ZrB2-SiC超高温陶瓷复合涂层设计、沉积机制及失效行为研究

Based on the demands of lightweight ultra-high temperature protection system for future hypersonic vehicles, this study aims to prepare ZrB2-SiC coatings on carbon based materials, which can withstand the severe service environment with temperature higher than 1800 ℃. The ZrB2-SiC coated carbon based materials integrate the advantages of ZrB2-SiC ultra-high temperature ceramics and carbon based materials, which have good oxidation and ablation resistance, light weight and good thermal shock resistance. To overcome such weaknesses as low density, poor oxidation and ablation resistance of the ultra-high temperature ceramic coatings prepared by traditional methods, this study will focus on the new technique, new mechanism, structure design and optimization and structure evolution of ultra-high temperature ceramic coatings prepared on carbon based materials. ZrB2 will be introduced using chemical vapor deposition, the growth mechanism and influence factors of ZrB2 coating will be revealed. ZrB2-SiC coating will be prepared by chemical vapor co-deposition, and the co-deposition mechanism will be studied and revealed. The thermal mismatch and thermal stress will be reduced by designing and optimizing composition and structure of multi-layer ZrB2-SiC composite coating. The oxidation and ablation mechanism and failure behavior of the multilayer ZrB2-SiC composite coating will be investigated. This study will provide theoretical and experimental basis for design, performance improvement and safety assessment of ultra-high temperature protection system of our country’s near space hypersonic aircraft.

本项目针对高超声速飞行器对轻质超高温热防护系统的需求，在碳基材料表面开展适用于1800℃以上服役环境的ZrB2-SiC超高温陶瓷涂层研究，充分发挥超高温陶瓷良好的抗氧化烧蚀性能和碳基材料轻质、抗热震性能好的优点。为克服传统工艺获得的超高温陶瓷涂层致密度低、抗氧化烧蚀性能不足的缺点，重点探索碳基材料表面超高温陶瓷涂层化学气相沉积新工艺、新机理、涂层结构优化设计及材料结构演化规律。通过化学气相沉积法引入ZrB2，研究ZrB2涂层的生长机制及影响因素。通过化学气相共沉积方法制备ZrB2-SiC复合涂层，揭示ZrB2-SiC涂层化学气相共沉积机理。设计并优化多层ZrB2-SiC复合陶瓷涂层的组分和结构，改善涂层与基体的热匹配性，研究多层涂层氧化烧蚀机制和失效行为。为我国临近空间高超声速飞行器超高温热防护系统的设计、性能提升及安全评估提供理论与实验依据。

航空航天领域对防热材料和结构的耐温极限、耐久性、轻质强韧化、抗氧化烧蚀性能具有苛刻的要求。本项目通过在碳基材料表面制备超高温陶瓷涂层的方法，将碳基材料轻质、高温强度高、韧性好的优点与ZrB2-SiC基陶瓷材料抗氧化烧蚀性能好的优点结合，显著改善了碳基材料抗氧化性能差和ZrB2-SiC基陶瓷材料密度大、韧性低和抗热冲击性能差的缺点。主要研究了ZrB2和ZrB2-SiC涂层制备新工艺及沉积机理；研究并优化了过渡层的组分、微观结构；开展了多层ZrB2基复合陶瓷涂层设计、优化及失效机制研究；研究了组分及结构演化对应力状态的影响。以ZrCl4、BCl3为先驱体，利用化学气相沉积法（CVD）制得了ZrB2，证明了CVD ZrB2涂层的可行性，优化了工艺参数。确定了包埋法制备的SiC/ZrB2-SiC涂层适宜用作中间过渡层，能够显著缓解涂层与基体的热失配。结合包埋法和CVD法制备的SiC/ZrB2-SiC/ZrB2/SiC涂层在O2和C2H2的流量分别为1800L/h和1900L/h的条件下，烧蚀~298s后的质量烧蚀率和线烧蚀率分别为0.27mg/s和0.57μm/s。材料发射率大小关系为SiO2≈CVD SiC>烧结SiC>石墨>ZrB2>ZrO2，结构演化和发射率是影响涂层温度响应的主要因素。研究表明：复合结构涂层的思路能够将ZrB2-SiC基陶瓷与碳基材料的优点相结合，是一个有价值的研究方向。尤其是CVD法制备ZrB2，为ZrB2基超高温涂层以及碳基材料的改性研究提供了新思路。