SiC／C层状陶瓷的断裂行为研究

利用流延法成膜和热压烧结工艺制备出了SiC层和石墨层交替排列、层厚均匀、界面清晰的SiC／C层状陶瓷。力学性能与单相SiC陶瓷相比，SiC／C层状陶瓷的抗弯强度略有降低，但断裂韧性却得到了大幅度的提高。层状陶瓷的载荷-位移曲线不同于单相陶瓷的1次性断裂曲线，而是呈锯齿状；同理论计算所得载荷-位移曲线相似。层状陶瓷的断裂路径呈台阶状，裂纹遇到弱界面时发生分叉产生并行扩展裂纹、晶须状微裂纹以及裂纹遇到弱界面时被吸收。认为裂纹偏转、裂纹分叉、裂纹并行扩展、裂纹遇弱界面被吸收等是SiC／C层状陶瓷的几种主要增韧机制。

Fracture Behavior of Multlayer SiC/C Composites

Multilayer SiC/C composites were fabricated by tape casting and hot pressed sintering.The SiC layers and the graphite layers were found to be aligned alternately and reasonably uniformly and their interfaces were straight and well distinguishable. Mechanical properties were measured and the results showed that the strength of multilayer SiC/C composites was slighhtly less than, while its fracture toughness was higher than that of monolithic SiC. Multilayer SiC/C composites revealed a saw tooth load displacement curve. This was different from catastrophic fracture curve for monolithic SiC, and similar to the theoretical curve. Cracks propagated through multilayer SiC/C composites mainly along a step like paths, accompanied by crack branching, crack parallel propagation. Whisker like microcracks and cracks being absorbed at the weak interface were also observed by SEM. The toughening mechanism in multilayer SiC/C composites was attributed to a combination of all these effects.