C/SiC复合材料的蠕变强化特性与机理

C/SiC composite is considered as an important structural material in aero engine with high thrust-weight ratio due to its outstanding mechanical properties. The damage and deformation caused by creep can result in failure and fracture of the components made of C/SiC during the services. The creep resistance could be greatly improved by the creep induced strengthening, by which the likehood of matrix cracking is reduced and the the advantage of superior creep resistance of carbon fibers could be taken.Therefore, the proposal will extensively investigate the creep induced strengthening of C/SiC. By utilizing the stress redistribution during the creep, the matrix cracking stress increases. The evolution of microsturcture, interface bonding and stress state will be explored to understand the mechanisms for the creep strengthening. The creep strengthening and its critical controllable factors and underlying mechanisms can be profoundly understood by above works. The research results would supply new knowledges to undertand the creep deformation and corresponding mechanisms of continuous fiber reinforced ceramic matrix composites (CFCC). Furthermore, the works will upgrade our understanding of present composite systems microscopically and macroscopically. Moreover, the results give us an distinct way to optimise the mechanical properties of CFCC by taking advange of each constituent. The related knowledge can provide improtant information in designing, manufacturing and application of the CFCCs and components.

C/SiC 是制造高推重比航空发动机热结构部件的关键材料。蠕变损伤和变形能够导致该材料在使用过程中失效和断裂，因此降低该材料的蠕变变形和避免蠕变损伤成为重要的课题。本项目在基体不发生明显损伤的前提下，基于蠕变过程中应力在C/SiC的基体和纤维间转移和分配，获得蠕变强化特性，显著降低基体开裂等损伤可能性，充分发挥碳纤维的优异蠕变抗力，从而明显降低蠕变变形，显著提高C/SiC的蠕变性能。揭示微观组织、界面和应力状态对蠕变变形和损伤的影响规律，掌握C/SiC的蠕变强化特性及其机制。研究结果从多尺度深入理解C/SiC的蠕变强化特性、关键控制因素及其机制，获得连续纤维增强陶瓷基复合材料(CFCC)的蠕变变形及机理的新知识，具有重要的学术价值。同时，从CFCC变形机制出发，充分发挥组元优势，优化CFCC性能提供了新方法，为CFCC的设计、发展和应用提供了新思路。

针对陶瓷基复合材料在航空航天高温热结构部件中高温长时应用的服役条件，本项目首先利用纤维和基体蠕变性能的差异，开展了C/SiC真空和空气环境下的蠕变试验，掌握其蠕变性能及损伤演化规律。进一步在基体不发生明显损伤的前提下，通过特定条件下的蠕变试验，使基体发生蠕变而纤维几乎不发生蠕变，利用应力再分配，将SiC基体应力转移到碳纤维上，从而提高材料的基体开裂应力，获得蠕变强化。系统研究了SiC陶瓷、高熵碳化物陶瓷的蠕变性能，以揭示基体在陶瓷基复合材料蠕变中的作用；研究了SiC/SiC复合材料的蠕变性能，揭示纤维对陶瓷基复合材料蠕变性能的影响规律；利用FIB、TEM和HRTEM等技术分析了陶瓷基体和纤维在蠕变过程中的微结构演变，从而深入揭示蠕变强化特性的关键影响因素。建立蠕变过程中的应力分配及演化模型，揭示蠕变强化过程中纤维和基体的应力和应变变化规律，从而揭示C/SiC的蠕变强化机制。.1) 通过C/SiC的高温拉伸和压缩蠕变实验，获得C/SiC材料的高温蠕变性能，建立了蠕变应力-温度-寿命的关系。揭示出C/SiC的拉伸蠕变损伤机理包括基体开裂、界面退化、纤维蠕变。压缩损伤机制主要在于基体蠕变。这些损伤机制在不同应力、温度下呈现不同的特点。.2）国产三代SiC/SiC复合材料在1300oC/80MPa下，蠕变断裂时间大于500h，说明了国产材料具备航空发动机应用的基本条件。二代材料最高应用温度为1200oC，三代材料最高应用温度为1350oC。SiC纤维的高温热稳定性是SiC/SiC高温长时应用的基础。.3）应用高温低应力拉伸蠕变试验，保证蠕变加载过程中或蠕变初期在不发生基体开裂等损伤，使SiC基体应力逐渐转移到碳纤维上，提高C/SiC的基体开裂应力。基体残余拉应力变为压应力，获得蠕变强化特性。.4）根据前面蠕变损伤机制和蠕变强化特性，研究了高熵碳化物陶瓷的高温压缩蠕变性能，验证了高熵陶瓷较单一陶瓷具有更优异的抗蠕变性能。进一步使用碳化硅纳米线改性SiC基体和界面，优化材料的微结构，以提高材料的力学性能。