High temperature anti-oxidation mechanism of residual Si in SiC coating prepared by pack cementation

The SiC coating for C/C composite was prepared by pack cementation technique.The phase composition and microstructure of SiC coating was analysed by XRD and SEM.The oxidation behavior of the composites with SiC coating was investigated at 1500 ℃ in air.The results show that coatings are mainly composed of α-SiC,β-SiC and free Si,and the XRD semi-quantitative analysis shows the content of free Si is different.The coating is more integrity with the higher content of free Si.The oxidation test shows that appropriate amount of free Si of coating can protect C/C composites better.As the residual Si's mass fraction is about 1.3% or 2.9%,the anti-oxidation performance of coating are good.The mass-loss of these SiC coated sample is respectively 0.19% and 0.16% after oxidation at 1500 ℃ in air for 7 h.