涂层初始缺陷诱导的C/SiC复合材料氧化损伤行为预测

Prediction for oxidation and damage behavior of C/SiC composites induced by initial coating defects

为评价涂层缺陷对陶瓷基复合材料力学性能的影响,以先驱体浸渍裂解(PIP)工艺平纹编织C/SiC材料为研究对象,观测统计了SiC涂层的初始缺陷形貌,并进行了900℃条件下的无应力氧化实验,获得了涂层缺陷附近纤维束的氧化损伤情况,模拟材料试验的实际特征建立了包含典型涂层缺陷的SiC基体与碳纤维束的材料细观模型。提出了一种基于扩散控制的氧化界面演化方法,并仿真不同缺陷条件下纤维束氧化损伤的空间扩展情况,得到材料强度、刚度衰减规律。结果表明,氧化气体由涂层缺陷进入材料内部,造成纤维束发生氧化损伤并进一步沿孔隙扩散,由此引起的材料质量损失和拉伸模量衰减的演化规律具有一致性,两者均可用于材料氧化程度的评价。涂层缺陷类型决定了纤维束的损伤发展和形貌特征,相同分布尺度下涂层开裂缺陷较剥落缺陷会导致更大的损伤区域和更显著的应力集中,通过不同类型涂层缺陷诱导的损伤程度对比,为高温服役热结构材料交付的质量评价提供支撑。

To evaluate the mechanical properties of ceramic composites affected by coating defects,the SiC coated plain woven C/SiC composite by precursor impregnation and pyrolysis(PIP)process was taken in consideration.Firstly,the observation and statistical analysis of initial defects on SiC coating were performed,then a non-stress oxidation test at 900℃was conducted,and the damage status of carbon fiber around coating defects was obtained.According to the actual characteristics of the oxidation test,a microscale model of SiC matrix and carbon fiber containing typical coating defects was established.Based on the evolution of oxidation interface under diffusion-controlled reaction mechanism,a simulation on the development of fiber overall damage was carried out and stiffness reduction was calculated.The results show that oxy-gases entered from coating defects diffuse through inner pores of composites and react with carbon fiber,causing tensile modulus reduction in consistency with weight loss,both of which are capable of evaluation on the oxidation extent of composites.The overall damage topography of carbon fiber is determined by the types of coating defects.Under the same distribution scale,damaged zone induced by cracking defects contains larger range of stress concentration compared with that induced by spalling defects.Judgement on the properties of thermal structure at high temperature is supported with the comparison of oxida-tion damage induced by different coating defects.