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本研究在炭/炭复合材料热解炭基体织构形成与转化的模型基础上,基于石墨微晶片层的表面结构特点,建立了蜂窝结构的热解炭沉积表面几何模型,并运用Monte Carlo方法模拟了在等温等压化学气相渗透(CVI)过程中热解炭基体沉积的动力学过程,研究了预制体比表面积(AS/VR)和入口气体分压对热解炭微观结构的影响。通过数值模拟并结合已公开发表的实验结果发现,在CVI工艺过程中一定的压力条件下,通过控制AS/VR可以获得不同织构的热解炭,预制体的AS/VR存在两个临界值,靠近反应器入口处的临界值为1.45 m-1和8.9 mm-1,靠近反应器出口处的临界值为0.3 mm-1,当AS/VR处于这两个临界值之间时,系统主要沉积高织构热解炭;在同一AS/VR且压强小于30 k Pa的条件下,通过控制反应气体压强的值也可以得到不同织构的热解炭,并且压强也存在一个临界值,当压强大于这个临界值时,系统主要沉积高织构热解炭。
In this paper, based on the model of texture and transformation of carbon / carbon composite pyrolytic carbon substrate, the geometric model of pyrolytic carbon deposition surface of honeycomb structure was established based on the surface structure of graphite microcrystalline layer. Monte Carlo method The kinetics of the pyrolytic carbon deposition during isothermal equi-pressure chemical vapor infiltration (CVI) was simulated, and the effect of preform specific surface area (AS / VR) and inlet gas partial pressure on the microstructure of pyrolytic carbon was investigated. Through the numerical simulation and the published experimental results, it is found that pyrolysis charcoal with different texture can be obtained by controlling AS / VR under certain pressure in the CVI process. There are two critical values for the AS / VR of the preform , The critical values near the reactor inlet are 1.45 m-1 and 8.9 mm-1, and the critical value near the reactor outlet is 0.3 mm-1. When AS / VR is between these two critical values, the system is predominant In the same AS / VR and the pressure is less than 30 kPa, pyrolytic carbon with different textures can be obtained by controlling the pressure of the reaction gas, and there is a critical value for the pressure At pressures greater than this threshold, the system mainly deposits highly textured pyrolysates.