Effect of La <sub>2</sub> O <sub>3</sub> content on the oxygen barrier ability of the HfB <sub>2</sub> ‐SiC coating at 1973 K
Deyu Qian, Yuexing Chen, Xuanru Ren, Leyu Wang, J. Paul Chen, Yan Zhao, Dalin Shi, Yuan Li, Haobo Du, Peizhong Feng
Abstract
Abstract To inhibit the destructive evolution of the HfB 2 ‐SiC coating during oxidation, La 2 O 3 was added to modify the oxygen‐blocking capability of the HfB 2 ‐SiC coating. The effect of La 2 O 3 content on the oxygen barrier capacity of HfB 2 ‐SiC was investigated. The addition of 5 vol.% La 2 O 3 lowered the oxidation activity and strengthened the inert oxygen barrier capacity of the HfB 2 ‐SiC coating, which made the oxygen permeability and maximum weight change rate of the coating decrease by 30.32% and 73.97%, respectively. Due to the solid solution reaction of the dispersed La 2 O 3 , HfO 2 , and SiO 2 nanoparticles, a stable Hf‐B‐La‐Si‐O multiphase glass was formed on the surface of the coating. Besides, the high‐melting‐point particles, such as HfO 2 , La 2 Hf 2 O 7 , and HfSiO 4 , dispersed in the glass layer as hard particles and formed a mosaic structure based on the Hf‐B‐La‐Si‐O compound, which increased the cumulative protection efficiency of the HfB 2 ‐SiC coating to 98.5% and reduced the inert factor value by 84.57%. However, the excessive consumption of SiO 2 glass by La 2 O 3 results in dendritization of the generated glass when the La 2 O 3 content is above 10 vol.%, which reduced the self‐healing capability of the generated glass and instead weakened the oxygen barrier properties of the HfB 2 ‐SiC‐La 2 O 3 coatings.