Effect of phase composition on the oxidation resistance of ZrB2-SiC coatings

ZrB 2 -SiC-Al 2 O 3 (ZSA) and ZrB 2 -SiC-Si (ZSS) coatings were prepared on the surface of C/C composites by atmospheric plasma spraying . During oxidation at 1200 ℃ for 10 h, the formation of B 2 O 3 in the ZSA coating volatilizes gradually, no glass phase is able to seal cracks and holes, resulting in poor oxidation resistance . On the other hand, the ZSS coating produces a large amount of borosilicate glass phase and still gains 0.8% weight after 10 h. During oxidation at 1500 ℃, a low viscosity SiO 2 glass phase forms on the ZSA coating, due to the presence of Al 2 O 3 and this glassy phase has a good ability to seal defects. However, the rapid volatilization of B 2 O 3 in the ZSS coating leads to the formation of large holes in the coating, and to progressively increased viscosity of SiO 2 glass phase, resulting in decreased oxidation resistance.