FCVI工艺致密化效率评价方法研究

Efficiency of the FCVI Process for Fabricating C/C Composites

针对用于制备C/C复合材料的强制流动热梯度化学气相渗透(FCVI)工艺,建立了预制体的孔隙结构模型,将孔隙分为闭孔孔隙与开孔孔隙,指出致密化过程就是开孔孔隙的填充过程,基于化学反应动力学和传热传质理论,提出了致密化剩余时间的概念,推导出一种用于预测FCVI工艺致密化效率和控制工艺参数的理论,该理论综合分析了致密化各时期的预制体密度分布与工艺效率的关系,指出在致密化各个时期预制体内的密度分布符合特定的数学关系才能保证最终获得最高的致密化效率,并定义了一个综合衡量致密化效率的指标-ψ.工艺试验表明:如果在工艺过程的各个时期ψ都接近于0,则可以保证该工艺获得最高的致密化效率,这种方法可以用于指导实际的FCVI工艺,并获得理想的致密化效率.

In order to deeply understand the forced-flow-thermal-gradient chemical vapor infiltration (FCVI) process for fabricating carbon-carbon composites, the model concerning pores in preforms was established in this paper, the pores in preforms were composed of opened pores and closed pores, the CVI process is the closing process of opened pores. On the basis of the chemical reaction dynamics and the heat and mass transmission theory, a new concept, the residual time of densification (RTD), was put forward, from which a theoretical method was deduced to predict the densification efficiency of the process and control the technique qualifications, based on this theory, the highest densification efficiency of FCVI process can be acquired when the density distribution of performs accord with a certain mathematical relationship during CVI process. As a result, the relationship between the density distribution of preforms and the process efficiency was analyzed comprehensively, and a variable factor, 0, was defined to evaluate the efficiency of FCVI process. The practical experiments showed that, if the 0 valued around 0 in any stage of the process, the highest densification efficiency of FCVI process can be acquired. Guided by the presented method, the densification efficiency was improved to a satisfactory level in practical FCVI processes.