浸渍-碳化工艺对碳/碳复合材料力学性能的影响

采用碳纤维针刺整体毡作为增强体,硼酚醛树脂作为基体先驱体,用浸渍碳化的方法制备C/C复合材料.考察了在不同的浸渍压力和碳化温度下材料力学性能的差异.分析结果表明:不仅密度是影响碳/碳复合材料力学性能的重要因素,纤维和基体的结合状况以及基体碳的结构也是决定材料强度和断裂方式的重要因素.随着工艺参数的改变,碳/碳复合材料的断裂模式可以由“假塑性断裂”向“脆性断裂”转变.     

基体碳对C/CF/Cu复合材料的影响

采用树脂碳化和碳气相沉积相结合的方法制备了碳／碳纤维（C／CF）先驱丝，用压力浸渗凝固成形方法制备了碳／碳纤维／铜（C／CF／Cu）复合材料，借助于扫描电镜下复合材料界面和相分布观察，以及显微硬度和滑动摩擦磨损测试，探讨了基体碳（树脂碳化碳和沉积碳）对C／CF／Cu复合材料成形、显微硬度及摩擦磨损的影响。结果表明，碳化和碳气相沉积处理的C／CF先驱丝相对致密，并阻碍铜液的压力浸渗成形，但该先驱丝硬度高于碳化处理的C／CF先驱丝。碳化和碳气相沉积处理的C／CF／Cu复合材料滑动摩擦磨损耐磨性高于纯铜，而且滑动摩擦因数也高于纯铜。证明C／CF／Cu复合材料是一种具有摩阻功能的复合材料。     

碳毡体密度对碳/碳复合材料抗氧化性能的影响

采用自加热化学液相沉积法制备碳/碳复合材料。考察了不同材料在不同温度、时间下的氧化失重率,研究了碳毡体密度与碳/碳复合材料氧化行为的关系。探讨了氧化温度和氧化时间对材料氧化侵蚀的影响机理。结果表明,毡体密度大的碳/碳复合材料具有更好的抗氧化性。扫描电镜观察材料氧化前后的显微形貌发现,基体碳更易被氧化。     

预氧丝在氧化镁／碳复合材料中的原位碳化及其强化作用

研究了碳纤维前驱体即预氧丝在氧化镁／碳复合材料中原位碳化及其强化作用。在氧化镁／碳复合材料中存在铝、镁添加剂时，预氧丝原位碳化后具有碳纤维的强度和强化效果。预氧丝在添加硅的氧化镁／碳材料中原位碳化时因与硅反应失去强度，在无抗氧化添加和的氧化镁／碳材料中原位碳化后，预氧丝因氧化失去强度，对基体无强化作用。     

熔铸法制备纳米碳增强铝基复合材料研究进展

纳米碳增强体具备优异的力学、热学、电学等性能,是金属基复合材料中理想的增强体之一。将纳米碳增强体与铝基体复合,可以获得具有优异力学性能及导热导电性能良好的复合材料,在新一代飞行器零部件材料展现出巨大潜力。目前急需低成本大规模化制备方法的推广应用,熔铸法是其大规模制备的首选。基于此,本文综述了近年来国内外采用熔铸法制备纳米碳增强铝基复合材料的研究进展,通过纳米碳增强体加入铝熔体方式的不同进行分类,详细介绍了搅拌铸造法、压力铸造法、半固态铸造法、压力浸渗法等纳米碳增强铝基复合材料中主要的铸造方法。分析总结了不同铸造方法的特点及铸件的力学性能,最后指出熔铸法制备纳米碳增强铝基复合材料过程中存在的关键科学问题,并且展望了未来的发展方向。     

基体碳对C/CF/Cu复合材料的影响

采用树脂碳化和碳气相沉积相结合的方法制备了碳/碳纤维(C/CF)先驱丝,用压力浸渗凝固成型方法制备了碳/碳纤维/铜(C/CF/Cu)复合材料,借助于扫描电镜下复合材料界面和相分布观察以及显微硬度和滑动摩擦磨损测试,探讨了基体碳(树脂碳化碳和沉积碳)对C/CF/Cu复合材料成型、显微硬度及摩擦磨损的影响.结果表明,碳化和碳气相沉积处理的C/CF先驱丝相对致密并阻碍铜液的压力浸渗成型,但该先驱丝硬度高于碳化处理的C/CF先驱丝.碳化和碳气相沉积处理的C/CF/Cu复合材料滑动摩擦磨损耐磨性高于纯铜,而且滑动摩擦系数也高于纯铜.C/CF/Cu复合材料是一种具有摩阻功能的复合材料.     

石墨化处理对三维针刺C/C复合材料力学性能的影响

以T700碳纤维三维针刺整体毡为预制体,利用高压液相浸渍-碳化周期循环致密工艺制备三维针刺中间相沥青基C/C复合材料.用XRD、SEM及力学性能测试研究了三维针刺C/C复合材料的微观结构与弯曲断裂机制.结果表明:随着浸渍-碳化次数的增加,三维针刺C/C复合材料的密度、抗弯强度和杨氏模量逐渐增大,石墨化处理使三维针刺C/C复合材料的石墨层间距减小,石墨化度提高.经2800 ℃石墨化处理后,三维针刺C/C复合材料中纤维与基体间界面结合减弱,复合材料的抗弯强度减小并表现出韧性断裂特征.     

碳／碳复合材料表面等离子喷涂陶瓷涂层的抗氧化性能

研究了有涂层与无涂层的碳／碳复合材料的高温氧化行为。等离子喷涂的陶瓷涂层，在氧化温度不大于１０００℃条件下，对碳／碳复合材料有良好的保护作用，无涂层的碳／碳复合材料在６００￣９００℃温度范围内的氧化机制相同；而有涂层时，氧化机制在７６０℃左右发生变化。碳毡增强碳基复合材料的氧化从表面碳毡开始，碳毡的氧化速率较基体碳的氧化速率大。     

超高温本体抗氧化碳／碳复合材料研究

通过向碳／碳复合材料基体中掺杂难熔金属化合物,研制出了一类集碳／碳材料优异的高温力学、热物理性能和超高温陶瓷材料非烧蚀性能于一体的超高温本体抗氧化碳／碳复合材料。攻克了难熔金属化合物在复合材料中分布以及组元与碳纤维反应控制关键技术,提高了复合材料的力学性能。静态和动态高频等离子风洞超高温本体抗氧化试验表明,在驻点温度达到2500℃,600s烧蚀后烧蚀量仅为碳／碳复合材料的1／5,给出了超高温本体抗氧化碳／碳复合材料氧化烧蚀抑制机理。     

不同碳质相增强银基复合材料的电接触行为

采用粉末冶金工艺制备碳质相质量分数为3%的不同碳质相(石墨、碳纳米管和石墨烯)增强银基复合材料,并对其微观组织和物理性能进行表征。对复合材料触头进行直流阻性负载条件下的电弧侵蚀试验,研究了不同碳质相对复合材料电弧特征、材料转移和质量净损耗的影响。结果表明,银-碳纳米管复合材料具有最佳的致密度、硬度和抗拉强度;而银-石墨烯复合材料具有最好的导电率。复合材料触头的材料转移方式均为阴极向阳极转移。同等电接触参数条件下,银-石墨烯复合材料具有最佳电接触性能,其燃弧时间最短、燃弧能量最低、材料转移量和质量净损耗最少。     

Fracture mechanism of 2D-C/C composites with pure smooth laminar pyrocarbon matrix under flexural loading

Using natural gas as carbon source, 2D needle felt as preform, 2D-C/C composites were prepared by thermal gradient chemical vapor infiltration. Their microstructures were observed under polarized light microscope (PLM) and scanning electron microscope (SEM), and the flexural behaviors before and after heat-treatment were studied with a universal mechanical testing machine. The fracture mechanism of the composites was discussed in detail. The results show that, carbon matrix exhibits pure smooth laminar (SL) characteristic including numerous wrinkled layered structures and some inter-laminar micro-cracks. With the decreasing density, the strength of the composites decreases and the toughness increases slightly; after 2500 °C heat-treatment, the inter-laminar micro-cracks in matrix increase, the strength decreases, and the toughness obviously increases. The fracture mode of the composites changes from brittle to pseudo-plastic characteristic due to more crack deflections in SL matrix.     

Effect of fiber characteristics on fracture behavior of C_f/SiC composites

Cf/SiC composites were prepared by precursor pyrolysis-hot pressing, and the effect of fiber characteristics on the fracture behavior of the composites was investigated. Because the heat treatment temperature of fiber T300 (below 1500℃) was much lower than that of fiber M40JB (over 2000℃), fiber T300 had lower degree of graphitization and consisted of more impurities compared with fiber M40JB, suggesting that T300 exhibits higher chemical activity. As a result, the composite with T300 showed a brittle fracture behavior, which is mainly ascribed to a strongly bonded fiber/matrix interface as well as the degradation of fibers during the preparation of the composite. However, the composite with M40JB exhibits a tough fracture behavior, which is primarily attributed to a weakly bonded fiber/matrix interface and higher strength retention of the fibers.     

Effects of precoating and calcination on microstructure of 3D silica fiber reinforced silicon nitride based composites

1 Introduction Continuous fiber reinforced ceramic matrix composites, such as C/SiC, C/Si-C-N, C/Si-O-C and SiC/SiC systems[1?5], have received considerable attention because of their excellent thermal stability, light mass and high toughness, etc. Among…     

准三维C/C复合材料的层间剪切性能及其断裂机理

以炭纤维针刺毡为预制体, 采用化学气相浸渗(CVI)法或结合液相法制备了热解炭、树脂炭和沥青炭基质的准三维C/C复合材料, 研究了这些材料的层间剪切性能及其断裂机理. 结果表明: CVI基质炭比沥青基质炭更有利于C/C复合材料的层间剪切性能的提高; 剪切强度随密度增高而增大, 致密度越高, 基体支撑越强, 同时微裂纹和孔隙度就越低, 断裂裂纹不易形成或扩展, 强度性能就越好; 纯沥青基质炭试样为"突发"的脆性断裂方式, 其他基质炭试样表现为韧性断裂方式.     

INFLUENCE OF HEAT TREATMENT ON OXIDATION PROPERTIES OF C／C COMPOSITES FABRICATED BY HIGH PRESSURE IMPREGNATION CARBONIZATION

Felt base carbon/carbon composites fabricated by super-high pressure impregnation carbonization process (SPIC) were heat treated at high temperature 2773K. The oxidation properties of felt base carbon/carbon composites were investigated at different temperatures (773-1173K), and the microstructures of carbon/carbon composites were studied by SEM and X-ray diffraction. The experimental results showed that the interlaminar distance of (002) plane (d002 ) deceased while the microcrystaUine stack height (Lc) increased. The oxidation rate of felt base carbon/carbon composites was invariable at certain temperatures. The oxidation mechanism of carbon/carbon composites changed remarkably at the oxidation temperature 973K. At the initial oxidation stage of carbon/carbon composites, carbon matrix was oxidized much more rapidly than carbon felt.     

Influence of load on sliding tribology of C/C composite with 40Cr steel couple coated by Cr

With the 40Cr steel couple coated by Cr, the sliding tribology behavior of two kinds of C/C composites with different matrix was tested using a M2000 wear tester. The results show that with the increasing of load, the friction coefficients of the composite with resin carbon matrix（RC） decrease quickly from 0.156 under 60 N to 0.123 under 150 N, while those of the composite with rough lamination/smooth lamination/resin carbon （RL/SL/RC） change only between 0.122 and 0.101. The wear volume loss of the two composites increases except for under 100 N. The SEM morphology shows that with the increasing of load, the worn surface of the composite with RC becomes more and more integrated while the size of the debris becomes less and less. The Raman spectrum shows that the graphitization on the worn surface of the fibers draws down after 100 N, the graphitization of the boundary between the fiber and the matrix carbon rises up to 150 N, but the graphitization of the matrix carbon draws down all the while. With the increasing of load, the graphitization on the worn surface of all the worn areas becomes closer and closer, which indicates the worn surface of the different component has the similar friction ability. The composites with RL/SL/RC have better tribological characteristic than the composite with RC.     

Densification Behavior and Performances of C/C Composites Derived from Various Carbon Matrix Precursors

Three types of carbon/carbon (C/C) composites were manufactured by densifying the needled carbon fiber preform through resin and pitch impregnation/carbonization repeatedly, as well as propylene pyrolysis by chemical vapor infiltration plus carbonization after the resin impregnation/carbonization. The densification behavior and performances (involving electric, thermal, and mechanical properties, as well as impurity) of the C/C composites were investigated systematically. The results show that besides the processing and testing conditions, the electric resistivity, thermal conductivity (TC), coefficient of thermal expansion (CTE), strength, and fracture, as well as impurity content and composition of the C/C composites were closely related to the fiber orientation, interfacial bonding between carbon fiber and carbon matrix, material characteristics of the three precursors and the resulting matrix carbons. In particular, the resin-carbon matrix C/C (RC/C) composites had the highest electric resistivity, tensile, and flexural strength, as well as impurity content. Meanwhile, the pitch-carbon matrix C/C (PC/C) composites possessed the highest TC and CTE in the parallel and vertical direction. And most of the performances of pyro-carbon/resin carbon matrix C/C composites were between those of the RC/C and PC/C composites except the impurity content.     

碳纤维在高温下的结构、性能演变研究

针对碳纤维在碳／碳烧蚀防热复合材料中应用的基础问题,论述了不同碳纤维结构、成分、表面特征,及其力学性能和热物理性能的高温演变规律,揭示了碳纤维灰分含量对碳纤维力学性能和热氧化性能的影响。确定了在碳／碳复合材料复合成型过程中,碳纤维结构受基体碳影响的变化规律和碳纤维表面特征对碳／碳材料宏观力学性能的影响。阐明了碳／碳复合材料中碳纤维的力学性能对纤维发生折断烧蚀的阻碍作用和通过控制碳／碳成型最高温度实现提高性能的途径。     

Mechanical Properties of Squeeze-Cast A356 Composites Reinforced With B4C Particulates

In this study, different volume fractions of B₄C particles were incorporated into the aluminum alloy by a mechanical stirrer, and squeeze-cast A356 matrix composites reinforced with B₄C particles were fabricated. Microstructural characterization revealed that the B₄C particles were distributed among the dendrite branches, leaving the dendrite branches as particle-free regions in the material. It also showed that the grain size of aluminum composite is smaller than that of monolithic aluminum. X-ray diffraction studies also confirmed the existence of boron carbide and some other reaction products such as AlB₂ and Al₃BC in the composite samples. It was observed that the amount of porosity increases with increasing volume fraction of composites. The porosity level increased, since the contact surface area was increased. Tensile behavior and the hardness values of the unreinforced alloy and composites were evaluated. The strain-hardening behavior and elongation to fracture of the composite materials appeared very different from those of the unreinforced Al alloy. It was noted that the elastic constant, strain-hardening and the ultimate tensile strength (UTS) of the MMCs are higher than those of the unreinforced Al alloy and increase with increasing B₄C content. The elongation to fracture of the composite materials was found very low, and no necking phenomenon was observed before fracture. The tensile fracture surface of the composite samples was indicative of particle cracking, interface debonding, and deformation constraint in the matrix and revealed the brittle mode of fracture.     

Experimental studies on drilling tool load and machining quality of C/SiC composites in rotary ultrasonic machining

Carbon fiber reinforced silicon carbide matrix (C/SiC) composites have great potential in space applications because of their excellent properties such as low density, superior wear resistance and high temperature resistance. However, the use of C/SiC has been hindered seriously because of its poor machining characteristics. With an objective to improve the machining process of C/SiC composites, rotary ultrasonic machining (RUM) and conventional drilling (CD) tests with a diamond core drill were conducted. The effects of ultrasonic vibration on mechanical load and machining quality were studied by comparing the drilling force, torque, quality of holes exit and surface roughness of drilled holes between the two processes. The results showed that the drilling force and torque for RUM were reduced by 23% and 47.6%, respectively of those for CD. In addition, the reduction in drilling force and torque decreased gradually with increasing spindle speed, while they changed slightly with increasing feed rate. Under identical conditions, RUM gave better holes exit than CD. Moreover, because of the lower lamellar brittle fracture and pit originating from carbon fibers fracture, the roughness of surface of drilled holes obtained with RUM was lower than CD and the maximum reduction was 23%.