Nanosized Hf6Ta2O17 particles reinforced HfC ceramic coating for high temperature applications

There is an urgent need for the thermal protection of carbon/carbon composites to increase their service span in aerospace field. As members of ultra-high temperature ceramics, HfC and ZrC are thought to be alternative materials, but their poor oxidation behavior and fracture toughness at temperature over 2000 degrees C prevent them from taking full advantages. Herein, we synthesized nanosized Hf6Ta2O17 powders and introduced them into HfC ceramic to tackle the above problems. Plasma-sprayed HfC coatings with Hf6Ta2O17 varied from 0 to 15 mol.% (0, 1.25, 2.5, 5, 15) were exposed to an oxyacetylene torch with a heat flux of 2.38 MW/m2. The one with 2.5 mol.% Hf6Ta2O17 showed the best ablation resistance. Smaller doping was unable to effectively hinder oxygen diffusion given the inadequate compactness of the formed scale, conversely substantial humps and ruptures formed on the samples with higher amounts, acting as straightforward paths for oxygen.

Automated summary

There is a urgent need to protect carbon/carbon composites in aerospace field by improving their thermal resistance. HfC and ZrC, as ultra-high temperature ceramics, are considered as alternative materials, but their poor oxidation behavior and fracture toughness at temperatures over 2000 degrees C limit their full potential. In this study, we synthesized nanosized Hf6Ta2O17 powders and incorporated them into HfC ceramic to address these issues. Plasma-sprayed HfC coatings containing varying amounts of Hf6Ta2O17 (0, 1.25, 2.5, 5, 15 mol.%) were subjected to an oxyacetylene torch with a heat flux of 2.38 MW/m2. The coating with 2.5 mol.% Hf6Ta2O17 exhibited the best resistance to ablation. Smaller doping amounts were ineffective in hindering oxygen diffusion due to inadequate scale compactness, while higher amounts resulted in significant humps and ruptures, creating direct paths for oxygen.