不同界面SiC/SiC复合材料的断裂行为研究

碳化硅纤维增强碳化硅复合材料(SiC/SiC)是极具前景的高温结构材料。通过先驱体浸渍裂解(PIP)工艺分别制备了PyC界面和CNTs界面SiC/SiC复合材料, 对两种SiC/SiC复合材料的整体力学性能以及界面剪切强度等进行了测试表征, 并对材料中裂纹的产生与扩展进行了原位观测。结果表明, 两种界面SiC/SiC复合材料弯曲强度相近, 但PyC界面SiC/SiC复合材料的断裂韧性约为CNTs界面SiC/SiC复合材料的两倍。在PyC界面SiC/SiC复合材料中, 裂纹沿纤维-基体界面扩展, PyC涂层能够偏转或阻止裂纹, 材料呈现伪塑性断裂特征; 而在CNTs界面SiC/SiC复合材料中, 裂纹在扩展路径上遇到界面并不偏转, 初始裂纹最终发展为主裂纹, 材料呈现脆性断裂模式。

Fracture Behavior of SiC/SiC Composites with Different Interfaces

SiC fiber reinforced SiC matrix composites (SiC/SiC) are promising materials for high temperature structural applications. In this work, SiC/SiC composites with Pyrolytic Carbon (PyC) interface or Carbon Nanotubes (CNTs) interface were fabricated by polymer infiltration and pyrolysis (PIP) process. Overall mechanical properties and interfacial shear strength of the SiC/SiC composites were characterized and crack growth processes were observed in situ by scanning electron microscope (SEM). The results indicate that flexural strengths of two types of SiC/SiC composites are similar, but the fracture toughness of the SiC/SiC composite with PyC interface is twice as much as that of the SiC/SiC composite with CNTs interface. Cracks propagate along the fibre-matrix interface in the SiC/SiC composite with PyC interface, which can be deflected or arrested by the PyC interface, hence the composite exhibits a pseudo-ductile fracture behavior. However, the CNTs interface fails to cease the crack in the SiC/SiC composite with CNTs interface, so the initial crack propagates rapidly through the fibers leading to final main crack, and a brittle fracture mode.