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 B-4-O-B-4 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.