Effect of a diffusion-enhancing hole on the densification of a thick-section 2D C/SiC composite

Diffusion-enhancing holes (DEHs) have been used to mitigate the large density gradients that are formed in the thick-section ceramic matrix composites (CMCs) fabricated by chemical vapor infiltration (CVI). However, the densification characters of the thick-section CMCs with DEHs through vapor infiltration remain a concern. Here, the densifications of a10-mm-thick two dimensional (2D) C/SiC composite with or without DEHs are investigated by experiments and calculations. Results showed both the measured densities, the predicted final densities, and the density growth rates (DGRs) for the composite with DEHs (diameters of 2 or 4 mm) are higher than those of the counterpart without DEHs, due to the forming of dense rings (DRs) around DEHs and the increased infiltration in the large pores (diameter > 52 μm). In addition, the diffusion increase in infiltration with DEHs is attributed to the increase of Knudsen diffusion resulted from the reopening of the blocked/sealed pores by DEH-machining.