The Effect of Heat Treatment on the Microstructure and Mechanical Properties of KD-II SiC Fibers in Air

The polycarbosilane-derived KD-II SiC fibers were exposed in air at 1200°C for 1-100h and the effect of heat treatment on structures and properties were studied by elemental analysis, XRD, SEM and tensile test. Experimental results indicated that oxygen content, grain size of SiO2 and oxide layer thickness increased, whereas the tensile strength decreased with rising the heat treatment time. When oxidizing over 20h, the amorphous silica crystallized into α-cristobalite and there were cracks on fibers surface and the cross section formed the skin-core structure with oxide layer wrapped inner SiC fibers after oxidizing for 100h. With the same experimental condition for Hi-Nicalon SiC fibers, the differences of oxidation resistance between KD-II and Hi-Nicalon SiC fibers were compared and the oxidation degradation of KD-II SiC fibers was analyzed.