Graphite Lubricant Research Articles

Enhanced wear resistance of in-situ nanoscale TiC reinforced Ti composites fabricated by additive manufacturing

The poor wear resistance of Ti alloys limits its application in the orthopedic and dental surgery field. TiC as an ideal reinforcement phase can improve wear resistance due to its high hardness, low coefficient of friction, and good bio-compatibility. However, the wettability of the interface between the TiC and Ti matrix is poor, which leads to low mechanical properties and wear resistance. In situ TiC formed through the addition of a C source can enhance interfacial bonding. In this work, the Ti-graphite composites are prepared by Laser powder bed fusion (LPBF). On the one hand, the LPBF can prepare various complex porous shapes according to the personalized customized demand. On the other hand, the LPBF can provide a high cooling rate, suppressing grain growth and refining grains, and also can obtain equally distributed nanoscale TiC particles. The results show that the composites are mainly composed of Ti, TiC, and residual graphite. With the increase of graphite content, the amount of TiC increases and the grain becomes smaller, and the microhardness increases from 317 HV0.2 to 408 HV0.2. Meanwhile, the Ti-1.5 wt%Gr composite has a low friction coefficient, volume of wear, and wear rate, which is attributed to the high hardness of TiC particles and lubrication of graphite. The oxide on the surface of the wear mark is mainly composed of TiO2 and TiO. The main wear mechanisms of the composites are oxidation wear and adhesive wear.

Multiscale study on the solid-liquid synergistic lubrication mechanism of graphite and liquid lubricant in polymer composites

Solid-liquid synergistic lubrication, in combination with the advantages of solid and liquid lubrication, has gained the great popularity in recent years. However, the mechanism of solid-liquid synergetic lubrication is still unclear. In this paper, graphite and poly α-olefin base oil (PAO) were used as self-lubricating additives to evaluate their synergistic effect. The results show that the composites possess good mechanical and excellent tribological properties with a nanoindentation modulus of 3.8 GPa, a coefficient of friction of 0.0998, as well as a wear rate of 1.3 × 10−14 m3/N·m. Both transfer film and lubricating oil film exist on the friction interface, and the lubricating oil film protects the counter ball from excessive oxidation. At the same time, with combination of molecular dynamics (MD) simulation and first-principles calculations, the synergistic lubrication mechanism of graphite and PAO was manifested. PAO destroyed the interlayer structure of graphite, making it easier to form a transfer film on the counter ball surface. The weak chemical bond between graphite and PAO facilitates more PAO molecules to gather at the interface while forming the transfer film, which benefits the formation of lubricating oil film. The synergistic effect of graphite and PAO molecules is critical in promoting the further reduction of COF.

Wear behaviour analysis of thermo-mechanically processed AA7075 and AA7075/SiC/Graphite composite

The current work focuses on investigating the tribological performance of AA7075 alloy and AA7075 hybrid composite with SiC and graphite reinforcements of 2 and 0.5 wt percentages, respectively. The alloy and hybrid composite are fabricated through stir casting and thermo-mechanically processed through hot rolling routes. Dry sliding wear characterization has been carried out using a pin-on-disc wear testing setup for alloy and composite under various processing conditions using experiments designed according to Taguchi's L9 orthogonal array. The technique for order preference by similarity to ideal solution (TOPSIS) method has been adopted to achieve a single multi-response index (MRI) considering the minimization of multiple objective functions for specific wear rate (SWR) and coefficient of friction (COF). The analysis of variance (ANOVA) results of the MRI indicated that sample processing condition and load were the most significant parameters. The wear mechanism at different experimental conditions was studied using Scanning electron microscope (SEM) micrographs, energy dispersive spectroscopy analysis and 3D surface profile of wear track. The AA7075 composites are found to be comparatively good in all experimental conditions compared to the base alloy due to load-bearing SiC particles and solid lubricant graphite as reinforcing elements. The mechanically mixed layer (MML) formation in hybrid composites helped achieve good tribological properties. The AA7075 alloy and hybrid composites cross rolled at 350 °C yielded better results than other samples. The wear mechanism was abrasive and adhesive at low temperature and low load conditions in both alloy and hybrid composites. Whereas, at higher temperatures and high loads oxidative wear mechanism with delamination was prevalent. The transition of SWR from mild to severe value occurs at 250 °C in all experimental cases. The specific wear rate was improved by 85.64 % between worst and best conditions, i.e., annealed alloy and cross rolled composite.

Enhanced tribological performance of MoS2 and hBN-based composite friction materials: Design of tribo-pair for automotive brake pad-disc systems

This research comprehensively analyzes the friction and wear behavior of composite friction materials when dry sliding against grey cast iron and laser-clad nickel-based (LC1) and iron-based (LC2) alloy discs. The composite friction materials (P1, P2, P3, P4, P5, and P6) under investigation contain graphite, MoS2, and hBN-based solid lubricant synthesized through the powder metallurgy technique. Tribological tests were conducted using a pin-on-disc configuration to simulate the dynamic interaction between the composite materials and the laser-clad grey cast iron discs. The tests were performed at a 60 N load, 6283.19 m sliding distance, and 2.094 m/s sliding velocity under dry sliding conditions. The results provide valuable insights into the effectiveness of MoS2 and hBN-based solid lubricant composites in reducing friction and wear when in contact with iron and nickel alloy-based laser-clad grey cast iron surfaces. The study elucidates the mechanisms governing tribological behavior, including the formation of friction plateaus and the role of laser-clad counter-discs in reducing wear. The specific wear rate of the nickel-based laser-clad counter disc (LC1) and iron-based laser-clad (LC2) system improved by 63.76 % and 48.32 %, respectively, compared to the conventional grey cast iron disc system when using the hBN-based pin (P6). Additionally, the specific wear rate of the hBN-based pin was 38.49 % lower than the conventional graphite-based pin when sliding against the grey cast iron counter-disc. Artificial Neural Network (ANN) was used to validate the wear rate of the best-performing tribological pair, namely the hBN-based pin (P6) and LC2 counter discs, through supervised learning.

Extremely enhanced friction and wear performance of hydrogen-free DLC film at elevated temperatures via Si doping

Hydrogen-free diamond-like carbon (DLC) films have garnered significant attention as a highly efficient solid lubrication material, but poor high-temperature lubrication and wear resistance limit their further application. Here, silicon-doped DLC (Si-DLC) films with different Si contents were deposited using a superimposed HiPIMS-DCMS deposition system to improve their high-temperature lubrication and wear resistance performance. The influence of Si content on the microstructure, mechanical and high-temperature friction and wear behavior of Si-DLC films was investigated. The results showed that Si-DLC films had a dense structure and nanoscale smooth surface. The Si doping enhanced the adhesion strength and relieved the residual stress of Si-DLC films, but decreased the hardness and Young's modulus. Meanwhile, Raman and XPS spectroscopy revealed significant local structural changes in Si-doped DLC films. Furthermore, the results showed that DLC films doped with low Si content displayed excellent tribological performance at elevated temperatures due to the graphite lubricating layer on the surface of wear marks. Specifically, Si-DLC film with 3.31 at% Si had an ultra-low average friction coefficient of 0.04 at 450 °C and still provided effective lubrication at temperatures up to 500 °C. In contrast, pure DLC film failed to lubricate at 450 °C due to the severe graphitization transition and Si-DLC film with 17.47 at% Si quickly failed to lubricate at 200 °C due to the SiC and SiO2. This work sheds light for the high-temperature application of DLC films doped with low Si content by superimposed HiPIMS-DCMS deposition system.

Paper-based disposable electrochemical sensor from readily available materials for cost-effective triclosan detection

This study introduces a disposable electrochemical sensor fabricated from readily available low-cost materials. The design features a three-electrode electrochemical cell made of a simple graphite dry lubricant and silicone sealant composite, screen-printed onto a sulphite paper substrate. The ideal composite mixture was stablished through factorial design. The sensors were applied to the electroanalytical detection of triclosan, an antimicrobial agent used in personal care products, with concerns about its impact on ecosystems and human health. A subsequent factorial design determined the optimal voltammetric conditions. This approach yielded a method with limits of detection and quantification of 0.05 μmol L–1 and 0.17 μmol L–1, respectively, with a linear range from 0.20 μmol L–1 to 10.30 μmol L–1 for triclosan. The method was successfully applied to analyze triclosan in tap water and personal care products, including toothpaste, mouthwash, and liquid soap, achieving recovery rates ranging from 96 % to 118 %.

Research on Friction and Wear Behaviors of Different Solid Lubricant Coatings on Aluminum-Based Piston Skirts

Abstract Stringent requirements in emissions drive the application of low-carbon fuel engines, which result in prominent friction and lubrication problems in the cylinder. Solid coating technology is an effective way to enhance the tribological performance of tribo-pairs and has great potential to solve friction and lubricant problems. In this work, graphite, molybdenum disulfide (MoS2), and tungsten disulfide (WS2) solid lubricant coatings were prepared on aluminum-based piston skirts, respectively. The friction and wear behaviors of three coatings were investigated using a self-designed piston skirt friction and wear apparatus. The chemical products generated on the worn surfaces were analyzed, and the combined effect of lubricating oil and solid lubricant coatings was confirmed. The results show that the solid coatings can effectively enhance the friction and wear characteristics of piston skirt-cylinder liner tribosystem, and WS2 coating has the best anti-friction and wear-resistant performance among the three coatings.

Effects of defect creation and passivation on graphite friction under ultra-high vacuum conditions

Graphite holds significant promise as a solid lubricating material for machine operation in ambient conditions. However, the intricacies of its mechanism remain a subject of debate at the nanoscale. In this study, atomic force microscopy (AFM) experiments conducted in ultrahigh vacuum (UHV) conditions provide direct evidence that the adsorption of water molecules significantly compromises friction performance, both on the basal plane and across step edges. This challenges the longstanding belief that the poor lubricating properties of graphite in a vacuum result from the desorption of water molecules. Moreover, the experimental findings put forth a compelling bond passivation hypothesis for graphite lubrication in ambient conditions. The process involves the introduction of defects with dangling bonds on graphite through annealing highly oriented pyrolytic graphite (HOPG) at elevated temperatures (≥773 K) in UHV conditions. Subsequently, these dangling bonds are gradually passivated by a small amount of residue atoms or molecules. Consequently, the continuously monitored friction force exhibits an exponential decrease over time following annealing. This study advances a molecular level understanding of low lubrication mechanism for graphite.

Tribological Properties of Al2O3/Graphite-Al2O3 Laminated Composites under Water Lubrication Conditions

High-performance Al2O3/graphite-Al2O3 laminated composites exhibit an excellent self-lubricating ability for moving components, such as sliding shaft sleeves and dynamic seals. The tribological behaviors of Al2O3/graphite-Al2O3 laminated composites should be studied extensively under water working conditions. Here, we attempted to explore the practicability of the Al2O3/graphite-Al2O3 laminated composite as a sealing material from a tribological point of view under water lubrication conditions. The tribological properties and mechanism of friction and wear of laminated composite ceramics were investigated under dry sliding friction, water environment, and suspended particle working conditions. It was found that the Al2O3/graphite-Al2O3 laminated composite has a better friction performance under water lubrication compared to dry sliding because of the separation effects formed by a water molecule film and a transfer film. Meanwhile, the wear rate under dry contact was found to be approximately six times that under water lubrication conditions. Under the water lubrication conditions, the formation of graphite films and water-adsorbed layers improved the anti-wear properties of the laminated materials, and the friction coefficient and the wear rate were as low as 0.16 and 1.76 × 10−6 mm3/Nm, respectively. Under the suspended particle working condition, the solid particles destroyed the graphite lubricating film and abrasive wear dominated the wear mode. The Al2O3/graphite-Al2O3 laminated composite demonstrates a potential for application in dynamic sealing and sliding components.

Microstructure and Properties of FeAlC-x(WC-Co) Composite Coating Prepared through Plasma Transfer Arc Cladding

Tungsten carbide (WC) is widely used in wear-resistant parts due to its excellent wear resistance. Iron-based alloys are used in the repair and remanufacturing of engine components due to their good compatibility with iron-based workpieces. In order to enhance the wear resistance of engine components in service under abrasive conditions, composite coatings have been prepared for cast iron engine components by adding WC-Co to iron-based powders. This study investigates the microstructure and wear properties of composite coatings of iron-based alloys reinforced with different contents of WC particles. The composite coatings mainly contained γ-Fe, α-Fe, WC and Fe3W3C. With the addition of the WC-Co strengthening phase, the average hardness of the FeAlC-x(WC-Co) composite coatings increases from 524 HV0.2 to 814 HV0.2. Wear test results showed that when the WC addition was 20%, it had the lowest frictional coefficient of 0.5 and the lowest wear mass loss of 1.3 mg. Compared to the original Fe-based alloy coatings, the WC particle-reinforced FeAlC composite coatings display improved wear resistance on a reduced friction basis, mainly benefiting from the high wear resistance of the graphite solid lubrication phase and carbides in the cladding.

The Effect of Varnishing and Soaking on Formability of the AW-5052-H28 Aluminium Alloy Sheets in Erichsen Cupping Test

This article presents the results of experimental tests on the stretch-forming ability of 0.21-mm-thick AW-5052-H28 aluminium alloy sheets used in the production of pull-off cups. Erichsen test under various tribological conditions (dry friction, lubrication with graphite lubricant) was used to assess the sheet formability. Punches with a various diameter of the spherical end (8 and 20 mm) were used in the tests. The effect of soaking conditions and varnishing variants on the value of Erichsen indices IE and IE11 was investigated. The sheets were soaked for 13 minutes at various temperatures: 185°C, 190°C and 200°C. In test conditions without lubrication, the lowest value of the IE index = 3.3 mm was observed for sheets in as-received state and for samples after soaking. However, the highest values of the Erichsen index in tests without lubrication were measured for varnished samples and repeatedly soaked. The tests conducted under lubrication conditions with graphite grease revealed usually higher values of the IE index compared to testing conditions without the use of grease. The values of the IE11 index were approximately twice lower than the IE indices. Observation of the bulge surface revealed a smooth surface, which means that the material is characterised by a fine-grained microstructure.

Enhancement of the mechanical and tribological properties of carboxylated acrylonitrile butadiene rubber filled with cryptocrystalline graphite by different preparation methods

AbstractAs a cost‐effective and environmentally friendly natural mineral, cryptocrystalline graphite (CG) is applied in rubber materials and its performance has been evaluated. In this work, the filler dispersion and mechanical and tribological properties of carboxylated acrylonitrile butadiene rubber (XNBR)/CG composites by different preparation methods were studied. XNBR/CG composites prepared by latex blending (XNBR/CG‐L) exhibited better mechanical and tribological performance, higher toughness, and lower heat build‐up than those prepared by mechanical blending (XNBR/CG‐M). These differences were ascribed to the filler dispersion degree, filler amount and dispersed size, and also filler–rubber interfacial interaction. Adding CG was conducive to improving the stability of the friction coefficient and reduced the wear rate via the formation of graphite lubricant and transfer films. The tribological performance of XNBR/CG‐L was superior to that of XNBR/CG‐M because of the improved tensile strength, tear resistance, and toughness as well as lower temperature rise. Scanning electron microscopy (SEM) and optical microscope observation showed a smoother worn surface, less and smaller wear debris of XNBR/CG‐L, and a more uniform transfer film on the steel counterpart surface. The relevant results provided new insight into the performance and structural design of CG/rubber composites.

Development and performance evaluation of self-lubricating cemented carbide

Nowadays, there is a trend in the industry to reduce or even eliminate the use of cutting fluid in machining operations. The high costs of purchasing, using, and disposing of fluids and problems related to environmental pollution and operator health favor the dry-cutting technique. However, in some machining processes, lubrication is required. In this cases, solid lubrication may be a solution. The present study investigated the development of self-lubricating cutting tool materials by adding graphite in WC – 10 wt% Co cemented carbide and how this graphite affects the sample's mechanical properties and wear behavior. The WC - 10 wt% Co cemented carbide was prepared by spark plasma sintering (SPS), and solid graphite lubricant was added at different concentrations. The samples were mixed in a high-energy ball mill and sintered at 1200 °C under 40 MPa. Microstructure, hardness, fracture toughness, and wear analyses were performed on the samples to understand the effect of graphite addition on sintered material properties. The chemical composition of the samples was analyzed by XRD and Raman spectroscopy. The wear measurement was performed by analyzing the volume of material lost by the samples during the pin-on-disk tests. Profilometry analyzes of the samples before and after the tests made it possible to measure the volume of lost material, allowing to verify the influence of the addition of solid lubricant on the wear rate of the samples. The results of the mechanical tests show that the highest hardness and the modulus of elasticity were 1578 HV and 870 GPa, respectively. The wear presented by the samples with 1% of graphite was up to 9 times less than the standard samples. The wear mechanisms are micro-cracking and fragmentation of WC grains; however, the presence of a solid lubricant avoids the steel counterpart material transfer for the pin surface. Also, it was observed the formation of a graphite and oxide tribolayer on the worn disc surface during the tests, thus avoiding excessive wear.

Improving the Antifriction Behaviors of Steel by Hybrid Treatments of MoS2 and Surface Texture

Abstract: In the present paper, the composite coatings with MoS2 and graphite in the epoxy resin were deposited on the textured surface of steel by laser and wire-electrode cutting technology to improve the anti-friction behaviors of the steel. The influences of the content of MoS2 and graphite and the types of surface texture on the anti-friction behavior were studied systematically. The experimental results show that the textured specimens with 1 mm space line and pentagon shape pore exhibit low friction behaviors under dry friction. CoF (coefficient of friction) of the pore and line textured with high content of MoS2 and graphite is reduced by 27.7% and 42.3% under dry friction and by 30.0% and 33.3% under starved lubrication, respectively. CoF of the texture and coating duplex-treated steel is much lower than that of the untreated steel due to the solid lubrication of MoS2 and graphite under dry friction. The possible antifriction and antiwear mechanism is discussed. It is concluded that the duplex-treated steel with the texture and coating exhibits good anti-friction behaviors and the composite coatings with solid lubricant are beneficial to improve the tribological properties of steel under starved and dry friction testing conditions. It is shown that hybrid surface treatment with the texture and solid lubricant coating is an effective way to improve the tribological properties of steel. Solid lubricant coatings deposited on the textured surface can be applied to improve the antifriction behaviors of steel under starved lubrication and dry friction.

Synthesis, characterization and tribological properties of solid lubricant graphite films produced by PECVD

Graphite, which is one of the mostly used solid lubricants, is commonly used in different industrial applications due to its low friction coefficient. However, the synthesis of graphite films can be a challenging process in some cases, where durable coatings are needed. Therefore, the aim of this study is to obtain graphite films with low friction coefficients and investigate their tribological properties. In order to achieve this, graphite films were synthesized on glass substrates by using Plasma Enhanced Chemical Vapor Deposition (PECVD) technique for different process times (30, 60 and 90 min). Reciprocating wear tests were performed to determine the tribological properties of the obtained graphite films. Afterwards, Raman, FT-IR, SEM and surface wettability analyzes were carried out to characterize the films. The results showed that the graphite film synthesized for 90 min exhibited higher wear resistance and lower friction coefficient than untreated and other treated samples because it had high film thickness and hydrophobicity. Also, it was seen that the thicknesses of the coatings increased depending on the treatment time and the contact angle measurements showed that all the graphite films exhibited hydrophobic behaviour.

On the tribological behaviors of Cu matrix composites with different Cu-coated graphite content

Graphite/Cu composite is widely used in pantograph slide plates. To further understand its lubrication behaviors, the tribological properties of graphite/Cu composites with different graphite content were studied using ball-on-disk wear tests. The results reveal that the composites contain only graphite and Cu phases. The tribological results show that the friction coefficient and wear rate of 7 wt.% graphite/Cu composite were decreased 7.7% and 12.7%, respectively, compared with 5 wt.% graphite/Cu. However, both friction coefficient and wear rate increased with the graphite content exceeding 7 wt.%. The excellent tribological properties of the composites were mainly attributed to the synergistic action of the oxidative trib o-layer and graphite lubricant film, which is composed of graphite, Cu, CuO, and Fe2O3. The wear mechanism of the graphite/Cu composites was mainly abrasive wear, accompanied by adhesion and oxidation wear.

Mechanical and Tribological Behavior of Austempered Ductile Iron (ADI) under Dry Sliding Conditions

In the current investigation, a vertically continuous casting technique was used to produce a ductile iron pipe. The ductile iron was austempered, and the tribological behavior of austempered ductile iron (ADI) was examined under various service conditions. The finding demonstrated that ADI’s tribological behaviors were significantly affected by normal loads and sliding speeds. Spheroidal graphite was preferential to be transferred from the matrix to the tribosurface in ADI under high normal loads, and high sliding speed accelerated the formation of the graphite lubricating layer on the tribosurface. Consequently, ADI’s friction coefficient dropped with the increase in normal load and sliding speed. When compared with the friction coefficient, the wear rate of ADI displayed a similar tendency in that it increased with an increase in normal load and reduced with an increase in sliding speed. The worn surface indicated that adhesive wear at low sliding speeds and abrasive wear at high sliding speeds were the primary wear mechanisms for ADI.

Influence of SiCp volume percentage on AA6063/SiCp MMC extrusion process: An experimental, theoretical and simulation analysis

Composites have been the most prominent incipient materials in a variety of industries over the past decades. The present work mainly investigates the influence of the SiC particulate (SiCp) weight percentage on AA6063/SiCp metal matrix composites extrusion and, it has been evaluated in extruded MMC billets for enhancing the billet quality. Graphite lubricants are used to decrease the friction between the die and the billet surface. Subsequently, the friction factor is theoretically determined and experimentally validated. It was concluded that SiCp concentration is the predominant factor influencing the extrusion load and friction factor. As a result, the extrusion load was increased with an increase in SiCp percentage. Furthermore, the experimental results were compared and validated by simulation analysis. The extruded billet surfaces were exhibited by a scanning electron microscope.

Influence of Materials on Dry Friction and Wear Performance of Harmonic Reducer Circular Spline

Ductile iron and alloy steel are mostly used as the circular spline materials of harmonic reducers. The study of the differences in wear resistance of different circular spline materials is a strong basis for the design of high-precision and long-life harmonic reducers. The dry friction behaviors under room temperature of two ductile iron (low-load SHF and high-load SHG) alloys and steel (40Cr) circular spline materials were studied with a quantitative analysis of the alloy composition, microstructure, hardness and wear resistance. The results showed that the microstructures of SHF, SHG and 40Cr were graphite nodules within a tempered sorbite matrix, graphite nodules within a pearlite matrix and tempered sorbite, respectively. The hardness was inversely proportional to the wear resistance. The wear resistance of ductile iron was better than that of 40Cr, with SHF having the best wear resistance. The microstructure of the SHF and SHG ductile iron had a length of 8.1 μm, 5.9 μm (Ti, V, Mo)/C and Cu/Mg second-phase particles. Compared with tempered sorbite, the self-lubricating layer formed by the graphite nodules can effectively reduce wear. The proportion and average diameter of the SHF graphite were 1.2% and 30.9% higher, respectively, than those of the SHG graphite, providing a higher graphite spalling probability and longer graphite lubrication distance.

INVESTIGATION OF THE SURFACE QUALITY OF AA6082-ZrO2-Gr MMCs USING ABRASIVE WATERJET MACHINING

Aluminium metal matrix composites have wide applications in the aerospace and automotive industries due to their excellent physical properties like hardness, tensile strength, etc. The reinforcement of ZrO2 hard ceramic particles and soft solid lubricant graphite on AA6082 produces a high-strength composite. This research aims to fabricate AA6082-ZrO2-Gr MMCs with different compositions and evaluate the abrasive-waterjet-machining (AWJM) parameters in the machining of the fabricated composites, which eliminates the thermal distortion and damage to the work material. The experiments were conducted by varying the dominant process parameters such as water pressure, traverse speed, abrasive flow rate and mesh size. The kerf taper angle was affected by the traverse speed and water pressure, while the surface roughness was affected by the abrasive flow rate, mesh size and water pressure. The abrasive mesh size of 120 provided the best surface finish.