Search

This paper presents possible modifications to the properties of grey cast iron by laser heat treatment. These modifications are analyzed especially with regard to wear properties as a result of graphite content, which is a well-known solid lubricant. Examples of applications of grey cast iron in cases where good wear resistance is required are presented. Laser hardening from the solid state, laser remelting, and laser alloying are characterized. In this study, changes in the surface layer caused by these treatments were analyzed (especially the influence on the microstructure—including graphite content—and wear properties). It was shown that all of these treatments enable the wear resistance of the surface layer to be enhanced, mostly due to the increase in the hardness and microstructure homogeneity. It was also proven that it is possible to retain the graphite phase (at least partially) in the modified surface layer, which is crucial in the case of friction wear resistance. In particular, laser hardening from the solid state does not eliminate graphite. Laser remelting and alloying cause the dilution of carbon from the graphite phase to the melted metal matrix, but, in the case of nodular cast iron, it is possible that not all of the valuable graphite in the surface layer is lost. [ABSTRACT FROM AUTHOR]

Epoxy resins inherently have low resistance to scratching. To increase the scratch resistance of epoxy resins, reinforcing solid lubricants into the resin is an option. For this purpose, in this study, polytetrafluoroethylene (PTFE) and graphite were reinforced in two different epoxy resins (rigid and toughened) at different reinforcement ratios (5, 10, and 15 wt%). The effects of solid lubricant reinforcement on the scratch behavior of rigid and toughened epoxy resins were examined both experimentally and statistically. Scratch tests were performed throughout a distance of 10 mm using a test apparatus under a load of 15 N and a scratch speed of 30 mm/min. Following the scratch tests, the COF (Coefficient of Friction) values, scratch hardness, scratch width, and depth of all samples were determined and compared to neat epoxy for each resin. In general, it has been determined that solid lubricant reinforcement at higher reinforcement ratios has a positive effect on the COF value (15 wt%). In the case of 15 wt% graphite reinforced rigid and toughened epoxy, a decrease of 15.90% and 17.77%, respectively, was obtained in the COF value compared to the neat epoxy. After the scratch tests, statistical analysis was performed according to RSM to support the experimental results, and ANOVA tables were obtained. Highlights: Epoxy adhesives exhibit low scratch resistance.Examining the impact of PTFE and graphite reinforcement on scratch behavior.Two types of epoxy and varied reinforcement ratios (5, 10, and 15 wt%) were studied.Solid lubricant reinforcement to epoxy positively affected scratch behavior. [ABSTRACT FROM AUTHOR]

The study first simulates formation of the graphene-stuck silicon nanoparticles from the silicon nanoparticle embedded into the annealed graphite. Covering graphene on nanoparticle can be more conveniently by using graphite instead of graphene. Graphene and silicon of the obtained nanoparticles show the tightly bonding situation to each other. In the annealing cases of 500, 1000 and 1500 K, the annealing at the higher temperature provides the stronger bond. The study then investigates their deformation and lubrication. The nanoparticles show the high stability under experiencing the pressure up to 3 GPa. As used as solid lubricants in contact with the diamond slab at 0.5–3 GPa, they provide the friction coefficients of 0.00022–0.00649, which strongly depend on the nanoparticle size. The nanoparticles provide the better mechanical and lubrication properties than the corresponding bare silicon nanoparticles. Thus, the study provides the method to cover graphene on nanoparticle from graphite and the obtained nanoparticles well experience the pressure and have the high lubricity. In order to avoid the damage to the silicon nanoparticle and graphite and increase the bond between them, the hole on graphite should have its radius larger than (or close to) the silicon nanoparticle radius plus the stable adsorption distance. The stability and lubricity are more advanced with increasing the nanoparticle size; therefore, experimental methods may be used to design such particles of large sizes for these behaviors. Friction dependent on the roughness is also investigated. [ABSTRACT FROM AUTHOR]

Carbon-based solid lubricants are excellent options to reduce friction and wear, especially with the carbon capability to adopt different allotropes forms. On the macroscale, these materials are sheared on the contact along with debris and contaminants to form tribolayers that govern the tribosystem performance. Using a recently developed advanced Raman analysis on the tribolayers, it was possible to quantify the contact-induced defects in the crystalline structure of a wide range of allotropes of carbon-based solid lubricants, from graphite and carbide-derived carbon particles to multi-layer graphene and carbon nanotubes. In addition, these materials were tested under various dry sliding conditions, with different geometries, topographies, and solid-lubricant application strategies. Regardless of the initial tribosystem conditions and allotrope level of atomic ordering, there is a remarkable trend of increasing the point and line defects density until a specific saturation limit in the same order of magnitude for all the materials tested. [ABSTRACT FROM AUTHOR]

Aluminium metal matrix composites play a very significant role in the modern world because of their versatile properties such as high strength to weight ratio, ductility, high recycle potential, corrosion resistance, electrical and thermal conductivity along with that aluminium alloys have slighter tensile strength and wear property. Attempts are made to improve required properties in the current work an attempt is made to review different solid lubricants which are reinforced with aluminium metal matrix composite, the key factor in solid lubricants is its structure and the force of the bond, in almost all the solid lubricant one of the important factors is hexagonal structure and week force between the atoms which slides rather than the chance to create dislocation, many lubricants like graphite, Molybdenum disulfide, hexagonal boron nitride have the hexagonal structure. The comparison is made on these solid lubricants, all the solid lubricants reinforced composite has a low coefficient of friction at low temperature but graphite and molybdenum disulfide cannot be operated at high temperature. [ABSTRACT FROM AUTHOR]

Polyamide polymers are widely used in tribological areas in a wide range of industries. The purpose of this study is to extend the tribological life of this material. For this purpose, composite materials were produced by adding solid lubricants such as graphite and wax to the polyamide 6 (PA6) matrix at different rates, and the synergistic effect of these composites on tribological behavior was investigated. Tribological experiments were carried out under dry sliding conditions and on themselves. The polyamide 6/graphite/wax composites were first produced in the form of granules in a twin‐screw extruder, and then test samples were molded using the injection molding technique. Wear tests were performed using a pin‐on‐disc wear device. Tribological tests were carried out at a sliding speed of 0.5 m s−1 and under loads ranging from 10 N to 250 N. Following the experiments, the friction coefficient, specific wear rate, and surface wear were determined under the condition of the materials working on each other. The results showed that the lowest specific wear rate and friction coefficient were obtained for the polyamide 6 composites containing 6 % wax and 15 % glass fiber working on each other. [ABSTRACT FROM AUTHOR]

The dispersion stability of carbon-based solid lubricants/lubricating oils remains a challenge to overcome. Recently, novel processing routes were developed to obtain 2D turbostratic graphite particles via solid-state reactions between B4C and Cr3C2 (GBC) and between SiC and Fe (GSF) that present outstanding tribological properties in a dry scenario, as well as functionalized graphene (GNH). This work investigated the suspension stability of GBC and GSF particles (0.05 wt.%) dispersed in a low-viscosity polyol ester lubricating oil and their tribological performance. Ammonia-functionalized graphene (GNH) particles were also used as a reference. In order to evaluate the dispersion stability, in addition to the classical digital image technique, a much more assertive, reliable, quantitative and rarely reported in the literature technique was used, i.e., the STEPTM (Space and Time-resolved Extinction Profiles) technology. Reciprocating sphere-on-flat tribological tests were carried out, in which before contact, 0.2 μL of pure oil and suspension (POE + 0.05 wt.% of solid lubricant) was applied on a flat surface. The results showed that the GBC particles remained remarkably stable and reduced the sphere wear rate by 61.8%. From the tribosystem point of view, the presence of GBC and GSF reduced the wear rate by 18.4% and 2.2%, respectively, with respect to the pure oil, while the GNH particles increased the wear rate by 4.2%. Furthermore, the wear rate was improved due to the highly disordered carbon tribolayer formation identified on both surfaces. [ABSTRACT FROM AUTHOR]

Copper-based solid lubrication inlay technology is widely used in industrial production, especially in low-speed and heavy load conditions, and the structure and distribution of the filling pore have a significant influence on the friction performance due to the distribution of contact stress. In this paper, based on the operating conditions of the bottom pivot of the Three Gorges gate, graphite is used as a solid filled lubricant. The effects of filling pore diameter, filling pore depth, and area distribution rate on the friction and wear properties were studied by orthogonal equivalent test on MMW-1A tester with grease. Combining the three-dimensional morphology test and ferrography analysis, the results show that: 1) the influence of three parameters on the test results are: filling pore diameter > area distribution rate > filling pore depth; 2) when the filling pore diameter is 3 mm, the area distribution rate is 12%, and the filling pore depth is 0.5 mm, which is the equivalent the optimal structure of the filling pore size under working conditions. According to this conclusion, the actual filling structure can be obtained based on the similarity theory. As Coulomb friction is material and contact stress related, the calculation of the stress distribution during dynamic operation is difficult and therefore the analysis is carried out experimentally. [ABSTRACT FROM AUTHOR]

The use of powdered graphite as a solid lubricant to reduce friction among soybean seeds during mechanical sowing aims to facilitate the seed flow into the seed reservoir, while reducing mechanical damage to the seed. The objective of this study was to evaluate the influence of graphite on the longitudinal deposition of soybean seeds using mechanical and pneumatic feeders at different distribution velocities. The experiment was performed on a static simulation-test bench, with a completely randomized design with two varying factors: graphite dose (0, 1, 2, 4, and 8 g kg-1 seed) and distribution velocity (5, 7, 9, and 11 km h-1 for the pneumatic feeder; and 3, 5, 7, and 9 km h-1 for the mechanical feeder). To assess the homogeneity of seed distribution, the frequency of parameters such as double, flawed, and acceptable spacings, coefficient of variation, and precision index were evaluated from five repetitions of 250 spacing each. For the pneumatic feeder, the optimal values to maximize precision of seed deposition were 4.6 g kg-1 and 6.7 km h-1 of graphite dose and distribution velocity, respectively. In turn, the optimal values to minimize undesirable spacing while maximizing accuracy with the mechanical feeder were 4.9±0.6 g kg-1 and 4.9±0.3 km h-1. Overall, regardless of feeding mechanism, the use of graphite promoted greater efficiency in the distribution of seeds owing to the higher level of fluidity inside the reservoir; however, high doses can cause the opposite effect. In addition, an excessive increase in speed influenced seed distribution negatively. [ABSTRACT FROM AUTHOR]

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

High specific strength and superior corrosion resistance are two key characteristics of the aerospace grade AA7075-T6 alloy. However, the surface behavior of AA7075-T6 is found to be deprived, because of its behavior of being prone to fretting fatigue and adhesive wear under dry sliding conditions. Thus, surface wear behavior improvement with the retention of the microhardness of the alloy is required for increasing its wider application. For this, surface isomorphous precipitates and the soft matrix need to be protected through dispersion of hard thermally stable ceramic SiC with solid-lubricant graphite particles. The dispersion through friction stir processing (FSP) avoids detrimental phase formations by processing the metal alloy below its melting point temperature. Thus, dispersion of SiC-Graphite inside the AA7075-T6 using FSP is the focal point of the study. The low and high wear rate samples have been analyzed using SEM imaging and elemental analysis through XRD and EDS mapping. In this study, reinforcing the SiC-Gr particles greatly improved the wear behavior of the AA7075 alloy. Wear resistance has been controlled by combining soft solid lubricant Gr particles with load-bearing hard SiC nanoparticles. In dry sliding action, the base alloy matrix was severely exposed to wear, but the hard SiC nanoparticles served as load-bearing asperities and improved the wear resistance. Simultaneously, the graphite layers generated the soft solid lubricating tribofilm further to reduce the wear and friction between mating surfaces. The wear mechanisms have changed prominently from adhesion to abrasion and delamination through reinforcing the SiC-Gr reinforcements. The graphite content in a hybrid ratio with SiC hard particles was found to have improved the wear resistance by 78%. The tendency of fatigue was more effectively improved in surface composites as compared to the base alloy. [ABSTRACT FROM AUTHOR]

Copyright of Lubrication Engineering (0254-0150) is the property of Editorial Office of LUBRICATION ENGINEERING and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Purpose: Carbon steel has a high application rate in modern industry, but this type of steel has the defect of high wear. This study aims to improve the surface friction and wear performance of carbon steel under such working conditions. Design/methodology/approach: In this study, a dry film lubricant based on graphite powder was prepared by the ultrasonic dispersion method, and deposited on the surface of carbon steel specimens by the simple pressure spraying technology. At the same time, molybdenum disulfide and polytetrafluoroethylene dry film lubricants were developed by the same method, and the comparative experimental study on friction and wear was carried out in the end-face friction tester. Findings: The results show that the deposition effect of graphite and molybdenum disulfide dry film lubricants on the surface of carbon steel is obviously better than that of polytetrafluoroethylene dry film lubricant. Compared with molybdenum disulfide and polytetrafluoroethylene dry film lubricant, graphite dry film lubricant has the best friction and wear performance on the surface of carbon steel. The working life of carbon steel specimens sprayed with graphite dry film lubricant decreases with the increase of pressure load and rotation speed. The combination of load and sliding speed will accelerate the transition of the coating to a stable direction. In addition, the micro lubricant particles formed in the wear process will form particle flow lubrication, and the appropriate addition of particle powder of the same material will also prolong the normal antifriction time of the lubricant. Originality/value: These findings developed a dry film lubricant that can effectively improve the friction and wear properties of carbon steel surface. [ABSTRACT FROM AUTHOR]

Copyright of Lubrication Engineering (0254-0150) is the property of Editorial Office of LUBRICATION ENGINEERING and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

At this research, the tribological properties of the composites obtained by adding graphite (G) and wax (W) as solid lubricant in to the polyamide 6 (PA 6) matrix under dry shear conditions were investigated. PA 6/graphite/wax polymer blends were prepared in twin screw extruder. The samples used in the research were produced by injection molding method. Abrasion tests were carried out pin on disk wear device in accordance with ASTM G99 standard. The tests were carried out at sliding speeds of 0.4 m/sec, 0.8 m/sec and 1.2 m/sec and sliding distance of 4000 m under the abrasion loads of 50N and 100N. Thanks to the solid lubricants (graphite, wax) added to the PA 6 matrix, the friction coefficient and wear rate decreased. Slip path temperature measurements on the pin showed that the PA 6/wax had lower temperature. Microstructures of wear surfaces of PA 6/graphite/wax were investigated using SEM. [ABSTRACT FROM AUTHOR]

In this work, self-lubricating composites containing MoS2 and graphite dispersed in an iron matrix were produced by powder metallurgy and sintering. Previous studies demonstrate that MoS2 reacts with iron matrixes during sintering, making the production of Fe-MoS2 composites rather difficult. Therefore, this study focused on a potential solution to avoid or reduce this reaction, whilst still providing good tribological properties. Our results show that the addition of graphite retards the reaction of MoS2 with iron and that the combination of MoS2 + graphite results in composites with an optimized coefficient of friction associated with a low wear rate both in nitrogen and air atmospheres. Through adequate control of the lubricant's particle size, composition, and processing parameters, self-lubricating iron-based composites with a low dry coefficient of friction (0.07) and low wear rate (5 × 10−6 mm3·N−1·m−1) were achieved. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study, the tribological behaviors at different temperatures of aluminium matrix composites (AMCs) with different amounts of ZrO2 added were investigated. Design/methodology/approach: Aluminium graphite (A356/2 wt% graphite (solid lubricant)) composite powders prepared by adding four different amounts (3 wt%, 6 wt%, 9 wt% and 12 wt%) of Zirconia (ZrO2) to the matrix were mechanically alloyed for 4 h. Wear tests were conducted at five different temperatures (20 °C, 100 °C, 180 °C, 260 °C and 340 °C) and for three different sliding distances (53 m, 72 m and 94 m) on the pin-on-disc type wear tester. Findings: Results of the study showed that the highest hardness and density value were measured for 12% ZrO2 added AMC material. Wear test results showed that weight loss increases with increasing temperature; weight loss decreases at all temperatures with the increasing amount of reinforcement in the matrix. Originality/value: In this paper, the tribological properties of aluminium matrix composites produced by the mechanical alloying method by adding different amounts of ZrO2 were determined by simulating the tribological properties at different loads and temperatures. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the influence of different counterbodies against Cu/magnesium phosphate treated graphite (Cu-MgPG) composite materials to find the best material combination in terms of friction coefficient and specific wear amount. A Cu matrix composite reinforced with 10 vol% magnesium phosphate treated graphite and pure Cu powder were prepared by powder metallurgy techniques under the same consolidation processing condition. The friction and wear properties of the composites were investigated at 10 N using a pin-on-disc tribometer on Al2O3, SiC and SUJ2 bearing steel counterbodies. The Cu-MgPG/Al2O3 pair showed the lowest friction coefficient, but the specific wear rate tended to increase slightly when compared with Cu/Al2O3 pair. On the other hands, the Cu-MgPG/SUJ2 pair showed about the same specific wear rate as the Cu/SUJ2 pair, but the friction coefficient was significantly reduced. These phenomena are thought to be due to the fact that the added graphite acts as a solid lubricant during sliding and also suppresses the oxidation behavior of the sliding material. [ABSTRACT FROM AUTHOR]

The development of a high-performance solid-lubricating composite with excellent self-lubricity over a broad temperature range in vacuum is significant to solve the frictional problems of spatial mechanisms. In this study, the vacuum tribological behaviors of nickel-matrix/Ag/(Ca, Ba)F2/graphite (0–2 wt%) composites were studied from 25 to 800 °C. The results show that the synergistic effects of solid lubricants can significantly improve the tribological properties of the composites in vacuum, with the graphite content contributing considerably. For 2 wt% graphite, a low friction coefficient (0.14–0.25) and the lowest wear rate ((0.12−4.78)×10−5 mm3·N−1·m−1) were observed in vacuum over the entire testing temperature range. Moreover, the wear mechanisms were clarified via analysis of the chemical composition and morphologies of the sliding surfaces. [ABSTRACT FROM AUTHOR]

Nanoparticles (NPs) of solid lubricants (SLs) as solo particles have proved to be excellent anti-wear additives (AWAs), anti-friction additives (AFAs), and extreme-pressure additives (EPAs) for greases. However, hardly any efforts are made to investigate possible synergism/antagonism in the functioning of NPs when added in combination. Graphite is well known as very efficient AWA and AFA but less effective as EPA, whereas PTFE is more known as very efficient EPA and less efficient as AWA and AFA for greases. Hence, it was thought worthwhile to explore the potential of these two particles together as EPA, AWA, and AFA for possible synergism, using multiple combinations of NPs of PTFE (P) and graphite (G) in various amounts (0, 1, 2, 3, and 4 wt. %) keeping the total amount fixed at 4%. It was observed that combo-particles in typical amounts proved to show synergistic action as EPA and AWA. However, as AFA, they showed antagonistic behaviour. In the case of EP, the highest gain (100%) was recorded for combo-grease (1% G and 3% P). In the case of AW performance, all combo-greases showed synergism and showed almost similar benefits (52–62%, depending on the load). However, a clear antagonism was observed in AF performance, barring one combination (1% G and 3% P). The wear mechanism was discussed using various analytical techniques such as scanning electron microscopy (SEM), Raman spectroscopy, and X-ray photo-electron spectroscopy (XPS). [ABSTRACT FROM AUTHOR]

In this work, the conventional short carbon fiber (SCF)/polytetrafluoroethylene (PTFE)/polyetheretherketone(PEEK) (SCF/PTFE/PEEK) composite was elected as the matrix, copper and graphite micron flakes were further blended to prepare PEEK self-lubricating composites. At a pressure of 12 MPa and a speed of 0.5 m/s, with a graphite content of 7.5 wt% and copper of 2.5 wt% (Gr 7.5 Cu 2.5), the composite exhibited a COF of 0.23 and the lowest wear rate of 4.1 × 10−7 mm3/Nm. Physicochemical analysis of the worn surface of the steel ring revealed that the introduction of appropriate amounts of copper facilitated the tribo-physicochemical reaction during the rubbing process, which favored the formation of a thin and tough transfer film of Gr 7.5 Cu 2.5 on the worn surface of the steel ring. [Display omitted] • Micron copper and graphite flakes were selected as synergistic wear-reducing agents for the PEEK self-lubricating composites. • The tribo-physicochemical reaction was proactively designed to improve the quality of the transfer film. • The Gr 7.5 Cu 2.5 possessed the lowest wear rate of 4.1 × 10−7 mm3/Nm. • The Gr 7.5 Cu 2.5 formed a thin and tenacious transfer film on the worn surface of the steel ring. [ABSTRACT FROM AUTHOR]

Abstract Understanding the mechanism of precision sliding contacts with thin, adherent solid nano lubricating particle films is important to improve friction and wear behavior and ensure mechanical devices have long service lifetimes. Herein, a facile and multistep approach for the preparation of graphene oxide (GO) is presented. Subsequently, surface modification of as-synthesized GO with octadecyl amine (ODA) is performed to prepare hydrophobic GO-ODA and with 6-amino-4-hydroxy-2-naphthalenesulfonic acid (ANS) to prepare amphoteric GO-ANS through a nucleophilic addition reaction. X-ray diffraction and ultraviolet-visible, Fourier transform infrared, and Raman spectroscopy provide significant information about the reduction of oxygen functionalities on GO and the introduction of new functionalities in GO-ODA and GO-ANS. The effects of particle functionalization for the improved control of particle adhesion to the tribocontact have been studied. Wettability and thermal stability were determined using the water contact angle, and atomic force microscopy and differential scanning calorimetry (DSC) were used to characterize particle adhesion to the tribocontact. The tribological performances of the particles have been investigated using macro- and micro-tribometry using pin/ball-on-disc contact geometries. The influence of particle functionalization on the contact pressure and sliding velocity was also studied under rotating and reciprocating tribo-contact in ambient conditions. With an increase in the contact pressure, the functionalized particles are pushed down into the contact, and they adhere to the substrate to form a continuous film that eventually reduces friction. Amphoteric GO-ANS provides the lowest and most steady coefficient of friction (COF) under all tested conditions along with low wear depth and minimal plastic deformation. This is because particles with superior wetting and thermal properties can have better adherence to and stability on the surface. GO-ANS has a superior ability to adhere on the track to form a thicker and more continuous film at the interface, which is investigated by field emission scanning electron microscopy, energy dispersive spectroscopy, and Raman analysis.

Raman spectroscopy is applied for the non‐destructive characterisation of the graphite which is used as solid lubricant in the friction material of semi‐metallic brake pads in vehicles. The characteristics (intensity, position, width) of the main Raman bands assigned to vibrational modes of the graphitic honeycomb structure (G‐band) and to defects (D‐band) are proved useful probes of the quality and wear status of the graphite lubricant because they are sensitive to the structural disorder. It is found that wear of the graphite lubricant proceeds in two stages: transformation of crystalline to nanocrystalline graphite and subsequent amorphisation. Moreover, the intensity of the defect‐related D′ peak is also used in order to obtain information about the nature of the defects. [ABSTRACT FROM AUTHOR]

In this paper, the mechanical characteristics for metal powder compaction with the addition of graphite powders are investigated to reduce the friction generated during the powder compaction process. The discrete element method model is developed for powder compaction with powder mixture containing steel-graphite and copper-graphite. Compaction experiments are performed for the validation of the model. Parameters involved with mixing conditions such as graphite mixing and graphite size ratio and its effects on compressive characteristics are explored. Optimal values for mixing conditions are defined. Also, the effects of powder mixing parameters are investigated through analysing stress transfer ratio from top to bottom punch and compressive force distribution throughout the powder compact. Significant improvements in mechanical properties are observed with the addition of graphite lubricants. Improved stress transfer rate by 57% (steel) and by 44% (copper) are obtained and decreased standard deviation of compressive force by 85% (steel) and by 67% (copper) are observed. [ABSTRACT FROM AUTHOR]

One of the developing areas of tribotechnical materials science is the development and study of nanocomposite materials for movable joints operating under extreme conditions, which are not only increased thermomechanical loads and high sliding speeds, but also, mainly, the effect of a gaseous medium, in particular, vacuum. Detonation-gas spraying was carried out with the developed nanocomposite powders of the Fe-Ti-SiC-MoS2-MgC2 system. Particles of solid lubricant corresponding to fractions of 30-40 μm were mixed with the initial nanopowders by the wet method. To eliminate powder adhesion to the chamber walls and optimize the process of spheroidization of a mixture of its components, we used a developed and tested technology with the use of ultrasound. Tests in vacuum were carried out on a friction machine M-22PV, designed for laboratory and experimental evaluation of tribological characteristics and quality control of coatings. Investigation of the wear resistance of coatings during friction, their tendency to set were evaluated by the intensity of wear in a vacuum (at a vacuum of 1.33×10-5 Pa). The study of the quality of surface layers, in which the processes of activation during friction proceed, were carried out using modern methods of physicochemical studies, including metallography, scanning electron microscopy, and X-ray structural phase analysis. As a result of external influences and the relative movement of the contact surfaces, the first and main manifestation of external friction arises - elastoplastic deformation, which causes the emergence of a set of surface phenomena that determine the essential properties and qualitative regularities of friction processes. The results of metallographic analysis and surface studies confirm the presence of a surface passivating film of molybdenum disulfide. The use of the optimal combination of the properties of MoS2 and graphite films significantly improves the tribotechnical characteristics. The recommended graphite content, as established, is 10-12% (wt.%), which corresponds to the maximum lubricating effect of the formed complex film, which prevents the adhesion interaction of juvenile surfaces, while individual foci of destruction are localized in the near-surface layers and annihilate in the process of grain boundary sliding, excluding any kind of damage. [ABSTRACT FROM AUTHOR]

Friction composites consist of many materials with various properties. Solid lubricant is one of these materials. The task of the solid lubricant in the composite is to protect the counter surfaces against wear and to reduce noise and vibration. Typical solid lubricants used in the friction composite are graphite, antimony trisulfide, molybdenum disulfide, copper sulfide, etc. The selection suitable solid lubricants for better braking performance is an important issue, as solid lubricants may decompose at high temperatures, leading to undesirable results. The particle size of the solid lubricant used is at least as important as itself. In this study, the effect of micro and nanoparticle-sized graphite on friction and wear behavior of friction composites was investigated experimentally. Two brake lining were prepared containing 10 wt.% nanographite and micrographite, were produced by powder metallurgy technique. The brake lining samples have been tested under Friction Assessment and Screening Test (FAST). The frictional and physical properties of the produced samples were determined by appropriate tests. According to the test results obtained, micro and nanoparticle size were compared in many respects and the most ideal size was determined for graphite. [ABSTRACT FROM AUTHOR]

In this work, hybrid AA2024—Graphite (0-6 wt.% @ 2%)/SiC (2 wt.%)/Si3N4 (2 wt.%) alloy composites were fabricated via semi-automatic stir casting method. The specimens of alloy composites compositions were analyzed to examine the effect of graphite phase reinforcement on the (1) physical and mechanical performance, (2) dry sliding wear/friction performance following ASTM G99 on Pin-on-Disc tribometer. A significant improvement in the physical, mechanical, and wear/friction performance was observed with graphite reinforcing phase. The surface morphology studies revealed the presence of tribo-layer or lubricating layer indicating the presence of solid lubricant graphite. The thickness of tribo-layer enhances with graphite content and accounts for wear/friction performance of hybrid alloy composites. [ABSTRACT FROM AUTHOR]

Copper and aluminum metals are classified relatively as softer materials that possess comparatively poor mechanical and wear characteristics; accordingly, this study has aimed an attempt to improve their properties and compare between them. At the present work, both copper and aluminum metals were used separately as a matrix composite for a comparative study. They reinforced with a fixed content of 4 vol% graphite as a solid lubricant and various content of 0, 1, 2, 3, and 4 vol% silver nanoparticles. The pure metals and the hybrid nanocomposites were manufactured by utilizing the powder metallurgy technique. Mechanical properties such as hardness, diametral compressive strength, and tensile strength were studied. Moreover, a dry wear test was performed by applying various loads of 5, 10, 15, and 20 N with constant sliding distance and speed of 1810 m and 1.5 m/s, respectively. In order to interpret the results and prove the preparation goodness, Field Emission Scanning Electron Microscope (FESEM) and Energy-Dispersive X-ray (EDX) analysis were employed to characterize the as-received composite powders, worn surface, and wear debris morphology. The results were revealed that the microhardness, diametral compressive strength, tensile strength, friction coefficient, and wear resistance were improved significantly by increasing silver nanoparticle content up to 2 vol% and 3 vol% in aluminum and copper matrix composites, respectively, and then deteriorated gradually as compared with pure metals. Convergence was observed in the wear rate results between the copper and aluminum matrix composites in the silver content of 2 vol%. Besides that, the increment in applied loads was associated negatively with the wear resistance. Lastly, the impact of improving silver nanoparticles content on strengthening the copper matrix composite is higher than aluminum matrix composite. [ABSTRACT FROM AUTHOR]

Understanding the mechanism of precision sliding contacts with thin, adherent solid nano lubricating particle films is important to improve friction and wear behavior and ensure mechanical devices have long service lifetimes. Herein, a facile and multistep approach for the preparation of graphene oxide (GO) is presented. Subsequently, surface modification of as-synthesized GO with octadecyl amine (ODA) is performed to prepare hydrophobic GO-ODA and with 6-amino-4-hydroxy-2-naphthalenesulfonic acid (ANS) to prepare amphoteric GO-ANS through a nucleophilic addition reaction. X-ray diffraction and ultraviolet-visible, Fourier transform infrared, and Raman spectroscopy provide significant information about the reduction of oxygen functionalities on GO and the introduction of new functionalities in GO-ODA and GO-ANS. The effects of particle functionalization for the improved control of particle adhesion to the tribocontact have been studied. Wettability and thermal stability were determined using the water contact angle, and atomic force microscopy and differential scanning calorimetry (DSC) were used to characterize particle adhesion to the tribocontact. The tribological performances of the particles have been investigated using macro- and micro-tribometry using pin/ball-on-disc contact geometries. The influence of particle functionalization on the contact pressure and sliding velocity was also studied under rotating and reciprocating tribo-contact in ambient conditions. With an increase in the contact pressure, the functionalized particles are pushed down into the contact, and they adhere to the substrate to form a continuous film that eventually reduces friction. Amphoteric GO-ANS provides the lowest and most steady coefficient of friction (COF) under all tested conditions along with low wear depth and minimal plastic deformation. This is because particles with superior wetting and thermal properties can have better adherence to and stability on the surface. GO-ANS has a superior ability to adhere on the track to form a thicker and more continuous film at the interface, which is investigated by field emission scanning electron microscopy, energy dispersive spectroscopy, and Raman analysis. [ABSTRACT FROM AUTHOR]

Ni-based alloys are resistant against wear and corrosion, and are widely applied in surface engineering. In this study, different amounts of graphite (0, 5 and 10 wt.%) are added to NiCrBSi powder as a solid lubricant. The pure and composite powders are deposited on 420 stainless steel through the high-velocity oxygen fuel process. The microstructure and properties of the coatings are examined through x-ray diffraction and scanning electron microscope. Vickers microhardness test is run for the coatings' hardness measurement. NiCrBSi has the highest hardness of 650HV. Hardness of the coatings decreases with the increase in the graphite content. The porosity measurement by ImageJ analyzer indicates that the NiCrBSi coating has the lowest porosity. To assess the ambient and high-temperature wear resistance of the coatings, ball-on-disk wear tests were run with 15 N load and the sliding distance of 1000 m at 25 °C and 450 °C. The results indicate that the NiCrBSi and NiCrBSi-10 wt.%Gr coatings have the highest wear resistance at ambient and high temperatures, respectively. The friction coefficient of the coatings containing lubricant is lower than that of the NiCrBSi coating. [ABSTRACT FROM AUTHOR]

Particulate matter produced during brake application was investigated, focusing on the effect of the solid lubricants in the brake friction composite, such as graphite, antimony trisulfide, and molybdenum disulfide. Results showed that the brake emission was significantly affected by the solid lubricant type and braking temperatures. Antimony trisulfide caused high brake emissions at moderate temperatures, whereas graphite produced high emissions at elevated temperatures. The brake emission at moderate temperatures was affected by the aggressiveness of the composites and the presence of friction films on the gray iron disc surface. In contrast, the brake emissions at elevated temperatures were determined by the thermal decomposition of the composite and the oxidation of solid lubricants. [ABSTRACT FROM AUTHOR]

This work presents a tribological evaluation of the influence of graphite and bronze fillers in two commercial composites in a dry sliding pin-on-disc test at the same contact severity ( P V a parameter) and four testing conditions (varying both normal force and sliding velocity). Both fillers, in comparison to pure PTFE, significantly affected the coefficient of friction (COF) and the mass loss. The sliding distance required to reach steady-state for COF was statistically equal for all three materials. The COF experienced a relevant influence of both normal force and sliding velocity. The graphite filler acted as a solid lubricant and exhibited reductions in COF (∼27% on average) and in mass loss (∼4.2 times lower on average). The bronze filler, on the other hand, had a COF increase of up to 5% for conditions with lower normal force but showed a significant reduction on the specific mass loss (∼5.3 times lower on average). Due to its higher thermal conductivity, the composite filled with graphite presented lower tribosystem temperatures in thermography evaluations. Good agreement of the temperature data was found considering a model that proposes the rate of heat generated by friction. With respect to wear of the composites, evidence of adhesion (transfer films to the counterface) and abrasive (microploughing and microcutting) wear mechanisms was found, in addition to the identification of preferential wear. [ABSTRACT FROM AUTHOR]

Polyimide-based solid lubricating films were prepared by simple and efficient spin coating proceeding. Several composite lubricating films were obtained by changing the composition and contents of inorganic solid lubricants in organic binder. The structure, physical phase, and performance of the synthesised lubricating films were characterised by using X-ray diffraction, scanning electron microscope, fourier transform infrared spectrometry, thermo gravimetric analyzer, and nano-indentation methods. And the friction coefficients of these composite lubricating films were measured by pin-on-disk structural tribometer. The results showed that all kinds of lubricating films had good adhesion strength. Compared with the pure polyimide film, the composite lubricating films exhibited better thermal and mechanical properties. These composite lubricating films, with MoS2 and graphite as solid lubricants, could effectively reduce the friction coefficient of polyimide film. Moreover, the friction coefficient of the composite lubricating film filled with the above two kinds of lubricant decreased to the minimum 0.141. [ABSTRACT FROM AUTHOR]

This research work focuses about fabrication and investigation on the influence of Titanium Carbide (TiC)-graphite particles reinforcement in wear behavior of Aluminium Matrix Composites (AMC). The stir casting technique was used to fabricate AMC reinforced with various weight percentage of TiC and graphite particles. Wear tests were conducted by using pin-on-disc wear testing machine. The hardness of the hybrid composites were recorded on the test specimen. The worn out surfaces of composites were analyzed using Scanning Electron Microscope (SEM). Results reveal that the presence of TiC and graphite particles improved the wear resistance. The wear of composite is primarily due to delamination and abrasion. The graphite particles serve as the solid lubricant on the wear of composite. The hardness of composite is improved with the decrease in weight percentage of graphite. SEM images reveal that the reinforcement particles in the matrix are homogeneously distributed. Also, worn-out surfaces of the composite were studied to observe wear track and wear mechanisms like plowing grooves, crack or cutting, and fragmentation. [ABSTRACT FROM AUTHOR]

Metallic coatings are essential in providing anti-friction and wear-resistant protection to soft metals. However, they often encounter challenges in offering sufficient protection under demanding friction and wear conditions. In this study, by combining a gradient structure with solid lubricant modification, we fabricated gradient-structured (GS) Ni/graphite composite coatings through electrodeposition, showcasing superior tribological properties. Experimental results indicate that the GS Ni/graphite coating, when rubbed against WC-5%Co alloy, exhibits a coefficient of friction (COF) of 0.33 and a wear rate of 1.14 × 10−5 mm3/N·m, marking reductions of 47 % and 93 % respectively compared to the softer Cu alloy substrate. Comprehensive stress field evaluations and subsurface microstructural analyses attribute this enhanced tribological performance to the effective accommodation of plastic deformation within the subsurface layer by the gradient structure, coupled with the lubricating function of graphite. The synergy of the gradient structure and graphite presence contributes to preventing cracking and promoting a more resilient subsurface layer, resulting in decreased COF and improved wear resistance. This study not only highlights the notable tribological advancements attainable with GS Ni/graphite composite coatings but also introduces an advanced approach for developing novel GS metal/solid lubricant coatings with enhanced friction and wear properties. • Gradient-structured Ni/graphite coatings were fabricated via electrodeposition. • Our coatings show significant reduction in both the coefficient of friction and wear rate. • Excellent wear resistance is attributed to the synergistic effects of gradient structure and graphite. • Gradient structure serves to accommodate plastic deformation within the subsurface layer. • Graphite provides lubrication, reduces shear stress and inhibits the form of brittle layers. [ABSTRACT FROM AUTHOR]

An orthogonal test was used to design different mixture ratios of molybdenum disulfide(MoS2), graphite, and SiO2 particles, which were filled with polytetrafluoroethylene (PTFE) composite. MoS2-, graphite-, and SiO2-modified PTFE was obtained by pressing and sintering, and the processing parameters were determined using progressive studies and experiments. The friction and wear properties of different PTFE composites lubricated with natural seawater were analyzed using an MMU-5G wear tester. A laser scanning confocal microscope was employed to examine the morphological characteristics of the worn surface. Moreover, the influence of particle proportions on the tribological property of composites was analyzed. Results show that the addition of SiO2, MoS2, and graphite can increase the bearing capacity, improve the wear resistance, reduce the friction coefficient, and increase the self-lubricating ability of the PTFE matrix. [ABSTRACT FROM AUTHOR]

Bu deneysel çalışmada, katkısız poliamid 6 (PA 6), %15 grafit katkılı poliamid 6 (PA6-15G) kompozit ve %15 grafit ve %6 vaks katkılı poliamid 6 (PA6-15G-6W). kompozit malzemelerin kendi üzerlerinde kuru kayma şartları altındaki aşınma ve sürtünme davranışları araştırılmıştır. Kompozit malzemelerin karışımı ikiz vidalı ekstruder kullanılarak hazırlanmış, tüm test numuneleri de enjeksiyonla kalıplama tekniği kullanılarak üretilmiştir. Çekme, darbe ve aşınma deneyleri ASTM standartlarında yapılmıştır. Aşınma ve sürtünme testleri, pim-disk aşınma cihazında gerçekleştirilmiştir. Aşınma testleri 0,5 m/s kayma hızında, 10N, 20N ve 30N yüklerde oda sıcaklığında yapılmıştır. Yapılan aşınma deneyleri sonucunda, PA6-15G-6W kompozitinin tribolojik özelliklerinin katkısız PA6 ve PA6-15G kompozitine göre daha iyi olduğu tespit edilmiştir. PA6-15G kompozitine vaks ilave edilmesiyle, kompozitin sürtünme katsayısı ve spesifik aşınma oranının azaldığı tespit edilmiştir. Deneylerde kullanılan malzemelerin aşınma mekanizmalarını belirlemek için optik mikroskopta aşınma yüzey mikro-yapıları alınmıştır.Anahtar Kelimeler: Polyamide, Triboloji, Mekanik özellikler, Grafit, Vaks, katı yağlayıcı

Bu deneysel çalışmada, katkısız poliamid 6 (PA 6), %15 grafit katkılı poliamid 6 (PA6-15G) kompozit ve %15 grafit ve %6 vaks katkılı poliamid 6 (PA6-15G-6W). kompozit malzemelerin kendi üzerlerinde kuru kayma şartları altındaki aşınma ve sürtünme davranışları araştırılmıştır. Kompozit malzemelerin karışımı ikiz vidalı ekstruder kullanılarak hazırlanmış, tüm test numuneleri de enjeksiyonla kalıplama tekniği kullanılarak üretilmiştir. Çekme, darbe ve aşınma deneyleri ASTM standartlarında yapılmıştır. Aşınma ve sürtünme testleri, pim-disk aşınma cihazında gerçekleştirilmiştir. Aşınma testleri 0,5 m/s kayma hızında, 10N, 20N ve 30N yüklerde oda sıcaklığında yapılmıştır. Yapılan aşınma deneyleri sonucunda, PA6-15G-6W kompozitinin tribolojik özelliklerinin katkısız PA6 ve PA6-15G kompozitine göre daha iyi olduğu tespit edilmiştir. PA6-15G kompozitine vaks ilave edilmesiyle, kompozitin sürtünme katsayısı ve spesifik aşınma oranının azaldığı tespit edilmiştir. Deneylerde kullanılan malzemelerin aşınma mekanizmalarını belirlemek için optik mikroskopta aşınma yüzey mikro-yapıları alınmıştır.Anahtar Kelimeler: Polyamide, Triboloji, Mekanik özellikler, Grafit, Vaks, katı yağlayıcı

Purpose This paper aims to investigate the effect of varying Wt.% (0-3 per cent) of graphite as a solid lubricant on the tribological properties of Fe-Cu-Sn alloy.Design/methodology/approach Powder metallurgy technique is used for the fabrication of Fe-Cu-Sn alloy with varying Wt.% of graphite. The tribological tests were conducted on a ball-on-disc universal tribometer under different testing conditions.Findings The friction coefficient decreases with sliding distance and load, but the wear rate increases with the increase in load. The G3 composition showed the best tribological properties under dry conditions. The wear mechanism of G0 composition shows adhesive wear and abrasive wear, while G1, G2 and G3 compositions show mildly abrasive wear.Originality/value This paper reported a new, cheap and wear-resistant self-lubricating Fe matrix material for gears and bearings. [ABSTRACT FROM AUTHOR]

Polymeric materials filled with micro-sized short carbon fiber (SCF) and various internal lubricants, i.e. graphite and PTFE etc., have been proved as a beneficial tribomaterial formulation in contact with a steel counterbody. The SCFs carry the most load applied on the tribosystem, while the internal lubricants improve the friction behavior of the polymer matrix. In the present study, the roles of rigid particles on the friction and wear performance of SCF filled Polybutylenterephthalate (PBT) with and without graphite were investigated by using a pin-on-disc (PoD) tribometer under dry sliding condition. The experimental results show that the tribocomposite filled with nanoparticles without graphite particles presents outstanding friction and wear performance especially under moderate and severe load conditions in combination with superior mechanical properties compared with graphite-filled tribocomposite. The friction coefficient and wear rate under a pv-condition of 3 MPa and 2 m/s are 0.18 and 0.8*10 −6 mm 3 /Nm, respectively. Based-on the optical analysis of the worn surfaces of the polymer samples and the transfer layers formed on the steel disc, the possible friction and wear mechanisms were discussed. [ABSTRACT FROM AUTHOR]

The aim of the paper is to test innovative minimal techniques, based on Minimum Quantity Lubrication (MQL) and Minimum Quantity Cooling (MQC) strategies, to improve the tool life and machined product surface quality when applied to finishing turning of difficult-to-cut alloys. Two different MQL and MQC solutions, both based on the addition of Solid Lubricants (SL), were proposed and tested, namely an MQL vegetable oil enriched with PTFE particles and an aqueous solution added with graphite at different percentages. The study proved that the newly developed strategies determined an increase of both the tool life and machined surface integrity, with the best results highlighted for the SL-assisted MQC strategies. [ABSTRACT FROM AUTHOR]

Solid lubricant materials are promising for high performance machines and mechanical systems. In this paper, the nickel alloy matrix solid lubricant composites containing Ag, BaF 2 /CaF 2 and three different amounts of graphite were prepared by hot pressed sintering method. The tribotests were performed sliding against Si 3 N 4 ball in air from room temperature to 800 °C. The effect of graphite content on the tribological behavior of the composites under high temperatures was studied. Micro-Raman, XRD and SEM analysis were used to analyze the morphologies and chemical composition of the worn surface and the wear mechanisms were also discussed. [ABSTRACT FROM AUTHOR]

In the present study, tribo-potential of a combination of two solid lubricants (SLs) viz. a special graphite i.e. thermographite (TG) and hexa boron nitride (hBN) in a series of composites with fixed amount of short glass fibers (GF 30 wt %) and Polyaryletherketone (PAEK- 50 wt%) was investigated under severe operating condition (Load 900 N (Pressure-28 MPa), speed >1.6 m/s) against mild steel disc till the composites failed. All the composites showed excellent performance under very high PV (pressure and velocity) values and the performance depended mainly on operating parameters and amount of two SLs in the composites. It was observed that 20% of a single SL (either TG or hBN) did not show very good results, although TG inclusion proved better than hBN. When these two SLs (20%) were used in combination, synergistic effect was observed and best performance was exhibited by a composite containing 5% hBN and 15% TG with the highest PV limits of 102.2 MPa m/s (900 N, 3.65 m/s) along with very low μ (0.04) and specific wear rate (5.68 × 10 −16 m 3 /Nm), followed by composite with 10% TG and 10% hBN. Combination of 15% hBN and 5% TG stood next in performance. Synergism in tribo-performance due to combination of two SLs was reported for oils and friction materials but not for high performance anti-friction materials. Such composites have excellent potential as materials for dry bearings, gears etc. The Scanning electron microscopy (SEM) and Energy Dispersive X-ray analysis (EDAX) studies on worn surfaces proved beneficial to understand how the fiber-matrix bonding was affected due to different combinations of SLs and how it affected wear performance. [ABSTRACT FROM AUTHOR]

Amorphous carbon films are widely used as solid lubricant coating. However, the mechanism response for its superlow friction has not been well explored. The previous results indicated that graphitic tribofilms are formed at rubbing interfaces, which leading to decreasing of friction coefficient. But in some cases, the friction coefficients of graphite (0.1–0.6) are much high than the amorphous carbon films (0.05–0.01), where the graphitic theory is quite limited and the interpretation is poor. Using high resolution transmission electron microscopy and Raman spectra, we monitor the structure evolution of tribofilms and friction coefficient drop during running-in. We demonstrate that a kind of graphene nano scroll particle was developed in the tribofilms consisting of outer graphene shell and inner amorphous core. And the relationship between friction drop and graphene nano scroll evolution suggests that, incommensurate contact of such nano scrolls, may be the dominant dissipation modes for amorphous carbon. [ABSTRACT FROM AUTHOR]

The incorporation of graphite as a solid lubricant in the formulation of brake friction material is well-recognized practice. However, achieving the desired level of performances using graphite is still a significant challenge, due to difficulty in dispersion and loading of graphite in composite materials. The present investigation was aimed at identifying the effect of graphite loading on the tribological and thermal properties of a composite made from phenolic resin modified with powdered acrylonitrile butadiene rubber (NBR). Five composites were prepared with different proportions of graphite (0–40 phr) to the phenolic resin. Thermogravimetric analysis (TGA) and thermal conductivity measurements were carried out to demonstrate the thermal stability and thermal conductivity behaviors. Both the thermal stability and thermal conductivity were found to increase with an increase in graphite content. On the other hand, the tribological properties were found to be optimum at a definite loading of graphite (30 phr). The change in surface morphology of these composites was studied before and after the friction test and correlated with the tribological properties. This investigation provides guidelines for achieving a high-performance composite using graphite for brake friction materials. [ABSTRACT FROM AUTHOR]

The production of self-lubricating composites containing second phase particles is one of the most promising choices for controlling friction and wear in energy efficient modern systems. To gain a better understanding of the wear behaviour of such materials, Fe-Si-C matrix composites containing solid lubricants added during the mixing step were studied in this work. The samples were produced using powder metallurgy route, with total contents of 5, 7.5 and 10% in terms of volume of hexagonal boron nitride (hBN) and graphite mixtures as the solid lubricants. The composite's tribological properties were evaluated under reciprocating sliding conditions and their mechanical properties were tested using tensile tests. Additionally, after interruptions at different stages of the reciprocating tests, the wear scars were characterised by Raman spectroscopy and scanning electronic microscopy, to evaluate the evolution of the wear with test time. Higher total solid lubricant contents greatly increased the scuffing resistance of the composites, but decreased the mechanical properties. Furthermore, increasing the hBN content reduced both properties. Among the composites studied, the samples containing 1% vol hBN and 9% vol graphite showed the best combination of mechanical and tribological properties. [ABSTRACT FROM AUTHOR]