Exploring Hf-Ta-O precipitation upon ablation of Hf-Ta-Si-C coating on C/C composites

To improve the ablation resistance of C/C composites, a Hf-Ta-Si-C coating was fabricated by chemical vapor co-deposition. The ablation resistances of Hf-Si-C and Hf-Ta-Si-C coatings were characterized comparatively. After introducing Ta, the ablation resistance, smoothness and integrity of the ablated coating improved. Hf-Si-O and Hf-Ta-Si-O glass wires were observed. To investigate the reaction processes of the two types of glass wires, TEM observation was carried out and coupled to molecular dynamics simulations. These illustrated that Hf and Ta atoms tend gather together at high temperature. To investigate the effect of Hf-Ta-O precipitation on the ablation behavior, supplementary experiments were carried out on bulk ceramics with the same target composition, confirming that precipitation reaction could accelerated the formation of a smooth and intact oxide layer, playing a positive role in protecting C/C composites.