CAJ | 학술논문

3D-C/SiC复合材料试样在空气介质中600℃、900℃和1300℃热曝露不同时间后,采用三点弯曲法测试了以室温弯曲弹性模量表征的损伤变化规律,并进行了SEM和EDS分析.结果表明:3D-C/SiC在热曝露15 h后,损伤变化可分为急剧上升(阶段Ⅰ)和平稳上升(阶段Ⅱ)两个阶段.阶段Ⅰ归因于炭纤维和炭层界面在空气中的直接氧化,阶段Ⅱ由复合材料内部氧的扩散所致.在复合材料制备过程的冷却阶段,因基体和炭纤维热膨胀系数不同所产生的基体微裂纹提供了氧化反应的表面与氧扩散的途径.在同一热曝露时间下,损伤随温度的上升而减少的原由可能是由于高温下裂纹收缩导致氧化表面减少,并降低氧向复合材料内扩散所致.
3D-C/SiC복합재료시양재공기개질중600℃、900℃화1300℃열폭로불동시간후,채용삼점만곡법측시료이실온만곡탄성모량표정적손상변화규률,병진행료SEM화EDS분석.결과표명:3D-C/SiC재열폭로15 h후,손상변화가분위급극상승(계단Ⅰ)화평은상승(계단Ⅱ)량개계단.계단Ⅰ귀인우탄섬유화탄층계면재공기중적직접양화,계단Ⅱ유복합재료내부양적확산소치.재복합재료제비과정적냉각계단,인기체화탄섬유열팽창계수불동소산생적기체미렬문제공료양화반응적표면여양확산적도경.재동일열폭로시간하,손상수온도적상승이감소적원유가능시유우고온하렬문수축도치양화표면감소,병강저양향복합재료내확산소치.
3D-C/SiC composites, exposed in air at 600, 900, and 1 300 ℃ for 0 to 15 h, were investigated by three point bend tests at room temperature, SEM, and energy dispersive spectroscopy. The results show that the damage curves, expressed as a relative change of elastic modulus, of the composites for a 15h exposure, could be divided into a sharply increasing stage (stage Ⅰ) and a steady increasing stage ( stage Ⅱ). Stage Ⅰ may be caused by a direct oxidation of the carbon fibers and interface carbon layers by the oxygen in air, and stage Ⅱ may be caused by a diffuse controlled oxidation of the inner part of the composites. The matrix micro-cracks, induced by a difference of coefficients of thermal expansion between matrix and carbon fibers in the cooling process after composite preparation act as oxygen diffuse paths and are where the oxidation takes place. The fact that the damage decreases with temperature for the same exposure time may be caused by the crack shrinking at high temperature, which decreases the oxidizable surface area and inhibits the diffusion of oxygen into the composites.