Effect of La₂O₃ content on the oxygen barrier ability of the HfB₂‐SiC coating at 1973 K

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 highmelting-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.