Oxidation Properties of High-Entropy Boride (Ti0.2Zr0.2Nb0.2Hf0.2Ta0.2)B2 Synthesized by DC Arc Discharge Plasma

High-entropy borides (HEB) are a new class of unique materials characterized by outstanding properties. In this paper, a comprehensive study of the oxidation properties of a high-entropy boride of the composition (Ti0.2Zr0.2Nb0.2Hf0.2Ta0.2)B2 is carried out for the first time. HEB was synthesized by a vacuum-free electric arc method by a direct current arc discharge of 100 A for 90 s. The oxidation stability of the obtained powder (Ti0.2Zr0.2Nb0.2Hf0.2Ta0.2)B2 was studied by two approaches. In the first case, it was found that the (Ti0.2Zr0.2Nb0.2Hf0.2Ta0.2)B2 sample is characterized by an oxidation temperature of ~800°С based on the assessment of phase transformations in situ during heating of the powder in the temperature range from 0 to 1200°С in air. In the second case, it was determined that the (Ti0.2Zr0.2Nb0.2Hf0.2Ta0.2)B2 powder can withstand temperatures up to ~700°С according to the results of the analysis of the composition of HEB during oxidation in an atmospheric furnace. The formation of oxides is confirmed by the results of scanning electron microscopy. The characteristics of HEB obtained in the work are consistent with the currently known literature data.