稀土氧化物对C/SiC-ZrC复合材料烧蚀产物的相稳定机制研究

C/SiC-ZrC composites have low density, high specific strength and modulus, good ultra-high temperature oxidation, ablation and thermal shock resistance, good toughness, etc. They have been regarded as the potential thermal protection materials for hypersonic space vehicles at ultra-high temperatures. However, the phase transition of ZrO2 and the evaporation and decomposition of SiO2 will cause the failure of the oxide scales at ablation conditions, which restrict the development of these materials. In this work, rare earth oxides (RE2O3) will be introduced into C/SiC-ZrC composites to stabilize the ablation products. C/SiC-ZrC-RE2O3 composites will be fabricated through the combination of precursor infiltration and pyrolysis (PIP) and electric coupling CVI (E-CVI) processes with different species and contents of RE2O3. The effects of RE2O3 on the microstructure, composition and ablation properties of the composites will be investigated. The relationship between the material ablation performance and the RE2O3 kinds and content should be established. Through test and theoretical calculation the products stabilizing mechanism based on the synergy of the inhibition of ZrO2 phase transformation and the promotion of oxidation film sintering will be revealed; also the ablation mechanism should be deeply understood. The results of this work will help to obtain carbon fiber reinforced ceramic composites with good ablation resistance.

C/SiC-ZrC复合材料具有密度低、比强度和比模量高、耐超高温、抗氧化、抗烧蚀、韧性好、抗热震等特点，是理想的高超声速飞行器超高温热防护材料。然而，超高温烧蚀条件下，氧化产物中ZrO2的相变和SiO2的挥发/分解导致的氧化膜剥落/开裂严重制约了该类材料的发展。为此，本项目拟在C/SiC-ZrC复合材料中添加稀土氧化物（RE2O3）作为基体来稳定烧蚀产物。通过电耦合化学气相渗透工艺结合聚合物前驱体浸渍裂解工艺制备含有不同RE2O3种类、含量的C/SiC-ZrC-RE2O3复合材料，分析稀土氧化物对材料微观结构、相组成、界面结构以及烧蚀性能的影响，建立RE2O3种类和含量与材料烧蚀性能之间的关系，通过试验和理论计算揭示基于抑制ZrO2相变和促进氧化膜烧结协同作用下的烧蚀产物相稳定机制，阐明材料烧蚀机理，获得烧蚀性能优异的碳纤维增强陶瓷基复合材料。

C/SiC-ZrC复合材料具有密度低、比强度和比模量高、耐超高温、抗氧化、抗烧蚀、韧性好、抗热震等特点，是理想的高速飞行器超高温热防护材料。然而，超高温烧蚀条件下，氧化产物中ZrO2的相变和SiO2的挥发/分解导致的氧化膜剥落/开裂严重制约了该类材料的长时间循环使用。本项目拟在C/SiC-ZrC复合材料中添加稀土氧化物（RE2O3）作为基体来稳定烧蚀产物，获得烧蚀性能优异的碳纤维增强陶瓷基复合材料。粉体实验研究表明Y2O3和Yb2O3在PIP-ZrC和PIP-ZrC-SiC陶瓷中分别以Zr-Y-O相和La2Zr2O7相存在，Yb2O3的引入对于抑制m相ZrO2的生成效果最佳。采用CVI结合PIP工艺制备了多种C/SiC-ZrC-RE2O3(RE=Y、La、Sc、Lu、Yb)复合材料，并研究了材料的循环氧乙炔烧蚀行为。1700 °C 烧蚀1000 s（200s×5次）后，C/SiC-ZrC-Y2O3复合材料烧蚀产物中m相ZrO2显著降低，主要以四方相Zr-Y-O为主，因此材料抗烧蚀性能显著提高（较未加Y2O3样品线烧蚀率降低28%）。材料1700 °C 、1000 s，1900°C、1000s, 2100°C、600s线烧蚀率分别为0.23 um/s、 0.43 um/s 和2.33 um/s。进一步适当提高Y2O3含量时，其还会与SiO2反应形成Y2Si2O7相，这有助于保持氧化膜完整性降低烧蚀率。在1900°C烧蚀600s条件下对比Y、La、Sc、Lu、Yb等氧化物的作用发现，添加Yb2O3时材料烧蚀性能最优。因此，本研究工作表明，选取适当的稀土氧化物种类和含量可有效稳定烧蚀产物相进而提升氧化膜完整性，从而达到提升材料循环烧蚀性能的目标。