SiC/Cr–Al–Si/glass multilayer oxidation resistant coating for carbon/carbon composites

Multilayer oxidation resistant SiC/Cr–Al–Si/glass coating for C/C composites was prepared by a three step method of pack cementation, plasma spraying and slurry dipping. The phase composition, microstructure and oxidation resistance of multilayer SiC/Cr–Al–Si/glass coating were studied by XRD, SEM and isothermal oxidation test at 1773 K in air respectively. Double layer SiC/Cr–Al–Si coating consisting of Al_3·21Cr_0·47, Cr₃Si and Al₂O₃ can protect C/C composites from oxidation for only 61 h due to its high porosity. When a layer of borosilicate glass doped with MoSi₂ was coated on the surface of the as sprayed Cr–Al–Si coating, multilayers of SiC/Cr–Al–Si/glass coating were formed such that they can protect C/C composites from oxidation for 95 h with only 5·3% weight loss and the corresponding weight loss rate is only 0·92×10⁻⁴ g cm⁻² h⁻¹. The positive effect of the borosilicate glass coating on the oxidation resistance of the coating may be attributed to its own fluidity at high temperature.