预制体对C／C复合材料热膨胀系数的影响

以天然气为前驱气体，整体碳毡和2D针刺碳毡为预制体，采用热悌度化学气相渗积技术制备了两种C／C复合材料，其表观密度均为1．74g／cm^3。借助光学显微镜和扫描电子显微镜观察了热解碳基体的生长特征和微观形貌，采用热膨胀仪测量了两种材料的热膨胀系数（CTE），研究了由不同预制体增强C／C复合材料的CTE，解释了造成材料不同方向CTE差异的主要原因。结果表明，随着温度升高，材料A和B的CTE是逐渐升高的，且Z向CTE值均大于XY向。当两种材料在Z向的纤维体积分数接近时，随着XY方向纤维体积分数增大，材料在Z向的CTE增大，在XY向的CTE降低，两种材料存XY和Z向的CTE旱如下分布：αB—z〉dAz〉αA—xy〉αBxY-C／C复合材料的CTE主要取决于纤维体积分数和排市、碳基体及材料中的孔隙分布情况，前者起决定作用。

Effect of Preform on Thermal Expansion Coefficient of C/C Composites

Using natural gas as precursor gas, intergrated carbon felt and 2D needle carbon felt as prefimns, two kinds of C/C composites were prepared by thermal gradient chemical vapor infiltration, and both of them have a same density of 1.74 g/cm3. With help of optical microscope and scanning electronic mieroscope, the growth characteristic and miero- structure of pyrolytic carbon matrix were observed, and thermal expansion testing machine was employed to measm＇e their thermal expansion coefficient （CTE）. The CTE of C/C composites reinforced by different preforms was studied, and the CTE difference in different direction was explained. The results show that, the CTEs of composite A and B gradually in- creases with increasing temperature, and the CTE in Z direction is higher than that in XY direction. When the fiber volume fraction of two composites in Z direction is near, with the fiber volume fraction in XY direction increasing, their CTEs in- crease in Z direction and decrease in XY direction displaying αB-z 〉 aA_Z 〉 α-xy 〉 αB-xy. The CTE of C/C composites mainly depends on the volume fraction and arrangement of carbon fiber in preform, carbon matrix and porous distribution, and the former has decisive function.