Ablative Property and Mechanism of ZrC-TaC/ZrC-SiC Coatings on C/C Composites under Different Heat Fluxes

In high-temperature aerobic environment, carbon materials have to be protected to delay the oxidation process. In this work, ZrC-TaC coatings were deposited by supersonic atmospheric plasma spraying on ZrC-SiC-coated C/C composites and ablation tests were conducted by oxyacetylene torch under different heat fluxes. When subjected to 4.2 WM/m2 for 20 s, the mass and linear ablation rates of the ZrC-TaC/ZrC-SiC coating system were 0.0076 g/s and 0.0005 mm/s, respectively. In the ablation process, the infiltration of the oxygen and liquid Ta2O5 into the inner layer resulted in significant oxidation of the ZrC-SiC inner layer. Due to the oxidation and microstructure evolution of the ZrC-TaC and ZrC-SiC layers, the porous Zr-Ta-O oxide layer, oxidized ZrC-TaC, and ZrC-SiC layers formed a better chemical combination and showed higher resistance to ablation. However, for a heat flux of 3.2 WM/m2, the molten Zr-Ta-O oxides that have good self-healing ability, were mainly formed on the ablative surface; liquid Ta2O5 together with trace oxygen could penetrate into the inner layers, resulting in the lack of chemical combination between the layers. As a result, the molten oxides were easy to denudate during the ablation and cooling process and showed lower resistance to ablation.