Friction and wear properties of copper matrix composites reinforced by tungsten-coated carbon nanotubes

Carbon nanotubes （CNTs） were coated by tungsten layer using metal organic chemical vapor deposition process with tungsten hexacarbonyl as a precursor. The W-coated CNTs （W-CNTs） were dispersed into Cu powders by magnetic stirring process and then the mixed powders were consolidated by spark plasma sintering to fabricate W-CNTs/Cu composites. The CNTs/Cu composites were fabricated using the similafprocesses. The friction coefficient and mass wear loss of W-CNTs/Cu and CNTs/Cu composites were studied. The results showed that the W-CNT content, interfacial bonding situation, and applied load could influence the friction coefficient and wear loss of W-CNTs/Cu com- posites. When the W-CNT content was 1.0 wt.%, the W-CNTs/Cu composites got the minimum friction coefficient and wear loss, which were decreased by 72.1% and 47.6%, respectively, compared with pure Cu specimen. The friction coefficient and wear loss of W-CNTs/Cu composites were lower than those of CNTs/Cu composites, which was due to that the interracial bonding at （W-CNTs）-Cu interface was better than that at CNTs-Cu interface. The friction coefficient of composites did not vary obviously with increasing applied load, while the wear loss of composites increased significantly with the increase of applied load.

Synergistic regulation of current-carrying wear performance of resin matrix carbon brush composites with tungsten copper composite powder

Resin matrix carbon brush composites(RMCBCs)are critical materials for high-powered electric tools.However,effectively improving their wear resistance and heat dissipation remains a challenge.RMCBCs prepared with flake graphite powders that were evenly loaded with tungsten copper composite powder(RMCBCs-W@Cu)exhibited a low wear rate of 1.63 mm^(3)/h,exhibiting 48.6%reduction in the wear rate relative to RCMBCs without additives(RMCBCs-0).In addition,RMCBCs-W@Cu achieved a low friction coefficient of 0.243 and low electric spark grade.These findings indicate that tungsten copper composite powders provide particle reinforcement and generate a gradation effect for the epoxy resin(i.e.,connecting phase)in RMCBCs,which weakens the wear of RMCBCs caused by fatigue under a cyclic current-carrying wear.

Wear and transfer characteristics of carbon fiber reinforced polymer composites under water lubrication

The tribological characteristics of carbon fiber reinforced polymer composites under distilled-water-lubricated-sliding and dry-sliding against stainless steel were comparatively investigated. Scanning electron microscopy (SEM) was utilized to examine composite microstructures and modes of failure. The typical chemical states of elements of the transfer film on the stainless steel were examined with X-ray photoelectron spectroscopy (XPS). Wear testing and SEM analysis show that all the composites hold the lowered friction coefficient and show much better wear resistance under water lubricated sliding against stainless steel than those under dry sliding. The wear of composites is characterized by plastic deformation, scuffing, micro cracking, and spalling under both dry-sliding and water lubricated conditions. Plastic deformation, scuffing, micro cracking, and spalling, however, are significantly abated under water-lubricated condition. XPS analysis conforms that none of the materials produces transfer films on the stainless steel counterface with the type familiar from dry sliding, and the transfer of composites onto the counterpart ring surface is significantly hindered while the oxidation of the stainless steel is speeded under water lubrication. The composites hinder transfer onto the steel surface and the boundary lubricating action of water accounts for the much smaller wear rate under water lubrication compared with that under dry sliding. The easier transfer of the composite onto the counterpart steel surface accounts for the larger wear rate of the polymer composite under dry sliding.

Tribological and electric-arc behaviors of carbon/copper pair during sliding friction process with electric current applied

The tribological behaviors of carbon block sliding against copper ring with and without electric current applied were investigated by using an advanced multifunctional friction and wear tester, and the electric-arc behaviors were analyzed in detail. The results show that the normal load is one of the main controlling factors for generation of electric arc during friction process with electric current applied. The strength of electric arc is enhanced with the decrease of normal loads and the increase of electric currents. The unstable friction process and the fluctuated dynamic friction coefficients are strongly dependent upon the electric arc. The wear volumes and the wear mechanism of carbon brush were affected by the electric arc obviously. As no electric arc occurs, no clear discrepancy of the wear volumes of the carbon samples with and without electric current applied could be detected. While the wear mechanisms are mainly mechanical wear. However, under the condition of the electric arc appearance, the wear volume of carbon with electric current applied increases much more rapidly than that without electric current applied and also increases obviously with the increase of electric current strengths and the decrease of normal loads. The wear mechanisms of carbon block are mainly electric arc ablation accompanying with adhesive wear and material transferring.

Properties of copper/graphite/carbon nanotubes composite reinforced by carbon nanotubes

Electroless Cu plating was used for flake G powder and CNTs, Cu-G-CNTs （copper/graphite/carbon nanotubes） composites were manufactured by means of powder metallurgical method. The influences of CNTs on the mechanical properties, conductivity properties, friction, and wear performance of the composite were examined. The results indicate that adding a small amount of CNTs can improve comprehensive property of the composites, especially mechanical property. However, excessive CNT, which is easily winding reunion and grain boundary seg- regation, results in performances degradation.

Surface Functionalized Carbon Nanofibers and Their Effect on the Dispersion and Tribological Property of Epoxy Nanocomposites

Surface functionalization of carbon nanofibers（CNFs） was carried out, i e, CNFs were firstly oxidized and then the surface was silanized by 3-Aminopropyltriethoxysilane（APTES） via an assembly method. A new kind of high wear resistance s-CNFs/epoxy composite was fabricated by in-situ reaction. FTIR spectroscopy was used to detect the changes of the functional groups produced by silane on the surface of CNFs. The tribological properties and microstructures of modified and unmodified CNFs/epoxy composites were studied, respectively. The expremental results indicate that APTES is covalently linked to the surface of CNFs successfully and improves the dispersion of CNF in epoxy matrix. The friction coefficients and the wear rates of s-CNFs/epoxy composites are evidently lower than those of u-CNFs/epoxy composites under the same loads. Investigations also indicate that abrasive wear is the main wear mechanism for u-CNFs/epoxy composite, with slight adhesive wear for s-CNFs/epoxy composite under the same sliding wear condition.

Preparation and tribological performances of Ni-P-multi-walled carbon nanotubes composite coatings

Multi-walled carbon nanotubes （MWNTs） were wet-milled in the presence of ammonia and cationic surfactant and then used as reinforcements to prepare Ni-P-MWNTs composite coatings by electroless plating. The tribological performances of the composite coatings under dry condition were investigated in comparison with 45 steel and conventional Ni-P coating, Micrographs show that short MWNTs with uniform length and open tips were obtained through the wet-milling process. The results of wear test reveal that the Ni-P-MWNTs composite coatings posses much better friction reduction and anti-wear performances when compared with 45 steel and Ni-P coating. Within the MWNTs content range of 0.74%-1.97%, the friction coefficient and the volume wear rate of the composite coatings decrease gradually and reach the minimum values of 0.08 and 6.22x10-15 m3/（N.m）, respectively. The excellent tribological performances of the composite coatings can be attributed to the introduction of MWNTs, which play both roles of reinforcements and solid lubricant during the wear process.

Mechanical properties and friction behaviors of CNT/AlSi_(10)Mg composites produced by spark plasma sintering

The mechanical properties and friction behaviors of CNT/AlSi10Mg composites produced by spark plasma sintering (SPS) were investigated. The results showed that the densities of the sintered composites gradually increased with increasing sintering temperature and that the highest microhardness and compressive strength were achieved in the specimen sintered at 450A degrees C. CNTs dispersed uniformly in the Al-Si10Mg matrix when the addition of CNTs was less than 1.5wt%. However, when the addition of CNTs exceeded 1.5wt%, the aggregation of CNTs was clearly observed. Moreover, the mechanical properties (including the densities, compressive strength, and microhardness) of the composites changed with CNT content and reached a maximum value when the CNT content was 1.5wt%. Meanwhile, the minimum average friction coefficient and wear rate of the CNT/AlSi10Mg composites were obtained with 1.0wt% CNTs.

Electroless plating Ni-P matrix composite coating reinforced by carbon nanotubes

Ni-P matrix composite coating reinforced by carbon nanotubes (CNTs) was deposit ed by electroless plating. The most important factors that influence the content of carbon nanotubes in deposits,such as agitation,surfactant and carbon nanot ubes concentration in the plating bath were investigated. The surface morphology,structure and properties of the Ni-P-CNTs coating were examined. It is found that the maximum content of carbon nanotubes in the deposits is independent of carbon nanotubes concentration in the plating bath when it is up to 5 mg/L. The test results show that the carbon nanotubes co-deposited do not change the str ucture of the Ni-P matrix of the composite coating,but greatly increase the ha rdness and wear resistance and decrease the friction coefficient of the Ni-P-C NTs composite coating with increasing content of carbon nanotubes in deposits.

Preparation of Ni-CNT composite coatings on aluminum substrate and its friction and wear behavior

Nickel-carbon nanotube(CNT) composite coatings with a Zn-Ni interlayer were prepared by electrodeposition technique on aluminum substrate. The effects of CNT concentration in plating bath on the volume fraction of CNTs in the deposits and the coating growth rate were investigated. The friction and wear behavior of the Ni-CNT composite coatings were examined using a pin-on-disk wear tester under dry sliding conditions at a sliding speed of 0.062 3 m/s and load range from 12 N to 150 N. Because of the reinforcement of CNTs in the composite coatings, at lower applied loads, the wear resistance was improved with increasing volume fraction of CNTs. Since cracking and peeling occur on the worn surface, the wear rates of composite coatings with high volume fraction of CNTs increase rapidly at higher applied loads. The friction coefficient of the composite coatings decreases with the increasing volume fraction of CNTs due to the reinforcement and self-lubrication of CNTs.

A comparative study on microstructural evolution and surface properties of graphene/CNT reinforced Al6061-SiC hybrid surface composite fabricated via friction stir processing

A comparative study on the surface properties of Al-SiC-multi walled carbon nanotubes (CNT) and Al-SiC-graphene nanoplatelets (GNP) hybrid composites fabricated via friction stir processing (FSP) was documented. Microstructural characterization reveals a more homogeneous dispersion of GNPs in the Al matrix as compared to CNTs. Dislocation blockade by SiC and GNP particles along with the defect-free interface between the matrix and reinforcements is also observed. Nanoindentation study reveals a remarkable ~207% and ~27% increment in surface nano-hardness of Al-SiC-GNP and Al-SiC-CNT hybrid composite compared to as-received Al6061 alloy, respectively. On the other hand, the microhardness values of Al-SiC-GNP and Al-SiC-CNT are increased by ~36% and ~17% relative to as-received Al6061 alloy, respectively. Tribological assessment reveals ~56% decrease in the specific wear rate of Al-SiC-GNP hybrid composite, whereas it is increased by ~122% in Al-SiC-CNT composite. The higher strength of Al-SiC-GNP composite is attributed to the mechanical exfoliation of GNPs to few layered graphene (FLG) in the presence of SiC. Also, various mechanisms such as thermal mismatch, grain refinement, and Orowan looping contribute significantly towards the strengthening of composites. Moreover, the formation of tribolayer by the squeezed-out GNP on the surface is responsible for the improved tribological performance of the composites. Raman spectroscopy and various other characterization methods corroborate the results.

Friction and wear characteristics of robust carbon–carbon composites developed solely from petroleum pitch without reimpregnation

Friction and wear characteristics correlating the fiber reinforcement percentage of carbon–carbon (C/C) composites solely developed from petroleum pitch matrices were investigated. This study exhibits the tribo-characteristics of C/C composites developed in a single-step carbonization process for varying loads for the first time without a reimpregnation process. A pin-on-disc tribometer with a sliding speed of 0.5 m/s and loads of 5, 10, and 20 N with a flat tool grade stainless steel pin as a static partner was employed. Further, polarized light optical and scanning electron microscopes (SEM) were utilized for a morphological analysis. Elastic modulus and strength were determined by a compression test. A result analysis is conducted to analyze sliding wear accompanied with minor abrasion. The composites with a high percentage of reinforcement exhibit credible wear resistance and mechanical robustness.

Friction and wear behavior of carbon fiber reinforced lithium aluminosilicate composites sliding against GCr15 steel

Carbon fibers reinforced lithium aluminosilicate matrix composites(Cf/LAS)were prepared by slurry infiltration combined with a hot press procedure.The friction,wear behavior,and wear mechanisms of Cf/LAS composites under dry sliding conditions were investigated.The results show that the coefficient of friction(COF)initially increased with the increase in carbon fiber content,and reached the maximum value of 0.20 for the 33%Cf/LAS composite.The COF increased sharply with increasing sample temperature from RT to 300℃.The COF remained stable in the temperature range of 300–500℃.The two wear mechanisms of LAS glass-ceramics are fatigue wear and abrasive wear.The Cf/LAS composites demonstrate slight spalling and shallow scratches.These results show that carbon fibers improve the mechanical properties and wear resistance of Cf/LAS composites.

High specific strength MWCNTs/Mg-14Li-1Al composite prepared by electrophoretic deposition, friction stir processing and cold rolling

Multi-wall carbon nanotubes reinforced Mg-14Li-1Al composite(MWCNTs/Mg-14Li-1Al) was prepared by the processes of electrophoretic deposition, friction stir processing, and cold rolling. The microstructure and mechanical properties of the composite were investigated. The results show that, the microhardness of the composite is up to HV 84.4, which is 91.38% higher than that of the as-cast matrix alloy(HV 44.1). The yield strength and ultimate tensile strength of the composite are 259 and 313 MPa, which are 135.45% and 115.86% higher than those of the as-cast matrix alloy, respectively, and a high specific strength of 221.98 k N·m/kg is obtained. In the composite, the MWCNTs serve as nucleation particles during the friction stir processing and cold rolling, causing dynamic recrystallization and grain refinement. Furthermore, MWCNTs hinder the movement of dislocations and transfer the load from the matrix alloy, thus improving the strength.

Influence of adding carbon nanotubes and graphite to Ag-MoS_2 composites on the electrical sliding wear properties

Silver matrix composite brushes were fabricated by means of powder metallurgy, which included pressing at 300 MPa and then sintering for 1 h in pure H2 protective atmosphere at 700 ℃ and repressing at 500 MPa. Four kinds composites with different compositions were produced, and the mechanical properties and electrical wear performance were investigated. The results showed that the composite added with carbon nanotubes had a higher hardness and strength, a lower contact voltage drop and an excellent anti-wear property in electrical sliding wear, because of the reinforcement ability of carbon nanotubes. Adding graphite to the composite also decreased the wear loss and contact voltage drop, because graphite had an electrical current conducting ability which not only made the current pass the lubricating films easily but also eliminated and reduced the arc and spark effectively.

铜合金表面激光制备Ni60-WC-Cu涂层的显微组织与摩擦磨损性能

激光熔覆涂层是解决铜合金零件因摩擦磨损导致失效的一种方法,但铜合金由于其对激光能量的高反射性、高导热性,使得在铜合金表面进行激光制备涂层成为一个难题。本文在白铜基体表面制备了不同WC含量的Ni60-WC-Cu复合涂层,对涂层相结构、微观形貌和显微硬度进行分析,并通过摩擦磨损试验,研究了涂层的耐磨性及磨损机理。结果表明:涂层中的相主要为NiW,其峰值随着WC含量的增加而增大;WC含量在20%与25%时观察到熔覆区出现大量的胞晶、枝晶组织,涂层顶部出现团聚状硬质相;涂层硬度均高于基体,WC含量为25%涂层的平均硬度为908.4HV;涂层耐磨性优于铜合金基体,随着WC含量增加,涂层耐磨性逐渐提高并均优于基体,氧化磨损、疲劳磨损和磨粒磨损;WC含量为25%时,涂层表现出最好的耐腐蚀性能;WC含量为20%时,表现出良好的导电率。

炭陶配副用碳纤维增强铜基摩擦材料及其摩擦学行为

炭陶配副用铜基摩擦材料在高速制动下难以兼具高摩擦因数与高耐磨性,为此,采用粉末冶金法制备短切沥青基碳纤维增强铜基摩擦材料,对材料力学、热学与摩擦学性能进行研究。研究结果表明:在室温下,碳纤维增强铜基摩擦材料布氏硬度提升14.8%,热扩散系数提高9.5%,比热容提升6.8%;在高速制动条件下(6000 r/min),碳纤维增强铜基摩擦材料摩擦耐磨性能显著提升,摩擦因数提升25.0%,稳定系数提升6.1%,且磨损量降低42.2%;加入碳纤维能显著提高表面平整度,增加机械混合层的厚度,降低磨屑直径,提高摩擦材料耐磨性;碳纤维增强铜基摩擦材料随速度增加发生从磨粒磨损、黏着磨损到氧化磨损、疲劳磨损的转变。

载流摩擦用铜-碳复合材料研究现状及展望

铜-碳(碳材料主要包括石墨、碳纤维、碳纳米管、石墨烯等)复合材料因其优异的导电性、导热性和润滑等性能,广泛应用在航天航空、轨道交通、电力电子、武器装备等领域的载流摩擦副中。随着载流摩擦副服役条件越来越苛刻,对铜-碳复合材料的使用性能要求越来越高。介绍铜-碳复合材料的种类和组成,指出铜-碳复合材料存在的问题如强度较低、铜基体与碳材料增强相之间不润湿等,综述铜-碳复合材料的界面改善、制备方法等,并对铜-碳复合材料的发展方向进行展望。

原位生长CNTs对于铜基复合材料性能的影响

通过化学气相沉积(chemical vapor deposition,CVD)法成功制备了CNTs/Cu-Al_(2)O_(3)复合材料。采用内氧化法制备Cu-Al_(2)O_(3)粉末,利用CVD技术改善碳纳米管(carbon nanotubes,CNTs)在铜基体中的分散性和界面结合,提高复合材料的性能。在制备的铜基复合材料中,Al_(2)O_(3)和CNTs双增强相的加入能够提高复合材料的力学性能,且CNTs独特的纤维结构有助于阻止熔融铜脱离基体表面,保持液态熔池稳定,避免复合材料导电率降低。双增强相的添加提高了复合材料的耐磨性、抑制了腐蚀坑的形成。Al的质量分数为0.35%的CNTs/Cu-Al_(2)O_(3)复合材料能够保证导电率较高的情况下得到较高的维氏硬度与致密度。为制备高性能铜基电接触材料提供了新思路。

Cu层包覆CNTs与原位自生纳米相协同增强铝基复合材料的微观结构及力学性能

以纯铝粉末、CuO粉末和Cu层包覆CNTs为原料,采用快速热压烧结方法制备Al-CNTs(Cu)-CuO复合材料,研究不同质量分数的CuO对复合材料中原位反应生成相特征及其对材料力学性能和磨损性能的影响。研究结果表明:提高铝基复合材料中CuO含量会显著促进Cu层包覆CNTs增强铝基复合材料中Al_(2)Cu及Al_(2)O_(3)纳米相的原位析出,不仅提高了铝基复合材料的强韧性匹配度,而且降低了磨损率,提高了耐磨性能。Cu层包覆CNTs与原位自生纳米相协同强化作用可以有效地提升铝基复合材料的综合服役性能,其在航空航天、轨道交通等领域具有十分广阔的应用前景。