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

The mullite and ytterbium disilicate (β-Yb 2 Si 2 O 7 ) powders as starting materials for the Yb 2 Si 2 O 7 /mullite/SiC tri-layer coating are synthesized by a sol–gel method. The effect of SiC whiskers on the anti-oxidation properties of Yb 2 Si 2 O 7 /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. Yb 2 SiO 5 , α-Yb 2 Si 2 O 7 , and β-Yb 2 Si 2 O 7 were gradually formed between 800 and 1000°C, and Yb 2 SiO 5 and α-Yb 2 Si 2 O 7 were completely transformed into β-Yb 2 Si 2 O 7 at a temperature above 1200°C. The weight loss of Yb 2 Si 2 O 7 /(SiC w –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 Yb 2 Si 2 O 7 /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-Yb 2 Si 2 O 7 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 SiO 2 (oxidation of SiC whiskers) and mullite particles.