the cladding layer is about 0.17 times that of the grade 45 steel, the friction coefficient is small, and the wear resistance is significantly improved. [ABSTRACT FROM AUTHOR]

The starting torque of self-lubricating spherical plain bearings (SSPBs) is a key parameter for evaluating the performance of bearings. Therefore, the starting torque of SSPBs should be controlled to within an allowable range. In this paper, the starting torque generation mechanism is analyzed, and the critical load for the separation of the liner from the outer spherical surface of the inner ring is determined. A mathematical model of the starting torque is established; the experimental and theoretical results of the starting torque are compared and analyzed, and then the accuracy of the mathematical model is evaluated by the deterministic coefficient R 2. The research reveals that a critical load exists for the starting torque. Below the critical load, the starting torque is dependent on the outer spherical radius of the inner ring, bearing wrap angle, and liner parameters such as the compressive elastic modulus, friction coefficient, and precompression of the liner; however, the starting torque is independent of the radial load. Above the critical load, the starting torque is also dependent on the radial load. The research results provide a theoretical basis for the design and application of bearings. [ABSTRACT FROM AUTHOR]

Fiction heat and temperature change affect the precision of high-temperature self-lubricating rolling bearings at high temperatures by changing the bearing clearance. In order to investigate the influence of bearing material physical properties and matching on bearing clearance at high temperature, based on the theory of heat conduction, a high-temperature self-lubricating roller bearing clearance change calculation model was established. Nano colloidal TiO2/cermet high temperature inner gradient lubrication layer material was used as high temperature rolling bearing roller material, and the effectiveness of the model was verified by the high - temperature rolling bearing clearance measurement experiment. The effects of frictional heat, environmental temperature changes and different material pairs on the working clearance of roller bearings were analyzed. Studies show that the change in the working clearance of a roller bearing increases with the rise of the ambient temperature. Compared with the change in the clearance caused by the change in the ambient temperature, the frictional heat has a smaller effect on the change in the clearance of the bearing. When the lubricating bearing pair is made of bearing steel material for the inner and outer rings, and the rolling elements are made of microporous ceramics, the clearance changes greatly. When the self-lubricating bearing pair is made of ceramic materials for the inner and outer rings and the rolling elements are made of microporous ceramics, the clearance changes smaller. [ABSTRACT FROM AUTHOR]

In this paper, polystyrene microsphere (PS) is selected as the pore-forming agent to prepare porous phosphate bonded ceramic coating. Then the mixed solution of polytetrafluoroethylene and polyamide-imide (PTFE-PAI) is pressed into the porous coating to prepare the composite coating. Besides, the microstructure and tribological properties of composite coatings were studied. The results show that the hydrophobicity of composite coating is improved because PTFE-PAI is pressed into the coating. Moreover, the coefficient of friction decreases with the increase of PS content due to the self-lubricating ability of polytetrafluoroethylene. Besides, the wear rate also decreases with the increase of PS content, because polytetrafluoroethylene forms a transfer film on the grinding ball, and the original ceramic coating framework can withstand shearing force due to its high hardness, which protects the composite coating and reduces the wear rate. With this self-lubricating capability, the composite coating with 6 wt-% PS showed the smallest wear rate. [ABSTRACT FROM AUTHOR]

In this paper, nanostructured Al2O3-40%YSZ (AZ) and nano-MoS2/Al2O3–40%YSZ (AZM) powders and coatings are prepared and studied to reveal the effect of nano-MoS2 on the friction and wear behavior of the coating. The morphology, surface roughness and hardness are observed and measured by a scanning electron microscope, a laser scanning confocal microscope and a micro-hardness tester. The ability to resist fracture of the coatings is evaluated by scratch tests. The friction and wear tests of the coatings are conducted by a ball-on-disc tribometer. The experimental results show that AZ and AZM coatings have similar morphology and roughness. But nano-MoS2 decreases the hardness and improves the ability to resist fracture of the coating. Besides, nano-MoS2 decreases the coefficients of friction of the coating when the normal loads are high. The wear rates of AZM coating decrease by 38.7%, 29.7%, 23.6% and 11% compared with those of AZ coating under normal loads of 5N, 10N, 15N and 20N. The addition of nano-MoS2 endows the coating self-lubricating function. The main wear mechanism of the coatings is micro-fracture accompanied by splat delamination and slight abrasion wear. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Shaanxi University of Science & Technology is the property of Journal of Shaanxi University of Science & Technology Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Lubrication mechanisms of plasma-sprayed Cr2O3-Ag nanocomposite coatings were studied by using ball-on-disk friction tests against tungsten carbide counterface at temperatures ranging from 25 to 500 °C. The Cr2O3-Ag nanocomposite coatings were fabricated from agglomerated granules of chromium oxide and silver nanoparticles by plasma spraying process under optimized parameters. The presence of semi-molten nanoparticle zones within the coating promoted a sliding wear behavior characterized by plastic deformation of nanostructured ceramic matrix coatings. The formation of a silver-rich tribofilm on top of the contact surface and tribodecomposition of Cr2O3, as well as tribo-oxidation of Ag at the sliding interface were found to be the controlling mechanisms of friction in these coatings at moderate to high temperatures. The lowest coefficient of friction (COF) at all temperatures was obtained for the Cr2O3-5 vol. % Ag coating due to the optimum condition of its silver-rich tribofilm. [ABSTRACT FROM AUTHOR]

A nickel alloy matrix high-temperature self-lubricating coating (77.5 wt% (Ni–Cr–Mo–Al)–12.5 wt% Ag–10 wt% BaF2/CaF2) was prepared by plasma spraying technique. Results show that the Vickers microhardness of coating is (2.9 ± 0.5) GPa, and the average bonding strength is about (35.6 ± 0.5) MPa. The coating rubbing against Inconel 718 superalloy pin exhibits superior tribological performance with coefficient of friction (COF) of below 0.25 and wear rate of 8.2 × 10–5–15.2 × 10–5 mm3·N−1·m−1 at a wide temperature range from 25 to 800 °C, and the COF and the wear rate are slightly reduced with temperature increasing. The low COF and wear rate were attributed to the synergistic effects of Ag, BaF2/CaF2, Ag2MoO4 and BaMoO4. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to study the effect of load on the tribological behaviour of Cu-based composites, so as to obtain a suitable applied load on these composites. Design/methodology/approach: Cu-based composites were prepared by powder sintering with direct current electric current heating and tested by Universal Mechanical Test-3 with a ball-on-disk at room temperature. Findings: The results showed that Cu-based composites are might suitable for working under low load. There is only mild damage on the surface under a load of 2 N. While it has microcracks and shows signs of cavitation at a certain depth at 20 N and 50 N. In addition, it is evident that there are three zones in the cross-section of the matrix, namely, a mechanical mixing layer, ceramic layer and substrate, respectively. Originality/value: There are two wear mechanisms at different loads, and the evolution of worn surfaces with sliding time is also involved. Thus, the developed material can be used for light load sliding electrical contact material applications. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Materials Engineering / Cailiao Gongcheng is the property of Journal of Materials Engineering Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Functional Materials / Gongneng Cailiao is the property of Chongqing Functional Materials Periodical Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

B4C ceramics were fabricated by pressureless sintering, and the tribological behaviors of B4C ceramics without and with a postannealing treatment at different temperatures were investigated. It was found that the pores of B4C ceramics prepared by pressureless sintering might cause large fluctuations in the coefficient of friction but did not increase the coefficient of friction. A B2O3 layer was not formed on the B4C ceramics after annealing at 700 °C, whereas an H3BO3 layer was formed on the B4C ceramics after annealing at 1000 and 1200 °C, respectively. B4C ceramics obtained a favorable self-lubricating property after annealing at 1000 or 1200 °C because of the formation of an H3BO3 layer during the annealing treatment. B4C ceramics annealed at 1200 °C exhibited the best self-lubricating properties, with the lowest coefficient of friction of approximately 0.08. The friction and wear mechanisms of B4C ceramics without and with a postannealing treatment are discussed in detail. [ABSTRACT FROM AUTHOR]

Cold massive forming, particularly forward extrusion of steel, is characterized by high material utilization, product quality, and resource efficiency. Currently, enormous quantities of mostly ecologically harmful lubricants are required, leading to the demand for lubricant‐free cold forming. Furthermore, cost savings are achievable due to shorter lead times. However, the requirements for the tools cannot be met without the application of wear‐resistant and friction‐reducing hard coatings. The self‐lubricating hard coatings (Cr,Al)N + Mo:S and (Cr,Al)N + W:S with attuned material design deposited by physical vapor deposition (PVD) offer high potential for the realization of dry cold forming of steel. The process chain for the comprehensive characterization of the developed coating systems comprises analyses of coating and compound properties as well as two different model tests to determine the tribological behavior. One of the used tribometers represents an open tribological system, which is particularly suitable for simulating the loads occurring during cold massive forming of steel. The analyses reveal that with Mo and S modified coatings exhibit higher potential for ecologically sustainable cold forming due to their better mechanical properties and compound properties between the coatings and the cold work steel substrate compared with W and S modified coatings. [ABSTRACT FROM AUTHOR]