3D-Cf/SiC复合材料在1500℃的拉-拉疲劳行为

摘要

The tension-tension fatigue tests were conducted at 1500°C under 10-4Pa vacuum with a sinusoidal loading-frequency of 20, 60Hz and stress ratio R of 0. 1 and 0. 5 for 3D-braided carbon fiber reinforced silicon carbide ceramic matrix composites (3D-C1/SiC) fabricated by chemical vapor infiltration (CVI) process. Morphology of fatigue fracture and microstructure of pyrocarbon interphase of 3D-C1/SiC composites were observed by SEM and HRTEM respectively. The results show that while stress ratio is 0. 1, the fatigue limit (based on 106 cycles) at 20Hz and 60Hz is 230MPa and 240MPa respectively. While stress ratio is 0. 5, the fatigue limit is 230MPa at 60Hz. Fracture morphology is more rough in low fatigue stress-ratio, high loading-frequency and more fatigue cycles, and the pull-out lengths of fiber and fibers bundles on the fracture surface is longer. Nanoscale pyrocarbon flake of interphase curls up evidently.%在1500℃,10<'-4>Pa真空中,采用应力比0.1和0.5,频率60Hz和20Hz的正弦波对三维编织炭纤维增强碳化硅基复合材料(3D-C<,f>/SiC)进行了拉-拉疲劳实验,利用SEM和HRTEM分别观察了疲劳试样的断口形貌和热解炭界面相的微结构.结果表明:若取循环基数为10<'6>次,当应力比为0.1时,20Hz和60Hz的疲劳极限分别是230MPa和240MPa,约为抗拉强度的88%和92%;当应力比为0.5时,60Hz的疲劳极限是230MPa,约为抗拉强度的88%.应力比低、加载频率高、循环周次多的断口粗糙度大,纤维(束)拔出较长.纳米尺度的热解炭界面相变形明显,由平直状变为卷曲状.