Ultra-high temperature ablation behavior of CVD-Hf5TaC6 solid solution ceramic coating for C/C composites: Experiment and first-principle calculation

To address the problem that the oxidized layer of HfC coating was loose and porous, HfxTayCx+y solid solution with good thermal stability and ablation resistance was proposed as coating for carbon/carbon (C/C) composites. In present work, HfC, TaC and the novel Hf5TaC6 solid solution coatings were synthesized on C/C composites by chemical vapor deposition. Combing with the ablation test and density functional theory calculations about oxygen-adsorption energies, the ablation mechanism of HfC, TaC and Hf5TaC6 solid solution coatings were investigated. The Hf5TaC6 solid solution coating showed superior ablation resistance than that of HfC and TaC coatings, benefitting from the solid-liquid composite oxide layer with HfO2 and Hf6Ta2O17 as solid structure to further stabilize the oxides and resist mechanical erosion, Ta2O5 as the liquid filler to heal cracks to inhibit the oxygen infiltration.