CVI+PIP复合工艺制备SiC_(f)/SiC复合材料的微观结构和水氧腐蚀行为研究

Microstructure and Wet Oxidation Behavior of SiC_(f)/SiC Composites Prepared with CVI+PIP Hybrid Process

采用化学气相渗透—前驱体浸渍裂解复合工艺制备了SiC_(f)/SiC复合材料,复合材料密度为2.5 g·cm^(-3),孔隙率为6%,表明复合工艺有效提高了复合材料的致密度。使用扫描电镜和透射电镜表征了复合材料的微观结构,SiC纤维由纳米级的SiC晶粒组成;热解碳界面相厚度约为300 nm,为层状结构,层片没有择优取向;CVI碳化硅基体纯度高、结晶度好;PIP碳化硅基体氧含量较高,为非晶相。在1300℃的水氧腐蚀环境下,由于水蒸气分压较高(90 vol.%)和气体流速较快(20 cm·s^(-1)),试样表现出持续失重,反应100 h后,总失重达2.36 mg·cm^(-2)。在水氧腐蚀的初始阶段,相比于PIP碳化硅基体,CVI碳化硅基体表现出了更好的耐水氧腐蚀性能。

SiC_(f)/SiC composites have been fabricated by using chemical vapor infiltration(CVI)and precursor infiltration and pyrolysis(PIP)hybrid techniques.Density and porosity of the as-prepared composite are 2.5 g·cm^(-3) and 6%,respectively,indicating that the density of the composites can be effectively increased by using the hybrid techniques.Microstructures of the SiC fiber,interphase,CVI SiC matrix,and PIP SiC matrix were analyzed by using SEM and TEM.The SiC fiber is composed of SiC nano grains.The PyC interphase possesses layered structure without preferred orientation,while the thickness of interphase is 300 nm.The CVI SiC matrix exhibits high purity and high crystallinity.The PIP SiC matrix has higher oxygen content and is amorphous.Corrosion behavior of composite was studied in a mixed water vapor and air environment.The composite exhibits sustained weight loss due to high partial pressure of water vapor(90 vol.%)and fast gas flow rate(20 cm·s^(-1)).The total weight loss was 2.36 mg·cm^(-2) after 100 h.At the initial stage of wet corrosion,the CVI SiC matrix exhibited better water vapor resistance than PIP SiC matrix.