Effect of La ₂ O ₃ content on the oxygen barrier ability of the HfB ₂ ‐SiC coating at 1973 K

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.