Effect of SiC whiskers on the anti‐oxidation properties of Yb2Si2O7/mullite/SiC tri‐layer environmental barrier coating for CMCs

Abstract

AbstractThe mullite and ytterbium disilicate (β‐Yb2Si2O7) powders as starting materials for the Yb2Si2O7/mullite/SiC tri‐layer coating are synthesized by a sol–gel method. The effect of SiC whiskers on the anti‐oxidation properties of Yb2Si2O7/mullite/SiC tri‐layer coating for C/SiC composites in the air environment is deeply studied. Results show that the formation temperature and complete transition temperature of mullite were 800–1000 and 1300°C, respectively. Yb2SiO5, α‐Yb2Si2O7, and β‐Yb2Si2O7 were gradually formed between 800 and 1000°C, and Yb2SiO5 and α‐Yb2Si2O7 were completely transformed into β‐Yb2Si2O7 at a temperature above 1200°C. The weight loss of Yb2Si2O7/(SiCw–mullite)/SiC tri‐layer coating coated specimens was 0.15 × 10−3 g cm−2 after 200 h oxidation at 1400°C, which is lower than that of Yb2Si2O7/mullite/SiC tri‐layer coating (2.84 × 10−3 g cm−2). The SiC whiskers in mullite middle coating can not only alleviate the coefficient of thermal expansion difference between mullite middle coating and β‐Yb2Si2O7 outer coating, but also improve the self‐healing performance of the mullite middle coating owing to the self‐healing aluminosilicate glass phase formed by the reaction between SiO2 (oxidation of SiC whiskers) and mullite particles.