高密度预制体制备炭/炭复合材料的弯曲力学性能与断裂机制

摘要

以丙烯作为碳源,氮气作为载气,采用初始密度为0.94 g/cm3三维正交PAN基12 K炭纤维预制体,利用自制的快速CVI炉制备基体热解炭结构为带状结构的C/C复合材料.力学性能测试结果表明,材料的弯曲断裂特征与制备过程中受到的高温热处理次数有关.从载荷-位移曲线来看,当C/C复合材料经过两次热处理时,C/C复合材料呈明显假塑性断裂特征.当C/C复合材料经过三次热处理时,载荷-位移曲线趋于稳定平滑,抗弯强度降低.从C/C复合材料断面的SEM图可以观察到材料断裂可以分为层间断裂和层内断裂,而层内断裂又因热解炭填充密度变化呈明显的分区断裂.由于热解炭和纤维含量在C/C复合材料中分布的差异,材料在不同的区域表现出不同的断裂特征,从而使得材料具备良好的弯曲强度同时具有一定的韧性特征.%C/C composites with banded structure pyroearbon were fabricated by fast chemical vapor infiltration (CVI),with C3H6 as carbon source,N2 as carrier gas,and three-dimensional (3D) 12K PAN-based carbon fabric with high density of 0.94 g/cm3 as preform.Experimental results indicated that the fracture characteristics of C/C composites were closely related to the frequency of high-temperature treatment (HTT) at the break of CVI process.According to the load-displacement curves,C/C composites showed a pseudoplastic fracture after twice of HTT.After three times of HTT,load-displacement curves tended to be stable with a decreasing bending strength at 177.5 MPa.Delamination failure and intrastratal fiber fracture were observed at the cross-section of C/C composites by scanning electronic microscope.Because the content of pyrocarbon and fibers has a different distribution in layers,the C/C composites show different fracture characteristics at various regions,which leads to good toughness and bending strength.