LA-CVI法制备C/SiC复合材料的传质机理与性能强化机制

Chemical vapor infiltration (CVI) method is the main manufacturing technology of C/SiC composite material industrialization which can avoid fiber damage at high temperature. But for thicker section and inner closure parts, the traditional CVI technology can not meet the requirements for the preparation of related components which may cause high deposition density gradient or no deposition. Therefore, this project is put forward to the new ideas which can support and promote the deposition process on thicker section and inner closure parts by machining femtosecond laser holes on the composite material during the deposition process. In order to improve the permeability and density, also strengthen the performance, we investigated the influence of micro channel on the deposition rate, density uniform and properties of the composite materials. Based on the above research results, It also can solve the basic scientific problems such as the diffusion mass transfer mechanism and rules with the deposition holes﹑the opening criterion of deposition process and the microstructure evolution and the strengthening mechanism after opening holes on C/SiC composites which breaks through the thicker sections and closed component by laser assisted chemical vapor infiltration technology (LA-CVI). This project will enrich CVI theory of composites and broaden the theory and method of the ceramic composites by means of controlling the microstructure and properties of C/SiC composite which can promote the further application in aviation spacecraft.

化学气相渗透(CVI) 法可避免高温对纤维造成的损伤，是C/SiC复合材料产业化的主要制造技术。但对于厚壁构件以及封闭构件，目前的CVI技术还存在沉积密度梯度大或沉积死角等问题，不能满足相关构件的制备要求。为此，本项目提出采用飞秒激光在沉积过程中对复合材料开孔，辅助和促进沉积过程，改善厚壁构件以及封闭构件沉积的新思路，研究微孔传质通道对复合材料沉积速率、密度均匀性、性能等的影响规律，以期提高复合材料的渗透率与致密度，调控其强韧化性能。基于以上研究结果，通过解决开孔沉积的扩散传质机理与规律、沉积过程开孔准则以及开孔对C/SiC复合材料的微结构演变和性能强化机制等基础科学问题，突破厚壁构件和封闭构件的高致密度、高强韧化的激光辅助化学气相渗透技术（LA-CVI）。本项目将丰富复合材料化学气相沉积理论，拓展陶瓷基复合材料微结构与性能调控的理论与方法，促进C/SiC复合材料在航空航天器的进一步应用。

本项目以提高C/SiC复合材料的渗透率与强韧化性能为目标，提出了采用飞秒激光辅助化学气相沉积法制备C/SiC复合材料的新思路。首先，全面深入地掌握了飞秒激光加工传质通道时，其加工工艺参数如：扫描方式、加工功率、扫描速度及螺旋线扫描间距对C/SiC复合材料的影响规律，并结合激光作用机理，获取飞秒激光制备传质通道的优化工艺。其次，系统研究了传质通道对复合材料沉积速率、密度均匀性的影响规律，并结合传质模型和相应模拟计算进行验证。结果表明：LA-CVI法致密化效果明显，C/SiC复合材料均具有致密带、致密化涂层与SiC颗粒三大典型固有形貌；复合材料的致密度随着传质通道间距的减小，呈现上升的趋势，致密化相对范围越大；复合材料的致密化范围随着传质通道纵向排数的增多而增大，致密均匀化效果显著；传质通道纵向排布为3排时，复合材料的承载能力与抗弯强度最佳；初始密度为1.5g/cm3的预制体，介入传质通道制备，其复合材料致密化效果的明显高于初始密度为1.8g/cm3的预制体。最后，研究了LA-CVI-C/SiC复合材料的力学性能，较CVI-C/SiC复合材料而言，弯曲强度提高了16.17%；压缩强度提高了13.8%；剪切强度提高了50%，拉伸强度基本不变。结合裂纹扩展失效模式与断面结构，分析了LA-CVI-C/SiC复合材料的力学性能与断裂失效行为，揭示了传质通道结构对C/SiC复合材料均匀性与力学性能调控机制。本项目的研究成果有助于准确理解LA-CVI法制备C/SiC复合材料的致密化机制，为优化设计C/SiC复合材料力学性能提供理论基础和实验依据，有利于促进C/SiC复合材料厚壁件在航空航天领域中的进一步应用。