不同预制体结构C/C复合材料的CVI致密化行为

采用化学气相渗透(CVI)工艺分别对整体毡和针刺毡厚壁预制体进行了500 h的致密化,研究了2种预制体的致密化效率、微观结构及密度分布情况。结果表明:预制体结构对C/C复合材料的致密化行为影响较大。致密化前期,整体毡预制体表现出较高的致密化效率,后期效率下降较快,热解炭包裹在纤维之间,材料内部密度分布不均,呈现两边高中间低的现象。针刺预制体在CVI前期致密化效率较低,热解炭主要包裹在纤维束外,致密化后期致密化效率下降较慢,致密后材料内部密度分布均匀。与整体毡预制体相比,针刺预制体的孔隙平直,分布均匀,更有利于碳源气体的深入渗透以获得均匀的密度分布。     

飞机炭刹车盘制备中各工艺参数对其摩擦磨损性能的影响

炭/炭刹车盘的摩擦磨损性能对飞机获得高能量刹车时的高摩擦磨损特性有重要的影响。通过控制炭/炭(carbon/carbon,C/C)复合材料制备过程中各工艺参数可以得到高性能刹车的炭刹车盘。影响C/C复合材料摩擦性能的因素有很多,综述了国内外研究现状,本文讨论了炭纤维预制体、致密化过程、高温热处理和机械加工对炭刹车盘摩擦磨损性能的影响以及这几个工艺参数的协同作用。     

C/C复合材料CVI致密化过程及影响因素研究进展

综述了C/C复合材料CvI致密化过程中,气相反应、表面反应和扩散共同作用控制热解炭沉积的特点;讨论了沉积温度、气体压力、碳源气体种类、滞留时间、预制体等因素的影响.     

致密化工艺对C/C复合材料性能的影响

以三种致密化工艺对2D炭布针刺预制体进行致密，得到三组C／C复合材料，对其进行力学、热学性能检测及微观结构分析，并用C／C复合材料抗热震指标对三种致密化工艺所制备试样的性能进行综合评价，考察并比较了不同致密化工艺对C／C复合材料性能的影响。结果表明，采用化学气相沉积、沥青高压浸渍炭化及树脂常压炭化工艺所制备的RLS试样具有较好的综合性能。     

一种新型炭／炭复合材料的快速致密化工艺探

通过对化学液气相快速致密化这种新型炭／炭复合材料快速制备工艺的步研究,以PAN基炭毡为预制体,低分子液态烃为碳源前驱体,采用电磁感应加热,在900℃－1100℃温度内,3小时制备了密度为1．78g/cm^3的炭／炭复合材料。研究结果表明此工艺较传统工艺的致密化周期缩短了100倍以上,同时指出这种工艺快速致密化预制体的机制是由于预制体内存在较高温度梯度和碳源扩散过程受控于化学反应力学。     

沉积工艺对致密热解炭密度及显微组织的影响

以乙炔、丙烯为碳源气体,采用流化床-化学气相沉积工艺于燃料颗粒表面沉积致密热解炭包覆层,在1 150～1 230℃沉积温度及碳源气体体积分数为7％～21％下开展正交实验,研究沉积温度及碳源气体浓度对致密热解炭密度的影响.采用阿基米德原理测量致密热解炭密度,用场发射扫描电镜观察致密热解炭微观结构.研究结果表明,致密热解炭...     

针刺C/C复合材料拉伸性能和韧性的研究进展

综述了近年来国内外针刺C／C复合材料拉伸性能和韧性研究进展,归纳了影响针刺C／C复合材料拉伸性能和韧性的主要因素,即炭纤维、炭基体、界面和针刺工艺参数等,初步得到了提高材料拉伸性能和韧性的方法：提高针刺C／C材料拉伸性能的方法主要是提高纤维体积分数;提高针刺C／C材料韧性的方法主要是改善致密工艺。在此基础上,对未来的进一步研究进行展望。     

镍催化制备炭/炭复合材料

利用催化化学气相沉积法制备炭／炭复合材料，研究了反应温度、前驱体气体含量、催化剂含量和时间对所制备的炭／炭复合材料密度的影响，采用扫描电镜观察分析了基体碳的形貌。结果表明，利用催化剂镍可制取密度达1．594g／cm^3的炭／炭复合材料，并有晶须状基体碳生成。在各种工艺参数中，对炭／炭复合材料的密度影响最大的是温度和前驱体气体，其次为催化剂含量，最后是时间。     

载气对碳/碳复合材料致密化过程及微观结构的影响

以天然气作为碳源,以H_2和N_2为载气,采用等温化学气相沉积工艺制备碳/碳复合材料。采用偏光显微镜、SEM、万能试验机等表征所制备碳/碳复合材料的微观结构、密度变化和力学性能等。研究了碳源气体与载气比例对碳/碳复合材料致密化速率和热解碳微观结构以及力学性能的影响。结果表明:载气对碳/碳复合材料的致密化速率以及微观结构有重要影响(相对于不添加载气的情况,添加H_2和N_2的混合气体后,碳/碳复合材料的最终密度从1.42g/cm~3提高到1.71g/cm~3,而密度梯度Δρ从0.15g/cm~3降到0.04g/cm~3)。H2对优化气相裂解成分,抑制致密化初期的表面结壳、促进高织构热解碳的形成有显著影响,而N_2则对抑制致密化后期的表面结壳效果显著。     

炭化压力对编织C/C复合材料致密过程及结构的影响

通过浸渍/高压炭化工艺在不同炭化压力下制备了高温煤沥青炭块及沥青基炭/炭（C/C）复合材料,并研究了不同炭化压力环境下对其密度和孔隙的影响.结果表明,随着炭化压力增大,沥青炭体积密度明显增加,孔隙填充效果明显改善;在编织C/C材料的致密过程中,压力越大其孔隙越小,分布越均匀,故产品致密效果越好.     

碳源对碳热法制备LiFePO4/C复合电极材料性能的影响

以廉价的Fe2O3为铁源,(NH4)H2PO4为磷源,Li2CO3为锂源,分别以乙炔黑、葡萄糖、PEG6000为还原剂和碳源,采用碳热还原法制备了LiFePO4/C复合材料。X射线衍射(XRD)分析表明用三种碳源都合成了橄榄石结构的LiFePO4。扫描电子显微镜(SEM)分析显示,以PEG6000为碳源合成的LiFePO4/C复合材料粒径较小,较均匀,且有较好的碳包覆。以充放电曲线、循环性能和交流阻抗等测试研究了材料的电化学性能,结果表明,以PEG6000为碳源合成的材料的电化学性能较好,0.1C、1C下首次放点比容量分别为144.7 mAh/g、132 mAh/g。     

C／C复合材料的工程化致密技术进展

20世纪90年代以来，世界各国均致力于开发C／C复合材料的工程化致密技术，以达到降低成本，拓展民用领域的目的。经过20多年的艰辛攻关，在快速化学气相渗透和新型液相浸渍炭化致密技术方面取得了长足的进步，为拓展C／C复合材料在民用领域的应用，奠定了良好的基础。     

液相气化快速致密化工艺研究

对一种新型快速炭／炭复合材料制备工艺－－液相气化快速致密化工艺进行了初步探索。研究表明，采用该工艺，致密化效率可以得到快速提高，数小时内制得密度达1．7g/cm^3以上的炭／炭复合材料，致密速率 达到37g/h。偏光显微镜观察表明，试样中热解炭具有较高的光学活性；束内小孔隙热解炭，绝大多数为光学各向异性组织，但具体归属粗糙组织（RL）还是光滑组织（SL），很难定论；束间大孔隙内的热解炭具有明显的锥状生长结构，是较典型的RL组织；在偏光显微镜下没有观察到试样中有炭黑出现。     

二维C/C复合材料层叠板制备工艺及其性能的研究

研究通过浸渍—炭化法制备二维C／C复合材料层叠板的工艺参数，分析了不同基体前驱体和增密次数对材料的密度、厚度和收缩率、体积电阻率和层间剪切强度的影响，并用扫描电子显微镜进行断口分析。结果表明：选用残炭率较高的基体前驱体和适当的增密次数是制备低成本二维C／C复合材料层叠板的关键；相同纤维体积的层叠板基体炭含量越高，电阻率越小，导电性能越好；单位体积含有炭纤维越多，纤维受损几率就越大，产生结构缺陷几率越高，导致电阻率增加，导电性能下降；本实验中二维C／C复合材料层叠板制备工艺简单可行，层叠板的密度达到1．40g／cm^3以上，剪切强度为1．5MPa，断口呈脆性断裂特征。     

A Review on Wear and Friction Performance of Carbon–Carbon Composites at High Temperature

Carbon–carbon (C/C) composite is one of the best ceramic matrix composite due to its high mechanical properties and applications at control environments in various sectors. Carbon–carbon composite is made of woven carbon fibers; carbonaceous polymers and hydrocarbons are used as matrix precursors. These composites generally have densities <2.0 g/cm³ even after densification. C/C composites have good frictional properties and thermal conductivity at high temperature. Also C/C composite can be used as brake pads in high‐speed vehicles. In spite of various applications, C/C composites are very much prone to oxidation at high temperature. Therefore, C/C composites must be protected from oxidation for the use at high temperature.     

The film-boiling densification process for C/C composite fabrication: From local scale to overall optimization

The film-boiling densification process is an alternative of chemical vapor infiltration involving a strong thermal gradient. It allows to fabricate composite materials starting from a fibrous preform lying in a boiling hydrocarbon precursor, the cracking of which results in a solid deposit constituting the matrix of the carbon/carbon composite. A modelling approach is presented and validated with respect to experimental data. Then, the sensitivity of the process is studied with respect to various parameters. Optimization guidelines are proposed, in conjunction with a discussion on the densification front that characterizes the process. It is thus possible to evaluate the minimal amount of power required, while maintaining the quality of the produced material, i.e., its bulk density and homogeneity.     

Effects of silanization of C/C composites and grafting of h-BN fillers on the microstructure and interfacial properties of CVI-based C/C-BN composites

A low-density carbon/carbon (C/C) composite/silane coupling agent/hexagonal boron nitride (h-BN) hybrid reinforcement was prepared by grafting polyethyleneimine (PEI)-encapsulated modified h-BN fillers onto a carbon fiber surface using 3-aminopropyltriethoxysilane (APS) as the connection to improve the distribution uniformity of h-BN fillers in quasi-three-dimensional reinforcements and the interfacial properties between the fibers/pyrocarbon (PyC) in the C/C-BN composites obtained after densification by chemical vapor infiltration (CVI). The microstructure and chemical components of the hybrid reinforcement were investigated. The transmission electron microscopy (TEM) sample was prepared using a focused-ion beam (FIB) for the h-BN/PyC interfacial zone. The interlaminar shear strength (ILSS) and impact toughness were analyzed to inspect the composites’ interfacial properties. The results show that APS and h-BN are uniformly grafted on the fiber surface in the chopped fiber web inside the C/C composite without a density gradient, and agglomeration occurred and significantly increasing the fiber surface roughness. The highly ordered h-BN basal plane may affect the order degree of PyC near the h-BN/PyC interface. The addition of h-BN reduces the PyC texture near it, causing the annular cracks to disappear gradually. The lower PyC texture and the rougher fiber surface strengthen the interfacial bond of the fiber/matrix. Consequently, the ILSS strength of the C/C-BN composites first increases and then decreases as the h-BN filler content increases and is always higher than that of the C/C composite, while the addition of h-BN fillers weakens its impact toughness. When the h-BN content in the C/C-BN composite is 10 vol%, the ILSS of the C/C-BN composites was 15.6% higher than that of the C/C composites. However, when the h-BN content is excessive (15 vol%), the densely grafted h-BN will bridge each other, reducing the subsequent CVI densification efficiency to form a loose interface, causing a decrease in the shear strength.     

Factors Affecting the Compaction and Densification Behavior of Ti(C,N)‐Based Cermet Powders

In this study, the effects of the major factors on compaction and densification behavior are investigated for Ti(C, N)‐based cermet powders. The relative density equation for green compact of composite powders is modified to predict the green density of Ti(C, N)‐based cermet powders prepared under different degrees of pressing pressures, and the theoretical values are found to be in good agreement with experimental results. It has been found that the composite powders with micron‐sized particles have a better compatibility than those with nano‐sized particles by analyzing the effects of the particle size and purity on the starting mono‐powders. It has also been found that the volume shrinkage and porosity of the former are lower than that of the latter. In addition, it shows that high oxygen content has a negative impact on both the compatibility of composite powders and the uniformity of pore size distribution of sintered cermets. It has also been discussed in this study how the pressing parameters such as pressing pressure, pressing temperature, and dwell time influence the resulting cermets. The results indicate that a better compatibity is reached at a pressing rate of 100 mm/min or a pressing temperature of 100°C.     

先驱体浸渗裂解法制备C/C-SiC复合材料的烧蚀性能

用先驱体浸渗裂解法制备了碳纤维增强碳(carbon fiber reinforced carbon,C/C)-SiC复合材料,用H2-D2火焰法检测其烧蚀性能.结果表明:C/C-SiC复合材料的烧蚀率随复合材料中的Si含量的增加而呈下降趋势;经过5次浸渍,C/C-SiC复合材料的密度从1.46 g/cm3增加到1.75 g/cm3,Si含量从5.06%增加到13.8%,线烧蚀率和质量烧蚀率分别下降474%和34.5%.密度为1.75g/cm3的C/C-SiC复合材料,其线烧蚀率和质量烧蚀率分别为2.22 μm/s和1.289 mg/s,其线烧蚀率和质量烧蚀率分别为密度1.78 g/cm3的C/C复合材料的21.7%和78.6%.基体中SiC的引入明显提高了C/C复合材料的抗氧化烧蚀性能.