Durable anti-oxidation mechanism and failure analysis of the ZrSiO4 compound glass coating for carbon/carbon composites

In order to improve the anti-oxidation property of glass coating for aviation thermal structural components such as C/C airplane brake disc under extreme conditions up to 1473 K, ZrSiO4 is doped to improve the stability of the glass coating and to prolong its service life. The microstructures of the ZrSiO4 compound glass (ZSO-glass) coating after different oxidation time at 1473 K were studied. The anti-oxidation mechanism and failure of the coating was comprehensively analyzed. The results show that the novel ZSO-glass coating prepared by slurry method displayed excellent oxidation resistance and protected the carbon/carbon matrix at 1473 K for 573 h with only 0.33 wt% weight-loss, and it also displayed good thermal shock resistance. The excellent oxidation resistance of the coating system is attributed to self-healing effect of glass phase and toughening effect of ZrSiO4 in the coating. The fine ZrSiO4 particles can inhibit crystallization of glass coating while the agglomerated ZrSiO4 particles with a little larger size can pin microcracks in the glass phase during oxidation. The reason for the failure of ZSO-glass coating is that bubbles gradually grow up during oxidation and finally break through the ZSO-glass coating forming main oxygen diffusion channels. The service life of the ZSO-glass/SiC coating can be predicted by the bubble growth model.