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The primary objective of this research is to investigate the structure and tribological properties of NiCr–Mo–Ag–O/Mo–V–Ag–O bilayer films in a wide temperature range (RT-1000 °C). The bilayer films were prepared by pulsed laser deposition (PLD) technology, so as to provide the theoretical basis and experimental guidance for the study of the synergistic lubricating effect of Mo and V bimetallic lubricating oxides. The NiCr–Mo–Ag–O composite target was fabricated by the hot-press sintering technique. Subsequently, a NiCr–Mo–Ag–O/Mo–V–Ag–O bilayer film was deposited on Inconel 718 by pulsed laser deposition (PLD). The tribological properties of the film were evaluated by HRT-1000 high-temperature ball-on-disc configuration at RT-1000 °C. The obtained results reveal that the NiCr–Mo–Ag–O target is marked by a compact structure and homogeneous composition. Furthermore, the composite film exhibits a smooth surface and dense structure, comprised of polycrystalline and amorphous phases. The measured hardness and elastic modulus of the film approximated 4.9 GPa and 153.5 GPa, respectively. Additionally, the lowest friction coefficient of the film is about 0.28 at 800 °C. Upon reaching this temperature, the cooperative lubrication resulting from NiMoO4, Ag2Mo2O7, and AgVO3 contributed effectively towards reducing the film's friction coefficient.

The evolution of pearlite into an amorphous wrapped nanolamellar heterostructure (AWNH) within the tribolayer is an important process for the formation and stabilization of a nanocomposite self-lubricating surface. Here, experimental characterizations were performed to show that an AWNH was an intermediate product of transformation of pearlite to oxide nanoparticles and played a supporting role as a self-lubricating layer of the substrate. Furthermore, the molecular dynamics simulation method was used to analyze the wear properties and load-bearing capacities of four different microstructures to reveal the unique AWNH deformation mechanism and its effect on the self-lubrication behavior. The results showed that the AWNH exhibited a low friction and good wear resistance, which could be ascribed to its high hardness, high plasticity, and outstanding interface deformation coordination ability. The shear bands were restricted by the nanolamellar structure, and the shear transition zone that formed at the interfaces caused the plastic deformation to be uniformly distributed, which provided favorable conditions for supporting the self-lubricating layer. The results of this study provide theoretical guidance for analyzing the deformation mechanisms and tribological behaviors of AWNHs and help to optimize self-lubricating material design.

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]

The self-lubricating mechanism of Cu–Pb bearing alloy is discussed by molecular dynamics (MD). MD friction tests are conducted on the pure Cu and Cu–Pb models. The Pb-rich secondary phases (PSPs) melt due to the frictional heat. The solid–liquid phase transition of Pb is characterized by the radial distribution function (RDF) and the potential energy. An obvious drop of motion resistance of the abrasive debris is observed in Cu–Pb alloy once the debris moves close to the soft PSP which protect the matrix from abrasion by embedding the debris and promoting the formation of a liquid lubricant film. The synchrotron radiation technology is employed to in-situ observe the phase transition of Pb, and the MD results match the experimental results well.

Abstract 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, T m = 329 °C) and polyphenylene sulfide (PPS, T g = 84 °C, T m = 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-F ω ), temperature-centrifugal force-shearing force (T-F ω -F τ ) 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.

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]

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.

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]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica 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.)

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]

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]

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]

A self-lubricating composite coating Al 2 O 3 /C was designed and sprayed via atmospheric plasma spraying (APS), in order to endow the alumina coating with certain lubricating properties under room temperature conditions. The raw feeding powders of boehmite-alumina-graphite (AlO(OH)/Al 2 O 3 /C) with particle sizes of 30–50 µm were prepared through hydroxylation treatment, physical stirring, and spray granulation process. The tribological properties of the Al 2 O 3 /C composite coating were systematically studied using a CSM friction tester. The prepared Al 2 O 3 /C composite coating exhibited fewer defects, lower coefficient of friction (COF), and slighter adhesion wear degree compared to single-component Al 2 O 3 coating. The graphite lubrication film was discovered on both the worn surface of the composite coatings and the friction pair after friction. The existence of the graphite lubrication film decreased the COF, and the reduction extent depended on the load, with a maximum reduction of 55 %. The composite coatings presented the best tribological properties when sliding against Si 3 N 4 balls at a higher load (5 N) because of the diverse wear mechanisms and the influence of graphite lubrication film, resulting in a reduction in the COF and wear rate by approximately 48 % and 11 times respectively. In addition, part of γ-Al 2 O 3 in the Al 2 O 3 /C composite coating transformed into α-Al 2 O 3 after the friction test. But the Al 2 O 3 coating remained phase stable, with no phase change occurring before and after the friction. The transformation from the γ-Al 2 O 3 to the α-Al 2 O 3 phase was positive as for the tribological performance. It could reduce the COF as well as improving the thermal conductivity and mechanical properties of the coating. [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]

In this study, we have analyzed the effect of elastic deformations on the static characteristics of finite self-lubricating journal bearings. This analysis takes into account the rheological lubricant behavior which obeys to Rabinowitsch law. The governing equations considering both the fluid flow in the porous bush and the fluid film lubricant are based on Rabinowitsch fluid model and solved numerically using the finite difference method. The static performances of the porous journal bearings have been investigated for various parameters such as the elastic deformation parameter, the nonlinear factor which characterizes the pseudo-plastic fluid, the eccentricity ratio and the bush permeability. Obtained results demonstrated that the pseudo-plastic lubricant decreases the characteristics of the porous journal bearings compared to the Newtonian fluid lubricant. This reduction is more pronounced where the effect of both elasticity and permeability of the bush have been considered.

A novel thermoplastic polyurethane (TPU) matrix composite was combined with tetra-needle zinc oxide whisker (T-ZnOw) and molybdenum disulfide (MoS2) particles. Frictional vibration experiments were conducted to study the effect of T-ZnOw and MoS2 particles on frictional vibration behaviors. The tribological properties and vibration behaviors of TPU composites were synthetically analyzed to reveal the effects of T-ZnOw and MoS2 on the friction excitation force and vibration reduction properties. The results showed that T-ZnOw enhanced anti-deformation property, and MoS2 weakened the friction excitation force in the friction process, which resulted in a lower coefficient of friction (COF) with a small amplitude, and eliminated the high-frequency vibration amplitude. In addition, the particle composition of 6% T-ZnOw and 9% MoS2 was controlled to obtain a low COF and the best vibration reduction properties. The knowledge obtained herein contributes to the understanding of the synergistic effects of T-ZnOw and MoS2 on COF and vibration reduction behaviors, and the development of a water-lubricated TPU composite stern tube bearing with low COF and good vibration reduction properties.

Lignum vitae was widely applied in water-lubricated bearing because of its green, pollution-free, excellent mechanical, and self-lubricating properties. The slow growth cycle is difficult to meet the bearing's rapid development. Lignum vitae chips were used to modify thermoplastic polyurethane (TPU) to extend its good self-lubricating properties and improve tribological behaviors. The results showed that lignum vitae improve TPU's shore hardness, elastic modulus, and elongation, but at the slight cost of tensile strength and thermal stability. Besides, lignum vitae chips endowed TPU with good hydrophilicity and water absorption properties, which conduced to form effective lubricating film and reduced COF behaviors. TPU with 6% lignum vitae chips had the best COF reduction and wear resistance. But excessive lignum vitae chips weakened elastic modulus and elongation to increase COF behaviors and wear process. The outcome obtained herein would provide strong theoretical guidance for developing novel green and sustainable composites with excellent tribological properties.

In this study, Cu-matrix composites incorporating Ni-coated graphite and WS 2 were synthesized using the discharge plasma sintering (SPS) method. X-ray diffraction analysis (XRD) and infrared Raman spectroscopy were employed for the physical phase analysis of the composites while scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) were utilized to examine and analyze the morphology and composition of the composite surfaces. The findings revealed that substituting graphite with an equivalent volume fraction of nickel-coated graphite significantly enhanced the hardness and compressive strength of the Cu-NCG composites by 10.4 % and 61.6 %, respectively. Additionally, the Cu-NCG-WS 2 composite exhibits the lowest coefficient of friction (0.13), corresponding to the lowest wear rate (5.75×10−5 mm3/Nm). This superior lubrication performance can be attributed to the fine debris present on the composite surface, which effectively fills in the cracks and pits, replenishes the broken lubrication film, and thereby restores a smooth surface, achieving effective lubrication. • SPS rapid heating, short sintering, high quality, reduces Cu-WS 2 interaction. • The hardness and compressive strength of Cu-NCG and Cu-NCG-WS 2 composites are significantly improved compared to Cu-G. • The Cu-NCG-WS 2 composite material has the smallest friction coefficient (0.13) and the lowest wear rate (5.75×10−5 mm³/Nm). [ABSTRACT FROM AUTHOR]

A ballistic experiment on a semi-infinite RHA target impacted by two thicknesses clade 93 W rods (200 μm 718 alloy and 400 μm 718 alloy) with an impact velocity of 1500 ± 50 m/s is conducted to investigate the influence of 93 W surface deposited coating on penetration performance. Moreover, the findings are compared with those of an unclad 93 W rod. This study aims to provide a comprehensive microstructural overview of the penetration process, including the solid-state penetrator flow and the exchange interaction mode of rod and target (R.T.) materials, using optical metallography and electron microscopy. Results indicate that the coating area is composed of approximately equiaxed or short columnar cellular crystals. Furthermore, a metallurgical fusion layer is formed between the substrate and the coating, ensuring excellent bonding strength of the coating. No significant difference in the rheological mode is found between the interfaces of the 200 μm 718 alloy and 93 W R.T. materials, while the 400 μm 718 alloy forms a barrier mix zone at the interface between the R.T. This phenomenon alters the exchange mode of the target material and affects the interface flow mechanism. The barrier mix zone also acts as a solid-state lubricant at the interface, reducing the resistance to the rod's penetration. The average penetration depth of the 400 μm clad rod is 6.89 % higher than that of the 93 W rod. This finding reveals the clad material enhances the rod's performance and provides self-lubricating characteristics. • The electric spark deposition coating has obvious directionality, which can not only reduce penetration resistance but also provide a certain degree of radial strength for the rod. • Revealed the penetration gain mechanism of clad rod. [ABSTRACT FROM AUTHOR]

Inspired by the mechanism of skiing, herein, a novel composite coating with excellent lubrication properties was developed by incorporating solid-liquid reversible lubricating phases into the inherent microcracks and pores of thermally sprayed ceramic coatings. The results indicate that the crystalline-amorphous heterostructure formed within the micro-nano cracks, enhancing their cohesive strength and toughness. Compared to traditional ceramic coatings, the friction coefficient of the composite coating has been reduced by 80 %, while the wear rate decreased from 2.89 × 10−4 to 6.44 × 10−7 mm3∙N−1∙m−1. Under the applied load and friction-induced heat, a thin liquid lubrication film is formed. Importantly, the lubricating phase continuously overflows from defects under the induction of frictional heat to replenish the lubricating film, ensuring long-term lubrication of the coating. [Display omitted] • Inspired by skiing mechanisms, a novel self-lubricating coating was developed. • The heterostructure formation improves the coating's mechanical properties. • The composite coating exhibited superior tribological properties. • A well-covered robust lubricating film was formed at the friction interface. • The lubricating phase overflows because of frictional heat, ensuring long-term lubrication. [ABSTRACT FROM AUTHOR]

For CoCrNi medium entropy alloy (MEA) with desired mechanical properties, its underperforming tribological properties have become a barrier to technical applications. In contrast to the introduction of extrinsic lubricants, this paper proposes a novel and simple strategy that several advanced CoCrNi-based self-lubricating and wear-resistant composites were fabricated by doping SiC precursors to in-situ introduce self-lubricating and reinforcement components. The self-lubricating composite reaches dry coefficient of friction (COF) 0.23 and ultra-low wear rate 8.1 × 10−6 mm3N−1m−1 (about 1/30 of CoCrNi MEA). It have robust adaptability to multiple lubes simultaneously, and the COF is rapidly stable to about 0.1. Because composite contains moderate lubricating, anti-wear and plasticity phases, which providing optimal trade-off between anti-friction and wear-resistance under different friction conditions. [ABSTRACT FROM AUTHOR]

The unsatisfactory wear resistance and lubrication performance of CoCrNi multi-principal elements alloys (MPEAs) have emerged as critical challenges, impeding their extensive utilization as advanced engineering materials, despite their desirable mechanical and physical properties. Incorporating graphite to obtain MPEAs-based self-lubricating composites is believed to improve the wear resistance. However, it is challenging to prepare composites with high strength, large plasticity, and excellent anti-friction performance simultaneously. The present study reports the fabrication of novel CoCrNi MPEA-based self-lubricating composites, consisting of in-situ graphite and high-hardness silicides/carbides as reinforcement, prepared by powder metallurgy and reactive sintering. The 20.6 vol% Gr@CoCrNi–SiC composite exhibits an optimal trade-off between strength and ductility, along with anti-friction and wear resistance which is superior to the reported composites with different solid lubricants. The wear mechanism is attributed to the coordinated deformation mechanism between the CoCrNi FCC matrix and silicides/carbides, and the stabile lubrication effect supported by the structural transformation from the original polycrystalline lattice structure to core-shell nanocomposite structure (similar to diamond-like carbon) of the in-situ graphite. This simple, economical and practical strategy contributes to the development of MPEA self-lubricating composites with excellent comprehensive properties. [Display omitted] [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]

304 stainless steel has poor tribological properties at medium and high temperatures, severely limiting its application to the important frictional motion auxiliary parts. In order to improve the tribological properties of 304 stainless steel,Ni60 powder was used as toughening phase,WS2 acted as precursor for synthetic lubricating phase,TiC used as high-hardness and wear-resistant phase,and high-energy laser beam was used to in-situ synthesize a self-lubricating and anti-wear composite coating on its surface. The phase compositions, microstructure,microhardness and surface topogr-aphies of the coating and substrate were characterized by XRD,SEM,microhardness tester,friction and wear tester and the probe-type surface profilometer, and the tribological properties as well as the corresponding wear mechanisms of the coating and substrate at 20,300,600,800 ℃ were systematically studied. Results indicate that the coating is mainly composed of Cr0.19Fe0.7Ni0.11,Ti2SC,Fe2C,Cr7C3,CrS and WS2. Although the average microhardness of the coating (302.0HV0.5) is slightly higher than that of the substrate (257.2HV0.5), the hardness of the upper region of the coating (425.4HV0.5) is about 1.65 times that of the substrate. The friction coefficients and wear rates of coating are lower than that of the substrate at all the isothermal tribological experiments. The coating possesses the best lubrication effect at 300 ℃ with friction coefficient of 0.3031, and the best wear resistance at 600 ℃ with a wear rate of 9.699×10-5 mm3·N-1·m-1.

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]

This paper reports on the fabrication and tribological performances of surface textured plasma electrolytic oxidized (PEO) coatings containing polytetrafluoroethylene (PTFE) on aluminum alloy (PEO/PTFE). The ordered arrays of circular dimples were created on PEO ceramic coating surface by laser surface texturing and vacuum penetration of nanosized-PTFE was followed in vacuum chamber. The tribological properties of PEO/PTFE and textured PEO/PTFE coatings were evaluated at load of 5–25 N using a UMT-4 tribometer under dry condition. The results shown that surface texturing can effectively reduce the friction coefficient of contact interface for 72,000 cycles at 5 N and greatly improve the bearing capacity of PEO/PTFE coating, because of the constantly compensation of lubricating PTFE film in the wear track. This study established a new approach to fabricate self-lubricating ceramic PEO coating on aluminum alloys.

The cooling rate during fabrication affects the microstructural features and interface strength in metal matrix composites (MMCs). Thus, the present investigation is focused on characterizing the effect of quenching medium on wear and friction response of self-lubricating Al-Cu dual matrix composites. Mica was reinforced in Al-Cu metal matrix composites with the variation of weight percentage as 1%, 2%, 3%, 5%, 8% and 10%. A standard powder metallurgy route was adopted for fabrication. The sintered composites were normalized, and quenched in water, and oil. A pin on disc study was carried to investigate the friction and wear behavior of normalized, oil quenched, water quenched and as-prepared (green) composites. The results revealed that oil quenched composites exhibited the lowest friction coefficient and highest wear loss. The highest friction coefficient of ~0.8 was observed for normalized composites, whereas the highest friction coefficient for water quenched composites was ~0.6. The oil quenched composites exhibited about 8 ~ 15 times higher wear loss as compared to normalized and water quenched composites. Worn surfaces were analyzed under a scanning electron microscope to know the dominant wear mechanisms. The developed composites find potential applications in automotive industry such as pistons for petrol and diesel engines.

In order to improve the anti-wear properties of 300M super-strength steel for aircraft landing gear shock absorbing strut, and to break through the technical bottleneck such as cracks induced by the excessive temperature gradient in laser cladding wear-resistant anti-corrosion self-lubricating coating, the "birth and death" method and the APDL procedure of ANSYS were used to simulate the molten pool's thermal cycle for the 300M super-strength steel's laser cladding wear-resistant anti-corrosion self-lubricating coating. The change of thermophysical parameters with different temperatures for self-lubricant and wear-resistant materials , latent heat in phase change, external heat exchange during laser cladding, laser cladding power, laser cladding scanning velocity and other factors, which affect the temperature field, molten pool, temperature gradient during the laser cladding process were considered. The results indicate that the melting of the substrate requires a combination of laser and molten powder, etc. to bring the effective energy conducted to the region reach the critical value of melting, the increase rate of the melting height of the substrate decreases first and then increases with the increase of the laser power, the decrease rate of the melting height of the substrate decreases first and then becomes larger with the increase of the laser scanning speed. Due to the comprehensive factors of different temperatures and cooling rates in different laser cladding areas, the vertical section of the laser cladding wear-resistant anti-corrosion self-lubricating coating bath is a spoon-shaped molten pool. With the increase of the laser power, due to the difference in the temperature response of the energy input to different regions of the cladding layer, the temperature gradient in the Z-direction and the maximum cooling rate increases. With the increase of laser scanning velocity, the laser input energy decreases, which decreases the combined effects of high-temperature region temperature and rapid local heating of the laser. Meanwhile, the temperature gradient in the Z-direction decreases. Under the condition of maintaining the bonding strength of the cladding layer, the substrate melting zone can be controlled to minimize and lower the temperature gradient by controlling laser parameters reasonably.