Long-term ablation mechanisms of the YB4-Al2O3-Si3N4 modified Cf/ HfC-SiC composites at 2600 C

In this work, the long-term and repeated ablation properties of the YB4-Al2O3-Si3N4 modified Cf/HfC-SiC composites were characterized by air plasma torch at 2600 degrees C for 300 s, twice. Both the structural stability and the viscosity of the oxide layer affected the ablation resistance of the composites. The structural stability of oxide layer was improved by forming nano c-HfO2 grains and the high-viscosity Al-Si-Y-O glassy phase, which increased the ablation resistance of the composites. However, the oxidation of Si3N4 resulted in the formation of NO, NO2 and excessive SiO2 glassy phase, which both leaded to a porous structure and reduced the viscosity of the oxides layer. Hence, the ablation resistance of the composites was reduced with addition of the Si3N4.