铝硅酸盐聚合物转化法制备SiCf/榴石复合材料断裂与氧化损伤机制

Ceramics derived from geopolymer possess many prominent properties of heat and corrossion resistance, forming complex-shaped components, low price and environmentally friendly nature, etc. Meanwhile, ceramics based composites with high strength and toughness can be obtained by the incorporation of fibers, which have wide potential applications in the area of aeronautics and astronautics, metallurgy, chemical engineering, and national defence, etc. However,there are only limited investigations on the ceramic based composites derived from geopolymer till now, and little work has been conducted on the high temperature failure mechanism of this kind of composites. Our preliminary investigations have proved that after proper heat treatment at certain high-temperature range, carbon fiber reinforced geopolymer composite can be directly converted into carbon fiber reinforced leucite composite, and room and high temperature mechanical properties can be enhanced greatly. However, once it is exposed to an elevated temperature for longer duration or at a higher temperature such as above 1200℃, the Cf/Leucite composites suffer from the problems of fiber oxidation and interface reaction, which are detrimental to the performance of the composites. In this project, SiC fiber will be adopted to substitute the carbon fiber, in order to improve the interface compatibility between fiber and leucite matrix and to enhance the high-temperature oxidation resistance of the composites. Microstructure, mechanical properties and fracture mechanism will be investigated during the post-heat treatment and sevice temperature. The oxidation kinetics and anti-oxidant mechanism of the composites will be systematically investigated. The research can achieve optimized property design of the SiC fiber reinforced leucite composites and reveal the high-temperature damage mechanisms of this kind of composite. Meanwhile, the relevant results will provide theoretical and technical supports for the optimization of SiCf/leucite composites and their engineering applications targeted for high-temperature heat-resistant components and will reveal their failure mechanisms at elevated temperature.

铝硅酸盐聚合物转化制备陶瓷材料具有耐热、耐腐蚀、可成型复杂形状构件、成本低、环境友好等优点，通过纤维强韧化可获得强度与韧性大幅度提高的陶瓷基复合材料，在航空航天、冶金、化工和国防等领域具有重要潜在应用。国内外在采用该技术制备纤维强韧陶瓷基复合材料及其高温损伤机制的研究仍很少。申请人前期工作表明，Cf/硅酸盐聚合物复合材料经适当高温处理后形成的Cf/榴石陶瓷基复合材料，表现出优异室温和高温力学性能，但高温长时间服役存在Cf氧化及界面反应导致性能恶化。若以SiCf代替Cf，不仅抗氧化性会大为改善，界面化学稳定性也可望迎刃而解。本申请拟研究复合材料在后续处理与服役环境下界面及基体的组织结构、力学性能及其断裂行为的演化规律，探讨其氧化动力学与抗氧化机理。该研究对进一步优化该复合材料体系，揭示其高温损伤机制，具有重要学术价值，也会为其在高温防热、高温构件等领域的工程应用提供理论指导与技术支持。

无机聚合物转化制备陶瓷材料具有耐热、耐腐蚀、可成型复杂形状构件、成本低、环境友好等优点，通过纤维强韧化可获得强度与韧性大幅度提高的陶瓷基复合材料。本项目系统研究了无机聚合物的聚合机理和陶瓷化机制、复合材料的力学性能和损伤机制等。研究结果表明，随着聚合时间的延长，碱性水溶液环境促使铝原子由初始的5配位和6配位完全转变为4配位、硅原子外部结合铝原子数目逐渐增多其化学环境由初始的Q4（0Al）完全转变为Q4（2Al），从而使无机聚合物的聚合度逐渐增加，宏观表现为显微结构更加致密；此外Li+的引入可以加速聚合速率，但是并不会改变最终聚合产物类型。随着处理温度升高，无机聚合物逐渐转变为铯榴石陶瓷，其热演化过程可分为结构弹性、脱水、脱羟基和烧结致密化四个阶段，其烧结机制为粘性流动占主导地位的液相烧结；而高温下白榴石生成机制为三维均匀析晶；锂离子的引入可以降低其烧结温度，并且其陶瓷化产物呈线性下降趋势。短碳化硅纤维的引入可显著改善无机聚合物的力学性能并提高其服役可靠性，当短碳化硅纤维长度为5mm时，复合材料的弯曲强度比基体提高5.5倍，并表现为非灾难性断裂特征，原位断裂分析表明复合材料的强韧化机制主要为微裂纹增韧、纤维断裂和拔出等机制。连续碳化硅纤维对无机聚合物的强韧化作用更为显著，尤其是当纤维含量为20vol.%时，其复合材料在x方向上的抗弯强度、弹性模量、断裂韧性和断裂功相比基体材料分别提高了14.4倍、3.4倍、15.2倍和81.5倍。不同纤维含量的复合材料x方向的抗弯强度均比z方向高，然而其断裂功则相反。复合材料在x方向上断裂机制是抗弯剪切破坏，而在z方向上是层间剪切破坏。复合材料的高温力学性能随测试温度的升高而逐渐增大。在1200℃时其高温弯曲强度、高温断裂功相比于室温性能，分别提高了171.0%和325.6%。而且，经高温测试后的室温硬度随温度升高而增大。然而，SiCf/KGP复合材料的高温力学性能随测试温度的升高而逐渐减小。在900℃时复合材料开始发生脆性断裂。在1100℃时其弯曲强度达到110.1MPa，其强度保留率为69.3%。复合材料性能下降的原因主要是纤维与基体的热失配以及界面反应。研究结果表明，无机聚合物为制备高性能陶瓷基复合材料提供了一条新途径，在，在航空航天、冶金、化工和国防等领域具有重要潜在应用。