碳纤维增强超高温陶瓷基复合材料的多相反应制备与抗烧蚀性能

Multiphase reaction fabrication and ablation resistance of carbon fiber-reinforced ultra-high temperature ceramic matrix composites

为提高C/C复合材料在2000℃以上有氧环境中的抗氧化烧蚀性能,本研究采用ZrB_(2)浆料浸渍、ZrC-SiC前驱体浸渍裂解与Si-Zr10共晶合金反应熔渗复合工艺制备了C/C-SiC-ZrB_(2)-ZrC复合材料,细致研究了复合材料在熔渗过程中的基体微观结构演变机理及其力学性能和抗烧蚀性能。结果表明,在反应熔渗结束后的降温阶段,部分ZrC陶瓷与残余Si熔体通过原位固-液反应转化为ZrSi_(2)和SiC,生成的亚微米级SiC颗粒均匀镶嵌于ZrC-ZrSi_(2)二元混合物中,最终形成ZrC-ZrSi_(2)-SiC三相混合微区。制备的C/C-SiC-ZrB_(2)-ZrC复合材料密度为3.18 g/cm^(3),开孔率为2.77%,其弯曲强度和弯曲模量分别为121.46±13.77 MPa和21.78±5.56 GPa。在其断口处能观察到较长且较多的单丝纤维拔出以及明显的界面脱黏,这表明复合材料的失效方式为韧性断裂。经2000℃,300 s的大气等离子体烧蚀,复合材料表现出优良的抗超高温烧蚀性能(质量烧蚀率和线烧蚀率分别为1.37×10^(-3)g/s和3.43×10^(-3)mm/s)。分析发现,烧蚀中心形成了独特的双层梯度氧化物结构,底部的ZrO2层可阻挡外部热量向材料内部基体的传递,表面由固相ZrO2颗粒和液相富SiO2的SiO2-ZrO2熔体组成的复合氧化层既能抵御高速气流的机械冲刷,又能抑制氧气向内部基体的扩散。

In this work,to improve the ablation resistance and oxidation performance of carbon fiber-reinforced carbon matrix(C/C)composites widely applied as aerospace high-temperature structural materials in an oxidizing environment above 2000℃,C/C-SiC-ZrB_(2)-ZrC composites were fabricated by hybrid processes of ZrB_(2)slurry impregnation,ZrC-SiC precursor infiltrationpyrolysis and reactive melt infiltration with a Si-Zr10 eutectic alloy.The matrix microstructure and the evolution mechanism of the prepared composites were investigated in detail by phase composition,microstructure analysis,model experiments,and thermodynamic calculation.The mechanical properties and ablation resistance of the composites were tested by three-point bending tests and an atmospheric plasma torch,respectively.The results showed that in the cooling stage after infiltration,in situ solidliquid reaction between ZrC ceramics and residual Si melt resulted in the formation of ZrSi_(2)and SiC,characterizing as such submicron SiC particles evenly embedded in the ZrC-ZrSi_(2)binary phases and finally generated a ZrC-ZrSi_(2)-SiC complex micro-region.The obtained composites with a density of 3.18 g/cm^(3) and an open porosity of 2.77% showed a flexural strength of 121.46±13.77 MPa and a flexural modulus of 21.78±5.56 GPa.Moreover,numerous fibers were pulled out and obvious interfacial debonding was observed in the fracture section,indicating that the failure mode of the composites was a ductile fracture.After plasma-arc ablation at 2000℃ for 300 s,the C/C-SiC-ZrB_(2)-ZrC composites exhibited excellent ultra-high temperature ablation behavior.The mass and linear ablation rates were 1.37×10^(-3)g/s and 3.43×10^(-3)mm/s,respectively.It was found that a unique double-layer oxide structure was formed in the ablation center.The ZrO2layer as the inner layer can inhibit heat conduction into the internal matrix to further improve the high-temperature resistance of the composites.The composite oxide layer composed of solid-phase ZrO2particles and liquid-phase SiO2-ZrO2melt rich in SiO2as the outer layer can not only resist mechanical scouring of high-speed gas flow but also inhibit the inward oxygen diffusion.