氧化对2D C/SiC复合材料阻尼行为的影响

Effect of oxidation on the damping behavior of 2D C/SiC composites

以化学气相渗透(CVI)技术制备的2D C/Si C复合材料为研究对象,探讨复合材料在700、1000和1300℃空气环境中发生不同形式和不同程度氧化损伤后的阻尼行为变化。采用扫描电子显微镜(SEM)观察和分析复合材料的微结构损伤,采用动态力学分析仪(DMA)测试复合材料损伤前后的阻尼性能。结果表明:在700℃和1000℃空气环境中,随着氧化时间的延长,2D C/Si C复合材料的阻尼性能先增大后降低;而在1300℃空气环境中,阻尼性能变化较小,且随氧化时间的延长未表现出明显的规律性。这是由于C/Si C复合材料的阻尼由炭纤维、热解炭界面和碳化硅基体,以及它们之间的相互作用共同形成。炭纤维和热解炭界面的氧化损伤会对复合材料阻尼特性产生两种影响机制,其一是使复合材料阻尼性能增大的机制,主要来自于热解炭界面相损耗引起的界面结合强度降低;其二是使复合材料阻尼性能降低的机制,主要来自于纤维的损耗和界面区的过度破坏。而碳化硅氧化生成的二氧化硅主要是通过影响碳相的氧化程度来影响复合材料的阻尼性能。

A carbon fiber preform was chemical vapor infiltrated with a pyrocarbon （PyC） interphase and a SiC matrix, and then coated with a SiC outer layer by chemical vapor deposition to prepare 2D C/SiC composites with a density of 2.1 g/cm3. The com- posites were oxidized at 700, 1000, 1300 ℃ for 2, 5 and 10 h, respectively. The damping behavior of the oxidized composites was measured by a dynamical mechanical analyzer and the microstructural damage produced by the oxidation was investigated by scan- ning electron microscopy. Results show that the damping of the composites oxidized at 700 ℃ and 1 000 ℃ increases initially and then decreases with increasing oxidation time while that of the composites oxidized at 1300 ℃ is independent of the oxidation time. The damping capacity of the C/SiC composites is determined by the carbon fibers, PyC interphase, SiC matrix and their interaction. The oxidation of the composites increases the damping by weakening the interfacial bonding due to the oxidation of PyC during the initial stage of oxidation, and decreases the damping by the oxidation loss of carbon fibers and excessive damage of the PyC inter- phase during the latter stages of oxidation. SiO2 formed at 1300 ℃ by the oxidation of SiC fills the voids produced by carbon oxida- tion, which increases the dampingand compensates for the decrease of damping produced by carbon loss and excess damage of the PyC interphase.