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.

Automated summary

This study characterized the long-term and repeated ablation properties of modified Cf/HfC-SiC composites with YB4-Al2O3-Si3N4 under an air plasma torch. The structural stability and viscosity of the oxide layer were found to affect the ablation resistance of the composites. By forming nano c-HfO2 grains and high-viscosity Al-Si-Y-O glassy phase, the structural stability of the oxide layer was improved, resulting in enhanced ablation resistance. However, the oxidation of Si3N4 led to the formation of NO, NO2, and excessive SiO2 glassy phase, which resulted in a porous structure and reduced the viscosity of the oxide layer. Therefore, the addition of Si3N4 decreased the ablation resistance of the composites.