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

Abstract

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.