Oxygen barrier resistance of HfB2-MoSi2-TaB2 coatings in a wide temperature region

Abstract

HfB2-MoSi2-based ultra-high temperature ceramic (UHTC) coatings have shown remarkable antioxidant effects owing to the formation of silicate glass layers with low oxygen permeability in high-temperature environments, which shows great potential in the antioxidation of carbon structural materials. To further enhance the oxidation resistance of the HfB2-MoSi2-based coating in a wide temperature region, the influence of volume ratio between HfB2 and TaB2 on the antioxidant capacity of the HfB2-MoSi2-TaB2 coatings was investigated. The addition of 15 vol% TaB2 in the 60HfB2-40MoSi2 coating delays the initial oxidation temperature of the 60HfB2-40MoSi2 sample from 300 °C to 500 °C, which decreased the oxidation loss by 75.85% during dynamic oxidation. In oxidation process at 900 °C and 1700 °C, the weight gains of the 45HfB2-40MoSi2–15TaB2 coating reduced by 78.56% and 63.14%, respectively. Due to the coexistence of 45 vol%HfB2 and 15 vol%TaB2, the suitable Ta5+ promoted the homogenization and dispersion of Hf/Ta-oxides, which forms the coral-like Hf/Ta oxides skeleton in the glass layer, thus preventing the oxygen penetration and decreasing the inert factor of the HfB2-MoSi2 coating at 1700 °C by 51.19%. However, excessive TaB2 weakened the self-healing ability of the Ta-Hf-Si-O glass layer and inhibited the oxygen barrier effect of the HfB2-MoSi2-TaB2 coating.