Influence of thermo-exposure at high temperature of flexural behaviors of 3D-C/SiC composite

By means of three-point bending under small load, 3D-C/SiC composites specimens of 50x5x3.5mm have been investigated after thermo-exposure at 600, 900 and 1300 degrees C in air at various time intervals. The specimens exposed for 15 hours at 1300 degrees C are bend to fracture at 1300 degrees C in air. And the fracture analysis has been detected by SEM. The results indicated that damage curves of 3D-C/SiC specimens exposed in 15 hours could be divided two stages involving increasing sharply stage (stage 1) and increase stably stage (stage 11). Stage I produces firstly. and lasts shortly. But damage variation is larger than that in stage It. With temperature increasing, the time of stage I shorten, and damage descends. In the same exposure time the damage evaluated by elastic modulus increases with temperature increasing. The, oxygen content is higher at high temperature according to energy spectrum, which demonstrates more SiO2 is obtained. After thermo-exposure at 1300 degrees C for 15 hours, the decrease degrees of flexuous strength and strain are more obvious than that of elastic modulus. Especially, the strain dropped to 2.5% of the sample without thermo-exposure.