Oxidation behavior of (Hf0.2Zr0.2Ta0.2Ti0.2Me0.2)B2 (Me=Nb,Cr) high-entropy ceramics at 1200 °C in air

The oxidation behavior of (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)B2 and (Hf0.2Zr0.2Ta0.2Cr0.2Ti0.2)B2 high entropy boride ceramics at 1200 °C was investigated to provide insights into their microstructural evolution and oxidation mechanism. The results showed that the oxide layer thickness of (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)B2 was about 112 μm, much thicker than the counterpart of (Hf0.2Zr0.2Ta0.2Cr0.2Ti0.2)B2 (∼62 μm). The differences in oxidation response and oxidation resistance between these two material systems were mainly pertained to the generation of different structures of oxide layer. For the (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)B2 sample, the oxide layer was composed of four-layer structure (porous-dense-porous-dense). In contrast, the oxide layers of (Hf0.2Zr0.2Ta0.2Cr0.2Ti0.2)B2 sample exhibited a distinctly laminated structure.