Corrosion behavior of Y₂O₃-doped mullite-ZrSiO₄ coatings applied on C/C–SiC composites in the presence of moisture at temperatures of 1373–1773 K

Commercial mullite powders show great potential for application in environmental barrier coatings. However, most of the commercial mullite powders contain amorphous silica, which produces volatile silicon hydroxide in hot steam. This leads to serious recession of mullite coatings in hot water vapor. In this study, a Y₂O₃-doped mullite-ZrSiO₄ coating was fabricated on C/C–SiC composites using the slurry painting method. The addition of Y₂O₃ resulted in the elimination of the residual silica and derived-cristobalite in the commercial mullite powder, leading to the formation of a stable mullite-Y₂Si₂O₇–ZrSiO₄ coating. This indicates that Y₂O₃ can efficiently enhance the phase stability of commercial mullite at high temperatures. In addition, the corrosion behaviours of Y₂O₃-doped mullite-ZrSiO₄ coatings were investigated at 1373, 1573, and 1773 K in a 95% H₂O-5% O₂ atmosphere. The coatings exhibited good corrosion resistance. The 15 mol% Y₂O₃ coating showed a weight loss rate of 1.62 wt % when exposed to hot steam for 10 h at 1573 K. This value is only 1/8th of that of the uncoated sample. Moreover, ZrSiO₄ improved the water corrosion resistance of the Y₂O₃-doped mullite-ZrSiO₄ coatings at 1573 K.