电耦合CVI致密C/C复合材料的成形工艺及机理研究

Carbon/carbon composites have been widely used in aerospace industry due to their excellent performance at ultra-high temperatures as structural and functional materials. The development of C/C has great effects on the performance of thermal protection systems (TPS) of hypersonic vehicles. However, the manufacture of C/C composites needs a long period and high cost, which always restricts their applications. Thus it is of great importance for the generalization of C/C composites to develop a novel manufacturing technique with a short fabrication period and a low cost. A rapid chemical vapor infiltration (CVI) technique, also namely electric coupling CVI, has been invented by the research team of the applicant for the preparation of C/C composites in 1999. Based on our previous research results of this invention, researches on the electric coupling CVI technique will be carried out under this study to achieve the short-period and low-cost fabrication of high-performance C/C. Through the investigations on the densification process, structural evolution, properties and controllable preparation of C/C composites in this work, the following research objectives can be achieved. The methods for the short-period and low-cost fabrication of C/C composites will be established. The rapid deposition and growth mechanisms of pyrolytic carbon (PyC) during the electric coupling CVI process will be clarified. The evolution rules of the PyC microstructure and material properties will be revealed in different electromagnetic fields, temperature fields and gas flow fields. The manufacturing parameters of the controllable preparation of C/C composites with different carbon fiber preforms by electric coupling CVI process will be obtained. These research results will generalize the application of C/C composites in aerospace industry and promote the manufacturing progress of the relative models.

C/C复合材料是一种性能独特的超高温结构-功能复合材料，在航天航空等多个领域具有广泛应用，已成为影响高超声速飞行器热防护系统性能的关键材料。然而，C/C复合材料制备周期长、制作成本高仍是制约其广泛应用的主要原因，开发一种低成本、高效率的高性能C/C复合材料制备技术已成为亟待解决的“瓶颈”问题。申请人所在课题组于1999年发明了C/C复合材料的快速CVI制备技术，即电耦合CVI。本项目拟在此基础上，通过对电耦合CVI制备C/C复合材料的沉积机理、结构演变、材料性能及可控制备研究，建立高性能C/C的低成本短周期的制备方法。同时，阐明电耦合CVI中热解碳的快速沉积机理及形成机制；揭示不同工艺条件下热解碳精细结构和材料性能的演变规律；获得不同预制体结构电耦合CVI工艺的可控制备参数。研究成果将有助于进一步开拓C/C复合材料在航空航天领域的应用，推动相关型号研制进度。

本项目针对我国高超声速飞行器热防护系统对低成本短周期高性能 C/C 复合材料的迫切应用需求，以电耦合CVI制备C/C复合材料为研究对象，采用实验和数值模拟技术相结合的方法，开展沉积机理、结构演变、材料性能及可控制备研究。研究发现，电磁场作用下，不对称的碳自由基电荷中心将出现固有电偶极矩，可使自由基在通电纤维周围附近做向加速运动，C3H7、C2H5、C2H4、C2H3等因具有更好的电磁场加速能力可能为成碳反应的占优基团。同时，在碳纤维表面引入电流可以大幅度降低碳氢自由基的吸附-脱氢势垒，加速热解碳沉积。850℃下电耦合CVI热解碳沉积速率可达22.7nm/s，较传统工艺高出1到3个数量级。同时热解碳沉积表观活化能较低，仅为57.9 kJ/mol。C/C复合材料致密化过程可分为低速生长期和高速生长期，研究了不同厚度（10-60mm）预制体沉积带推移规律，获得了快速沉积向慢速致密化过渡的节点，通过升高温度，可有效提高致密化效率。采用优化后工艺可在20小时、33小时和52小时内获得10mm厚、密度1.78g/cm3，30mm厚、密度1.71g/cm3和60mm厚、密度1.6g/cm3的C/C复合材料，弯曲强度分别为201MPa、177MPa、142MPa。基于电耦合CVI工艺特点，结合树脂浸渍裂解实现大厚度（20mm~60mm）、高密度（1.85~1.9g/cm3）C/C复合材料的高效制备，成品件制备周期在2-4个月。基于本项目研究成果，开发出多种基于电耦合CVI技术制备的高性能C/C 和C/陶复合材料构件，形成了系列大尺寸构件、异型构件的研制与成形能力，为航天单位多个型号提供支撑，同时在多个民用领域得到广泛应用并实现批量供货。项目执行期间，发表论文15篇，申请发明专利6项；获辽宁省自然科学二等奖一项（本项目研究内容直接相关）；项目负责人获省部级人才计划2项，省部级奖励4项。