Oxidation behaviors of (Hf_0.25Zr_0.25Ta_0.25Nb_0.25)C and (Hf_0.25Zr_0.25Ta_0.25Nb_0.25)C-SiC at 1300–1500 °C

In this work, high-entropy ceramics (Hf_0.25 Zr_0.25Ta_0.25Nb_0.25)C (HZTNC) and HZTNC doped with 20 vol% SiC (HZTNC-SiC) were fabricated by spark plasma sintering. Their oxidation behavior was investigated over the temperature range of 1300–1500 °C for up to 60 min. Both HZTNC and HZTNC-SiC exhibited good oxidation resistance, and their weight change as a function of oxidation time obeyed a parabolic law. Through XRD, microstructure observation, and elemental mapping analysis of the oxide layers, it was found that the formation of Nb₂Zr₆O₁₇, Hf₆Ta₂O₁₇, and (Ta, Nb)₂O₅ mixed-oxide layers effectively protected the matrix from further oxidation. Microcracks began to appear on the oxide layer of HZTNC at high temperatures after 60 min of oxidation. However, the addition of SiC in HZTNC suppressed these microcracks at high temperatures due to the active oxidation of SiC. Compared with the oxides formed on HZTNC, the additional formation of Hf(Zr)SiO₄ on HZTNC-SiC could further improve its oxidation resistance over HZTNC ceramics.