基于微裂纹分形特征的超高温陶瓷热冲击性能表征方法研究

The hypersonic aircraft with long period and high Mach number flight will suffer severe aerodynamic heating, which requires excellent performances for thermal protection structures. Ultra-high Temperature Ceramics (UHTCs) have been studied in recent decades for manufacturing critical thermal protection structures to solve this problem. Under thermal shock conditions, sharp decrease of UHTCs strength may seriously affect the reliability of thermal protection structures. According to this problem, our project will study the propagation behavior of microcracks under thermal shocks, which may lead to catastrophic destruction of UHTCs. Firstly, the typical microstructure parameters of ZrB2 based UHTCs will be studied, and their influence on fractal dimensions of microcracks will be investigated. Secondly, characterization methods will be proposed for describing the propagation patterns of indentation-induced microcracks. Furthermore, the correlation model will be established between the fractal dimension of microcracks and the stress intensity factor in crack tip under thermal shocks. Then, we attempt to understand how UHTCs microstructures affect their thermal shock properties. This project will provide novel methods for improving UHTCs thermal shock resistance, which has significance for further application of UHTCs on thermal protection structures.

由于高超声速飞行器高马赫数及长时间的气动加热恶劣服役环境，用于制造关键热防护结构的超高温陶瓷（Ultra-high Temperature Ceramics，UHTCs）备受国内外关注。UHTCs强度在热冲击条件下迅速衰减会严重影响热防护结构的可靠性。本课题针对热冲击作用下微裂纹扩展导致UHTCs灾难性破坏的问题，重点研究ZrB2基UHTCs典型微结构参数对微裂纹分形维数的影响规律，提出压痕诱发微裂纹扩展形态表征方法，建立微裂纹分形维数与热冲击作用下裂纹尖端应力强度因子的关联性模型，获得UHTCs微结构对热冲击性能的影响规律。本课题的研究将为提高UHTCs的抗热冲击性能提供新的思路，对推动UHTCs在热防护结构上的实际应用具有重要的理论意义。

由于高超声速飞行器高马赫数及长时间的气动加热恶劣服役环境，用于制造关键热防护结构的超高温陶瓷（Ultra-high Temperature Ceramics，UHTCs）备受国内外关注。UHTCs强度在热冲击条件下迅速衰减会严重影响热防护结构的可靠性。本课题针对热冲击作用下微裂纹扩展导致UHTCs灾难性破坏的问题，重点研究ZrB2基UHTCs典型微结构参数对微裂纹分形维数的影响规律，提出压痕诱发微裂纹扩展形态表征方法，建立微裂纹分形维数与热冲击作用下裂纹尖端应力强度因子的关联性模型，获得UHTCs微结构对热冲击性能的影响规律。应用放电等离子烧结技术，制备了ZrB2-20vol.%SiC，ZrB2-20vol.%SiC-1wt.%BNNP和ZrB2-20vol.%SiC-3wt.%BNNP三种UHTCs，对理论模型进行了验证。本课题的研究将为提高UHTCs的抗热冲击性能提供新的思路，对推动UHTCs在热防护结构上的实际应用具有重要的理论意义