针刺成型C／C预制体的研究进展

预制体作为C／C复合材料的增强结构,它的发展必定会推动C／C复合材料应用于更广闾的领域。文章综述了针刺成型C／C预制体技术在国内外研究进展,并概述了影响针刺C／C预制体性能的主要因素,包括炭布、网胎以及针刺工艺参数等,并对我国针刺技术的发展提出了一些建议。     

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。     

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。     

轴棒法C／C复合材料室温及高温拉伸性能研究

研究了轴棒法C／C复合材料在室温及高温下的轴向拉伸性能,并用扫描电镜观察了高温拉伸试样的断口形貌。结果表明,轴棒法C／C复合材料在室温及高温下的断裂模式不同,且高温下的拉伸强度高于室温下的拉伸强度;以常压炭化结束的C／C复合材料开孔率变大,室温及高温下的拉伸强度小于以高压炭化结束的C／C复合材料。     

针刺炭纤维预制体结构单元对C/C复合材料性能的影响

采用6K炭纤维无纬布/网胎交替叠层及12K炭纤维无纬布/网胎交替叠层,在针刺工艺,致密化、热处理工艺完全相同的情况下,制备了密度为1.8g/cm3的热解炭/树脂炭双元基体的两种C/C复合材料产品,考察了针刺预制体结构单元对C/C复合材料性能的影响.结果表明,两种C/C复合材料的热学（垂直方向导热系数）、电学性能及石墨化度基本相当;而针刺6K炭纤维无纬布/网胎预制体C/C复合材料的拉伸、弯曲、压缩、层间剪切强度分别为127MPa,189MPa,263MPa,24.6MPa;其平行方向导热系数为54.6W/m＆#183;K,比常规针刺12K炭纤维无纬布/网胎预制体C/C复合材料相应提高了38％,32.2％,32.8％,38.9％,21％,彰显了细化针刺预制体结构单元对C/C复合材料力学性能的显著影响.     

C／C镜筒复合材料的性能研究

镜筒是高分辨率光学望远镜中的重要零件,其选材和加工质量的好坏及刚度直接决定着最终产品的性能。本试验研究了所研制C／C镜筒复合材料的力学、热学性能,分析了体积密度、炭纤维角度变化以及最终工艺状态对c／c复合材料热膨胀系数的影响。研制的C／C复合材料试验件环向拉伸强度≥160MPa,-40E～60℃线膨胀系数仅为-0．09×10^-6 ／K,在满足各项性能指标要求的基础上,成功通过正弦、脉冲振动、动力冲击、真空出气性、光反射等一系列试验考核。     

C/C复合材料用多自由度异形针刺头装置

C/C复合材料相比传统石墨材料具有更优异的保温性能、更高的强度、更好的韧性,且不易破碎,可有效降低生产能耗、提升设备使用寿命,从而降低整个生产的成本。在编织C/C复合材料坯体时,因坯体形状、尺寸不同,现有针刺设备满足不了生产需求,为满足C/C复合材料坯体生产要求,提出了一种多自由度异形针刺头装置,该装置和现有设备同时使用,可满足不同形状、不同尺寸的编织要求,操作简单方便。     

化学气相沉积致密针刺C/C复合材料的结构及力学性能研究

以T300炭纤维无纬布、网胎为原材料,层叠针刺成型炭纤维预制体,并采用化学气相沉积工艺对预制体进行致密,制成密度为1.55 g/cm3的针刺C/C复合材料。对针刺C/C复合材料的微观结构进行了观察分析,并对材料力学性能进行了测试。结果表明:化学气相沉积致密的针刺C/C复合材料呈现出以层间大量垂直纤维束为节点的类钉板状网状结构,这种特殊结构使材料层间结合更好,材料整个结构更加紧密;针刺C/C复合材料内部纤维被沉积形成的热解炭所包裹,热解炭的织构类型为光滑层(SL)和粗糙层(RL)并存;针刺C/C复合材料的各项力学性能均达到了较高水平,并且高温力学性能比常温力学性能有了很大幅度的提高。     

SiC含量对C/C-SiC复合材料弯曲强度及抗氧化性能的影响

选用聚碳硅烷（PCS）为前驱体，对密度分别为1．34g／cm^3，1．52g／cm^3和1．62g／cm^3的针刺炭布C／C材料进行液相致密化处理，制得密度达1．75g／cm^3的C／C-SiC复合材料，并与密度为1．85g／cm^3的同结构高密度C／C材料的弯曲强度和抗氧化性能进行了对比分析。结果表明：密度为1．34g／cm^3的C／C材料经过PCS致密化处理，在保持高密度C／C材料的弯曲强度同时，显著提高了材料的抗氧化性能。     

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。     

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。     

The effect of heat treatment on tensile properties of 2D C/SiC composites

Two-dimensional (2D) carbon fiber reinforced silicon carbide (C/SiC) composites with different initial strength were prepared by chemical vapor infiltration (CVI). After tensile property testing, results exhibited that as the heat-treatment temperature (HTT) increases to 1900°C, the tensile strength and toughness of the low strength specimen (LSS) increased by 110% and 530%, while the high strength specimen (HSS) increased by 5.4% and 550%, respectively. As observed from morphologies, the heat treatment increases the graphitization of the amorphous PyC interphase, which leads to the weakening of interfacial bonding strength (IBS). Meanwhile, the defects arising from heat treatment cause thermal residual stress relaxation. Therefore, the tensile strength and toughness of LSS with relatively high initial IBS increase significantly as HTT increases. For HSS with moderate initial IBS, the heat treatment slightly improves the tensile strength, but significantly improves the toughness. Consequently, the post-heat-treatment tensile properties of 2D C/SiC composites can be regulated by varying HTTs and different initial strength.     

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。     

In situ tensile damage characterization of C/C composites through X-ray computed tomography and digital volume correlation

Carbon fiber reinforced carbon matrix (C/C) composites have been used in aerospace applications due to their excellent performance. Exploring their failure mechanisms is a subject of extensive research. Nowadays, to obtain information about changes in the failure processes, a technology known as in situ X-ray computed tomography is used. In this paper, tensile loads were applied to 3D fine-woven punctured and needle-punched C/C composites perpendicular to the punctured and needle-punched directions. In situ X-ray computed tomography was employed to observe damage development, and digital volume correlation was used to assess the laboratory X-ray computed tomographs to measure local strains. Assimilation of pores is observed in C/C composites, with cracks evolving from original micro-pores. While fine-woven punctured C/C composites present an elegant linear failure, needle-punched C/C composites present a traditional non-linear failure. This difference is due to the different structures of the preforms. Furthermore, the C/C composites are weak at the sites where they are punctured or needle-punched.     

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.     

Effects of precursor concentration on the microstructure and properties of ZrC modified C/C composites prepared by precursor infiltration and pyrolysis

To improve the ablation resistance of C/C composites, ZrC modified composites were fabricated by precursor infiltration and pyrolysis combined with gradient chemical vapor infiltration process. The effects of ZrC precursor concentration on the microstructure, mechanical and ablation properties of the composites were studied. Results showed that with the increase of ZrC precursor concentration, the ZrC content and macroscopic uniformity of the composites increased but with obvious ZrC particle aggregation and the flexural strength decreased gradually. As the concentration of ZrC precursor improved to 60%, the fracture mode of the composites transformed from toughness to brittleness which was mainly attributed to the improved graphitization degree and reaction damage of carbon fiber in the precursor pyrolysis process. However, the ablation resistance was enhanced with the increasing precursor concentration which was resulted from the formation of ZrO₂ in center ablation region and continuous ZrO₂ coating in brim region serving as a barrier to heat and oxygen transfer.     

涂层工艺对C/C复合材料结构和弯曲性能的影响

采用热处理和包埋工艺制备了Ｃ／Ｃ复合材料的ＭｏＳｉ２／ＳｉＣ抗氧化涂层,对组织结构、界面、弯曲断口进行了显微观察,分析了氧化保护涂层及其工艺对其机械性能的影响,结果表明,该工艺在Ｃ／Ｃ复合材料表面生成涂层的同时,使基材内部的界面也被硅化;并且发现,热解炭基体比炭纤维更易与Ｓｉ反应生成ＳｉＣ。Ｃ／Ｃ复合材料经涂层工艺处理后,弯曲强度降低;热处理过程中发生的材料氧化是弯曲强度下降的主要原因