双界面纤维独石ZrB2基超高温陶瓷强韧化机制及抗烧蚀机理研究

The project aims to develop fibrous monolithic ZrB2-based ultrahigh temperature ceramics (UHTCs) with improved strength and toughness, thermal shock resistance and oxidation ablation resistance so as to satisfy the service requirements of materials operated under ultrahigh temperature. Considering the advantages of bionic structures, the concept of bionics is used in structure design of ZrB2-based UHTCs. The preparation and properties of fibrous monolithic ZrB2-based UHTCs with novel double interface structure are investigated. ZrB2 based materials are used as cells of the double interface fibrous monolithic ultrahigh temperature ceramics, while the cell boundaries are composed of internal and external layers. The inner layer is SiCw or Si3N4w toughened materials, and the outer layer is HfB2 or ZrB2 based materials. The fibrous monolithic precursor are formed by wet spinning to precisely control the microstructure of the composites, process parameters are optimized and formation mechanism is revealed. Further studies are carried out on factors affecting mechanical properties under ambient, high and ultrahigh temperatures. Thermal shock failure mechanism, degradation laws of mechanical properties are investigated, oxidation and ablation mechanism and corresponding inhibition methods are also studied. The project are supposed to solve the key problems that peeling off easily and poor ablation resistance when fibrous monolithic composites are used under thermo-mechanical coupling conditions. Additional research will hopefully solve the bottleneck problem that UHTCs are intrinsically brittle, and thus to obtain ultrahigh temperature ceramics with both high toughness and ablation resistance. The achievements are expected to provide theoretical support for improving the reliability and the dimensional ability of UHTCs under service conditions.

本项目基于超高温服役环境对材料强韧化、抗热冲击与抗烧蚀性能的需求，将仿生思想应用于超高温陶瓷材料微观结构设计，开展新型双界面纤维独石ZrB2基超高温陶瓷设计、制备及性能研究。双界面纤维独石超高温陶瓷材料的胞体为ZrB2基材料，胞体界面层由内外两层组成，内层为SiCw、Si3N4w晶须材料，外层为HfB2、ZrB2基材料。通过湿纺法成型纤维独石前驱体，优化工艺参数，揭示形成机理，实现对材料微结构的精确控制；研究材料的室温、高温力学性能主控因素和增韧机理；研究热冲击损伤失效机制与力学性能退化规律，揭示抗氧化烧蚀机理及抑制途径。本项目将解决传统纤维独石复合材料热力耦合环境下容易剥落，抗烧蚀性能差等关键难题。有望突破超高温陶瓷材料的本征脆性这一瓶颈问题，从而实现超高温陶瓷材料的复合强韧化与抗烧蚀性能的协同与匹配，为提高超高温陶瓷材料在服役环境下的可靠性和维形能力提供理论支撑。

针对航空航天超高温服役环境对材料强韧化、抗热冲击与抗烧蚀性能的需求，本项目将仿生思想应用于超高温陶瓷材料微观结构设计，开展新型双界面纤维独石ZrB2基超高温陶瓷设计、制备及性能研究。研究了湿纺法成型纤维独石前驱体的控制因素和形成机理，进而实现了纤维独石前驱体形貌的可控；研究了浸渍料浆粘结剂、分散剂、固液比、溶剂等对双界面层厚度的影响，探明了纤维独石前驱体和内外界面层结合机制；研究了干燥、脱脂、热压烧结等制备参数组合，建立了双界面纤维独石ZrB2基超高温陶瓷致密化的控制策略；研究了材料室温、高温断裂行为，揭示了双界面纤维独石ZrB2基超高温陶瓷裂纹扩展与能量消耗机制；研究了双界面纤维独石ZrB2基超高温陶瓷的抗热冲击性能，分析热冲击载荷下材料组织结构、裂纹成核及扩展规律，弄清了材料热冲击损伤失效机制及抑制途径；研究了SiCw、BN作为胞体内界面层对双界面纤维独石ZrB2基超高温陶瓷的抗烧蚀性能影响，明确了烧蚀过程中的材料的导热率和发射率是影响表面温度响应的主要因素，弄清了材料氧化层的演变规律，烧蚀机制及抑制方法。通过优化设计，获得了胞体为ZrB2基材料，胞体内界面层为SiCw晶须材料，胞体外界面层为ZrB2基材料的双界面纤维独石超高温陶瓷材料，改变弱质胞体界面层形成的贯通三维网络路径，在热流密度为9.34MW/m2的等离子体火焰温度3000℃下300s长时间烧蚀测试，线性烧蚀率和质量烧蚀率分别为-0.3µm∙s-1和-0.11mg∙s-1，试样保持完整，显示出非烧蚀特性。实现了超高温陶瓷复合强韧化与抗烧蚀性能的协同提高，为提高超高温陶瓷材料在服役环境下的可靠性和维形能力提供理论支撑。