Oxidation and ablation behaviour of multiphase ultra-high-temperature ceramic Ta0·5Zr0·5B2–Si–SiC protective coating for graphite

Abstract

To provide reliable oxidation protection for carbon materials under harsh high-temperature aerobic environments, a dense monolayer-multiphase ultra-high-temperature ceramic Ta0·5Zr0·5B2–Si–SiC (TZSS) coating was fabricated by a combination of dipping and in-situ reaction. The oxidation resistance of the TZSS coating was investigated at 1923 K in air. The results indicated that the TZSS coating could offer at least 70 h of oxidation protection for the matrix material. The synergistic oxygen-blocking effect of the thick oxide layer formed during the oxidation test and the inner coating, played a key role in the oxidation protection process. These were responsible for the excellent oxidation resistance ability of the TZSS coating. Additionally, the ablation performance of the TZSS coating was also investigated under increased heat flux from 2.4 MW/m2 to 4.2 MW/m2. The ablation behaviours changed from the oxidation and evaporation of coating materials to mechanical scouring, corresponding to increased mass and linear ablation rates. Interestingly, after ablation for 40 s under a heat flux of 4.2 MW/m2, a new microstructure composed of “lath-like” Ta4Zr11O32 solid solution grains was found in the ablation center. This oxide layer possessed few micropores, which could provide reliable protection for the matrix material under ultra-high-temperature oxygen-containing airflow erosion, thus preventing further damage to the composite.