Enhanced oxidation resistance of high-entropy diborides by multi-component synergistic effects

Oxidation resistance is critical for high-entropy diborides (HEBs) to be used as thermal structural components under oxygen-containing high-temperature environments. Here, we successfully realize the exploitation of (Zr, Ta, Cr, W) B₂ HEBs with superior oxidation resistance by comprehensively screening their compositions. To be specific, 21 kinds of HEB-xTM (x = 0–25 mol%, TM = Zr, Ta, Cr, and W) samples are fabricated via an ultrafast high-temperature sintering technique. The as-fabricated HEB-5Cr samples show the best oxidation resistance at 1673 K among all the samples. Subsquent oxidation investigations further confirm the as-fabricated HEB-5Cr samples possess superior oxidation resistance with the parabolic oxidation behavior across 1473–1773 K. Such superior oxidation resistance is believed to result from the multi-component synergistic effects. Particularly, the Ta⁵⁺ and W⁴⁺ cations with high ionic field strengths can promote the formation of ⁴B–O–⁴B linkages between [BO₄] tetrahedrons by charge balance, which can stabilize the three-dimensional skeletal structure of B₂O₃ glass and consequently result in an improved viscosity of the B₂O₃ glassy layer. In addition, the ZrO₂ and Cr₂O₃ with high melting points can dissolve into the B₂O₃ glass to increase its glass transition temperature, leading to an enhanced viscosity of the B₂O₃ glassy layer.