【作者】 王建方；

【导师】 陈朝辉；

【作者基本信息】 中国人民解放军国防科学技术大学 ， 材料学， 2003， 博士

【摘要】 本文针对先驱体浸渍裂解工艺制备陶瓷基复合材料过程中碳纤维损伤严重的问题，以聚碳硅烷(PCS)制备Cf/SiC复合材料为重点，采用SEM、TEM、IR、XRD、XPS、TG等表征手段，分析了先驱体裂解过程、纤维基体界面和碳纤维损伤过程，系统地研究了原料(碳纤维、先驱体等)和制备工艺条件等在Cf/SiC复合材料制备过程中对碳纤维损伤的影响，建立了碳纤维损伤程度的表征方法和损伤机理模型，制备了纤维表面涂层并利用涂层碳纤维制备了单向Cf/SiC复合材料。 本文首次应用复丝拉伸强度测试来表征PIP工艺中碳纤维的损伤程度，较好地解决了陶瓷基复合材料中碳纤维损伤程度如何表征这一棘手的问题。试验对比的结果表明，碳纤维原丝强度与其标称强度值相差不大，碳纤维强度测试结果的误差范围为12～17％。测试结果可以明显反映出不同工艺对碳纤维损伤的差别，为研究碳纤维在PIP工艺过程中的损伤提供了手段。 探明了PIP工艺制备CMCs过程中碳纤维的损伤形式。研究结果表明，碳纤维的损伤包括了化学损伤、高温损伤和热应力物理损伤。PIP工艺第一周期对碳纤维损伤最大，第一周期中碳纤维的强度损失率远大于后续多个周期浸渍裂解中碳纤维强度损失的总和。碳纤维损伤的主要形式是热应力物理损伤。化学损伤并不是导致碳纤维强度下降的主要因素，其中先驱体化合态的氧并不会对碳纤维产生明显的损伤，纠正了人们长期以来的错误认识。 首次探明了碳纤维热应力物理损伤机制，即碳纤维表面附着的先驱体在高温下无机化形成陶瓷体，同时伴随着大的体积收缩，在碳纤维的牵引下，基体的体积收缩以开裂形式出现，裂纹的取向以垂直于纤维轴向为主，由于碳纤维与基体热膨胀系数失配，致使碳纤维在降温过程中受到复杂热应力，引起碳纤维损伤。由此建立了碳纤维的四种热应力物理损伤模型，即基体体积收缩应力损伤模型、热应力拉伸损伤破坏模型、热应力弯折损伤破坏模型和热应力剪切损伤破坏模型。其影响因素主要为基体裂纹大小、基体硬度、碳纤维表面缺陷、碳纤维模量等。目前，类似的损伤模型尚未见报道。 本文首次较系统地对不同先驱体和不同碳纤维在PIP工艺制备CMCs过程中对碳纤维损伤的影响进行了研究。结果表明，PSO裂解后生成的基体硬度较小且延伸性好，可以缓解基体及界面的应力集中，碳纤维强度保留率较高；PSZ裂解过程中除了体积收缩对碳纤维带来物理损伤外，还与碳纤维发生严重的化学反应，使碳纤维强度大幅下降。低强度碳纤维容易在热应力拉伸或弯折破坏模式下损伤；高模量碳纤维高温损伤小，但国防科学技术大学研究生院学位论文容易以热应力剪切破坏模式下断裂;环氧树脂表面胶刚性较大，氧含量较高，使碳纤维容易受到化学损伤和热应力弯折损伤，均不宜用来制备C灯siC复合材料。高强度、低模量和柔性表面胶的碳纤维可望得到性能较好的C刀SIC复合材料。 采用先驱体转化法制备并研究了碳纤维表面涂层SIC和si一O一C，并利用涂层碳纤维制备了单向Cf/SIC复合材料。结果表明，适当厚度的SIC涂层和si一O一C涂层可以起到缓冲层和阻挡层的作用，减小碳纤维的化学损伤和物理损伤。较厚的涂层将导致碳纤维之间粘连，通过热应力损伤碳纤维。涂层碳纤维所制备的单向C刀siC复合材料力学性能测试结果显示，5%PSO和3%PCS涂层碳纤维所制备的单向C分siC复合材料性能较高，分别为797.4MPa和777.2MPa，其涂层厚度分别为0.135 pm和0.09pm，适合于用来制备Cf/siC复合材料。 本文较系统地研究了浸渍和热处理工艺条件对碳纤维损伤和材料性能的影响，阐明了制备Cf/siC复合材料应当采用的工艺条件，并建立了PIP工艺制备CMCs过程的浸渍模型。研究结果发现，高温加压可以使基体内部裂纹减小或消失，减小了对碳纤维的物理损伤;升温速率的提高不仅通过先驱体快速原位裂解避免了大裂纹的产生，从而减少了对碳纤维的物理损伤，同时通过缩短高温处理阶段时间减少了碳纤维化学损伤。采用快速升温裂解高温加压工艺(1600℃、10MPa)制备得到的C刀siC复合材料性能最优。 浸渍工艺的分析和模拟可以推导出浸渍时间函数为:怜f(基体尺寸，基体孔径大小及分布，先驱体溶液表面张力、接触角及粘度，浸渍压力)。浸渍不完全将导致碳纤维受力情况更加复杂，并导致材料致密化困难。超声在有利于浸渍效果的同时使碳纤维表面缺陷加深，时间一般不应超过10min。更多还原

【Abstract】 Focusing on serious damage of carbon fibers in ceramic matrix composites (CMCs) prepared by precursor infiltration pyrolysis (PIP), and with emphasis on carbon fiber reinforced silicon carbide composites (Cf/SiC) derived from polycarbosilane (PCS), the influences of raw materials (including carbon fibers and precursors, etc.) and preparing conditions on carbon fiber damage during the preparation of Cf/SiC composites were investigated systemically. Pyrolysis process, fiber-matrix interface and carbon fiber damage process were observed by SEM, TEM, IR, XRD, XPS and TQ etc. The characterization method of carbon fiber damage degree was established and the models for carbon fiber damage mechanism were also established. The carbon fiber coatings and unidirectional Cf/SiC composites with coated carbon fibers were prepared and studied.The multifilament tension strength test was firstly applied to characterizing carbon fibers damage degree in CMCs during PIP, which as an intractable problem was resolved successfully. The test results show that the measured strength is similar to marked strength, and with a deviation of 12-17%. The differences of carbon fiber damage caused by different preparing conditions are showed clearly. A good test method is applied for studying carbon fiber damage in PIP process.The mechanism of carbon fiber damage during preparation of CMCs by PIP was clarified firstly. The results show that the damage of carbon fibers includes chemical damage, heat damage and physical damage of thermal stress. The carbon fiber damage mainly occurs in the first cycle of PIP, in which carbon fiber strength lose is greater than the total strength lose in following cycles, and the main form of damage is physical damage of thermal stress. The chemical damage is not the main factor of strength lose. It was first proved that the combined oxygen does not damage carbon fibers obviously, which corrects the long-term misunderstanding about the influence of oxygen on carbon fiber damage.The mechanism of physical damage of carbon fibers was clarified firstly. The precursor which attached on carbon fibers changes to inorganic ceramic under high temperature with large volume shrinkage which appearing at cracks with fiber traction and the cracks are mainly vertical to fiber axis. Because of mismatched coefficients of thermal expansion, carbon fibers suffer multiple thermal stresses and are damaged. The physical damage modelsof carbon fibers are established, which are matrix shrink stress damage model, thermal tension stress damage model, thermal bend stress damage model and thermal shear stress damage model. The influence factors are crack size, matrix hardness, carbon fiber surface defect and carbon fiber modulus. Similar damage models have not been reported before.The influence of different precursors and carbon fibers on carbon fiber damage during preparation of CMCs by PIP was systemically studied firstly. The results show that PSO pyrolysis matrix has low hardness and good extensibility which can relax stress concentration in matrix and interface, and damages carbon fibers slightly. However, PSZ derived matrix damages carbon fibers largely in physical and chemical ways. The carbon fibers with low strength are broken easily according to thermal tension and bend stress damage models, and the carbon fibers with high modulus are broken easily according to thermal shear stress damage model in spite of less damage caused by heat. The carbon fibers with surface glue of epoxy resin are damaged easily in physical and chemical ways because of high oxygen extent and rigidity of epoxy resin. So, the carbon fiber with high strength, low modulus and flexible surface glue is suitable for the preparation Cf/SiC composites with high properties.The Coatings of SiC and Si-O-C were prepared by precursor pyrolysis and studied, and the unidirectional Cf/SiC composites with coated carbon fibers were also prepared and studied. The results show that coatings with suitable thickness can reduce damage degree of carbon fibers as b更多还原