密度对C/C复合材料热力学性能的影响

摘要

Three kinds of C/C composites with density of 1.70 g/cm3,1.82 g/cm3 and 1.89 g/cm3 were prepared.The materials employing needled preform were densified by chemical vapor deposition and pitch impregnation-high pressure carbonization (HPIC) process.The density was controlled by times of HPIC.The results showed that the tensile strength decreased with the increasing density.When the density was low,bonding strength of interface between fiber and matrix was low which could delay the fracture of fiber and increase the tensile strength,the tensile fracture of sample possessed the characteristic of pseudo-plastic fracture.Consisted with the shear strength,the compress strength rose and then fell with the increase of density.With the increasing density,the expansion coefficient increased.Interstices among microcrystals absorbed a little amount of expansion during heating process,therefore,the fall of density was beneficial to the decrease of expansion coefficient of C/C.With the increasing density,the thermal conductivity coefficient increased obviously,and microcrystals enlarged which contribute to the transfer of vibration of crystal lattice and increase of thermal conductivity coefficient.The factor of thermal stress rose and then fell with the increasing density.The C/C with the density of 1.82 g/cm3 possessed high thermal shock resistance as thermal structure components.In the course of C/C R&D,the density target can be designed according to synthetical demands of mechanical and thermal properties.%采用针刺预制体经化学气相沉积与沥青浸渍-高压碳化致密工艺制备C/C复合材料,通过控制沥青浸渍-高压碳化致密次数,获得了密度分别为1.70 g/cm3、1.82 g/cm3、1.89 g/cm3的三种C/C材料,测试材料的力学、热学性能.结果表明材料拉伸强度随密度升高而降低.当密度较低时,纤维/基体界面结合强度相对较低,可以延缓纤维断裂的发生;拉伸断口显示出假塑性断裂特征,有利于材料拉伸强度的提高.材料的压缩强度与剪切性能密切相关,且均随密度升高表现出先升后降的趋势.材料的热膨胀系数随密度升高而增大,材料中微晶之间的空隙在受热过程中可以吸收一部分膨胀量,因此对于C/C材料,降低密度有利于降低热膨胀系数.材料导热系数随密度升高而明显增大,且随密度升高,微晶尺寸增大,有利于晶格振动的传递,从而使得导热系数增大.热应力因子随密度升高而先升后降,作为热结构件使用时,采用密度为1.82 g/cm3的C/C材料可以获得相对较高的抗热震能力.在C/C材料研究开发中,可以综合对材料力学、热学性能的要求来对C/C材料密度指标进行设计.