热处理温度对炭/炭复合材料性能的影响

EFFECT OF HEAT TREATMENT TEMPERATURE ON THE PROPERTIES OF CARBON - CARBON COMPOSITES

对同一种炭/炭复合材料,经过不同温度热处理后的微观结构、石墨化度、导热系数、抗弯强度和摩擦磨损性能进行了对比研究。试验表明:随着最终热处理温度的提高,易石墨化的热解炭偏振光下光学活性增强,而难石墨化的热解炭微观结构几乎没有变化;炭/炭复合材料的晶粒逐渐长大,层面间距缩小,石墨化度有较大提高;平行炭布方向的导热系数和垂直炭布方向的导热系数均有上升。同时,由于基体炭与炭纤维两者热膨胀系数的差别,热处理温度的提高,降低了基体与增强纤维的的结合强度,使炭/炭复合材料的抗弯强度降低。试验还表明:随着热处理温度的提高,炭/炭复合材料的摩擦表面逐渐形成薄而致密的自润滑膜,摩擦系数在经过一个峰值后趋于平稳状态,磨损量下降明显。经1800℃热处理的质量损失主要是由氧化造成的。

The microstructure, graphitization degree, heat transfer coefficient, bending strength and the tribological properties of the carbon-carbon composites after heat treating with different ultimate heat treatment temperatures (HTT) were studied. The results show that with the increase of the HTT from 1800-2700°C, different changes occur in the rough lamina and smooth lamina structures. The optical activity of pyrolytic carbon of rough lamina is increased while there is not any change in the microstructure of smooth lamina under polarized light; with the increase of crystal size and graphitization degree, the interlayer distance of pyrolytic carbon decreases; and the heat transfer coefficient in either parallel or perpendicular directions of the fiber increases. On the other hand due to the difference of thermal expansion coefficient between the fiber and matrix, with the increase of the HTT, the bending strength decreases because of the decrease of interface strength. At the same time, with the increase of the HTT, a thin and dense film on the friction surface is formed, which leads to the decrease of the friction coefficient and the wear loss. The mass loss after heat-treatment at 1800°C is mainly due to the oxidization.