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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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]

Setting the micro-texture in the cutter–chip contact area of a micro-textured tool rake face can effectively improve the tool's cutting performance. However, an unreasonable design for the micro-groove morphology and size and the selection of inappropriate cutting parameters will cause a secondary cutting phenomenon during the cutting process. To explore the optimum micro-texture morphology size and cutting parameters, micro-texture self-lubricating ceramic cutting tools with different morphology parameters (micro-texture location distribution: MSTD-1, MSTD-2, MSTD-3; groove spacing: MSTS-1, MSTS-2, MSTS-3; groove width: MSTW-1, MSTW-2, MSTW-3) were formed in situ and by hot pressing sintering, and a dry cutting 40Cr comparison test with a non-textured tool (MST-0) was conducted. The results revealed that the MSTD-2 tool effectively reduced the cutting force, friction factor, and rake face wear and relieved the secondary cutting phenomenon while cutting 40Cr. A theoretical analysis showed that the micro-texture morphology parameters and cutting speed were the main factors affecting the secondary cutting, with a smaller groove width and higher cutting speed associated with a lighter chip impact. [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]

In this study, copper-coated (Cu-coated) boron carbide (B4C) particles were successfully prepared by electroless Cu plating onto B4C particle surfaces. These Cu-coated B4C particles were combined with Cu-coated graphite particles and Cu powder, which were then used to prepare a new type of Cu-matrix self-lubricating composite by powder metallurgy. Uncoated B4C particles were used to prepare corresponding composites and all composites characterized by phase composition, microstructure, density, porosity, hardness, compressive yield strength, and friction wear. The results showed that Cu-coated B4C particles improved wettability between the particles and matrix and possessed increased interface-bonding strength with the matrix. With the same B4C content, Cu-matrix/graphite composites reinforced by Cu-coated B4C had lower porosity and wear resistance, as well as higher hardness and compressive strength, than composites reinforced by uncoated B4C. Considering the wear and friction coefficients, composites containing 0.5 wt % Cu-coated B4C exhibited better friction and wear resistance properties. [ABSTRACT FROM AUTHOR]

Graphite particles and boron carbide (B4C) particles were added into copper matrix composites by powder metallurgy to form a new composite-reinforced and lubricated system. The effects of different amounts of B4C particles on the properties of composites were studied. With addition of 2 wt % graphite powder as the solid lubricating phase, the effects of B4C particle content on the microstructure, density, porosity, Vickers hardness, compressive strength, and the friction and wear properties of the copper-matrix/graphite self-lubricating composite materials were investigated. The results indicate that increasing addition of B4C particles significantly improved the density, Vickers hardness, compression strength; friction and wear properties of composites. However, excess B4C particles also increased porosity. The connected netted B4C particles disrupt the continuity of the metal matrix causing serious decreases in density, Vickers hardness, compression, and the friction and wear properties of the composite material. Of the tested composites, the materials containing 1.5 wt % B4C showed the best friction and wear resistance properties. [ABSTRACT FROM AUTHOR]

Two kinds of metal-PTFE multilayer composites, which were composed of a steel backing, a middle layer of sintered porous bronze and a surface layer of polytetrafluoroethylene (PTFE) filled by carbon nanotubes (CNTs) or not, were prepared. The wear properties of metal-PTFE multilayer composites oscillating against 45 carbon steel under dry condition were evaluated on an oscillating wear tester, and the effect of CNTs on wear behaviour of metal-PTFE multilayer composites was studied. The results showed that the worn surface of metal-PTFE multilayer composites was characterized by adhesive wear, abrasive wear and fatigue wear. The CNTs greatly increased the adhesion strength of PTFE in the metal-PTFE composites and thereby greatly reduced puck, ploughing, and fatigue failure of PTFE during wearing. The PTFE filled with CNTs prevented direct contact between the mating surfaces and served as fine self-lubricating film, in which the oscillating wear mechanism of the composites was changed to a slightly adhesive wear. Therefore, the CNTs significantly decreased the weight loss and obviously increased the wear resistance of metal-PTFE multilayer composites. [ABSTRACT FROM AUTHOR]

In the present investigation, a newly fabricated Al6061 reinforced with various quantity (0.4-1.6 wt%) of nano SiC in steps of 0.4 and fixed quantity (0.5 wt%) of micro graphite particle’s hybrid nanocomposites were prepared by ultrasonic assisted stir casting method. The influence of nano SiC and graphite content on the mechanical and tribological properties of Al6061 hybrid nanocomposites were studied. The pin-on-disc equipment was used to carry out experiment at 10-40 N applied load, 0.5 m/s sliding speed and 1000 m sliding distance. The Al/SiC/Gr hybrid nano-composite and matrix alloy wear surfaces were characterized by FESEM equipped with an EDS, 3D profilometer to understand the wear mechanisms. The results of Al/SiC/Gr self-lubricating hybrid nano-composites showed improved wear resistance than the Al6061 matrix alloy. The co-efficient of friction of Al/SiC/Gr hybrid nano-composites were lower than those of the unreinforced alloy at various applied load. Compared to matrix alloy, the surface roughness of Al/SiC/Gr hybrid nano-composites had significantly reduced to 66% at low load and 75% at high load. Self-lubricating Al/SiC/Gr hybrid nanocomposites showed superior surface smoothness compared to matrix alloy. [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 reactions between MoS and several metallic powders, including Ni, Al, and NiAl, were studied by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The DSC results revealed that MoS started to react with Ni and Al at 630 and 560 °C, respectively, but did not react with NiAl even at 1200 °C. The XRD results indicated that the reaction products of MoS and Ni were a series of new sulfides and molybdenum compounds, including NiS, NiS, and NiMo, and those of MoS and Al were AlS and various aluminides. Additionally, the compositions of the products varied with the reaction temperature. Because these new sulfides did not possess self-lubricating properties, the consumption of MoS should be avoided. According to these reactions, a synthetic route for the NiAl/MoS composite using Ni, Al, and MoS composite powders was proposed and demonstrated. During the synthesis process, the composite powders were first compressed under a pressure of 180 MPa. The resulting green compacts were heated to 500 °C with a heating rate of 20 °C/min, and then to 530 °C with a heating rate of 1 °C/min. The holding time at 530 °C was 4 h. The phase composition and microstructure of the as-synthesized composite were studied by XRD and SEM. The results showed that MoS remained stable during the synthesis process. Friction and wear tests demonstrated that the composite exhibited good self-lubricating properties with a low friction coefficient of about 0.2 and a small wear rate of 1.04 × 10 mm N m. [ABSTRACT FROM AUTHOR]

To enhance the anti-friction and anti-wear properties of the WC/TiC/Co carbide, micro-EDM was selected to fabricate textured micro-holes on the carbide surface, and graphite was embedded into the micro-holes to form self-lubricating tools. Dry machining tests on AISI 1045 hardened steel were carried out with the self-lubricating tool and conventional ones. The cutting temperature and tool wear were investigated and compared. The results showed that the self-lubricating tool embedded with graphite exhibited excellent efficiency and stability in reducing cutting temperature, and then the tool wear was reduced compared to that of the conventional one. Through the analysis of test results and cutting temperature distribution theory, the mechanisms responsible are put forward: the first one is the formation of a graphite film on the tool rake face, which is conducive to reducing the temperature of chip and tool caused by tool-chip friction and chip deformation; the other one is attributed to the reduced actual contact length at the tool-chip interface due to the micro-holes, which is propitious to lower the temperature of chip and tool caused by tool-chip friction, supply more graphite, and store chip debris. [ABSTRACT FROM AUTHOR]

This work is a review of previous works, presenting and discussing the most important results obtained by an ongoing research program towards the development of innovative, low-cost, self-lubricating composites with a low friction coefficient and high mechanical strength and wear resistance. Special emphasis is given to uniaxial die pressing of solid lubricant particles mixed with matrix powders and to metal injection moulding associated with in situ generation of solid lubricant particles. Initially, a microstructural model/processing route (powder injection moulding followed by plasma-assisted debinding and sintering) produced a homogeneous dispersion of in situ generated solid lubricant particles. Micrometric nodules of graphite with diameter smaller than 20 μm were formed, constituting a nanostructured stacking of graphite foils with nanometric thickness. Micro Raman analysis indicated that the graphite nodules were composed of turbostratic 2D graphite having highly misaligned graphene planes separated by large interlamellae distance. Large interplanar distance between the graphene foils and misalignment of these foils were confirmed by transmission electron microscopy and were, probably, the origin of the outstandingly low dry friction coefficient (0.04). The effect of sintering temperature, precursor content, metallic matrix composition and surface finish is also reported. Furthermore, the influence of a double-pressing/double-sintering (DPDS) technique on the tribological performance of self-lubricating uniaxially die-pressed hBN + graphite-Fe-Si-C-Mo composite is also investigated. Moreover, the tribological behaviour of die-pressed Fe-Si-C matrix composites containing 5, 7.5 and 10 wt% solid lubricants (hBN and graphite) added during the mixing step is analysed in terms of mechanical properties and wear mechanisms. Finally, the synergy between solid lubricant particles dispersed in a metallic matrix and fluid lubricants in a cooperative mixed lubrication regime is presented. [ABSTRACT FROM AUTHOR]

The NiAl matrix self-lubricating composite was fabricated by powder metallurgy technique. The tribological behavior of the composite sliding against commercial SiN, SiC and AlO ceramic balls was investigated from 20 to 1000 °C. It was found that the composite demonstrated excellent lubricating properties with different friction pairs at a wide temperature range, which can be attributed to the synergetic effect of Ag, fluorides, and molybdates formed by oxidations. The NiAl matrix self-lubricating composite/SiN couple possessed the stable friction coefficient and wear rate. [ABSTRACT FROM AUTHOR]

Tribological investigations of polymers and polymers with additives, using the SMC-2 device, were showed in the present work. Friction coefficient and contact temperature of sliding friction couples, containing different basic materials (PA66 and POM, with two types of nanoparticles, with five different concentrations 0; 0.5; 3; 7.5 and 15% by volume) were investigated. Self-lubricating polymers and steel friction couples have been tested without any lubrication. Research has shown, that the concentration of copper and graphite nanoparticles exceeding 5% leads to coagulation part, that reduces frictional properties of the base material. [ABSTRACT FROM AUTHOR]

In order to improve the tribological properties of ceramic composites, AlO/TiC-AlO/TiC/CaF self-lubricating laminated ceramic composites were prepared by vacuum hot pressing sintering. Experiments were conducted to get mechanical properties and the friction and wear properties were also measured with friction and wear tester. The worn surfaces were observed by scanning electron microscope (SEM) and energy dispersion spectrum (EDS). The wear resistance properties and the self-lubricating effect of ceramic composites were analyzed. Results show that the AlO/TiC-AlO/TiC/CaF self-lubricating laminated ceramic composites layers are well-defined with a higher bonding strength and the mechanical performances are uniform enough to overcome the anisotropy of weak laminated ceramic composites. In addition, the fracture toughness of AlO/TiC layers is also improved. Its friction coefficient and wear rates decrease with the increase of rotation speed and load. AlO/TiC-AlO/TiC/CaF self-lubricating laminated ceramic composites have good wear resistance because of the tribofilm formed by the CaF solid lubricants. The wear mechanisms of AlO/TiC/CaF layers are abrasive wear and AlO/TiC layers are adhesive wear. [ABSTRACT FROM AUTHOR]

The self-lubricating composites NiAl-BaF-CaF-Ag-Cr, which have varying fluoride contents, were fabricated by the powder metallurgy technique. The effect of fluoride content on the mechanical and tribological properties of the composites was investigated. The results showed that an optimal fluoride content and a balance between lubricity and mechanical strength were obtained. The NiAl-6.2BaF-3.8CaF-12.5Ag-10Cr composite showed the best friction coefficients (0.29-0.38) and wear rates (4.2 × 10-2.19 × 10mm N m) at a wide temperature range (room temperature to 800°C). Fluorides exhibited a good reduced friction performance at 400 and 600°C. However, at 800°C, the formation of BaCrO on the worn surface due to the tribo-chemical reaction at high temperatures provided an excellent lubricating property. [ABSTRACT FROM AUTHOR]

highly ordered porous alumina template with pores of 45 nm in diameter was synthesized by a two-step electrochemical anodizing process. The influence of pore-enlargement treatment on the porous structure and tribological properties of the film was investigated, and ultrasonic impregnation technology was applied on it to form self-lubricating surface. The structure of the self-lubricating film and its tribological properties were investigated in detail. It can be concluded that the optimum time of pore-enlargement treatment is 20 min. The diameter of the pores and the surface porosity of the film are about 70 nm and 30%, respectively, while the film maintains the property of its high hardness. Under the same friction condition, the frictional coefficient of the self-lubricating film is 0.18, much lower than that of the anodic aluminum oxide template, which is 0.52. In comparison with the lubricating surface of non-porous dense anodic aluminum oxide template, the lubricating surface fabricated by the ultrasonic impregnation method on the porous anodic aluminum oxide template keeps longer period with low friction coefficient. SEM examination shows that some C particles have been embedded in the nanoholes of the anodic aluminum oxide template by the ultrasonic impregnation technology. [ABSTRACT FROM AUTHOR]

Newly developed self-lubricating Fe-Cr-C-Mn-Cu cast composite alloys were investigated to study the role of Cu-rich second phase particles which smear on the wear surface during sliding. The wear resistance of the material was improved with an increasing copper concentration. The improved wear resistance was probably obtained by forming a protective tribofilm, which prevented metal-to-metal contact through smearing of the embedded Cu-rich second phase particles. This formation of protective oxide films during sliding is likely to improve the wear resistance of austenitic Fe-Cr-C-Mn-Cu cast composite alloys. [ABSTRACT FROM AUTHOR]

A TiN-matrix coating with a thickness of about 400 μm was prepared by reactive high velocity oxygen fuel (HVOF) spraying on carbon steel in air. The phase composition, microhardness, and antiabrasion properties of the coating were investigated using x-ray diffraction (XRD), an energy dispersive spectrometer (EDS), a scanning electron microscope (SEM), a Vickers microhardness tester, and block-on-ring abrasive equipment. The abrasion mechanism of TiN-matrix coating under dry abrasion conditions was also discussed. The results indicate that the composition of the coating is main phases of TiN and TiN0.3, minor phases of Ti2O3, and TiO2. The TiN-matrix coating possesses high microhardness and relatively good toughness. Furthermore, the friction coefficient of the coating decreases with the increment of applied load. The interstratified distribution of titanium oxides can act as a solid lubricant during the wear test. The main abrasion mechanism of the TiN-matrix coating is adhesion wear. In addition, the coating with self-lubricating property can improve the antiwear property of the substrate significantly. [ABSTRACT FROM AUTHOR]

Ten kinds of self-lubricating composites with different amounts of sintering aids and solid lubricants in Al2O3 matrix were fabricated by hot-pressed sintering. Their friction and wear behaviours in unlubricated sliding against Al2O3 were tested by using a pin-on-disk wear tester at 650°C. It was shown that the amount of sintering aids strongly affected friction coefficient and wear rate of the Al2O3–20Ag20CaF2 composite, the appropriate amount of sintering aids was 10 wt% for beneficial effect on the reduction of wear at 650°C. Also it was shown that the addition of equal quantities of Ag and CaF2 in Al2O3 matrix can promote the formation of the well-covered lubricating film, and effectively reduce the friction and wear. The composite with 40 wt% of lubricants (20 wt% Ag, 20 wt% CaF2) presented an optimum tribological behavior at 650°C (friction coefficient μ is about 0.3, wear rates are about 4 x 10-6 mm3/N,m and 5 x 10-7 mm3/N,m for the disk and pin, respectively). [ABSTRACT FROM AUTHOR]