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

To inhibit the destructive evolution of the HfB2-SiC coating during oxidation, La2O3 was added to modify the oxygen-blocking capability of the HfB2-SiC coating. The effect of La2O3 content on the oxygen barrier capacity of HfB2-SiC was investigated. The addition of 5 vol.% La2O3 lowered the oxidation activity and strengthened the inert oxygen barrier capacity of the HfB2-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 La2O3, HfO2, and SiO2 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 HfO2, La2Hf2O7, and HfSiO4, 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 HfB2-SiC coating to 98.5% and reduced the inert factor value by 84.57%. However, the excessive consumption of SiO2 glass by La2O3 results in dendritization of the generated glass when the La2O3 content is above 10 vol.%, which reduced the self-healing capability of the generated glass and instead weakened the oxygen barrier properties of the HfB2-SiC-La2O3 coatings.