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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]

Inspired by rhombic textures on shark skin surface, this paper designs bionic micro-textures filled by solid lubricants SnAgCu and Ti3C2TX to improve the tribological properties of 42CrMo steel. Compared with 42CrMo steel, the average friction coefficient and wear depth of 42CrMo-SnAgCu-Ti3C2TX with bionic micro-textures at 25 N were separately decreased by 41.52 and 79.07%, and decreased by 50.77 and 80% at 35 N, respectively. Two-dimensional material Ti3C2TX can be well combined with SnAgCu to promote the formation of a smooth and continuous lubricating film on the worn surface, which plays an excellent antifriction and wear resistance role under the specific working conditions. [ABSTRACT FROM AUTHOR]

To improve the tribo-performance of molybdenum disulphide lithium grease (MDLG), the tribological behaviors of 42CrMo under grease lubrication with Ti3C2 as an additive were systematically studied. The results show that when the concentration of MXenes-Ti3C2 in MDLG is 2 wt.%, the friction coefficient and wear volume loss could be respectively reduced by a maximum of 69 and 98%. This is mainly attributed to the graphitization of MXenes-Ti3C2 induced by the friction. It retards the breakage of soap fibers and in turn significantly improves the tribological performance of MDLG under the low speed and high load conditions. In order to predict better working conditions for obtaining the excellent tribological behavior, the experimental results were used to develop a Genetic Algorithm-Artificial Neural Network (GA-ANN) model. Under the predicted working conditions, the estimated friction coefficient (R2 = 0.993) and wear volume loss (R2 = 0.934) were close to the experimental results. This study could provide the support for the application of MXenes-Ti3C2 as an additive in the lubrication grease. [ABSTRACT FROM AUTHOR]

To improve the tribological performance of CSS-42L bearing steel, smooth surfaces (SSs), groove-textured surfaces (GSs), GSs with Sn-Ag-Cu (GSs-SAC), and GSs with Sn-Ag-Cu-Ti3C2 (GSs-SACT) were prepared on CSS-42L. In addition, experimental studies were conducted on tribological properties. The obtained results indicated that GSs-SACT exhibited the best anti-friction and noise reduction performances. These remarkable tribological performances were attributed to the synergistic effects of grooves, Sn-Ag-Cu, and MXene-Ti3C2. The inconsistent rules of frictional forces were improved by the grooves and SACT, which inhibit the friction-induced noise. The micro-nano size-effects of MXene-Ti3C2 enhanced the repairing effect and anti-friction property of composite lubricants, which improved the profile characteristics of GSs-SACT. [ABSTRACT FROM AUTHOR]

In order to meet the stricter friction performance requirements of large machinery in the application field of slewing bearing, 42CrMo steel is taken as the research object. Through the preparation of smooth surface, groove textured surfaces with different densities and deposited Sn-Ag-Cu (SAC) solid lubricants, the tribological properties of samples with different surface treatments were, respectively, studied under the grease lubrication. The results show that the design of grooves can effectively alleviate the secondary damage of wear debris on the sample surfaces. Under the grease lubrication, the sample with SAC deposited on the surface has the smallest friction coefficient and deformation, which is mainly attributed to the synergistic effect among grooves, solid lubricants, and grease. [ABSTRACT FROM AUTHOR]

To expand the applications of MXene-Ti3C2 in the field of oil lubrication, rounded groove surfaces filled with Sn-Ag-Cu-Ti3C2 on CSS-42L bearing steel (RGSs-SACT-600) were prepared. Block-on-ring friction and vibration tests under oil lubrication were carried out. The results showed that the synergistic effects of Sn-Ag-Cu-Ti3C2 and grooves improved the variation characteristics of friction forces and reduced friction and vibration on the surfaces. Sn-Ag-Cu-Ti3C2 with excellent adsorption to lubricating oil suppressed the oil film rupture and improved the heat dissipation at the friction interface. The tribochemical reactions were induced by Sn-Ag-Cu and Sn-Ag-Cu-Ti3C2, improving the tribological properties on the worn surfaces. Under low speed and high load, RGSs-SACT-600 with uniform profiles had excellent bearing capacity and antifriction performance. [ABSTRACT FROM AUTHOR]

M50 steel is one of the most widely used high-performance bearing steels, and the tribological properties are related to its service life. In this paper, the dry sliding tribological tests of M50, M50-Sn-Ag-Cu and M50-Sn-Ag-Cu-Ti3C2 against Si3N4 ceramic balls under different loads were carried out. Through the analysis of worn surface and cross section of wear scar, as well as characteristics of friction signal, the causes of frictional noise are discussed, and the influence of Ti3C2 on the frictional noise is revealed. The results show that the addition of Ti3C2 can significantly improve the tribological performance of M50-Sn-Ag-Cu-Ti3C2, reduce the intensity of frictional noise and suppress its high-frequency components. Frictional noise is caused by the system energy dissipation due to the contact surface roughness. The synergistic effect of Ti3C2 and Sn-Ag-Cu makes the lubricant be easily extruded to the contact surface, which will form a protective layer on the worn surface, thus reducing the surface roughness and frictional noise and improving the tribological performance. [ABSTRACT FROM AUTHOR]

Improving the tribological properties and reducing the friction noise of Inconel 625 is of great significance for the extended application of Inconel 625 in mechanical parts and other fields. In this paper, composite anti-wear surfaces (CASs) with micro-texture filled by Sn-Ag-Cu (SAC) were prepared. The tribological and frictional noise properties of CASs and smooth surface (SS) with different texture spacing during dry sliding friction process were studied through a series of experiments, tests and analyses. The results show that CASs can improve tribological properties and noise suppression performance significantly. With the texture density of 25 % (CASs-1200), the friction coefficient is 0.464 under a load of 20 N, the wear rate is about 2.65×10−5 mm3/(N·m), and the friction noise is 88-89.5 dB. Due to the synergistic effect of surface microgrooves and solid lubricants, the excellent tribological performance of CASs was realized. Microgrooves make the lubricant mixture be easier precipitated onto the worn surface. An intact lubrication film with high shear fitness was formed on the worn surface, reducing the direct contact between the grinding ball and the substrate. Meanwhile, it reduces the radiated energy generated by the collision between the counterpart ball and matrix and the transition of counterpart ball on the uneven small platform, so as to achieve the effect of noise suppression. Especially, suppression effect of high-frequency noise in 2400-3000 Hz is close to 100 % in CASs-1200, inhibiting the high-frequency scream effectively. [ABSTRACT FROM AUTHOR]

The poor tribological performance of TC4 alloy limits its wide application in engineering field. Inspired by the layered structure of shell, the bionic composite coating of TC4-SnAgCu (TSAC) on TC4 was designed. The coatings with three different lubricant concentration ratios of TC4-5wt.%SnAgCu (TSAC-5), TC4-10wt.%SnAgCu (TSAC-10) and TC4-15wt.%SnAgCu (TSAC-15) were prepared using laser additive manufacturing (LAM) technology, respectively. Tribological tests were, respectively, carried out at the loads of 10 N, 15 N, 20 N and 25 N. The results show that compared with TC4, TC4 with bionic coating has better tribological behaviors and reducing ability of friction-induced vibration and noise. Furthermore, at 20 N and room temperature, the complete lubrication film is more easily formed on the worn surface of TSAC-10. Hence, TSAC-10 obtains the minimum friction coefficient and average equivalent noise pressure, which are, respectively, reduced by 21.28 % and 18.76 % compared to those of TC4. [ABSTRACT FROM AUTHOR]

The bionic rhombic textures with SnAgCu and Nb2C were used to improve tribological properties of M50. Compared with M50, friction coefficient and wear depth of M50-SnAgCu-Nb2C with 45° textures at 15 N were separately decreased by 42.67 and 70.37%, and those of M50-SnAgCu-Nb2C with 60° textures at 25 N were, respectively, decreased by 42.04 and 65.03%. Nb2C can promote the combination and spread of composite lubricants in bionic textures, and a uniform and dense lubrication layer was formed at the interface. The synergistic effect of SnAgCu-Nb2C and bionic textures can play an excellent antifriction and wear resistance role under specific working conditions. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to investigate the friction noise properties of M50 matrix curved microporous channel composites filled with solid lubricant Sn-Ag-Cu (MS). Design/methodology/approach: Pure M50 (MA) and MS are prepared by selective laser melting and vacuum-pressure infiltration technology. The tribological and friction noise properties of MA and MS are tested through dry sliding friction and then the influential mechanism of surface wear sate on friction noise is investigated by analyzing the variation law of noise signals and the worn surface characteristics of MS. Findings: Experimental results show that the friction noise sound pressure level of MS is only 75.6 dB, and it mainly consists of low-frequency noise. The Sn-Ag-Cu improves the surface wear state, which reduces self-excited vibration of the interface caused by fluctuation of friction force, leading to the decrease of friction noise. Originality/value: This investigation is meaningful to improve the tribological property and suppress the friction noise of M50 bearing steel. [ABSTRACT FROM AUTHOR]

High wear is the primary failure mechanism of Inconel 625 in mechanical parts. The surface modification is workable method to improve tribological performance of Inconel 625. In this paper, the groove-textured surfaces with different widths and pitches were prepared on the surfaces of Inconel 625 by electrical discharge machining technology. The Sn-Ag-Cu solid lubricant was deposited on the grooves. The synergistic effects of Sn-Ag-Cu solid lubricant and groove-textured surface on the tribological performance of Inconel 625 were studied. Results show that the groove-textured surface of Inconel 625 filled with Sn-Ag-Cu solid lubricant shows the lowest friction. Compared with the untextured sample, the friction coefficients of groove-textured sample with the groove density of 20% and the groove-textured sample with the groove density of 25% filled by Sn-Ag-Cu are reduced 35% and 48%, respectively. The textures can trap wear debris under the dry sliding condition. In addition, Sn-Ag-Cu alloys filled in the grooves supply the sufficient lubricant at the contact interface during the sliding process. The lubricating film on the contact surface is formed gradually, which is mainly due to the shear adaptability and low melting point of Sn-Ag-Cu alloy. It shows that deposition of Sn-Ag-Cu solid lubricant coating on the groove-textured surface is an effective way for improving the friction and wear performance of Inconel 625. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to explore the damage mechanism of a lubricating film on the worn surface of solid self-lubricating composites under different loads. Design/methodology/approach: By comparing the actual stress with the strength, it is possible to determine the approximate wear state of the lubricating film. To prove the validity of the mathematical model that can predict the initiation of micro cracks or even the failure of the lubricating film, M50-5 Wt.% Ag self-lubricating composites (MA) was prepared. Tribological tests of the composites against Si3N4 ceramic balls were conducted at room temperature from 2 to 8 N. The electron probe microanalysis images of the lubricating film verify the wear state of the lubricating film. Findings: The study found that the back edge of the contact area is the most vulnerable to destruction. The tensile stress and the equivalent shear stress have a positive correlation with load and friction coefficient. When the load is 4 N, an intact lubricating film covers the worn surface because the tensile stress and the equivalent shear stress are below the tensile strength and the shear strength, respectively; under other working conditions, the lubricating film is destroyed. Originality/value: This paper has certain theoretical guidance for the study of tribological properties of solid self-lubricating composites. Moreover, this mathematical model is appropriate to be applied for the other composites. [ABSTRACT FROM AUTHOR]

Abstract The potential tribological properties of load-adaptive M50-based self-lubricating composites under various loads were investigated. Pure M50 and M50 composite containing 10 wt%(50Sn40Ag10Cu) (MSAC) samples were prepared by spark plasma sintering. Besides, samples M50 and MSAC, which were all surface-scattered with C60 microparticles, were defined as M-C and MSAC-C, respectively, and the tribological tests of M50, MSAC, M-C, and MSAC-C sliding against Si 3 N 4 ball from 2 to 18N at 0.2 m/s-350 °C were performed. Results show that MSAC-C exhibits the excellent friction and wear performance within the range of loads. Analysis indicates that this phenomenon is mainly due to the formation of a composite lubricating film rich in soft metal lubricant Sn-Ag-Cu and C60 microparticles. Graphical abstract Image 1 Highlights • Sn-Ag-Cu provides excellent lubricating properties within the low loads from 2 to 12N. • C60 provides excellent lubricating properties within the high loads from 12 to 18N. • (Sn-Ag-Cu)-C60 has the merit of load-adaptive action to produce good lubrication. • Compounds of Fe 2 O 3 , CuO produced friction process can enhance lubrication capacities. [ABSTRACT FROM AUTHOR]

As one of the most widely used high-performance bearing steels, the service life of M50 steel is closely related to its tribological properties. In this paper, the dry sliding tribological tests of M50 matrix composite containing 5.0 wt.% Ag and 5.0 wt.% carbon fiber (CF) against Si3N4 ceramic balls are carried out under different applied loads. The morphologies and compositions of worn surfaces and the cross sections of worn scars are systematically characterized to explore the wear mechanisms. The results indicate that M50-Ag-CF composites (MAC) exhibit the excellent tribological properties at 10 N, whose friction coefficient and wear rate are 0.212 and 1.6 × 10−6 mm3 N−1 m−1, respectively. The excellent tribological performance can be attributed to the synergistic effect of Ag and CF. Massive Ag is enriched on the friction surface to form a lubricating film, thus reducing the surface roughness and friction coefficient. Meanwhile, CF acts as a reinforcement and improves the wear resistance of M50 matrix composites. [ABSTRACT FROM AUTHOR]

Dry tribological tests of M50 matrix composites containing 0, 2.5, 5.0, and 7.5 wt% Ag are undertaken at 0.2 m/second 15 N from 25°C to 450°C against Si3N4 ceramic balls. The results indicate that the tribological performance is strongly dependent on the content of solid lubricant Ag. M50 matrix composites containing 5.0 wt% Ag exhibits the great tribological performance with the low friction coefficients of 0.23 to 0.43 and less wear rates of 1.89 to 3.52 × 10−6 mm3 N−1 m−1 from 25°C to 450°C, which is attributed to the formation of thick lubricating film on the worn surface. Furthermore, the migration model of solid lubricant Ag in M50 matrix composites is established to predict the thickness of formed lubricating film. [ABSTRACT FROM AUTHOR]

M50 steel is the main material used in aircraft bearings, and its friction performance will directly affect the reliability and service life of the whole bearing. Hence, this paper focuses on the tribological behavior and self-healing function of as-prepared M50 steel-based self-lubricating material covered with surface micropores filled with Sn-Ag-Cu (MMSAC). Friction results show that MMSAC exhibits the distinguished tribological behavior. Analysis indicates that this is mainly due to the lubricating film formed on the worn surface and the self-healing behavior on the worn surface of MMSAC. Sn-Ag-Cu in micropores can precipitate onto the friction surface to form the lubricating film, while the volume expansion caused by the oxidation of Sn and Cu plays an important role in filling cracks. [ABSTRACT FROM AUTHOR]

Abstract As the main steel used in aircraft bearings, tribological properties of M50 directly affect the performance of aero-engines. In this paper, the anti-friction and wear properties of friction surface of M50-10 wt%(50Sn40Ag10Cu) composites (MSACC-2) sliding against Si 3 N 4 ball from 25 to 450 °C were investigated. XRD, XPS, EPMA, FESEM, and EDS mapping were conducted to understand the major mechanism leading to the improvement in the sliding behavior of MSACC-2. Results show that the surface of MSACC-2 exhibits excellent anti-friction and wear performances from 25 to 450 °C. At 350 °C, MSACC-2 shows the best tribological performance (0.18–0.27, 1.5–2.2 × 10−6mm3N−1m−1). It is attributed to the formed lubricating structure on the friction surface which is composed of the upper surface lubricating layer and underneath load-bearing layer. The surface lubricating layer mainly contains massive added Sn-Ag-Cu, intermetallic compounds of Cu 6 Sn 5 and Ag 3 Sn produced during the preparation process, and FeSn, FeSn 2 and oxides formed in friction process. The load-bearing layer can support the surface lubricating layer to play an outstanding anti-friction and wear effect. Moreover, the martensitic phase transformation on surfaces caused by Sn-Ag-Cu and the action of cyclic stress of Si 3 N 4 balls makes MSACC-2 have more excellent wear resistance performance. Graphical abstract Image 1 Highlights • The surface of MSACC-2 exhibits excellent anti-friction and wear properties. • 50Sn40Ag10Cu is an ideal solid lubricant for M50 over a wide temperature range. • Lubricating structure on surface consists of lubricating layer and load-bearing layer. • Lubricating layer contains added Sn-Ag-Cu and Ag 3 Sn, FeSn 2 produced during friction. • Phase transformation on surface makes MSACC-2 exhibit the best wear resistance. [ABSTRACT FROM AUTHOR]

As the main steel used in the aero-engine main shaft bearings, the tribological properties of M50 can directly affect the performance of aero-engine. The purpose of this study is to design the reasonable composition of Sn-Ag-Cu alloy and investigate the wear mechanisms of M50-10 wt.%(Sn-Ag-Cu) composites (MSACC) prepared by SPS sliding against Si3N4 ball from 25 to 550 °C at 12 N-0.25 m/s. XRD, EPMA, FESEM and EDS mappings are conducted to understand the major mechanisms leading to the improvement in the sliding behavior of MSACC. The results indicate that MSACC with different specifications of Sn-Ag-Cu alloy shows excellent friction and wear properties from 25 to 550 °C compared to M50. M50-10 wt.%(50Sn40Ag10Cu) (MSACC-2) shows the distinguished tribological performance for the lower friction coefficients of 0.22-0.61 and less wear rates of 1.7-4.1 × 10−6 mm3 N−1 m−1, which is attributed to the formed excellent lubricating structure consisting of the lubricating film with massive Sn-Ag-Cu alloy and intermetallic compounds formed during the friction process, as well as the underneath mixed layer who can well support the lubricating film due to the good intersolubility between the designed Sn-Ag-Cu alloy and M50 (Fe). [ABSTRACT FROM AUTHOR]

The sliding friction and wear behaviors of TiAl-multilayer graphene (MLG)-silver composites (TMSCs) sliding against Si 3 N 4 balls from 0.10 to 0.30  m/s were studied in this paper. The tribological test results showed that friction coefficient and wear rate of TMSCs decreased with the increasing of sliding speed from 0.10 to 0.30  m/s. TMSCs exhibited the lower fiction coefficient and the less wear rate at 0.30  m/s, which was attributed to the formation of intact tribo-film containing MLG and Ag on the worn surface. In the formed tribo-film, Ag worked as the solid lubricant to provide good lubricating effect, while MLG with high strength played the active role in enhancing the anti-rupture ability of tribo-film. It indicated that TMSCs obtained the excellent tribological performance due to the remarkable synergistic effect of MLG and Ag. Moreover, the friction heat increased with the increase of sliding speed, which made contributions to the formation of tribo-film. [ABSTRACT FROM AUTHOR]

M50 steel is widely used in aero-engine bearings and other high-temperature bearings. However, the poor wear of M50 steel resistance restrains its further applications. In this paper, the sliding tribological behaviors of M50 steel, M50-Ag composites (MAC) and M50-Ag-TiC composites (MATC) against Si3N4 ball were investigated from 150 to 600 °C at 15 N-0.2 m/s. MATC showed better tribological properties in comparison with M50 and MAC. Especially at 450 °C, MATC obtained the lowest friction coefficient of 0.15 and smallest wear rate of 1.3 × 10−5 mm3 N−1 m−1. The excellent tribological performance of MATC during the friction test was attributed to the continuous lubricating film containing lubricant Ag and reinforcement TiC, as well as the subsurface compacted layer that could well support the lubricating film to prevent it from being destroyed. At 600 °C, because of the tribo-chemical reaction between Ag and Mo oxide during sliding process, the newly formed Ag2MoO4 lubricating film was well spread out on the friction surface, which could continuously improve the tribological behavior of MATC. This investigation was meaningful to improve the anti-friction and wear resistance of M50 matrix bearing over a wide temperature range. [ABSTRACT FROM AUTHOR]

It was significant to study the longevity of mechanical component by analyzing the effect of friction layer on the predicting models of wear rates and friction coefficients. In this study, based on the changes in applied load F and testing temperature T, the friction and wear behaviors of TiAl-10 wt.% Ag were carried out sliding against Si3N4 ball (6 mm in diameter). At 0–80 min, the prediction models of friction coefficients and wear rates were constructed by the method of bivariate rational interpolation. The predicting accuracies of Pcomp-f: 94–98.7% (friction coefficient) and Pcomp-w: 87.7–98.5% (wear rate) indicated that the constructed prediction model was able to evaluate the friction coefficients and wear rates of TiAl-10 wt.% Ag. The high predicting accuracies were mainly attributed to the excellent plastic fluidity of silver, the smooth morphology of wear scar, and the friction layer of low grain strain. [ABSTRACT FROM AUTHOR]

In order to study the effect of scanning velocity on the microstructure and tribological properties of Ni3Al matrix composites containing graphene nanoplatelets (NGs), a series of NG samples are successfully synthesized by laser melt deposition under the various scanning velocities from 300 to 500 mm s−1. The sliding friction tests of NG against GCr15 steel balls are carried out under 10 N and 0.2 m s−1 at room temperature. The microstructures, tribological properties and wear mechanisms of the NG samples are analyzed. The results show that the scanning velocity can be optimized to effectively control the surface hardness and relative density, as well as tribological performance of NG. The NG sample synthesized under scanning velocity of 450 mm s−1 has a dense and fine microstructure as well as excellent properties such as higher relative density (98.6%), lower friction coefficient (0.23) and wear rate (5.5 × 10−6 mm3 N−1 m−1). The lower substrate layer with dense and stable structure plays an important role in supporting the upper glaze layer with rich graphene and oxides, as well as nanocrystalline structure, which contributes to the excellent friction-reducing and wear resistance performances of NG. The research results could be used to guide the selection of suitable scanning velocity and study the wear mechanisms of NG for having excellent tribological performance. [ABSTRACT FROM AUTHOR]

In order to improve tribological performance of NiAl-based alloy, NiAl matrix composites containing 1.5 wt.% multilayer graphene (MLG) are prepared through additive manufacturing (AM) and spark plasma sintering (SPS), which are denoted as NMAM and NMSPS, respectively. Tribological behaviors of NMAM and NMSPS against SiN balls are researched under constant speed (0.2 m/s) and varied loads (from 4 to 16 N) for evaluating the tribological properties of NMAM and NMSPS. The results present that NMAM exhibits the excellent tribological properties [low friction coefficients (0.26-0.40) and considerable wear resistance (2.8-4.6 × 10 mm N m)] as compared to NMSPS, which attributes to the uniform enrichment of MLG with properties of high tensile strength and being easily sheared off on the worn surfaces. Owing to the use of spherical prealloyed powder containing multilayer graphene and the characteristics of layer by layer depositing in the AM process, NMAM has a more compact and uniform substrate, which persistently provides a source of the formation of continuous and stable frictional layer. Due to the characteristics of AM rapid solidification, NMAM has the small grain size and well-compacted microstructure, which can effectively reduce the probability of spalling wear and lead to the increase in wear resistance of materials. The research can offer the reference for self-lubricating materials prepared by AM technology. [ABSTRACT FROM AUTHOR]

This article was dedicated to explore the combined lubrication of silver, MoS and carbon nanotubes (CNTs) based on the changes in applied loads and sliding speeds. The results showed that the formed lubricating films played the major role in undertaking the equivalent stress, as well as effectively reduced friction resistance and material loss. It led to small friction coefficient and less wear rate at 1.2 m/s. At 1.2 m/s-16 N, an integrated lubricating film containing Ag, CNTs and MoS was continuously formed, which well provided the excellent lubricating property, resulting in lower friction coefficient (0.19) and less wear rate (1.56 × 10 mm/N m). The formation of Ag and CNTs enriched islands acted as the bearing areas and played the major role in resisting friction resistance. Meanwhile, solid lubricant MoS was enriched in the lubricating film and effectively protected lubricating film from being destroyed, resulting in small friction coefficient and less wear rate at 1.2 m/s-16 N. [ABSTRACT FROM AUTHOR]

This study aimed to explore the possibility of improving the tribological performance of NiAl matrix composites by graphene addition. Friction and wear experiments of as-prepared specimens were conducted under different conditions using a pin-on-disk wear testing machine. NiAl matrix composites containing graphene showed satisfactory performance in friction coefficient and wear resistance compared to NiAl matrix composites without graphene. For the active effect of graphene, the friction coefficient and wear rate of NiAl matrix composites were maintained at relatively lower values. The beneficial antifriction and antiwear effects of graphene gradually failed when the applied load was above 8 N. Graphene in NiAl matrix composites played an active role in the formation of a friction layer, which was beneficial to the lower friction coefficient and wear rate. In light of this research, graphene plays an active role in reducing the friction coefficient and wear rate. Hence, graphene has great potential in applications as an effective solid lubricant to promote tribological behavior. [ABSTRACT FROM AUTHOR]

A favorable hardness ratio (Hdisk/Hpin = Hd/Hp) could lead to a transition to mild wear during sliding contact. To determine a more appropriate Hd/Hp value for the sliding wear, the dry sliding pin-on-disk wear tests of Ni3Al matrix composites (NMCs) with multilayer graphene (MLG) are undertaken at Hd/Hp values of 0.99, 0.83, 0.42, and 0.35 at sliding speeds of 0.1, 0.3, 0.5, and 0.7 m/s. It is found that the tribological properties of NMCs are strongly affected by the various hardness ratios. At 0.1 m/s, the friction coefficient decreases with a decrease in Hd/Hp value. The low friction coefficient is 0.14 and the wear rate is 0.9 × 10-5 mm3 N-1m-1 under the ceramic counterpart with Hd/Hp of 0.35. At 0.7 m/s, the tribological properties show the opposite trend with a decrease in Hd/Hp. At an Hd/Hp of 0.35, the smooth compact layer on the worn surface could decrease the friction at 0.1 m/s, and the improved hardness in the subsurface by strain hardening would play an important role in the improvement of wear resistance. Under the metal counterpart with Hd/Hp of 0.99, plastic deformation only occurs on the contact surface and the MLG could suppress further shear deformation in the subsurface, leading to a low wear rate (2.4 × 10-5 mm3 N-1m-1) and friction coefficient (0.15) at 0.7 m/s. [ABSTRACT FROM AUTHOR]

In this study, the effect of friction layer thickness and subsurface nano-hardness of wear track on tribological behavior of γ-TiAl matrix composites is investigated. The results of dry sliding tribolocial tests of γ-TiAl matrix composites with 0-2.25 wt.% multilayer graphene (MLG) (0.25 wt.% in tolerance) under different applied loads are reported. The testing results show that the optimized addition amount of MLG is 1.75 wt.% at 12 N (friction layer thickness 3.23 µm, subsurface nano-hardness of wear track 9.03 GPa). It can be found that a continuous and thick friction layer is formed in γ-TiAl-1.75 wt.% MLG at 12 N, resulting in a lower friction coefficient of 0.31 and wear rate of 2.09 × 10 mm N m. During dry sliding process, the high subsurface nano-hardness of wear track leads to the increase in resisting plastic deformation capacity and reduces the material loss. Meanwhile, the thick friction layer contains MLG with high tensile strength which is easily sheared off. Hence, γ-TiAl matrix composites show excellent tribological performance of a friction-reducing and an increase in wear resistance. The investigation shows that γ-TiAl-1.75 wt.% MLG, due to its excellent tribological behavior at 12 N, can be chosen as a promising structural material for minimizing friction- and wear-related mechanical failures in sliding mechanical components. [ABSTRACT FROM AUTHOR]

The contact stresses of materials in moving mechanical assemblies are rather important for minimizing friction and decreasing machinery energy dissipation. In this study, the effect of contact stresses on the friction and wear behaviors of TiAl-10 wt.%Ag was studied at 0-240 min using the united methods of experiment research, numerical simulation and theoretical analysis. The results showed that the high contact stresses led to the plastic deformation of TiAl-10 wt.%Ag at 0-50 min. The friction coefficients and wear rates decreased rapidly with the lowering of contact stresses from 1034.28 to 710.52 MPa. At elastic deformation stage (50-240 min), the forming of lubricating film was beneficial to the decrease in friction coefficients and wear rates at 50-150 min, whereas the lower contact stresses caused the increasing of friction coefficients and wear rates. The competition between film lubrication and contact stresses caused the lowering of friction coefficients and wear rates at 50-150 min. At 150-240 min, the lubricating film maintained the equivalent lubricating behaviors, whereas the lowering of contact stresses led to the slight improving of friction coefficients and wear rates. This study was meaningful for optimizing applied loads to realize the excellent contact stress state and tribological behavior of mechanical parts. [ABSTRACT FROM AUTHOR]

A dislocation-density-based model is selected to investigate the mechanisms of the improvement in the mechanical and tribological performance of the tribo-layer during sliding friction. Ni 3 Al matrix composites are used for validating the analysis model. The experimental results show that the existing model can be successfully applied to predict the friction and mechanical performance of the tribo-layer which is formed during the sliding contact. The thermal effect caused by the frictional heat and crack propagation have been incorporated into the model. The grain growth and the thermal effect play an important role in the improvement of the wear resistance and decrease of friction. [ABSTRACT FROM AUTHOR]

In order to improve the efficiency and durability of the kinematic pair systems, the research continues for novel materials and lubricants that can potentially reduce friction and wear. This article was dedicated to explore the combined lubrication of graphene nanoplatelets (GNPs) and MoS nanospheres (NSs) at different testing temperatures. Furthermore, the glaze layer with grain refinement could have a strong bearing capacity and resist the damage caused by high stress. At 450 °C, a integrated lubricating film containing GNPs and MoS NSs was continuously formed to provide the low-strength junctions at the interface, resulting in a lower friction coefficient of 0.15 and a smaller wear rate of 1.56 × 10 mm N m. Meanwhile, the GNPs played the role of reinforcement particles and improved loading carrying ability, while MoS NSs demonstrated the effect of repairing with being pressed into the microfurrows of the worn surface. [ABSTRACT FROM AUTHOR]

An investigation is conducted on the unexplored synergistic effects of multilayer graphene (MLG) and Ti3SiC2 in self-lubricating composites for use in high-temperature friction and wear applications. The tribological properties of TiAl matrix self-lubricating composites with different solid lubricant additions (Ti3SiC2-MLG, MLG) are investigated from room temperature to 800°C using a rotating ball-on-disk configuration. Tribological results suggest the evolution of lubrication properties of MLG and the excellent synergistic lubricating effect of MLG and Ti3SiC2 as the testing temperature changes. It can be deduced that MLG has great potential applications as a promising high-temperature solid lubricant within 400°C, and a combination of MLG and Ti3SiC2 is an effective way to achieve and maintain desired tribological properties over a wide temperature range. [ABSTRACT FROM AUTHOR]

The textured surface is one of the hotspots in the field of tribology research on reducing friction and wear. By calculating and optimizing the micro-texture structure, researchers designed and prepared textures with excellent tribological properties on the mechanical part surfaces. In this work, the tribological performance of 42CrMo matrix composite textured surfaces (CTSs) with different textured densities under grease lubrication was studied. The CTS was composed of 42CrMo alloys and SnAgCu-MXenes-Ti 3 C 2 (SACM). The results showed that when the textured density ρ of CTS was 36%, the friction coefficient (0.090) and wear rate (5.4 × 10−9 mm3N−1m−1) of counterpart ball could be respectively reduced by 75.7% and 38.6% compared with those of counterpart ball against the untextured sample. CTS could enhance the stability of friction system. Mxenes-Ti 3 C 2 wrapped by SnAgCu could form the lubricating layer containing sub-micron rollers on the worn surface, effectively reducing the friction and wear of samples under grease conditions. [Display omitted] • The composite textured surfaces (CTSs) were designed and prepared. • MXenes wrapped by SnAgCu could form sub-micrometer rollers in wear scar. • CTS exerted tribological enhancement function under starvation. • CTS could produce excellent synergistic effect with grease. [ABSTRACT FROM AUTHOR]

Inspired by shell surface structure, the surface textures were extracted by curve fitting method and the corresponding bionic wavy textures filled with SnAgCu-WS 2 composite solid lubricants were prepared on the surface of TC4. The coupling effect of bionic wavy textures and SnAgCu-WS 2 and the effect of variable reciprocating friction frequency on the tribological properties of TC4 were explored. The results show that bionic textures improve the precipitation efficiency of SnAgCu-WS 2 , and the sliding effect of WS 2 promotes the spreading and repairing of composite solid lubricants in the wear track, thus improving the formation quality of the lubricating film and its adaptability to the change of reciprocating frequency. [Display omitted] • Bionic textures with lubricants were used to improve tribological performance of TC4. • Bionic wavy textures improve the precipitation efficiency of SnAgCu-WS 2. • Sliding effect of WS 2 promotes spreading and repairing of lubricants in wear track. • Coupling effects improve adaptability to the change of reciprocating frequency. • The average friction coefficient of TWs-SACW02 is reduced to 0.219 at 20 N and 1 Hz. [ABSTRACT FROM AUTHOR]

Many studies have shown that the excellent tribological properties of materials are primarily attributed to the formation of expected frictional layer on the worn surface. This article is dedicated to explore the possible formation and acting mechanism of frictional layer of TiAl-12Ag-5TiB composite. At normal load of 12 N, a frictional layer that consists of wear-induced layer and plastic deformation layer is observed. The soft wear-induced layer supported by the harder plastic deformation layer leads to the low friction coefficient and high wear resistance. The harder plastic deformation layer is induced by repetitive tribo-contact and considerable plastic deformation. Its high hardness improves the wear resistance of composite, and fine-grained structure promotes the diffusion of lubricating phase during dry friction process. The soft wear-induced layer can be divided into tribofilm and mechanically mixed layer. The mechanically mixed layer that consists of Ag and Ti-Al Oxides can continuously be provided to the worn surface to form a tribofilm with low shearing stress junctions, lowering the friction coefficient. [ABSTRACT FROM AUTHOR]

This research was carried out on the beneficial effect of graphene additive in self-lubricating composites for use at different loads of tribological application. The dry friction and wear behaviors of NiAl self-lubricating matrix composite with graphene (NSMG) were investigated at different loads at room temperature. Finite element method served as aided method to analyze the stress condition of contact pair, which would provide another perspective to comprehend the relationship between tribological behaviors and different degrees of load-induced deformation. In the load range of 2-16 N, the results indicated that NSMG showed excellent tribological performance at load of 16 N due to the formation of anti-friction tribo-film on the worn surface. Moreover, suitable load would lead to the contact situation transfer from multi-point contact to area contact, which could contribute to the beneficial effect on friction behavior of NSMG. [ABSTRACT FROM AUTHOR]

Studies have been carried out to explore the friction and wear behaviors of NiAl matrix self-lubricating composites containing graphene nanoplatelets (NG) against an Si3N4 ball from 100 to 600°C with a normal load of 10 N and a constant speed of 0.2 m/s. The results show that NG exhibits excellent tribological performance from 100 to 400°C compared to NiAl-based alloys. A possible explanation for this is that graphene nanoplatelets (GNPs) contribute to the formation of a friction layer, which could be beneficial to the low friction coefficient and lower wear rate of NG. As the temperature increases up to 500°C, the beneficial effect of GNPs on the tribological performance of NG becomes invalid due to the oxidation of GNPs, resulting in severe adhesive wear and degradation of the friction layer on the worn surface of NG. GNPs could hold great potential applications as an effective solid lubricant to promote the formation of a friction layer and prevent severe sliding wear below 400°C. [ABSTRACT FROM AUTHOR]

To better understand respective lubrication effects and mechanisms of graphite, multi-walled carbon nanotubes (MWNTs), and multilayer graphene (MLG), comparison of tribological properties of NiAl matrix composites (NAMC) containing graphite, MWNTs, or MLG is investigated. Tribological results clearly indicate that the incorporation of solid lubricant remarkably improves the tribological properties of NAMC. NAMC containing MWNTs have better tribological properties than that containing graphite. NAMC containing MLG have the best tribological properties. EPMA, AFM, and FESEM analyses of worn surfaces suggest that the discontinuous island-like solid lubricant-rich films with different compacting extent forms on the worn surfaces of NAMC containing solid lubricant. The worn surface of NAM shows the slighter delamination and comparatively more compact films than that of NAC; in contrast, the worn surface of NAG presents the slightest delamination and the most compact films. It is concluded that graphite, MWNTs, and MLG indeed possess different lubrication effects and mechanisms. [ABSTRACT FROM AUTHOR]

Multilayer graphene (MLG) shows an attractive prospect for the demanding engineering applications. This paper reports the mechanical and tribological properties of MLG reinforced Ni 3 Al matrix composites (NMCs) under dry sliding at varying sliding speed. The hardness and elastic modulus of the NMCs are significantly influenced with MLG content. It is found that the hardness and elastic modulus of the NMCs are found to be increased by increasing MLG content up to 1.0 wt.%, while decreased when MLG content is above 1.0 wt.%. Tribological experiments suggest that MLG can dramatically improve the wear resistance and decrease the friction coefficient of the NMCs. Such marked improvement of wear resistance is attributed to the reinforcing mechanisms of MLG, such as crack deflection and pull-out, and reduction of friction coefficient is related to the formation of a tribofilm on the sliding contact surface. [ABSTRACT FROM AUTHOR]

Ni3Al-MoS2-TiC composites (NMTC) were fabricated using spark plasma sintering. The effect of TiC content on tribological properties and antiwear mechanisms of NMTC at high temperatures was investigated. The results showed that NMTC containing 10 wt% MoS2 and 6 wt% TiC exhibited the excellent tribological properties from 25 to 600°C. At 400°C, NMTC had the lowest friction coefficient of 0.28 and the considerable lower wear rate of 3.02 × 10−5 mm3 N−1 m−1. The excellent tribological properties of NMTC were attributed to the synergetic action of the lubricant-phase MoS2 and reinforcing-phase TiC. [ABSTRACT FROM AUTHOR]

The tribological properties of Ti3SiC2/TiAl composite (TTC) slid against a GCr15 steel counterface were investigated at sliding speeds in the range of 0.2–0.8 ms−1and loads that ranged from 2 to 8 N. The results showed that the tribological properties of TTC strongly depended on the covering percentage of tribofilm on the TTC worn surface, which varied with changes in sliding speed and load. The tribofilm mainly consisted of Al-Ti-Si oxides, which provided a self-antifriction action that resulted in a reduction in the friction coefficient and an increase in the wear rate. [ABSTRACT FROM AUTHOR]

TiB was chosen to further improve the tribological properties of TiAl matrix self-lubricating composites containing Ag. The possible synergetic action of a combination of TiB and Ag was investigated using a pin-on-disk high temperature tribometer from room temperature to 600 °C. The tribological test results indicated that the addition of TiB obviously enhanced the wear resistance of the composites over a wide temperature range. Moreover, the composites containing TiB had a low friction coefficient at 600 °C. The subsurface analysis of cross sections of worn surfaces showed that TiB played the role in wear-resistant skeleton and restricted the plastic flow of Ag during dry friction process. The investigation showed that TiB and Ag could exhibit good synergistic effect on improving the tribological properties of composites. [ABSTRACT FROM AUTHOR]

The main objective of this work has been the characterization of wear behavior of the graphene nanoplates (GNPs) in Ni3Al matrix composites (NMC). The friction and wear behaviors of NMC with the addition of 1 wt.% GNPs against Si3N4 ball are tested under different loads using a constant speed of 0.2 m/s. Tribological test results have revealed that small amounts of GNPs are able to drastically improve the antifriction and antiwear properties of NMC. A possible explanation for these results is that, the GNPs not only provide an enhanced effect for NMC to produce better wear resistance, but also form a local protective layer on the contact surfaces to reduce the friction. The investigation shows that GNPs hold great potential applications as an effective solid lubricant for Ni3Al matrix composites and possibly other alloys. [ABSTRACT FROM AUTHOR]

The progress in aerospace field requires a new NiAl matrix composite that can stand against wear and decrease the energy dissipation through decreasing friction. In this study, the tribological behavior of NiAl–1.5 wt% graphene composite is investigated at room temperature under a constant load of 12 N and different sliding velocities. The results show that the friction coefficient and wear rate increase with increasing sliding velocity from 0.2 to 0.4 m/s due to the adhesion between the sliding bodies and tearing of the graphene layer. The friction coefficient and wear rate tend to decrease at a sliding velocity of 0.6 m/s as a result of severe plastic deformation and grain refinement of the worn surface. However, at 0.8 m/s the friction coefficient reaches a minimum value and the wear rate increases and changes the wear mechanism to fatigue wear. It can be concluded that various wear mechanisms lead to different tribological performance of NiAl–1.5 wt% graphene composite. [ABSTRACT FROM PUBLISHER]

More durable, low-friction self-lubricating materials in modern industry are greatly needed for tribological systems. The current paper presents the tribological performance of TiAl matrix self-lubricating composites (TSC) containing MoS, hexagonal BN and TiSiC designated as MhT against GCr15 steel counterface under several sliding speeds from 0.2 to 0.8 m s and applied loads from 6 to 12 N. The results suggested that MhT played an important role in decreasing friction coefficients and wear rates. The covering percentage of transfer layers on worn surfaces varied with the changing of sliding speeds and applied loads, hence resulting in the distinct friction and wear characteristics of TSC. TSC containing 10 wt% MhT exhibited the best excellent tribological performance at 10 N-0.8 m s, which could be due to the formation of the best compaction and largest coverage of transfer layer on the worn surfaces. [ABSTRACT FROM AUTHOR]

Research on the friction layer is needed to minimize friction- and wear-related mechanical failures in moving mechanical assemblies. Dry sliding tribological tests of NiAl matrix composites (NMCs) with 1.5 wt% graphene nanoplatelets (GNPs) sliding against different counterface balls are undertaken at the condition of 10 N-0.234 m s in this study. When sliding against GCr15 steel, a uniform and thick friction layer is formed, resulting in a lower friction coefficient (0.29-0.31) and wear rate (2.0-3.1 × 10mmNm). While sliding against AlO and SiN, the formation and stability of the friction layers are restricted in the severe wear regime, and the NMCs exhibit higher friction coefficients and wear rates. Therefore, various counterface balls have a great effect on the stability and thickness of the friction layer, thus affecting the tribology performance of NMCs. The result also shows that GNPs exhibit enrichment and self-organized microstructures in the friction layer. In addition, the friction layer is also found to be divided into two layers, protecting the subsurface from further damage and reducing shear. [ABSTRACT FROM AUTHOR]