Cu-coated Graphite Research Articles

Thermal Conductivity and Microstructure of Cu-Coated Graphite Flake/Ti Alloy Composites Fabricated by Spark Plasma Sintering

Thermal Conductivity and Microstructure of Cu-Coated Graphite Flake/Ti Alloy Composites Fabricated by Spark Plasma Sintering

Cr3C2 reinforced Cu-graphite composites fabricated by a novel in-situ decomposition using Cu-coated graphite and Cu-coated Cr2AlC

Cu-graphite composites are widely used as an important friction material in various fields. However, these composites suffer from weak interfacial bonding and low strength of the Cu matrix. This study focuses on enhancing the properties of these composites by plating Cu on the surfaces of graphite and Cr2AlC, followed by vacuum sintering. The microstructure and interface properties of the composites were investigated using SEM, EDS, and XRD techniques. It was observed that, under the peeling action of molten Cu, Cr2AlC decomposes in situ to synthesize Cr3C2 as reinforcement. Furthermore, a reaction between Cr atoms from Cr2AlC and carbon atoms on the graphite surface forms an interfacial transition layer, significantly improving the interfacial bonding between the Cu matrix and graphite. The resulting composites demonstrate favorable density, hardness, and lubrication properties, with a relative density of 96.2 %, hardness of 86.2 HV, and friction coefficient of approximately 0.15.

Study on the microstructure and properties of Cu-graphite-Cr3C2 composites prepared by in-situ reactive synthesis

Cu-graphite-Cr3C2 composites were synthesized via spark plasma sintering (SPS) using different gas environments, including argon and air, to blend the raw materials consisting of Cr2AlC, Cu-coated graphite, and pure Cu. The microstructure and physical properties of the composites were thoroughly investigated. The findings revealed that Cr3C2, synthesized in situ from Cr2AlC, was firmly embedded in the Cu matrix. Additionally, a layer of Cr3C2 was formed at the interface between the Cu matrix and graphite. The composites showed a high relative density, which above 96 %. The composites fabricated with the raw materials mixed in an argon gas environment had a hardness of 72.6 HSD and an electrical conductivity of 1.102 × 106 S·m−1. Whereas, the hardness and electrical conductivity of the composites fabricated with the raw materials mixed in an air gas environment increased to 75.6 HSD and 1.314 × 106 S·m−1, respectively. Furthermore, Cu-graphite-Cr3C2 composites fabricated with the raw materials mixed in air rather than argon exhibited better lubrication performance and wear resistance, the average friction coefficient and wear rate were measured to be 0.4644 and 2.682 × 10−7 mm3/N·m, respectively.

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.

Microstructure and frictional properties of copper-tin composites containing graphite and MoS2 by rapid hot-press sintering

Rapid hot-press sintering was employed to prepare the self-lubricating composites using Cu-Sn alloy, Cu-coated graphite, and Cu-coated MoS2 powder as raw materials. The effects of the sintering temperature on the microstructure, interfacial characteristics, and friction properties of the composites were primarily examined. The findings demonstrated that as the sintering temperature rose from 680 °C to 780 °C, the copper alloy matrix's grain size grew. The composites' density and hardness increased and subsequently declined as the sintering temperature rose. Moreover, the interfacial bonding between the copper-coating lubricant and the copper alloy matrix was improved by raising the sintering temperature. The average friction coefficient of the composite grew and then fell as the sintering temperature rose, and the wear initially increased, then decreased, and then increased again. The copper-tin composite had good frictional properties because a composite lubricating film made of graphite, MoS2, and metal oxides formed on the worn surface. Among them, the comprehensive friction performance was best at the sintering temperature of 760 °C, with an average friction coefficient of 0.11 and a wear rate of 2.332 × 10−6 mm3N−1·m−1. The wear mechanism was the combined coupling effect of abrasive wear, adhesive wear and oxidative wear.

Influence of sintering pressure on microstructure and tribological properties of Copper–Tin composites containing graphite and MoS2

Powder metallurgy was employed to facilitate self-lubricating composites using Cu-coated graphite powder, Cu-coated MoS2 powder and Cu-Sn alloy powder as raw materials. Investigations were conducted into how the sintering pressure affected the composites’ density, hardness, microstructure, and tribological properties. The results demonstrated that the porosity of the composites was reduced, the density increased from 6.46 g cm−3 to 7.32 g cm−3, the matrix grains were refined, and the hardness increased from 53.55 HV to 86.41 HV with an increase in sintering pressure from 30 MPa to 65 MPa. Additionally, raising the sintering pressure improved the interface bonding between the matrix and the solid lubricant graphite, MoS2. High sintering pressure was found to decrease the time needed for initial running-in and stabilize the volatility of friction coefficient. When the sintering pressure increased, the material’s friction coefficient first reduced and then increased while the wear rate first increased and then declined. Composites have good friction and wear qualities as a result of the production of a composite lubricating film containing graphite, MoS2, metal oxide, etc on the wear surface. Wear was brought on by the combined effects of abrasive wear, adhesive wear, material loss as a result of friction surfaces’ transverse crack expansion, and oxidation wear.

Low-Pressure Cold Spraying of Copper–Graphite Solid Lubricating Coatings on Aluminum Alloy 7075-T651

Although aluminum alloy 7075-T651 is widely used in the automobile and aircraft manufacturing industries, its durability must often be increased by improving the surface properties of components to better resist wear and oxidation. We propose herein the deposition of copper–graphite solid lubricating coating on aluminum alloy 7075-T651 by using the low-pressure cold-spraying technique. The microstructure, deposition efficiency, mechanical properties, and dry sliding wear behavior of the copper–graphite coatings were investigated. The results showed that addition of Cu-coated graphite particles could decrease the plastic deformation of adjacent copper particles in the coatings. The deposition efficiency, hardness, and bonding strength of the copper–graphite coatings decreased (by 49%, 21%, and 70%, respectively) with an increase in the Cu-coated graphite content in the feedstock from 0 to 20 wt.%. The copper–graphite coating with Cu-coated graphite content of 20 wt.% showed the lowest friction coefficient (about 0.15) and wear rate (6.00 × 10−5 mm3/N m). Compared with aluminum alloy 7075-T651, the friction coefficient and wear rate were decreased by 57% and 78%, respectively, which can mainly be ascribed to the formation of a low-shear-strength graphite-rich solid lubricating film on the worn surface. When the Cu-coated graphite content exceeded 10 wt.%, the dominant wear mechanism changed to mild abrasive wear, in contrast to the oxidative wear of the pure copper coating.

Effect of nanoboron carbide particles on properties of copper-matrix/graphite composite materials

In this study, a new type of copper (Cu)-matrix self-lubricating composite was successfully prepared, which was based on nanoboron carbide (n-B4C) particles, Cu-coated graphite, and Cu powders, combined by powder metallurgy. These composites contained 2 wt% graphite as the lubricating phase and 0.2, 0.3, 0.5, 0.8, and 1.2 wt% n-B4C as the reinforcing phase. The effects of different amounts of n-B4C particles on composite properties and the composite wear mechanism were examined. All composites were characterized in terms of microstructure, density, porosity, hardness, compressive yield strength, and friction wear. The results showed that, with n-B4C particle addition, the hardness, compressive strength, friction, and wear properties were improved. With >0.2 wt% n-B4C, composite porosity gradually increased, and hardness, compressive strength, and friction and wear properties sharply decreased. With n-B4C addition, the main wear mode of the composites changed from adhesive to abrasive wear, then to adhesion and peeling wear with increased n-B4C particle content.

The study of microstructure characterization: Cu modified Cu-Ni-graphite composite

ABSTRACTCu-coated graphite was applied to modify the interface of Cu-Ni-graphite composite used as switch slide baseplate. Up to now, interfacial characterization and modification mechanisms of Cu modified Cu-Ni-graphite composite are seldom researched. In this study, Cu-coated graphite was deposited by chemical plating, and Cu modified Cu-Ni-graphite composite was prepared by powder metallurgy. Both the microstructure characterizations of Cu-coated graphite and interfacial morphologies of the composite were investigated. Then, the comparison of mechanical properties of unmodified and Cu modified Cu-Ni-graphite composite was discussed. The results showed that the Cu coating was made of fine particles with uniform distribution and with the average thickness of 1.05 μm. The mutual diffusion was about 2.54 μm width at the interface. The interfacial modification mechanism of Cu coating in the composite was that the decreasing of diffusion activity both in the graphite and matrix; and the increase of diffusion driving force at the interface. The interfacial bonding method in the transition from mechanical bonding to the combination of mechanical bonding and diffusion bonding. Compared with the unmodified composite, the flexural strength raised 24.4%, and hardness increased by 9%.

Microstructure, Mechanical Properties and Dry Sliding Wear Behavior of Cu-Al2O3-Graphite Solid-Lubricating Coatings Deposited by Low-Pressure Cold Spraying

In this study, Cu-Al2O3-graphite solid-lubricating coatings were deposited on the 304 stainless steel substrate by low-pressure cold spray technique. The influences of Cu-coated graphite content on the microstructure, mechanical properties and dry sliding wear behavior of the Cu-based solid-lubricating coatings were investigated. The results showed that the mixture addition of Al2O3 and Cu-coated graphite is an effective strategy to improve the solid lubricity of Cu-based coatings while simultaneously retaining favorable mechanical properties and bonding strength. When the Cu-coated graphite content increased from 0 to 20 wt.% in the spray powder, the Brinell hardness and the interface bonding strength of the Cu-based coatings declined, but the solid-lubricating property improved obviously. The Cu-based solid-lubricating coating with 10 wt.% Al2O3 and 10 wt.% Cu-coated graphite exhibited the lowest friction coefficient of 0.29, which was attributed to the formation of a lubricating tribo-layer and the reduction in cracks on the worn subsurface. Additionally, the wear mechanism changed from adhesive wear to abrasive wear and delamination with the increase in graphite content.

Study on the Tribological Performance of Copper-Based Powder Metallurgical Friction Materials with Cu-Coated or Uncoated Graphite Particles as Lubricants.

The tribological performance of copper-based powder metallurgical material is much influenced by the interfacial bonding between the components and matrix. By adding Cu-coated or uncoated graphite particles as a lubricant, two types of copper-based powder metallurgical materials were prepared via spark plasma sintering (SPS). The hardness, relative density, and thermal conductivity of the two specimens were firstly measured. Using an inertial braking test bench and temperature measuring instrument, the average friction coefficients, instantaneous friction coefficients, and friction temperatures of the two specimens were tested under different test conditions, and the wear rates were calculated accordingly. Based on the analysis of surface morphologies and elements distribution after the tests, the mechanisms of wear and formation of friction films were discussed. The results show that with the lubricant of Cu-coated graphite, the hardness, relative density, thermal conductivity, and interfacial bonding between the graphite and matrix can be greatly improved. Under the same test condition, the average friction coefficient, wear rate, and friction temperature of the specimen with added Cu-coated graphite are both lower than those of the specimen with added uncoated graphite. The two specimens show different variation trends in the instantaneous friction coefficient during the tests, and the variation of the instantaneous friction coefficient at a high initial test speed is also different from that at a low initial test speed for each specimen. The two specimens also show differences in the continuity of friction film and the content of graphite and oxide in the friction film.

Tribological properties of Al-20Si-5Fe-2Ni-Graphite solid-lubricating composites

Abstract Solid-lubricating composites show great potential for tribological applications. In this study, the Al-20Si-5Fe-2Ni-Graphite composites with 0–30 wt. % copper-coated graphite were fabricated by spark plasma sintering. Effect of Cu-coated graphite on the phase, microstructure, hardness, strength and dry sliding wear behavior of the composites was investigated. The results indicated that the formation of Al2Cu interface can enhance the mechanical properties of the composites. The friction coefficient and wear rate of the composites were dependent on the amount of copper-coated graphite and applied load. The composite containing 30 wt. % Cu-coated graphite exhibited the lowest friction coefficient and wear rate. The related mechanism was discussed.

Sliding Tribological Behavior of Al–Fe–V–Si–Graphite Solid-Lubricating Composites at Elevated Temperatures

Aluminum alloy metal matrix composites (Al-MMCs) have been considered as promising materials for aerospace and automotive industries due to their excellent balance of physical, mechanical, and tribological properties. In the present work, the Al–Fe–V–Si alloy matrix composites with 0–20 wt. % copper-coated graphite were fabricated by hot-pressed sintering. The dry sliding tests were carried out at various temperatures ranging from room temperature (RT) to 350 °C. The microstructure, phase, hardness, and worn surface of the sintered composites were examined in detail. The effect of copper-coated graphite amount on the properties of the composite was also investigated. The results show that the Al–Fe–V–Si–graphite composites mainly consist of α-Al, Al8Fe2Si intermetallic, and graphite phases. The addition of Cu-coated graphite can decrease the friction coefficient and wear rate from RT to 350 °C. The Al–Fe–V–Si–graphite composite containing 10 wt. % copper-coated graphite exhibits better wear properties than other composites. The favorable lubricating properties were attributed to the tribolayer with graphite lubricating film formed on the worn surface.

Synthesis of Cu-coated Graphite Powders Using a Chemical Reaction Process

Synthesis of Cu-coated Graphite Powders Using a Chemical Reaction Process

Influence of Metal-Coated Graphite Powders on Microstructure and Properties of the Bronze-Matrix/Graphite Composites

In this study, the bronze-matrix/x-graphite (x = 0, 1, 3 and 5%) composites were fabricated by powder metallurgy route by using Cu-coated graphite, Ni-coated graphite and pure graphite, respectively. The microstructure, mechanical properties and corrosive behaviors of bronze/Cu-coated-graphite (BCG), bronze/Ni-coated-graphite (BNG) and bronze/pure-graphite (BPG) were characterized and investigated. Results show that the Cu-coated and Ni-coated graphite could definitely increase the bonding quality between the bronze matrix and graphite. In general, with the increase in graphite content in bronze-matrix/graphite composites, the friction coefficients, ultimate density and wear rates of BPG, BCG and BNG composites all went down. However, the Vickers microhardness of the BNG composite would increase as the graphite content increased, which was contrary to the BPG and BCG composites. When the graphite content was 3%, the friction coefficient of BNG composite was more stable than that of BCG and BPG composites, indicating that BNG composite had a better tribological performance than the others. Under all the values of applied loads (10, 20, 40 and 60N), the BCG and BNG composites exhibited a lower wear rate than BPG composite. What is more, the existence of nickel in graphite powders could effectively improve the corrosion resistance of the BNG composite.

Preparation of graphite@Cu powders from ultrasonic powdering technique

Cu-coated graphite (graphite@Cu) powders were fabricated using our invented device through ultrasonic flow electrodeposition. The effects of NaH 2PO 2, ultrasonic, current density, load of graphite powders, flow velocity, and deposition time on copper were investigated. The results showed that graphite@Cu composite powders with copper content of 50–75 wt.% were electrodeposited in the proper electrolyte. NaH 2PO 2 could decrease polarization resistance of electrodeposition and improve the Cu coverage of graphite particles. The composite powders could be effectively dispersed in the electrolyte by ultrasonic.

Wear and mechanical properties of sintered copper–tin composites containing graphite or molybdenum disulfide

Copper-based sintered composites produced by powder metallurgy processes are now widely used in tribological engineering parts, e.g. bearings and bushes. Also composites based on copper–tin alloys containing a solid lubricant have been developed as self-lubricating materials under extreme conditions of load, atmosphere and temperature. It is well known that the addition of graphite serves to reduce friction and wear in copper–tin alloys. However it should be noted that the addition of graphite or molybdenum disulfide (MoS 2) has an adverse effect on the composites’ mechanical properties. In this paper, the lubricant graphite and MoS 2 powders were coated with Cu to reinforce their bonding to the Cu particles in the composites during sintering. The hardness, microstructure and bending strength of the sintered specimens were examined. The friction and wear properties of the materials were estimated by a cylinder-on-plate wear machine under dry conditions at room temperature in air. Although mechanical properties of the composites decreased with increasing amount of added graphite or MoS 2, the use of Cu-coated lubricant powders improved the bending strength. Graphite was very effective in reducing the wear and friction of the composites. Particularly, the 40 vol.% graphite composites showed a very low coefficient of friction of 0.15. Furthermore, the wear rate of the Cu-coated graphite specimens was much lower than that of the uncoated graphite specimens. By contrast, the wear rates of the MoS 2 composites increased considerably with the amount of MoS 2 addition. This behavior is thought to be due to the absence of MoS 2 and the presence of brittle CuMo 2S 3 compounds in the sintered composites.

Friction and wear of copper–graphite composites made with Cu-coated and uncoated graphite powders

Copper–graphite composites of graphite contents of 8, 15, and 20 wt.% made by powder metallurgy route using either Cu-coated graphite powders or mixture of copper and graphite powders. The Cu-coating process of graphite powders was carried out using electroless coating technique. For comparison, parallel compacts of pure copper were made under the same consolidation processing applied for copper–graphite composites. The wear testing was carried out using a pin-on-ring tribometer. Cylindrical pins of 7.9 mm in diameter, and 12±1 mm in length made from the investigated materials were rubbed against a rotating steel ring (SAE 1045) of surface hardness of 62 HRc, at a constant sliding velocity of 0.2 m s −1 The applied normal load varied from 50 to 500 N. Continuous wear data were obtained during each test; the decrease in length of the tested pin, and the friction force with reference to the sliding distance. Extensive metallographic investigation was carried out using both optical and scanning electron microscopy, to study the structural changes at the surface and sub-surface of each tested pin. The removed particles from each tested sample (debris) were collected and examined with scanning electron microscopy, and X-ray diffractometer. It was found that the investigated materials showed three distinct wear rate regimes: low, mild, and severe. Moreover, composites made by Cu-coated and uncoated graphite have lower wear rates and friction coefficients than those made from pure copper. In addition, the Cu-coated graphite composites showed the lowest wear rates and could withstand higher loads upto 450 N for 8 and 15 wt.% coated graphite, and 500 N in case of Cu-20% coated graphite, while the uncoated graphite composites could withstand loads up to 300 N for 8 wt.% containing graphite and 250 N for 15 and 20 wt.% graphite. The wear mechanisms of pure copper compacts at each wear rate regime were believed to be oxidation–delamination, delamination, and seizure wear mechanisms, whereas the involved wear mechanisms of either of composites were the same, and they were: oxidative-dominant, strain-induced delamination, and sub-surface delamination.