Tensile Properties and Fracture Behavior of Different Carbon Nanotube-Grafted Polyacrylonitrile-Based Carbon Fibers

The tensile properties and fracture behavior of different carbon nanotube (CNT)-grafted polyacrylonitrile-based (T1000GB) single carbon fibers were investigated. Grafting of CNTs was achieved via chemical vapor deposition (CVD). When Fe(C₅H₅)₂ (also applied via CVD) was used as the catalyst, the tensile strength and Weibull modulus of the carbon fibers were improved, possibly due to the growth of dense CNT networks on the carbon fibers, which may have led to a reduction in the number of strength-limiting defects. Separately, at lower concentrations of an Fe(NO₃)₃·9H₂O catalyst in ethanol, which was applied via dipping, the tensile strength of CNT-grafted fibers was nearly identical to that of the as-received fibers, although the Weibull modulus was higher. For higher concentrations of the Fe(NO₃)₃·9H₂O catalyst, however, the tensile strength and the Weibull modulus were lower than those for the as-received material. Although the density of the CNT network increased with the concentration of the Fe(NO₃)₃·9H₂O catalyst in the ethanol solution, heating of the ethanolic Fe(NO₃)₃·9H₂O catalyst solution generated nitric acid (HNO₃) due to decomposition, which damaged the fiber surfaces, resulting in an increase in the number of flaws and consequently a reduction in the tensile strength. Therefore, the tensile strength and Weibull modulus of CNT-grafted carbon fibers vary due to the combination of these effects and as a function of the catalyst concentration.     

碳纤维表面生长纳米碳管及其增强的炭/炭复合材料

采用化学气相沉积工艺在碳纤维表面生长了纳米碳管,将此种碳纤维作为增强材料,以中间相沥青为基体炭前驱体采用浸渍炭化工艺制备了炭/炭复合材料.观察了所得复合材料断口的微观形貌,测试了抗弯强度及热物理性能.结果表明,碳纤维表面的纳米碳管可以有效地提高纤维与基体的粘结力,复合材料的抗弯性能提高了50%,而对复合材料的导热性能影响较小.     

SiC纤维表面去碳处理对PIP-SiCf/SiC复合材料力学性能以及界面影响

采用强度测试、SEM、HRTEM等分析测试手段对纤维表面去碳前后SiC纤维强度、复合材料力学性能、纤维表面形貌、复合材料断口形貌以及复合材料界面特征进行分析表征.结果表明,去碳处理后,纤维表面的固有缺陷暴露出来,纤维强度下降约15%,但由其制备的复合材料强度下降只有原纤维制备复合材料的1/6;复合材料断口非常平整,纤维...     

Effect of Strain Rate on Tensile Properties of Carbon Fiber Epoxy-Impregnated Bundle Composite

The tensile tests for high tensile strength polyacrylonitrile (PAN)-based (T1000GB) carbon fiber epoxy-impregnated bundle composite at various strain rates ranging from 3.33 × 10^?5 to 6.0 × 10² s^?1 (various crosshead speeds ranging from 8.33 × 10^?7 to 1.5 × 10¹ m/s) were investigated. The statistical distributions of the tensile strength were also evaluated. The results clearly demonstrated that the tensile strength of bundle composite slightly increased with an increase in the strain rate (crosshead speed) and the Weibull modulus of tensile strength for the bundle composite decreased with an increase in the strain rate (crosshead speed), there is a linear relation between the Weibull modulus and the average tensile strength on log-log scale.     

Strengthening of C/SiC Composites by Electrophoretic Deposition of CNTs on a SiC Coating

The current study reports the enhancement of mechanical properties of carbon fiber-reinforced silicon carbide ceramic matrix composites (C/SiC CMCs) by the application of a carbon nanotube/silicon carbide (CNT/SiC) coating. CNTs were deposited on the surfaces of C/SiC composites using electrophoretic deposition (EPD), after which infiltration by SiC was achieved through a chemical vapor infiltration process. An EPD duration of 5 min was associated with a 40% increase in the ultimate flexural strength relative to that of composites with a pure SiC coating. The observed enhancement was rationalized by the microstructural observations of SiC infiltration into the porous CNT morphology and the subsequent formation of CNT/SiC layers on the surfaces of the composites and by the inherent toughness of the SiC whiskers. The flexural strength decreased with EPD durations greater than 5 min due to the formation of thick CNT meshes, which decreased the open porosity and thereby obstructed further SiC infiltration. This is a viable methodology for the improvement of mechanical properties of CMCs by the introduction of a ceramic coating containing CNT.     

Raman Strain Sensing and Interfacial Stress Transfer of Hierarchical CNT-Coated Carbon Fibers

Hierarchical reinforcements of carbon fibers (CFs) coated with carbon nanotubes (CNTs) were produced via two different methodologies, namely chemical vapor deposition (CVD) and wet chemical treatment. These advanced smart structural materials are possible candidates for inherent strain sensing and improved interfacial properties when incorporated in the volume of structural fiber-reinforced polymer composites. The morphology and wetting properties of the hierarchical CFs were evaluated via SEM and contact angle measurements. Enhanced values in the strain-induced Raman sensing ability of the hierarchical reinforcement produced via CVD in comparison with the uncoated fibers were measured at single fiber level. The residual stress transfer profiles of both the hierarchical and the uncoated carbon fibers were also evaluated using the Raman spectroscopy in order to evaluate the phase interaction in the hierarchical structure. Compressive residual stresses in the order of 1.5 GPa were found to act on the CF surfaces, while tensile residual stresses were measured for both the CNT-coated systems. The effects of the preparation process of the CNT coatings on the residual stress profiles were also prominent, with the CVD-grown coatings resulting in higher tensile residual stresses, 1.76 GPa instead of 1.22 GPa for the coatings produced via wet chemical treatment. The change in the residual stress profiles established the interaction between the CFs and the CNTs via an anchoring mechanism which significantly altered the stress field at the vicinity of the interface.     

炭/炭复合材料抗氧化抗热震铱涂层的研究进展

铱是航天领域1800 ℃以上炭/炭复合材料抗氧化抗热震涂层的首选材料。本文介绍了物理气相沉积、金属有机物化学气相沉积、熔盐电解沉积和双层辉光等离子沉积等4种主要制备铱涂层的方法,讨论了铱涂层与炭/炭复合材料基体之间过渡层的材料选择,总结了铱涂层的地面试车测试结果,分析了影响铱涂层寿命的因素,指出今后我国制备铱涂层的技术途径应采用熔盐电解沉积 (Electroformed Deposition, 简写为ED)、双层辉光等离子沉积 (Double-glow Plasma Deposition, 简写为DPD)方法。     

Electrical and mechanical properties of copper chloride-intercalated pitch-based carbon fibers

Using chlorine vapor transport we have intercalated pitch-based fibers, highly oriented pyrolytic graphite (HOPG), and natural single crystals of graphite with CuCl₂. In this paper we report mainly on the electrical properties of pitch-based fibers heat treated to 2500, 2750 and 3000 °C and then intercalated. The electrical resistivity both above and below room temperature, the tensile strength, and Young's modulus are reported. In very high magnetic fields at 4 K the fibers exhibit Shubnikov-de Haas oscillations, which means this powerful technique is now available as a diagnostic tool for intercalated fibers.     

碳界面层制备工艺对SiC_f/SiC材料力学性能的影响

用低压化学气相沉积(LPCVD)法,以丙烯(C_3H_6)为碳源,氮气(N_2)为稀释气制备了2.5维连续碳化硅纤维增韧碳化硅(SiC_f/SiC)复合材料的碳界面层,其厚度为～0.1 mm.研究了不同丙烯含量(体积分数,下同)(60%,50%,45%)对碳层形貌、微观结构及SiC_f/SiC力学性能的影响.结果表明:当C_3H_6含量为60%时,热解碳层表面光滑,石磨化度高;当C_3H_6为50%和45%时,碳层粗糙,有很多较大颗粒存在,石磨化度低.3种复合材料的弯曲强度差别不大,分别为303,311和320 MPa.然而,当C_3H_6含量为60%时,材料韧性断裂,断裂功高;为50%和45%时,材料脆性断裂,断裂功低.不同的纤维拔出滑移阻力是SiC_f/SiC断裂行为不同的原因.     

Microstructure and mechanical properties of 3D fine-woven punctured C/C composites with PyC/SiC/TaC interphases

The 3D fine-woven punctured C/C-(P_yC/SiC/TaC) composites, composed of P_yC/SiC/TaC interphases and pyrocarbon (PyC) matrix, were synthesized by isothermal chemical vapor infiltration (ICVI) methods. The alternating layers and the structure of these composites were examined by polarized light microscopy (PLM), X-ray diffractometry (XRD) and scanning electron microscopy (SEM). It is found that the P_yC matrix has rough laminar (RL) structure, the TaC layer has NaCl-type cubic structure, and the SiC layer has few wurtzite type 10H-SiC besides β-SiC structure. The effects of fiber coating and the bulk density on the tensile and flexural properties of composites along X or Y and Z direction were investigated. It is shown that fiber coated 3D woven punctured C/C composites have good tensile and flexural strength, and the maximum of flexural strength is 375 MPa in X or Y direction at density of 1.89 g/cm³, which is about three times higher than that of samples without TaC/SiC fiber coating. The flexural strength and bending strength increase with increasing the density of the composites. The analysis of fracture surfaces reveals that fibers and fiber bundles are pulled out in composites, indicating that the composite exhibits a non-linear failure behavior through propagation and deflection of the cracks.     

磁控溅射法制备碳/碳复合材料 SiC/MoSi2-ZrB2 涂层的结构及抗氧化性能研究

通过磁控溅射法在碳/碳复合材料表面成功制得了SiC/MoSi2-ZrB2陶瓷涂层并对结构及其在高温有氧环境中的抗氧化性能进行了研究。结果表明制备的SiC/MoSi2-ZrB2陶瓷涂层呈柱状晶结构且均匀性良好,其在1273K和1773K的有氧环境中氧化60min失重率分别是5.6×10-2 g/cm2 和 6.3×10-2 g/cm2。     

Effect of Spark-Plasma-Sintering Conditions on Tensile Properties of Aluminum Matrix Composites Reinforced with Multiwalled Carbon Nanotubes (MWCNTs)

In this study, aluminum (Al) matrix composites containing 2 wt.% multiwalled carbon nanotubes (CNTs) were fabricated by powder metallurgy using high-energy ball milling (HEBM), spark plasma sintering (SPS), and subsequent hot extrusion. The effect of SPS conditions on the tensile properties of CNT/Al composites was investigated. The results showed that composites with well-dispersed CNTs and nearly full-density CNT/Al can be obtained. During HEBM, CNTs were shortened, inserted into welded Al powder particles, bonded to Al, and still stable without CNT-Al reaction. After consolidation, Al₄C₃ phases formed in composites under different sintering conditions. With the increase of sintering temperature and holding time, the strength decreased. Conversely, the ductility and toughness noticeably increased. As a result, a good balance between strength (367 MPa in ultimate tensile strength) and ductility (13% in elongation) was achieved in the as-extruded CNT/Al composite sintered at 630°C with a holding time of 300 min.     

CeO2在镀镍碳纤维增强铝合金基复合材料中的作用

以稀土氧化物CeO2为添加剂,研究CeO2对镀镍碳纤维增强铝合金基复合材料碳纤维的分布、气孔率以及力学性能的影响,利用扫描电镜分析和拉伸力学性能检测等探讨了CeO2在镀镍碳纤维增强铝合金基复合材料中的行为。结果表明:CeO2能够使碳纤维均匀分布在复合材料中,而不产生分层及团聚;而且能够降低复合材料的气孔率,使轧制态复合材料的抗拉强度、屈服强度分别提高23%和26%。     

炭纤维增强镁基复合材料的制备

对炭纤维进行了表面化学镀镍处理并通过扫描电镜(SEM)评价了炭纤维化镀层。利用粉末冶金热挤压方法制备了短切炭纤维增强镁合金复合材料并通过超景深金相显微镜观察了纤维在复合材料中的分布。研究了材料中炭纤维含量为0～4%时对复合材料的影响。结果表明,镀镍炭纤维在复合体中均匀分散,炭纤维质量分数为4.0%的镁预制体采用压制压力为420MPa,烧结温度为550℃,保温0.5h后在480℃用280MPa的压力进行热挤压得到的复合材料力学性能较佳。     

碳纤维-FeCoCrNiAl高熵合金颗粒混杂增强7075铝基复合材料的力学性能及断裂行为

为探究双相增强体对铝基复合材料拉伸性能和断裂行为的影响,采用真空热压烧结工艺在580 ℃,30 MPa条件下保温10 min制备了FeCoCrNiAl高熵合金颗粒增强7075铝基复合材料（HEA_p/Al）,Ni-Co-P镀层修饰碳纤维增强7075铝基复合材料（CF/Al）和FeCoCrNiAl高熵合金颗粒及Ni-Co-P镀层修饰碳纤维混杂增强铝基复合材料（CF-HEA_p/Al）。并对不同复合材料微观结构及拉伸性能进行分析表征及比较。结果表明：CF-HEA_p/Al复合材料的屈服强度（YS）与极限拉伸强度（UTS）随纤维含量的升高（体积分数由0至40%）呈现先增大后降低的变化,延伸率则逐渐降低。鉴于Ni-Co-P镀层修饰碳纤维与FeCoNiCrAl高熵合金颗粒的混杂强化效应, CF-HEA_p/Al复合材料的YS和UTS较HEA_p/Al与CF/Al复合材料明显提高,且其断口表现出基体韧性断裂及纤维拔出与断裂的多种失效特征。     

Improved properties of carbon fiber paper as electrode for fuel cell by coating pyrocarbon via CVD method

The fabrication of a pyrocarbon coated carbon paper and its application to the gas diffusion lay (GDL) of proton exchange membrane (PEM) fuel cell were described. This carbon paper was fabricated by using conventional carbon paper as the precursor, and coating it with pyrocarbon by pyrolyzing propylene via the chemical vapor deposition (CVD) method. For comparison, conventional carbon paper composites were also prepared by using PAN-based carbon fiber felt as the precursor followed by impregnation with resin, molding and heat-treatment. SEM characterization indicates that pyrocarbon is uniformly deposited on the surface of the fiber in the pyrocarbon coated carbon paper and made the fibers of carbon felt bind more tightly. In contrast, there are cracks in matrix and debonding of fibers due to carbonization shrinkage in the conventional carbon paper. Property measurements show that the former has much better conductivity and gas permeability than the latter. In addition, current density-voltage performance tests also reveal that the pyrocarbon coating can improve the properties of carbon paper used for electrode materials of fuel cell.     

连续纤维增主基复合材料研究概况

重点了介绍了连续纤维境强钛基复合材料的３种复合方法,即箔材－纤维－箔材法、等离子喷射涂层法和物相沉积法,开发的强化纤维有ＳｉＣ纤维和Ａ１２Ｏ３单晶纤维,并介绍了它们的研究进展,最后讨论了一些复合材料的性能循呼复合材料的损伤评价技术。     

中间相沥青基炭/炭复合材料的微观结构与力学性能

借助偏光显微镜、扫描电镜、透射电镜以及力学性能测试研究了微观结构对中间相沥青基炭/炭复合材料力学性能的影响.结果表明基体炭在偏光显微镜下呈现出光学各向异性,在SEM和TEM下呈片层条带状结构.基体炭与纤维之间的界面不连续,为"裂纹型"界面.材料受载破坏时裂纹通过改变扩展路径而延缓其扩展速度,在纤维-基体界面处以及基体炭层片之间引起滑移,在断口形貌上体现出断裂台阶适中且与纤维拔出交替进行,表现出韧性破坏的断裂特征.材料具有较高的力学性能,抗弯强度达到257MPa.     

TENSILE PROPERTIES OF COATED CARBON FIBER REINFORCED MAGNESIUM COMPOSITES

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The effect of partially carbonized fibers on the mechanical properties of carbon/carbon composites

The carbon/carbon (C/C) composite with satisfactory mechanical properties were obtained through introduction of partially carbonized fibers as a precursor. Applying this procedure the production cost of C/C composites may be significantly reduced. Stabilized PAN fibers were partially carbonized at temperatures ranging from 400 to 1000 °C and reinforced with phenolic resin, resole type. Cured composite were carbonized up to 1000 °C in an inert atmosphere. Monofilament tensile test strength, Young's modulus and tensile strength of partially carbonized fibers were determined. Mechanical properties of carbon/carbon composites (flexural strength and flexural modulus) determined by using three-point bending test. The effect of partially carbonized fibers on the mechanical properties of C/C composites was examined by scanning electron microscope (SEM) through analysis of the fracture surface. The C/C composite reinforced with partially carbonized fibers at 600 °C showed quite satisfactory flexural strength. This confirms assumptions that through co-carbonization of partially carbonized fibers and resin C/C composite with suitable mechanical properties could be obtained.