化学气相渗透2D-SiCf/SiC复合材料的蠕变性能及损伤机理

Creep Properties and Damage Mechanisms of 2D-SiCf/SiC Composites Prepared by CVI

研究了采用化学气相渗透工艺制备2D-SiCf/SiC复合材料的真空蠕变性能,蠕变温度为1200、1300和1400℃,应力水平范围为100~140 MPa。用扫描电子显微镜(SEM)和高分辨透射电子显微镜(TEM)分别观察分析了2D-SiCf/SiC复合材料的蠕变断口形貌和微观结构。结果表明,2D-SiCf/SiC复合材料的主要蠕变损伤模式包括基体开裂、界面脱粘和纤维蠕变。桥接裂纹的纤维发生蠕变并促进了基体裂纹的张开、位移增大,进一步导致复合材料蠕变断裂,在复合材料蠕变过程中起决定性作用。2D-SiCf/SiC复合材料的蠕变性能与SiC纤维微观结构的稳定性密切相关。在1200℃/100 MPa时,纤维晶粒没有长大,复合材料的蠕变断裂时间大于200 h;蠕变温度为1400℃时,纤维晶粒明显长大, 2D-SiCf/SiC复合材料蠕变断裂时间缩短至8.6 h,稳态蠕变速率增大了三个数量级。

The creep properties of 2D-SiCf/SiC composites prepared by chemical vapor infiltration were studied.The creep temperatures were 1200,1300 and 1400℃,and the stress levels ranged from 100 MPa to 140 MPa.Scanning electron microscope was used to observe the fracture morphology,and their microstructure was analyzed by high resolution transmission electron microscope.The results show that the creep damage modes of 2D-SiCf/SiC composites mainly include the generation of matrix crack,interfacial debonding and fiber creep.The creep of bridging fibers leads to increase of the opening distance of the matrix cracks and further creep rupture of the composite.The microstructural stability of the SiC fiber plays a critical role in the creep properties of 2D-SiCf/SiC composites.SiC grains in the fibers of 2D-SiCf/SiC composites do not grow when it is crept at 1200℃/100 MPa.However,the grains grow significantly when the creep temperature increases to 1400℃.The creep rupture time decreases to 8.6 h from above 200 h,and the steady-state creep rate increases by three orders of magnitude.