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。     

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。     

预制体孔隙结构对炭/炭复合材料ICVI制备工艺的影响

研究了预制体孔隙结构对ICVI工艺致密化过程及基体热解炭微观结构的影响。结果表明：2D针刺炭毡致密化速度高于炭布叠层预制体，1K炭布叠层预制体的致密化速度高于3K炭布叠层；在致密化过程中，热解炭均匀沉积在纤维表面，预制体AS／VR比值变化是导致热解炭微观结构发生改变的根本原因。     

甲烷CVI工艺致密不同尺寸炭/炭复合材料实验与数值模拟研究

在温度为1 348 K,压强15 kPa和停留时间1.0 s下,以甲烷为前驱体对两种不同厚度(16 mm和26 mm)2D炭纤维布预制体进行CVI热解炭致密.经120 h致密化后,将制备得到的炭/炭复合材料进行均匀切分,并测量样品的密度分布.实验结果表明,对于不同厚度的预制体,致密化后在气体流动的外侧密度都偏高,且样品...     

热梯度CVI制备炭/炭复合材料及其研究进展

按预制件内部的温度分布不同，可以认为，均热法及热梯度法是化学气相沉积制备炭／炭复合材料的两种基本工艺。对于圆筒或圆盘形工件，热梯度CVI具有增密快，炭的有效利用率高，可实现工业规模化生产的优点，是一种很有前景的CVI工艺。本文介绍了热梯度CVI制备炭／炭复合材料的工艺原理、工艺特点及其最新研究进展。     

工艺参数对炭/炭复合材料针刺预制体力学性能的影响

研究了不同的工艺参数对炭／炭复合材料针刺预制体力学性能的影响，结果表明，针刺密度、针刺深度等工艺参数对预制体的X-Y向拉伸强度，Z向拉伸强度，剥离强度均有明显的影响。     

炭／炭U型加热器的制备与性能

研究了炭布与薄网胎交替叠层针刺制成准三向结构U型加热体预制体,经糠酮树脂浸渍／炭化致密工艺,并通过真空高温处理制备了炭／炭复合材料U型加热器。结果表明,其弯曲强度为122MPa,压缩强度182MPa,层间剪切强度为14．9MPa。其电阻值可达到0．10～0．21Ω。在多晶硅氢化炉中应用寿命达到6个月～9个月,凸显出高电阻值和长使用寿命的两大特色。     

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...     

炭/炭复合材料的热物理性能

综述了炭／炭复合材料的热物理性能及其影响因素。炭／炭复合材料热导率的大小由炭纤维的类型、取向、体积分数以及基体的结构类型决定，热处理工艺也对它有很大的影响。炭／炭复合材料的热导率随温度升高一般先升高后降低。炭／炭复合材料在低温时具有负热膨胀系数，影响其这一性能的因素除了坯体结构和基体     

炭纳米纤维添加剂对炭/炭复合材料力学性能影响

采用等温CVI工艺制备出5种不同炭纳米纤维含量（质量分数分别为0，5％，10％，15％和20％）的炭／炭复合材料。发现添加炭纳米纤维的炭／炭复合材料具有很高的力学性能，在加入炭纳米纤维为5％时，相对于没有添加炭纳米纤维的炭／炭复合材料，弯曲强度增大了76．3％，弹性模量增大了55．5％，但添加量增大到20％时，强度和模量都逐渐降低。     

致密工艺对C/C复合材料摩擦性能的影响

采用针刺全炭纤维网胎无纬布整体结构预制体为骨架，经化学气相沉积（CVD）、树脂浸溃（RD固化致密及炭化、石墨化制得C／C复合材料。研究了粗糙层（RL）和树脂炭（RC）对摩擦性能的影响。结果表明，RL结构的C／C复合材料的摩擦性能较好，稳定性较高，是用作飞机刹车材料的前提；采用CVD＋RI制备且石墨化后的C／C复合材料具有优良的摩擦磨损特性；CVD试样的密度较低时，摩擦系数较高，但磨损较大，较难形成完整的摩擦膜。     

轴棒法C／C复合材料微观结构及性能分析

采用轴棒法4D预制体、煤沥青为前驱体,经过常压、高压相结合的液相浸渍一炭化的致密工艺,制备出高密度轴棒法C／C复合材料。研究了轴棒法C／C复合材料的微观结构及其对轴向室温、高温（2800℃）拉伸破坏形式的影响。结果表明：轴棒法C／C复合材料轴向增强体采用炭棒,出现了一个特殊的界面,即炭棒与基体的“间隙”,主要原因是炭棒内部结合较强和纤维、基体的热膨胀系数不匹配而引起的;间隙的存在,使得轴棒法C／C复合材料的轴向室温、高温拉伸破坏形式出现较大差异,室温拉伸由于界面结合强度弱而引起的炭棒完整的拔出,未起到纤维应有的增强作用;高温拉伸却由于受热膨胀,间隙愈合,界面结合变强,试样从有效部位断裂,纤维增强作用明显提高。     

酚醛炭基C／C复合滑板材料的催化石墨化及其性能研究

通过溶剂分散法在酚醛树脂浸渍剂中引入催化剂,采用多次液相浸渍-炭化增密和催化石墨化处理的方法,制备出密度为1．60g·cm^-3左右、石墨化度大于77％的酚醛炭基C／C复合材料。对比考察了催化剂的引入和催化剂种类对酚醛炭基C／C复合材料石墨化度、电阻率、抗折强度和摩擦磨损性能的影响,探讨了酚醛炭基C／C复合材料用作受电弓滑板材料的可能性。结果表明：硼酸或二茂铁等催化剂的引入可显著提高酚醛炭基C／C复合材料的石墨化度,降低其电阻率和摩擦系数,改善其弯曲断裂韧性;添加硼酸催化剂的酚醛炭基C／C复合材料的导电性、抗折强度和摩擦磨损性能明显优于德国纯炭整体滑板材料,可望用作高速电力机车的受电弓滑板材料。     

炭/炭复合材料在半导体制造行业的应用

综述了传统炭/炭复合材料和膨胀石墨基低密度炭/炭复合材料在半导体制造业直拉(CZ)法单晶硅炉中的应用。指出了在CZ单晶炉内炭/炭复合材料比石墨材料热场零部件的优势所在,并认为随着硅单晶直径的增大,炭/炭复合材料取代石墨材料将成为硅晶体生长炉热场系统的首选材料。     

高温热处理对C/C多孔体显微结构的影响

以三维针刺碳毡作为预制体,先采用树脂单向加压浸渍结合热压固化制备了CFRP复合材料,然后通过树脂热解碳化制备出C/C多孔体。文章重点研究了高温热处理对C/C多孔体显微结构的影响。通过扫描电子显微镜观察了材料的显微结构,使用阿基米德方法测定材料的密度和气孔率,并利用压汞仪分析了材料的孔隙分布,利用X射线衍射分析碳基体的石墨化程度。结果显示,高温热处理后材料的密度降低,孔隙率增大;高温热处理没有改变材料中孔隙的类型,但使材料中三类孔隙尺寸均增大;经过高温热处理材料的石墨化度提高,部分块状碳基体转变为片层状石墨碳结构。     

Influence of CLVD thermal gradient on the deposition behavior,microstructure and properties of C/C-ZrC composites

Chemical liquid vapor deposition (CLVD) is a rapid preparation method, but it is rarely involved in fabrication of C/C-UHTCs composites and its technology parameters are hardly discussed. In the present study, C/C-ZrC samples were prepared by CLVD process, and the effects of thermal gradient on the deposition behavior, microstructure and properties were investigated. Results exhibited the density, ZrC content and uniformity of the composites increased as the thermal gradient decreased from 30.4 to 9.8?°C/mm, indicating the deposition behavior was improved gradually. When the thermal gradient was 30.4?°C/mm, the deposition behavior of the specimen was poor, which resulted in the high porosity, small numbers of ZrC blocks and uneven distribution. Therefore, the specimen had a low flexural strength with brittle fracture and poor ablation resistance. As the thermal gradient decrease to 9.8?°C/mm, there was an excellent deposition in the composites, and the composites possessed large amounts of ZrC particles and their dispersion were improved remarkably. In this case, the composites displayed a non-brittle fracture with high strength, and the linear and mass ablation rates were reduced, which indicated an improvement of anti-ablation property. Nevertheless, the deposition was deteriorated evidently when the thermal gradient reached to 0?°C/mm. The density, ZrC content and uniformity of the sample became poor, leading to the decline of mechanical property and ablation resistance.     

Evaluation of the moulding process for production of short-fibre-reinforced C/C-SiC composites

For the production of C/C-SiC brake discs via the liquid silicon infiltration method (LSI), the hot pressing process is the state of art technique for the moulding of the CFRP composites. This technique consists of several manual steps which increase production cost. The overall cost can be reduced by implementing injection moulding process.In this paper the influence of the moulding process (hot pressing, injection moulding) on the properties of semi-finished and final products during the production of short-fibre-reinforced C/C-SiC composites by means of the LSI process are examined. The starting polymer is chemically characterised. Carbon-fibre-reinforced plastic (CFRP) composites are fabricated by hot pressing, as well as injection moulding process. The CFRP composites are converted into porous C/C composites by pyrolysis. Liquid silicon is infiltrated to form dense C/C-SiC composites, which are further investigated during the course of this paper. Significant differences in properties of the composites are discussed.     

Effects of initial density during laser machining assisted CVI process and its influence on strength of C/SiC composites

Novel laser-assisted chemical vapor infiltration (LA-CVI) technique has been used to improve the density and strength of carbon fiber reinforced SiC composites (C/SiC). Initial density of C/SiC before laser machining played an important role in determining the final density and strength of composites. Results show that final density and bending strength of lower initial density composites were better than that of higher initial density samples after LA-CVI process, while the porosity exhibited opposite behavior. Micro-CT and COMSEL simulation results verify that after LA-CVI process, dense band width of C/SiC with initial density of 1.5 g/cm³ was twice as that of C/SiC with initial density of 1.8 g/cm³. This led to crack propagation bypassing the micro-hole. In conclusion, low initial density when laser machining was carried out resulted in better properties of final composites.     

Construction of sandwich-structured C/C-SiC and C/C-SiC-ZrC composites with good mechanical and anti-ablation properties

Four kinds of sandwich-structured C/C-SiC and C/C-SiC-ZrC composites with or without a SiC interphase deposited by isothermal chemical vapor infiltration (ICVI), were designed and fabricated by a joint process of electromagnetic coupling chemical vapor infiltration (ECVI) and precursor infiltration and pyrolysis (PIP). The fabricated composites are macroscopically nonhomogeneous materials with low density, high strength and low ablation rate. The interphase and matrix constituents had remarkable effects on the mechanical and ablation properties of these composites. The C/C-SiC composites with an ICVI-SiC interphase exhibited the highest flexural strength of 306.5 MPa. While the C/C-SiC-ZrC composites with the interphase showed the best anti-ablation performance with low linear and mass ablation rates of 0.37 μm/s and 0.04 mg/cm²·s, respectively, after the ablation for 500 s under an oxyacetylene flame test at around 2000 °C.