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Inspired by the scales on the surface of crucian carp, the biomimetic fan-shaped textures were designed and prepared on the TC4 contact surface and filled with solid lubricant SnAgCu-Nb2C (SACN). The coupling effects of fan-shaped textures and solid lubricants on the tribological properties of TC4 under variable frequency conditions were investigated. The results indicated that the fan-shaped textures could promote the precipitation of lubricants and provide sufficient lubricants for the worn surface, forming a uniform lubricating film on the worn surface, thus improving the tribological properties. In addition, at the low-frequency stage, the coupling of lubricants and textures had strong adaptability to frequency changes. [ABSTRACT FROM AUTHOR]

Inspired by the ability of biological structures to resist water pressure and flow resistance, this regulating mechanism was applied on the hydraulic cylinder. Bionic rhombic textures were combined with SnAgCu-Ti2C3Tx (ST) to improve the tribological properties of 42CrMo. After optimizing the texture parameters, the friction tests were performed on optimal experimental parameters-ST, predicted optimal structural parameters-ST and control experimental groups under dry/oil lubrication. Herein the optimized structural parameters were more conducive to the spreading of solid lubricants. The lubricating film was firmly bonded with substrate. The synergistic effect of optimized structural parameters, ST and oil lubrication can significantly improve the tribological properties of 42CrMo. [ABSTRACT FROM AUTHOR]

Inspired by the fan-shaped scale and mechanism of mucus secretion of crucian carp surface, the bionic scale textures were designed and combined with Sn-Ag-Cu-Nb2C to fabricate TC4-based self-lubricating composites (TTSACN). The optimal textured parameters (radius = 710 μm, width = 300 μm, depth = 390 μm) were obtained by response surface methodology (RSM). The friction and wear behaviors of TTSACN under dry friction conditions were studied. The experimental results showed that the optimal bionic texture could capture wear debris and promote the restoration and migration of lubricants on the worn surface, improving the formation quality of lubricating film. Compared with TC4, the friction coefficient and wear loss of TTSACN with optimal bionic texture were reduced by 23.03% and 96%, respectively. [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]

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]

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]

In order to further understand the role of MXene-Ti3C2 in oil–solid synergistic lubrication, three kinds of microporous channel composites, M50, M50-Sn-Ag-Cu and M50-Sn-Ag-Cu-Ti3C2, were designed and prepared in this study. Tribological behaviors under different environmental conditions of oil lubrication and dry friction were analyzed. The results show that M50-Sn-Ag-Cu-Ti3C2 exhibits excellent tribological properties under oil lubrication. Mxene-Ti3C2 enhances the strength of solid lubricant film, so that the oil film can give full play to the antifriction and wear resistance of solid lubricant film. The synergistic effect of lubricating oil, solid lubricants and bionic curved microchannel reduces the friction coefficient and wear rate. The vibration acceleration along the reciprocating direction is also reduced. [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]

In view of the uneven lubricating film of M50 aviation bearings under high load, it is of great significance to explore how to improve its friction performance through the synergistic lubrication of solid lubricant and lubricating oil. Inspired by the material transport of leaf veins, a bionic microchannel was designed for the contact interface. M50, M50-SnAgCu (MS) and M50-SnAgCu-Nb2C (MSN) biomimetic composites are prepared, respectively. The tribological properties of the material under dry friction and three grades of Mobil oil (DTE 24, DTE 25 and DTE 26) were investigated through ball-on-disk friction. The high-hardness Si3N4 ball is used as the counterpair. The results show that the average friction coefficient and wear rate of MSN are reduced by 29.63% and 28.36%, respectively. In addition, the furrows on the worn surface were significantly reduced. The synergistic lubrication of SnAgCu-Nb2C and the DTE 26 oil makes M50 have a excellent antifriction and wear resistance. The results can provide guidance for the research of synergetic lubrication behavior of materials. [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]

Improving the friction-induced noise suppression performance of TC4 has far-reaching significance for its wide application in the field of robots and semiconductors. The friction noises of TC4 with solid lubricant (Sn-Ag-Cu) filled into dimples (TCS) and TC4 were predicted by simulation analysis. The noise reduction performance of TCS during dry rotary sliding was discussed. TCS with dimple size of 0.6 mm (TCS-0.6) exhibited the prominent performance of noise reduction, which was attributed to the synergistic effect of dimples and solid lubricant. During the dry sliding process, the debris were contained by dimples, the stress distribution in matrix was modified by lubricant, and the defects were decreased. Hence, the roughness of worn surface was reduced, which was beneficial to obtaining the stable friction coefficient. Inhibiting the unstable vibration by controlling the friction coefficient of the system can effectively demote the friction-induced noise. [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]

Improving the tribological performance of TC4 has far-reaching significance for its wide application in the field of automobile and robot. The lubricating behaviors of TC4 with mixed solid lubricant (Sn-Ag-Cu with TiC) filled into surface dimples (TAC) during dry rotary sliding were systematically investigated. The results show that TAC has better tribological properties than TC4 and TC4-P. It attributes to the synergistic effect of surface dimples and mixed solid lubricant. The mixed solid lubricant in dimples is easier to be extruded to the frictional interface. The uniform and wear-resistant lubricating layer containing SAC and TiC is formed on the worn surface of TAC, reducing the direct impact of counterpart ball on substrate material. The fluidity of SAC endows TAC with the ability of self-repairing. [ABSTRACT FROM AUTHOR]

Based on the microporous structure lubrication method, Ti6Al4V(TC4)-based self-lubricating composites (TC4-SAC) with microporous channels filled by lubricant Sn-Ag-Cu are prepared. The effects of microporous channel parameters on stress and deformation of TC4-SAC are analyzed by finite element method. In addition, the friction and wear behaviors of TC4-SAC with different microporous channel parameters are compared, and the self-lubricating mechanisms of TC4-SAC are also analyzed. The results show that microporous channel parameters have a significant influence on the mechanical and tribological performance of TC4-SAC. Moreover, when the vertical depth of microporous channel = 3.5 mm, the micropore pitch = 3 mm, and the micropore diameter = 0.8 mm, TC4-SAC can obtain the best mechanical property and self-lubricating characteristic. [ABSTRACT FROM AUTHOR]

To overcome the poor tribological performance of M50 and widen its working range under high temperature, M50-Sn-Ag-Cu composites with curved microchannels (MCCs) and straight microchannels (MCSs) were prepared by Laser Additive Manufacturing Technology, respectively. Tribological properties of M50-based composites were studied. The results showed that MCCs had the better tribological performance. At 25 °C-15 N-0.2 m/s, compared with MCSs, the average friction coefficient of MCCs at the stable friction stage was reduced by 10.7%. In contrast to MCSs, MCCs had a wider operating temperature range than MCSs, and the average friction coefficient of MCCs was decreased by 23.4 at.% 350-450 °C. According to the simulation results, the lubricant expansion of MCCs was 1.56 times that of MCSs at 400 °C. The curved microchannels design makes the storage and formation capacities of the lubricating film be enhanced without weakening the bearing capacity of MCCs. The two-way opening design of the curved microchannels could reduce the stress concentration between lubricant and friction interface, hence ensuring the efficient precipitation of lubricant. The research work could have a guiding role for widening the temperature range of M50 composites and improving the reliability of high-end equipment bearing. [ABSTRACT FROM AUTHOR]

Friction noise will not only affect the life of equipment, but also endanger human health. It is imperative to reduce the friction noise of mechanical system. Tribological properties and friction noise of Ti6Al4V alloy (TC4) and Ti6Al4V-4.6 wt.% MoS2-3.7 wt.% TiC (TMT) self-lubricating composites under 5, 10 and 15 N at 0.2 m/s are investigated using a self-built friction noise experimental apparatus. The results show that MoS2 and TiC have the good synergistic effects on tribological and friction noise performance. A lubricating film enriched with MoS2 is formed on the worn surface to reduce the stick–slip and surface roughness, and the energy of transition on the worn surface is reduced; hence, the friction noise is decreased. TiC can improve the hardness and wear resistance of TMT, and it supports the lubricating film to hinder the development of plowing grooves and peeling pits to a deeper level. The worn surface and friction noise performance of TMT are best at 10 N. This study has the far-reaching implications for improving the tribological properties and inhibiting friction noise of TC4 alloys. [ABSTRACT FROM AUTHOR]

Ti6Al4V alloy has broad application prospects in the aircraft industry. However, when it is served as frictional motion components, the poor friction and wear properties may greatly influence the reliability and working life of the entire mechanical system. Therefore, this paper mainly investigates the tribological performance and self-repairing functionality of Ti6Al4V-multilayer graphene (MLG)-Ag composites (TMAC) from 25 to 600 °C. The results show that TMAC obtains better tribological behavior in comparison with Ti6Al4V alloy (TC4), Ti6Al4V-MLG composites (TMC) and Ti6Al4V-Ag composites (TAC). It should be ascribed to the synergistic action of the reinforcement MLG and lubricant Ag, which are crushed and spread out by mechanical and thermal stress in the friction process, leading to the formation of a lubricating film on the wear scar. Along with the spreading of lubricating film, Ag and MLG can precipitate onto the microdefective areas, thus playing an important role in repairing the wear scar of TMAC. [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]

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]

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]

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]

M50 steel is widely applied to manufacture aircraft bearings where service lives are mainly determined by the friction and wear behaviors. The main purpose of this study is to investigate the tribological behaviors and wear mechanisms of M50-1.5 wt.% graphene composites (MGC) prepared by laser additive manufacturing (LAM) (MGC-LAM) sliding against Si3N4 ball from 25 to 550 °C at 18 N-0.2 m/s. XRD, EPMA, FESEM, and EDS mapping were conducted to understand the major mechanisms leading to the improvement in the sliding behavior of MGC-LAM. The results indicated that MGC-LAM showed the excellent friction and wear performance at 25-550 °C for the lower friction coefficient of 0.16-0.52 and less wear rate of 6.1-9.5 × 10−7 mm3 N−1 m−1. Especially at 350 °C, MGC-LAM obtained the best tribological performance (0.16, 6.1 × 10−7mm3 N−1 m−1). It was attributed to the dense coral-like microstructure, as well as the formed surface lubricating structure which is composed of the upper uniform lubricating film with massive graphene and the underneath compacted layer. [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]

The dry sliding friction and wear behaviors of TiAl matrix self-lubricating composite (TMSC) containing multilayer graphene (MLG), silver (Ag) and MLG-Ag sliding against SiN balls from 25 to 750 °C were comparatively studied in this paper. The results suggested that TMSC containing MLG-Ag (TMA) showed better tribological properties over the wide temperature range, if compared to TMSC only containing MLG or Ag. Moreover, TMA exhibited the lower fiction coefficient and the less wear rate at 450 °C, which was attributed to the formation of intact lubricating films containing MLG and Ag on the worn surface. Furthermore, in the formed lubricating films, 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 lubricating films. The study indicated that TMA obtained the excellent tribological performance at 450 °C due to the remarkable synergistic effect of MLG and Ag. [ABSTRACT FROM AUTHOR]

The application of NiAl-based alloy (NA) in the field of aerospace was limited by its poor tribological properties. For improving the tribological performance of NA, multilayer graphene (MLG) and TiSiC were added in NiAl matrix composites. Tribological behavior of NiAl matrix composites containing 1.5 wt.% MLG and 10 wt.% TiSiC (NMT) against SiN ball at 12 N-0.2 m/s from 25 to 750 °C was investigated. The results showed that NMT exhibited the excellent tribological behavior [lower friction coefficients (0.26-0.57) and less wear resistance (3.1-6.5 × 10 mm N m)] due to synergetic effect of MLG and TiSiC over a wide temperature range from 25 to 750 °C. At 25-350 °C, part of MLG enriched on worn surface could play a role in reducing friction and improving wear resistance. At 350-550 °C, although MLG gradually lost the lubricating properties, the partial decomposition of TiSiC could continually improve the tribological properties of NMT. At 550-750 °C, TiSiC on worn surface was oxidized to form lubricating film, while TiSiC in the subsurface played an important role in supporting the film, resulting in the excellent high-temperature tribological performance. The research had good guiding significance for the preparation of wide temperature range self-lubricating material and the study of synergetic effect of complex solid lubricants. [ABSTRACT FROM AUTHOR]

The tribological performance is a key factor for M50 steel that is widely used in aero-engine main-shaft bearings. In this study, the tribological properties of M50 matrix self-lubricating composites with different contents of TiSiC against SiN ceramic counterpart are investigated at 15 N-0.2 m/s from 25 to 450 °C. The results showed that M50 with 10 wt.% TiSiC (MT10) exhibits the lower friction coefficients (0.21-0.78) and less wear rates (1.78-3.14 × 10 mm N m) at 25-450 °C. Especially at 350 °C, MT10 shows the lowest friction coefficient and wear rate owing to the formation of smooth lubricating layer containing TiSiC and oxides. TiSiC and compacted Ti-Si-oxides are uniformly distributed in the lubricating layer, which can well improve the anti-friction and anti-wear performance of MT10. The mechanically mixed layer containing massive TiSiC can sustain the lubricating layer, resulting in the increase of anti-wear performance of MT10. MT10 could be applied under the practical conditions of friction and wear for its outstanding anti-friction and anti-wear performance. [ABSTRACT FROM AUTHOR]

In this investigation, the effect of TiC particulate reinforcement and sintering parameters on tribological behavior of TiAl metal matrix composite (TMMC) has been studied and compared with commercially conventional gray cast iron to evaluate the use of TMMC as brake disk material in an automobile. Three sample disks of TMMC containing TiC particulate reinforcement (D1-5 wt.%, D2 and D3-10 wt.%) were produced by the spark plasma sintering process. D3 compared with D2 was sintered at a higher temperature to evaluate the effect of SPS parameters on the wear characteristics of TMMC. All experiments were performed on pin-on-disk tribotester under a dry sliding condition with different loads (10-11.5 N) and sliding velocities (0.2-0.9 m/s). It is found that higher content of TiC increased TMMC hardness and density. XRD technique has been used to analyze the phase composition. Owing to the high sintering temperature, α-2 TiAl phase was formed which further enhanced the matrix anti-wear capability. Scanning electron microscope (SEM) was used to capture the wear track and observe wear mechanism. Energy-dispersive spectroscopy (EDS) has been used to analyze the tribofilm and wear debris. The results showed that the tribofilm for TMMC was mainly composed of metal oxides. Oxidation of Al and Ti due to frictional heat provides wear-resistant protective layer. Under almost all sliding conditions, TMMC, especially disk D3, exhibited minimum wear rate and stable friction coefficient, whereas gray cast iron exhibited lower and unstable friction coefficient as well as higher wear rate. TMMC has shown superior tribological characteristics over gray cast iron in terms of low wear rate along with stable and adequate friction coefficient which is necessary for braking operation and life of brake disk. However, further investigation on full-scale automobile conditions is needed for its practical application. [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]

Tribological behaviors of TiAl-multilayer graphene-microsphere composites (TMMC) are investigated at different loads in this paper. The tribological results show that TMMC exhibit excellent wear and friction performances from 4 to 20 N for the formation of the intact and smooth tribo-films containing multilayer graphene (MLG) and WS-SiO microsphere (WSM) on the worn surfaces. During the sliding process, MLG and WSM are ground out of TMMC to form the tribo-films on the worn surfaces, which is beneficial to the decreasing in friction coefficients and wear rates. MLG is easy to be sheared for the weak interlayer binding force, which can reduce the friction coefficients and wear rates. WSM can repair the tribo-film by filling its worn pits, resulting in the smooth worn surface and excellent tribological performance of TMMC. Moreover, the hardness of TMMC is increased for the addition of MLG and WSM, which makes contributions to the improvement of tribological behaviors of TMMC. [ABSTRACT FROM AUTHOR]

In order to analyze the effects of friction layer thickness on the tribological performance of NiAl matrix self-lubricating composites containing Ag and MoO tabular crystals (NiAl-Ag-MoO), the dry sliding tribological tests of NiAl-Ag-MoO against SiN ball are undertaken under 4-16 N and 20-800 °C at 0.2 m/s. The results show that the friction layer thickness of NiAl-Ag-MoO is obviously affected by the applied loads and ambient temperatures. At 12 N-400 °C-0.2 m/s, NiAl-Ag-MoO exhibits excellent tribological performance, and the friction layer thickness obtained the maximum value of about 5 µm. Moreover, the simulation results, which based on the building of finite element models with different thickness of the friction layer, indicate that the decreased degree of the maximum equivalent stress in the substrate of NiAl-Ag-MoO with maximum thickness of friction layer is the larger one (about 39%), if compared to other thickness. It could avoid the generation of cracks and the spalling of subsurface materials during the dry sliding process, resulting in the excellent tribological performance. The results could be used to guide the selection of suitable working conditions and study the self-lubricating mechanisms of NiAl-Ag-MoO for having stable friction layer structure and excellent antifriction and antiwear performance. [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]

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]

The objective of searching the optimum applied load was to minimize friction and decrease wear in mechanical moving components. The friction and wear behaviors of TiAl-10wt.%VO nanowires (TiAl-10wt.%VO) were evaluated sliding against the fixed AlO balls with the Vickers hardness of 18.07 GPa at the applied loads of 6-24 N. The testing results showed that the smaller friction coefficient and wear rate of TiAl-10wt.%VO were obtained at 18 N, if compared to those at 6, 12 and 24 N. The smaller friction coefficient and wear rate were mainly attributed to the forming of cambiform structure of large crystalline grain, the higher totals of oxide interionic potential and the higher thickness of friction layer at 18 N, if compared to those at the other applied loads. It was obvious that the applied load of 18 N was reasonable for obtaining the lower sliding friction coefficient and the less wear rate of TiAl-10wt.%VO. [ABSTRACT FROM AUTHOR]

In this study, the friction and wear behaviors of TiAl matrix composites with MTC (TMSCT) and TiAl matrix composites with MoO powder (TMSCP) are investigated. The results reveal that TMSCT show the excellent tribologcial performance, if compared to TMSCP. The direct contact layers of TMSCP against different counterface balls obtain huge cracks overall, whereas only fine crack is generated in TMSCT against AlO ball, where MTCs are distributed around the crack evenly. The finite element simulations show that only the stress of TMSCT against AlO ball exceeds the yield strength of TMSCT. It reveals that MTCs in TMSCT can reduce the stress for the weak binding force of multilayer structure and make the direct contact layers be more stable by preventing the propagation of crack after the crack being produced, resulting in the excellent antifriction and antiwear properties of TMSCT against different counterface balls. [ABSTRACT FROM AUTHOR]

In order to improve the tribological properties of NiAl self-lubricating composites, VO nanowires with average width of 39 nm were synthesized by hydrothermal method. Furthermore, NiAl self-lubricating composites containing VO nanowires (NAV) were successfully fabricated using spark plasma sintering technique. The tribological characteristics and wear mechanisms of NAV were evaluated at different sliding speeds, counterface ball materials and elevated temperatures. The results revealed that the frictional properties of NAV improved slightly with adding VO nanowires at room temperature if compared to NiAl self-lubricating composites without solid lubricant as investigated in previous studies, while the wear mechanisms of NAV change widely with the change of the counterface ball materials and sliding velocities. VO nanowires showed a beneficial effect on tribological performance of NAV at high temperatures owing to the formation of the VO-enriched glaze film at temperatures above 700 °C, which acts as the lubricous and protective mask against the severe wear. [ABSTRACT FROM AUTHOR]

Microstructure and functional mechanism of friction layer need to be further researched. In the present work, the friction coefficients and wear rates are analyzed through response surface methodology to obtain an empirical model for the best response. Fitting results show that the tribological performance of NiAl matrix composites (NMCs) with graphene nanoplatelets (GNPs) is better than that of NMCs without GNPs, especially at high sliding velocities and high loads. Further research suggests that the formation of integrated friction layer, which consists of a soft microfilm on a hard coating, is the major reason to cause the differences. Of which, the wear debris layer (WDL) with a low shear strength can reduce the shear force. The ultrafine layer (UL), which is much harder and finer, can effectively avoid fracture and improve the load support capacity. Moreover, the GNPs in WDL and UL can be easily sheared and help to withstand the loads, trending to be parallel to the direction of shear force. [ABSTRACT FROM AUTHOR]

The sliding velocities and applied loads are often varied to minimize friction and decrease mechanical energy dissipation in moving mechanical assemblies. In this study, TiAl matrix composites containing MoS and multiwalled carbon nanotubes (MWCNTs) are fabricated using spark plasma sintering. The testing conditions are chosen as 0.3 m/s-6.5 N; 0.5 m/s-11.4 N; and 0.7 m/s-16.3 N. The sliding tribological property of TiAl matrix composite containing MoS and MWCNTs (TMC-MM) is evaluated based on a ball-on-disk tribometer. The results show that the tribological performance of TMC-MM is excellent for the lower friction coefficient and less wear rate at 0.7 m/s-16.3 N. Massive MWCNTs are pulled out from TMC-MM at 0.7 m/s-16.3 N, and made to adhere to wear surface due to the existence of MoS with high adhesion property, resulting in the formation of smooth isolated island-like layer. It could protect the lubrication film formed on the worn surface, and be beneficial to the excellent tribological behavior of TMC-MM. [ABSTRACT FROM AUTHOR]

The friction and wear behaviors of TiAl matrix self-lubricating composites (TMSC) with MoO tabular crystal (MTC) against GCr15 steel ball are tested using a constant load of 10 N and a constant speed of 0.2 m/s from room temperature to 600 °C. The result shows that, during the sliding friction and wear process, the MTC which has the microstructure of multiple layers could reduce the shear stress, leading to the reduction of friction coefficient. Meanwhile, TMSC with MTC exhibits the excellent tribological performance over a wide temperature range, if compared to TiAl based alloy. Moreover, MTC can improve the tribological properties of TMSC obviously below 400 °C. [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]

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]

A research is conducted on the possible beneficial synergistic effects of multiple additives in self-lubricating composites for use in high temperature friction and wear-related mechanical assemblies. Dry sliding tribological tests of NiAl matrix self-lubricating composites (NMSCs) on a HT-1000 ball-on-disk high-temperature tribometer are undertaken against SiN at 25-800 °C. The results show that the subsurface microstructures beneath wear scar of NMSCs change with addition of different lubricants, which have great effects on tribological mechanisms and tribological performances. NMSC with addition of MoS and TiSiC exhibits distinct subsurface microstructure beneath wear scar and excellent tribological performance among all samples. [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]

More durable, low-friction bearing materials are needed for turbine components and other high-temperature bearing applications. The current study presents the sliding friction and wear behavior of a TiSiC/TiAl composite (TTC) against a SiN counterface at temperatures ranging from 25 to 800 °C in air. The load was 10N, and the sliding speed was 0.2 m/s for all tests. The friction coefficient of both the TiAl and the TTC composite increased with rising temperature up to 400 °C, but beyond that, the friction coefficient of the TTC decreased, making it more lubricative than TiAl at the higher temperatures. It is proposed that at high-temperatures, TiSiC-formed oxides that were incorporated into a well-consolidated tribo-film drastically reducing the friction coefficients and wear rates of the TTC material. [ABSTRACT FROM AUTHOR]

The self-lubricating composites of NiAl-TiSiC-TiC-C (NMC) with varying TiSiC contents were fabricated by spark plasma sintering technique. Dry sliding pin-on-disc friction and wear tests of NMC against SiN ceramic ball were undertaken at 25, 200, 400, 600, and 800 °C in air, respectively. The results showed that NMC with 15 wt.% TiSiC lubricant owned the excellent tribological properties over a wide temperature range from 25 to 800 °C, whose friction coefficients and wear rates were about 0.17-0.58 and 0.31-4.2 × 10 mm/N/m, respectively. A possible explanation for these results was that the subsurface microstructure self-refinement and the special stratification morphology of the tribo-layer were beneficial to the reduction of friction coefficient. Meanwhile, the protective action of the tribo-layer for the frictional surface could also decrease the wear rate. [ABSTRACT FROM AUTHOR]