Water vapor corrosion behavior and failure mechanism of air sprayed bi-layer Yb2Si2O7/SiC and tri-layer Yb2Si2O7/ (SiCw-Mullite)/SiC environmental barrier coating

Abstract

To improve the corrosion resistance of Cf/SiC composites in a water vapor oxygen coupled environment, the bi-layer Yb2Si2O7/SiC and tri-layer Yb2Si2O7/(SiCw-Mullite, SM)/SiC environment barrier coatings were designed and prepared on the surface of Cf/SiC composites by chemical vapor deposition and sol-gel method united with air spraying. Results show that the mass loss of bi-layer Yb2Si2O7/SiC coating coated samples was 17.24 ​× ​10−3 ​g ​cm−2 after 200 ​h oxidation at 1673 ​K, and the average compression strength retention rate was only 79.44% due to the formation of wide penetrating cracks. Comparatively, SiC whiskers in SM middle coating can not only increase the crack propagation resistance of mullite middle coating, but also alleviate the difference of coefficient of thermal expansion between Yb2Si2O7 outer coating and mullite middle coating. Therefore, the mass loss of tri-layer Yb2Si2O7/SM/SiC coating coated samples was only 2.93 ​× ​10−3 ​g ​cm−2 after 200 ​h oxidation at 1673 ​K, and the average compression strength retention rate was up to 98.79%.