铜包石墨含量对铜锰铝复合材料摩擦磨损性能的影响

为改善铜锰铝合金的烧结性能,并提高其在干摩擦下的摩擦磨损性能,以铜包石墨作为自润滑相加入到铜锰铝合金中,采用等离子真空压力烧结方法制备铜锰铝/石墨复合材料,分析铜包石墨含量对复合材料的密度、硬度的影响,探讨不同复合材料在干摩擦和油润滑条件下的摩擦磨损性能.结果表明:相比真空和氢气还原气氛下的烧结方式,等离子体烧结铜锰铝...     

Dry sliding wear of fly ash particle reinforced A356 Al composites

In the present study aluminium alloy (A356) composites containing 6 and 12 vol. % of fly ash particles have been fabricated. The dry sliding wear behaviour of unreinforced alloy and composites are studied using Pin-On-Disc machine at a load of 10, 20, 50, 65 and 80 N at a constant sliding velocity of 1 m/s. Results show that the dry sliding wear resistance of Al-fly ash composite is almost similar to that of Al₂O₃ and SiC reinforced Al-alloy. Composites exhibit better wear resistance compared to unreinforced alloy up to a load of 80 N. Fly ash particle size and its volume fraction significantly affect the wear and friction properties of composites. Microscopic examination of the worn surfaces, subsurfaces and debris has been done. At high loads (>50 N), where fly ash particles act as load bearing constituents, the wear resistance of A356 Al alloy reinforced with narrow size range (53–106 μm) fly ash particles were superior to that of the composite having the same volume fraction of particles in the wide size range (0.5–400 μm).     

Tribological behaviour of polymeric coatings. Part I. Aramid particle‐reinforced epoxy nanocomposite systems

An epoxy‐based nanocomposite containing a low concentration of nanometric TiO₂ (4 vol. %), graphite powder (7.21 vol. %), and 2–14 vol. % aramid particles was developed as a coating material. The mechanical and tribological performance of the composites was investigated. The epoxy filled only with TiO₂ possessed significantly improved impact strength and flexural properties, whereas the further incorporation of graphite and aramid particles had a deleterious effect on most of the mechanical properties, except the modulus. The tribological behaviour of the composites was tested in sliding and fretting modes. Under sliding conditions, the addition of nanometric TiO₂ alone significantly improved the wear resistance and decreased the coefficient of friction compared to the neat epoxy. The sliding wear and friction behaviour was further enhanced with the incorporation of graphite and aramid particles. Contrary to the sliding wear behaviour, the fretting wear and friction behaviour was worse for the epoxy filled only with TiO₂, but was significantly enhanced by the incorporation of graphite and aramid particles. The optimum aramid particle content for sliding and fretting wear of the epoxy‐based nanocomposite was determined as 10 vol. %.     

Effect of the Graphite Content on the Tribological Behavior of Al/Gr and Al/30SiC/Gr Composites Processed by In Situ Powder Metallurgy (IPM) Method

The influence of graphite content on the dry sliding wear characteristics of Al6061/Gr composites along with Al6061/30SiC/Gr hybrid composites has been assessed using a pin-on-disc wear test. The composites with different volume fraction of graphite particles up to 13% were processed by in situ powder metallurgy (IPM) technique. The porosity and hardness of the resultant composites were also examined. It was found that an increase in the graphite content reduced the porosity, hardness, and friction coefficient of both types of composites. The hybrid composites were more porous and exhibited higher hardness and lower coefficient of friction at identical graphite contents. The increased graphite content in the range of 0–13 vol.% resulted in increased wear rate of Al/Gr composites. The Al/30SiC composite exhibited a lower wear rate as compared with the base alloy and graphite addition up to 9 vol.% improved the wear resistance of these hybrid composites. However, more graphite particles addition resulted in increased wear rate. SEM micrographs revealed that the wear mechanism was changed from mostly adhesive in the base alloy sample (Al/0Gr) to the prominently abrasive and delamination wear for Al/Gr and Al/SiC/Gr/composites.     

Tribological properties of nickel-based self-lubricating composite at elevated temperature and counterface material selection

Solid lubricating materials are necessary for development of new generation gas turbine engines. Nickel-based self-lubricating composites with graphite and molybdenum disulfide as lubricant were prepared by powder metallurgy (P/M) method. Their tribological properties were tested by a MG-2000 high-temperature tribometer from room temperature to 600 °C. The structure of the composite was analyzed by XRD and worn surface morphologies were observed by optical microscope. The effects of counterface materials on tribological behavior of composites were investigated. It was found that chromium sulfide and tungsten carbide were formed in the composite by adding molybdenum disulfide and graphite, which were responsible for low-friction and high wear-resistance at elevated temperatures, respectively. The average friction coefficients (0.14–0.27) and wear rates (1.0–3.5 × 10⁻⁶ mm³/(N m)) were obtained for Ni–Cr–W–Fe–C–MoS₂ composite when rubbed against silicon nitride from room temperature to 600 °C due to a synergetic lubricating action of graphite and molybdenum disulfide. The optimum combination of Ni–Cr–W–Fe–C–MoS₂/Ni–Cr–W–Al–Ti–C showed lower friction than other counter pairs. The graphite played the main role of lubrication at room temperature, while sulfides were responsible for low friction at high temperature.     

Dry-Sliding Tribological Properties of Bronze–Graphite Composites

Bronze-uncoated and nickel-coated graphite composites were fabricated by powder metallurgy route. The tribological behaviors of composites sliding against AISI52100 steel ball under dry sliding condition were studied using a ball-on-disk tribometer. The nickel-coated graphite composites showed much better tribological properties in comparison with bronze and uncoated graphite composite. The friction coefficient of nickel-coated graphite composites decreased with increasing nickel-coated graphite content. However, the specific wear rate increased with the increase in nickel-coated graphite. The composite containing 15?wt% nickel-coated graphite showed the best self-lubricating properties because the compacted and stable mechanical mixed layer was formed on the worn surfaces. The wear mechanism of bronze 663 is adhesive wear and abrasive wear. The uncoated nickel-coated graphite composite shows the adhesive wear and delamination characteristics. However, the wear mechanism of nickel-coated composites is mildly abrasive wear.     

Tribological Performance of Microwave-Heat-Treated Copper–Graphite Composites

Copper–graphite composite is a tribological composite that can be used in sliding electrical contact applications requiring low friction and wear in addition to high electrical conductivity. The graphite powder (5 wt%) was mixed with the copper powder, and then composite was fabricated through powder metallurgy (P/M) route. P/M product generally requires secondary operations such as rolling, extrusion, etc. to improve their mechanical properties. Post-heat-treatment technique is also applicable to improve the properties of P/M components. Microwave-post-heat-treatment research studies are gaining momentum nowadays due to the improved quality of products with reduced time, energy, and associated cost. Microwave post-heat treatment of copper–graphite composites for different heat treating duration was carried out in a hybrid microwave heating setup. Microstructural studies were carried out using SEM with EDAX. Microwave-heat-treated samples exhibited reduced porosity, improved density, and hardness. In order to understand the friction and wear properties of microwave-heat-treated copper–graphite composites, pin-on-disk wear experiments were conducted. For comparison, untreated copper–graphite composites were also subjected to similar studies. Microwave-heat-treated samples exhibited reduced coefficient of friction and specific wear rate when compared to the untreated ones. The wear mechanism of untreated composites was observed to be plastic deformation characterized by large wear fragments, whereas the mechanism of heat-treated composite was delamination observed through peel off tribolayer.     

石墨含量对铜基石墨自润滑复合材料摩擦过程中石墨润滑膜的影响

为研究石墨含量对铜基石墨自润滑复合材料摩擦过程中形成石墨润滑膜的影响,采用粉末冶金法制备了不同石墨含量的铜基石墨自润滑复合材料,测试了复合材料的力学性能,用自制环-块摩擦试验机测试评估了材料的耐磨性能,用光学显微镜实时原位观察了摩擦表面组织形貌的变化,用扫描电镜对磨痕进行观察和分析,通过能谱仪成分扫描分析接触面石墨润滑膜的覆盖率。结果表明:随着复合材料中石墨含量的增加,材料的力学性能逐渐降低,石墨润滑膜的覆盖率先升高后降低,磨损量先减小后增大;当石墨体积分数为14%时,石墨润滑膜的覆盖率最高,磨损量最小,耐磨性能最好。     

Tribological behaviour of sintered 316L stainless steel impregnated with MoS2 plain bearing

The mechanical and tribological properties of sintered 316L stainless steel impregnated with molybdenum disulfide (MoS₂) were investigated. Tests were carried out at room temperature for two specific ranges of PV value (1.1 and 1.8 MPa m/s). The results prove that the friction coefficient and the wear are strongly influenced by the addition level of MoS₂.

In this paper, MoS₂ powder was mixed with 316L powder before being processed via compacting and sintering steps. The microstructure, hardness, tensile strength and elongation at breaking point of the sintered specimens were evaluated. The friction and wear properties of the materials were examined by a partial plain bearing wear test rig under dry conditions at room temperature and in air. Although some of mechanical properties of the composite decreased with increasing MoS₂ amount, the MoS₂ was very effective in reducing the friction and wear of the composites. Particularly, the sintered 316L–15% MoS₂ materials at 1.1 PV value showed a reduction of friction coefficient by approximately 20–25% when compared to the sintered 316L specimen without addition of MoS₂. In addition, wear of specimen with addition of MoS₂ was also reduced to some extent (5–10% weight loss reduction) at this specific PV value.     

Friction and wear properties of Ni–Cr–W–Al–Ti–MoS2 at elevated temperatures and self-consumption phenomena

The composites of Ni–Cr–W–Al–Ti–MoS₂ with different adding amount of molybdenum disulfide (6–20 wt.%) were prepared by powder metallurgy (P/M) method. Their mechanical properties and tribological properties from room temperature to 600 °C were tested by a pin-on-disk tribometer. The effects of amounts of molybdenum disulfide, temperature, load, and speed on the friction and wear properties of composite were discussed. Besides, the tribological properties against different counterface materials, such as alumina, silicon nitride and nickel-iron-sulfide alloys were also investigated. Results indicated that the molybdenum disulfide was decomposed during the hot-press process and the eutectic sulfides of chromium were formed. The hardness and anti-bending strength can be improved by adding 6 wt.% molybdenum disulfide due to reinforcement of molybdenum. The friction coefficients and wear rates of composites decrease with the increase of adding amount of molybdenum disulfide until a critical value of 12 wt.%. The composite with 12% MoS₂ shows the optimum friction and wear properties over the temperature range of RT 600 °C. The friction coefficients of composite with 12% MoS₂ decrease with the increase of temperature, load, and sliding speed, while the wear rates increase with the increasing temperature and are insensitive to the sliding speed and load. The friction coefficients of less than 0.20 at 600 °C and mean wear rates of 10⁻⁵ mm³/N m are obtained when rubbing against alumina due to the lubrication of sulfide films and glaze layer formed on the friction surface at high temperature, while a relatively low wear rate of around 10⁻⁶ mm³/N m presents when rubbing against nickel-iron-sulfide alloys. At high temperature, wear rates of composite containing sulfide are inversely proportional to friction coefficients approximately.     

The tribological properties of bronze–SiC–graphite composites under sea water condition

Bronze–SiC–nickel coated graphite composites were fabricated by powder metallurgy technique (P/M). The tribological properties of composites sliding against AISI321 stainless steel pin were studied under sea water condition. The graphite is an effective solid lubricant in sea water environment. The SiC improved the hardness and tribological properties of composites. The friction coefficient of bronze–SiC–graphite composites increased with the increase of SiC. However, the specific wear rate of bronze–SiC–graphite composites decreased with increasing SiC. Bronze-2 wt% SiC-11.7 wt% nickel coated graphite composite showed the best tribological properties due to the synergistic effects of reinforcements.     

Sliding wear of graphite crystallized chromium white cast iron

The effects of sliding velocity, heat-treatment and graphite shape on sliding wear of graphite crystallized chromium white cast iron were studied. Two types of graphite crystallized chromium white cast irons having flaky or spheroidal and another type of 2.6C–15Cr white cast iron were prepared for this study. The effect of sliding velocity on wear resistance was studied by the Okoshi type and pin-on-disk type wear tests on materials which have experienced “as cast” and “heat-treated” conditions. The Okoshi type wear test results are divided into two relationships depending on sliding velocity or distance. Two regimes, initial wear and steady-state wear, existed for wear loss and sliding distance. A characteristic form of wear curve with a peak and a minimum was obtained when correlating wear loss and sliding velocity. The wear resistance of graphite crystallized chromium white cast irons were superior to that of 2.6C–15Cr white cast iron. In the results of pin-on-disk tests, there was no clear difference in the reported wear loss and friction coefficient among the alloys. However, an opposite tendency has appeared in the wear loss and friction coefficient: the wear loss value reached a peak in the wear curve at 0.52 m/s, while the friction coefficient reached a minimum at 0.52 m/s.     

Friction and wear of diamond-containing polyimide composites in water and air

Polyimide-based composites containing fine diamond powder were fabricated using spark plasma sintering. The based material was polyimide (PI) containing a small amount of polytetrafluoroethylene (PTFE). Two types of diamond powder were used: one synthesized by statically high pressure, i.e., high-pressure diamond (HD), and the other synthesized by shock compression, i.e., shock-compression diamond (SD). We evaluated their tribological properties using a reciprocating friction tester in water and air using an Al₂O₃ mating ball. Adding HD to the polyimide-PTFE-based material decreased the composite's friction in water, but the effect of this addition in air was negligible. The specific wear rate of composites with different HD content was similar to that of the based material alone in water, while the wear of composites decreased with the addition of diamond in air. The effect of diamond powder size on friction and wear of composites was generally low in both water and air. The addition of SD decreased the friction coefficient of composites, but SD content only negligibly affected the friction in water and air. The specific wear rate was minimal at SD content of 5 vol.%, when diamond content was varied. Wear was almost independent of diamond powder size. SD reduced composite friction and wear better than HD; regardless of environment, its friction coefficient was less than 0.1 and the specific wear rate was in the level of 10⁻⁷ mm³/N m in both water and air.     

Experimental Study on the Tribological Properties of Powder Lubrication under Plane Contact

Powder lubrication has been studied using a plane contact tribometer. Four kinds of powders—polytetrafluoroethylene (PTFE), graphite, MoS₂, and ball-like copper—were used during the experiments. The results show that powder can be introduced into frictional clearance without any special treatment. The powder's physical properties significantly influence the tribological characteristics in the powder lubrication. The friction coefficient and wear are obviously decreased when the powders are PTFE, graphite, and MoS₂, which are excellent solid lubricants. At lower load capacity, powder lubrication using ball-like copper had certain antifriction effects, but it rapidly became worse with increasing load capacity. Observation with optical microscopy showed that the lubricant film is dynamically formed on the rubbing surfaces in most experiments.     

Tribological behavior of microwave processed copper–nanographite composites

Excellent properties offered by nanographite particles are exploited as a reinforcement to the copper matrix. The effects of graphite particle size, spatial distribution, normal load and sliding speed on the friction and wear performance of microwave sintered copper metal matrix composites were studied using a pin-on-disc tribometer. Copper–nanographite composites show higher wear resistance and low coefficient of friction compared to copper–graphite composites. High surface area of nanographite particles embedded in copper matrix exhibited high adherent graphite tribo-layer at the contact surface. Formed graphite layer reduces the sub-surface deformation of the composite by way of reduced frictional force.     

Run-in behavior of nanocrystalline diamond coatings studied by in situ tribometry

The friction performance of nanocrystalline diamond coatings was evaluated using in situ tribometry with sapphire counterfaces. Coatings were grown by microwave plasma assisted chemical vapor deposition in an Ar–H–CH₄ plasma, with H ranging from 0 to 36%. In situ examination of the sliding contact, combined with ex situ analysis of the sapphire counterface revealed that the velocity accommodation mode was interfacial sliding of a carbonaceous transfer film versus the coating wear track. For most tests, the contact diameter increased during the first 50 sliding cycles and then remained constant. The in situ measure of the contact diameter was found to correlate confidently to ex situ measurements of counterface wear. The performance of the diamond coatings, characterized by quick run-in to low friction was best when a small but detectable graphite peak was present in the X-ray diffraction (XRD) profile. The relative intensity of the XRD graphite peak was also found to directly correlate with the peak position of the C1s → π* transition as measured by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Increasing the relative amount of graphite-bonded sp² carbon in the NCD films decreased run-in cycles to low friction.     

Development of fly ash-based automotive brake lining

Coal-fired power plants all over the world generate huge amounts of fly ash each year, 70 million tons of which are produced in the United States alone. Only 40% of all fly ashes generated in the USA find beneficial applications and rest have to be disposed off, which is burden for the generation industry. Fly ash particles possess certain characteristics that make them suitable for use in friction composites as a filler material. An attempt has been made through this research to incorporate more than 50 wt% of fly ash particles in automotive brake lining friction composites. This paper presents the research carried out on development of friction composites, using fly ash obtained from a specific power plant in Illinois. Ingredients such as phenolic resin, aramid pulp, glass fiber, potassium titanate, graphite, aluminum fiber and copper powder were used in the composite development phase, in addition to the fly ash. The developed brake lining composites have exhibited consistent coefficients of friction in the range of 0.35–0.4, and wear rates lower than 12 wt%.     

Fabrication of copper–TiC–graphite hybrid metal matrix composites through microwave processing

The significant requirements such as wear resistance and better tribological properties in addition to good electrical conductivity necessitate the development of copper-based advanced metal matrix composites for electrical sliding contact applications. Though the addition of graphite to copper matrix induces self-lubricating property, the strength of the composite reduces. The improvement in the strength of the composite can be achieved by reinforcing harder ceramic particles such as SiC, TiC, and Al₂O₃. In this paper, the development of hybrid composite of copper metal matrix reinforced with TiC and graphite particles through microwave processing was investigated. The effects of TiC (5, 10, and 15 vol.%) and graphite (5 and 10 vol.%) reinforcements on physical and mechanical properties of microwave-sintered copper–TiC–graphite hybrid composites are discussed in detail. Micrographs show the uniform distribution of reinforcements in copper matrix. Microwave-sintered composites exhibited higher relative density, sintered density, and hardness compared with conventionally sintered ones.     

无铅铜基石墨复合材料性能研究

以化学镀方法制备的镀镍石墨粉取代铜基轴承材料中的铅,采用粉末冶金方法制备无铅铜基石墨复合材料,考察铜基石墨复合材料的界面结合、力学性能及其摩擦磨损特性。结果表明:化学镀方法在石墨表面形成的镀镍层能改善铜与石墨之间的界面结合,提高铜基石墨复合材料的力学性能;2%镀镍石墨无铅铜基复合材料的减摩、抗黏着性能及承载能力都优于典型铜铅材料。     

Analysis of Tribological Performance of Cu Hybrid Composites Reinforced with Graphite and TiC Using Factorial Techniques

In this study, a copper hybrid metal matrix composite reinforced with graphite (5, 10, and 15 vol%) and TiC (5, 10, and 15 vol%) was processed by a powder metallurgy route. Optical micrographs confirm the uniform distribution of reinforcements in the copper matrix. The hardness of the composites decreased with the addition of graphite. However, the addition of TiC into the copper matrix increased the hardness of the composites due to its high hardness. The influence of graphite percentages, load, sliding speed, and sliding distance on the wear of the as-sintered hybrid composites was studied based on the design of experiments. Analysis of variance (ANOVA) was used to study the effect of the parameters on the wear weight loss of the hybrid composites. The weight loss due to wear of the hybrid composites decreases from 0.1345 to 0.0830 g as the volume percentage of graphite increases from 5 to 15%. Results indicated that the normal load has greater static influence of 43.85%, sliding distance has an influence of 29.84%, percentage of graphite has an influence of 15.17%, and sliding speed has an influence of 1.83% on the weight loss of copper hybrid composites due to sliding wear. The worn-out surfaces were analyzed using electron microscopy, which reveals that the addition of both hard ceramic reinforcement TiC and soft solid lubricant graphite significantly improves the tribological performance of the copper composites.