高导热C/C复合材料的微观结构与力学性能

Microstructure and Mechanical Properties ofHigh Thermal Conductivity C/C Composites

采用中间相沥青基碳纤维(MPCF)与中间相沥青热模压后,通过化学气相渗透和前驱体浸渍裂解致密化,制备得到单向(1D)、两向正交(2D)密度为1.97 g/cm^(3)的高导热C/C复合材料。基体碳包括中间相沥青碳(MPC)、热解碳(PyC)与树脂碳。通过扫描电子显微镜(SEM)进行微观结构表征,采用纳米压痕技术与三点弯曲方法进行力学性能表征,分析探究高导热C/C复合材料的微观结构及其对微观结构与力学性能的影响。结果表明,MPCF为内辐射外洋葱的混合型结构,MPCF内辐射结构与MPC的石墨微晶取向度较高,MPCF外洋葱结构与PyC的石墨微晶取向度较低;石墨微晶取向度越高,弹性模量越低。MPC、PyC及MPCF之间构筑了多层次的界面结构;1D-C/C、2D-C/C的弯曲强度分别为240.77和143.12 MPa,多层次的界面结构在弯曲破坏中能有效改变裂纹扩展路径而减缓裂纹扩展,使材料的韧性得到提高,弯曲断裂模式表现为“假塑性”断裂。

After hot molding process by using mesophase pitch-based carbon fiber(MPCF)and mesophase pitch,through the chemical vapor infiltration and precursor impregnation process,the high thermal conductivity C/C composites were prepared.The matrix carbon includes mesophase pitch carbon(MPC),pyrolytic carbon(PyC)and resin carbon.Through SEM,nano indentation and three-point bending,the microstructure of C/C composites and the influence on the micro mechanical properties and bending properties were analyzed.The results show that the MPCF is a hybrid structure with internal radiation and external onions.The orientation of graphite microcrystalline in the MPCF inner radiation structure and MPC is higher than that in the MPCF external onion structure and PyC.The higher the orientation of graphite microcrystals is,the lower the elastic modulus is.A multi-layer interface structure is built between MPC,PyC and MPCF,which is changes the crack growth path in the bending failure to slow down the crack growth,and improves the toughness of the material,shown as“pseudoplastic”fracture.