Comparison of the oxidation behaviors of SiC coatings on C/C composites prepared by pack cementation and chemical vapor deposition

SiC coatings were prepared on carbon/carbon composites by pack cementation (PC) and chemical vapor deposition (CVD). The PC coating was composed of hexagonal platelets of α-SiC, while the CVD coating consisted of spherical particles of β-SiC. Their oxidation behaviors were investigated at 1173 K, 1473 K and 1773 K. Compared with the CVD-SiC coating, bubbles appeared in the PC-SiC coating at lower oxidation temperature and the oxide layer was thicker, which might be ascribed to the formation of aluminosilicate glass in the PC-SiC coating. With the increasing temperature, the oxidation behavior of the PC-SiC coating transformed from linear to parabolic with dramatically improved oxidation resistance, which might be attributed to the decreased viscosity of SiO₂-rich glass and the good healing effect for cracks. The oxidation protective ability of the CVD-SiC coating was worse than that of the PC-SiC coating, because of the higher viscosity of pure SiO₂ glass and the inferior interface adhesion between the coating and the substrate.