共查询到20条相似文献,搜索用时 156 毫秒
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凸轮轴重熔淬火表面孔洞缺陷形成原因分析 总被引:4,自引:0,他引:4
由灰铸铁制成的汽车发动机凸轮轴,其常见的加工缺陷之一是凸桃表面出现大面积细小的孔洞。通过分析,认为铸件中石墨化元素含量过高,共晶度偏大,导致铸件组织中石墨聚集,形成粗大石墨相,使得石墨形态不符合质量要求。这是凸轮轴表面重熔淬火过程中产生大量孔洞的直接原因。 相似文献
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石墨炉原子吸收法测定重质油中钒含量 总被引:2,自引:0,他引:2
本文通过对普通石墨管,热解涂层石墨管和L'VOV平台中钒吸收信号和灰化曲线的比较,发现使用热解涂层石墨管效果最好,选择热解涂层石墨管,不加基体改进剂,测定原料油中钒含量,方法的特征质量为20.67pg/0.0044A。 相似文献
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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。 相似文献
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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. 相似文献
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The influence of graphite content on the dry sliding and oil impregnated sliding wear characteristics of sintered aluminum 2024 alloy–graphite (Al/Gr) composite materials has been assessed using a pin-on-disc wear test. The composites with 5–20 wt.% flake graphite particles were processed by in situ powder metallurgy technique. For comparison, compacts of the base alloy were made under the same consolidation processing applied for Al/Gr composites. The hardness of the sintered materials was measured using Brinell hardness tester and their bending strength was measured by three-point bending tests. Scanning electron microscopy (SEM) was used to analyze the debris, wear surfaces and fracture surfaces of samples. It was found that an increase in graphite content reduced the coefficient of friction for both dry and oil impregnated sliding, but this effect was more pronounced in dry sliding. Hardness and fracture toughness of composites decreased with increasing graphite content. In dry sliding, a marked transition from mild to severe wear was identified for the base alloy and composites. The transition load increased with graphite content due to the increased amount of released graphite detected on the wear surfaces. The wear rates for both dry and oil impregnated sliding were dependent upon graphite content in the alloy. In both cases, Al/Gr composites containing 5 wt.% graphite exhibited superior wear properties over the base alloy, whereas at higher graphite addition levels a complete reversal in the wear behavior was observed. The wear rate of the oil impregnated Al/Gr composites containing 10 wt.% or more graphite particles were higher than that of the base alloy. These observations were rationalized in terms of the graphite content in the Al/Gr composites which resulted in the variations of the mechanical properties together with formation and retention of the solid lubricating film on the dry and/or oil impregnated sliding surfaces. 相似文献
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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. 相似文献
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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. 相似文献
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Investigations on the influence of graphite filler on dry sliding wear and abrasive wear behaviour of carbon fabric reinforced epoxy composites 总被引:1,自引:0,他引:1
In this experimental study, the dry sliding wear and two-body abrasive wear behaviour of graphite filled carbon fabric reinforced epoxy composites were investigated. Carbon fabric reinforced epoxy composite was used as a reference material. Sliding wear experiments were conducted using a pin-on-disc wear tester under dry contact condition. Mass loss was determined as a function of sliding velocity for loads of 25, 50, 75, and 100 N at a constant sliding distance of 6000 m. Two-body abrasive wear experiments were performed under multi-pass condition using silicon carbide (SiC) of 150 and 320 grit abrasive papers. The effects of abrading distance and different loads have been studied. Abrasive wear volume and specific wear rate as a function of applied normal load and abrading distance were also determined.The results show that in dry sliding wear situations, for increased load and sliding velocity, higher wear loss was recorded. The excellent wear characteristics were obtained with carbon-epoxy containing graphite as filler. Especially, 10 wt.% of graphite in carbon-epoxy gave a low wear rate. A graphite surface film formed on the counterface was confirmed to be effective in improving the wear characteristics of graphite filled carbon-epoxy composites. In case of two-body abrasive wear, the wear volume increases with increasing load/abrading distance. Experimental results showed the type of counterface (hardened steel disc and SiC paper) material greatly influences the wear behaviour of the composites. Wear mechanisms of the composites were investigated using scanning electron microscopy. Wear of carbon-epoxy composite was found to be mainly due to a microcracking and fiber fracture mechanisms. It was found that the microcracking mechanism had been caused by progressive surface damage. Further, it was also noticed that carbon-epoxy composite wear is reduced to a greater extent by addition of the graphite filler, in which wear was dominated by microplowing/microcutting mechanisms instead of microcracking. 相似文献
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Tribological properties of solid lubricants (graphite, h-BN) for Cu-based P/M friction composites 总被引:3,自引:0,他引:3
Cu-based P/M friction composites containing graphite at weight fractions in the range of 0%, 2%, 5%, 8%, 10%, corresponding to the hexagonal boron nitride (h-BN) at weight fractions in the range of 10%, 8%, 5%, 2%, 0%, were fabricated by a P/M hot press method, respectively. The effects of graphite and h-BN on tribological properties of Cu-based P/M friction composites were investigated on a block-on-ring tester. Worn surfaces, microstructures and wear debris of the composites were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Results indicate that lubrication effects of graphite are superior to those of h-BN. With the increase of graphite content wear rates were decreased significantly. Added graphite with low contents of h-BN can stabilize friction and wear properties of Cu-based P/M friction composites. 相似文献
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Polyimide (PI)-based composites containing single-wall carbon nanohorn aggregate (NH) were fabricated using the spark plasma sintering (SPS) process. For comparison, composites with carbon nanotube (NT) and traditional graphite (Gr) were also fabricated. The NH was produced using CO2 laser vaporization and a graphite target and the NT was produced by a chemical synthesis method. We evaluated the friction and wear properties of the PI-based composites with a reciprocating friction tester in air using an AISI 304 mating ball. NH drastically decreased the wear of PI-based composites; the specific wear rate of composite with NH of only 5 wt% was of the order of 10−8 mm3/Nm, which was two orders of magnitude less than that of PI alone. The wear reduction ability of NT seemed to be slightly inferior to that of NH, although it was considerably better than that of Gr. NH and NT lowered the friction of composites. The friction coefficient of composite with 10 wt% NH was less than 0.25, although it was slightly higher than that of composite with 10 wt% Gr. There was no clear difference in the friction reduction effect of NH and NT. The further addition of Gr to composites with NH or NT rather deteriorated the antiwear property of composites, although the friction coefficient was slightly reduced. The transferred materials existed on the friction surface of the mating ball, sliding against composites with three types of carbon filler. These transferred materials seemed to correlate with the low friction and wear properties of composites. 相似文献
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This article analyzes the influence of graphite reinforcement, load, sliding speed, and sliding distance on tribological behavior of A356 aluminum matrix composites reinforced with silicon carbide and graphite using the full-factorial design. The wear rates of A356/10SiC composite material and A356/10SiC/1Gr and A356/10SiC/3Gr hybrid composites have been analyzed. The composites were obtained by a modified compocasting procedure. Tribological tests were performed on a block-on-disc tribometer without lubrication. The testing included sliding speeds of 0.25 and 1.0 m/s, normal loads of 10 and 20 N, and sliding distances of 300 and 900 m. The analysis of the obtained results was performed using the full-factorial method based on the signal-to-noise (S/N) ratio. The effects of load, sliding speed, weight percentage of graphite reinforcement, and sliding distance on the wear rate are 38.99, 17.87, 13.95, and 11.25%, respectively. The best tribological characteristics were exhibited by the A356/10SiC/1Gr hybrid aluminum composite. 相似文献
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短玻璃纤维和石墨填充PTFE的摩擦磨损特性研究 总被引:3,自引:2,他引:3
利用自主研制的往复式摩擦试验机对短玻璃纤维(SGF)及石墨填充聚四氟乙烯(PTFE)复合材料的摩擦磨损特性进行了研究,探讨了共混材料对PTFE摩擦学性能的影响。利用扫描电子显微镜对材料的磨损表面进行了观察和分析。研究结果表明,短玻璃纤维有效提高了PTFE的承载能力,石墨的加入起到了减小摩擦的作用,在较高载荷下,短玻璃纤维和石墨填充的PTFE复合材料表现出优异的抗磨性能。 相似文献
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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. 相似文献