原位生成ZrB2增强SiBCN陶瓷在热震及烧蚀下的损伤机制研究

Because of their excellent stability, high temperature creep resistance and oxidation resistance performance, SiBCN ceramics have a broad application prospect in the field of aerospace materials. However, the high temperature performance of ceramics are still under 1800℃. Ultra high temperature ceramic ZrB2 has a lot of properties such as good ablation behavior and chemical stability. In this project, a sol-gel method is proposed to introduce ZrB2 to SiBCN matrix, and then through the spark plasma sintering process to prepare high performance ZrB2/SiBCN ceramics. Complementary the advantages of ZrB2 and SiBCN ceramics that could improve the sintering properties and high temperature erosion resistance, etc. This work will investigate the influence of sol-gel introduced ZrB2 on mechanical and thermal properties as well as the strengthening and toughening mechanisms for the ZrB2/SiBCN ceramics. The influence of ZrB2 phase on thermal shock behavior together with ablation performance will be considered. Besides, the synergistic of thermal shock resistance and ablation resistance mechanisms of sol-gel introduced ZrB2 together with SiBCN will also be discussed. All the above works will provide theoretical and technical supports for processing of high performance SiBCN ceramics, which have academic and engineering application value.

SiBCN陶瓷因其优异的组织稳定性，抗高温蠕变和抗氧化等性能在航空航天领域有着广泛的应用前景。但其长时间使用温度仍不能超过1800℃。本项目拟采用溶胶凝胶法引入具有优异的耐烧蚀及化学稳定性的超高温第二相ZrB2至SiBCN基体，通过放电等离子烧结技术制备出致密的ZrB2/SiBCN复相陶瓷，将ZrB2与SiBCN陶瓷的优势互补，解决超高温第二相ZrB2难烧结以及提高SiBCN复相陶瓷高温抗烧蚀性能等问题。项目首先研究通过Sol-gel法引入ZrB2对SiBCN基体的力、热等性能的影响，分析并探讨ZrB2/SiBCN复相陶瓷的强韧化机理；通过热震与烧蚀实验评价ZrB2对SiBCN陶瓷损伤行为的影响；阐明第二相ZrB2及SiBCN陶瓷的协同抗热震及耐烧蚀机理，揭示在热震及烧蚀条件下的损伤机制。研究结果可为制备优异SiBCN陶瓷提供理论与实验指导，具有学术及工程应用价值。

课题针对SiBCN陶瓷长期在高温条件下服役问题，通过溶胶凝胶法引入颗粒细小的ZrB2的前驱体制备出ZrB2/SiBCN复相陶瓷。结果表明：ZrB2的引入能够有效促进复相陶瓷的致密化，添加ZrB2含量为15 wt%至SiBCN陶瓷的致密度可达到98 %。通过添加第二相后，两种体系复相陶瓷的致密度及力学性能与SiBCN基体相比均有明显提高。复相陶瓷的力学性能随着ZrB2的含量增加而增强，ZrB2含量为20 %时其力学性能最优异。ZrB2的引入使得裂纹弯曲扩展，断裂方式主要为穿晶断裂。片层状的BN(C)相的拔出在一定程度上能够提高复相陶瓷的断裂韧性。复相陶瓷氧化性能的测试结果表明，随着氧化温度的提高，SiC氧化后生成的非晶态SiO2能够起到填充孔隙和保护陶瓷不被进一步氧化的作用。复相陶瓷的氧化机理为反应和扩散的混合控制。抗热震及耐烧蚀性能测试表明：随着温度的升高，复相陶瓷的热扩散系数降低，热膨胀系数升高，热震残余强度也呈现出下降的趋势。材料表面的氧化及陶瓷内部的热膨胀系数不匹配是导致断裂的主要原因。引入ZrB2第二相至SiBCN基体中后，复相陶瓷的耐烧蚀性能明显提高。复相陶瓷的主要烧蚀机理为机械剥蚀、高温气流冲刷及热氧化烧蚀等。引入Cf后，复相陶瓷的热扩散系数增大，热膨胀系数减小，抗热震性能明显提高。