Effect of SiC whiskers on the anti‐oxidation properties of Yb <sub>2</sub> Si <sub>2</sub> O <sub>7</sub> /mullite/SiC tri‐layer environmental barrier coating for CMCs
Ling Pan, Pengju Chen, Peng Xiao, Ling He, Wei Zhou, Yang Li
Abstract
Abstract 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.