HIGH-TEMPERATURE PROPERTIES OF SIC SIC FOR FUSION APPLICATIONS/

Ceramic matrix composites (CMCs) such as SiC/SiC exhibit novel mechani cal properties relative to their monolithic counterparts. The crack ve locity (da/dt) versus stress intensity (K) relationship for monolithic ceramics can be described by a simple power law relationship whereas SiC/SiC was found to exhibit a multistage da/dt versus K relationship similar to that for stress corrosion of metals. A K-independent stage II was followed by a strongly K-dependent stage III similar to monolit hic materials. Evidence also exists that the fracture resistance of th ese materials is greater if cracks are produced by subcritical growth processes relative to machined notches. Oxygen was found to increase d a/dt and decrease the K for the stage II to stage III transition while cyclic loads produced little damage at low K values but there was som e evidence for increasing damage with increasing number of cycles and K.