涂层孔隙对基体碳/碳材料的氧化损伤模拟

Simulation of Oxidation Damage of Coating Crack on Carbon/Carbon Matrix Materials

碳/碳(C/C)复合材料广泛应用于高超声速飞行器,其表面有碳化硅(Si C)基的保护涂层,旨在将氧气与底层基体C/C隔离。涂层中存在的孔隙成为氧气直达底层C/C材料的通道。C/C材料被氧化,侵蚀出空穴,严重时造成局部热防护失效。针对原有的气体扩散两步模型进行了改进,去掉了O2/CO反应界面固定的限制,考虑了空穴中扩散的影响,提出了折合孔隙深度与弯曲因子的处理方法。采用改进模型模拟涂层下面C/C材料氧化空穴半径,计算值与试验测量值吻合良好,验证了模型的有效性。改进模型可用于预测涂层保护的基体C/C材料的氧化空穴尺寸和评估氧化损伤。

Carbon/carbon(C/C) composites are widely used for hypersonic aircraft. Their surfaces are coated with silicon carbide(SiC) matrix composites to cut off the air from the C/C substrate underneath. Cracks in protective coatings become pathways for oxygen to the C/C substrate. The C/C substrate was eroded by oxygen and then cavities were formed. In severe cases, the cavities can cause the failure of the local thermal protection system. This paper modified the original two-step diffusion-controlled oxidation model by removing the restriction that the interface of the O2/CO reaction was fixed. The effect of gas diffusion in the void was considered. The treatment of equivalent pore depth and tortuosity factor was also proposed.The modified model was used to simulate the radii of oxidation cavities within the C/C substrate. Numerical results agree well with experimental results, which verifies the validity of the model. The improved model can be utilized to predict the geometry dimension of oxidation cavities and evaluate oxidation damage.