Modelling the densification of porous structures in CVI ceramic composites processing

Abstract

A model based on random pore structure of the substrate is developed to describe the isothermal CVI process. This model takes into account the diffusion of the ceramic precursor, the deposition reaction of the vapour and porosity changes during CVI. The model is used to predict the concentration profile of the precursor inside the substrate as well as the porosity distribution as a function of time. The mass gain or deposition rate during the infiltration is predicted also. Numerical simulations are performed to study the effects of Thiele modulus of deposition and the pore structure parameter. The results show that there exists a pore mouth-blocking phenomenon for the substrate for high Thiele modulus and pore structural parameter values. The final uniformity of the densification is strongly dependent on the initial Thiele modulus and the initial pore structure. The effect of the initial surface area of the substrate is shown to be significant during the initial stage of the infiltration.