Non-equimolar (Hf,Zr,Ta,W)B2 high-entropy diborides enable superior oxidation resistance

Abstract

Developing superior oxidation resistance of high-entropy diborides is critical for extending their potential applications in harsh environments. Herein, we developed non-equimolar (Hf,Zr,Ta,W)B2 high-entropy diborides with superior oxidation resistance by adjusting W contents for the first time. The as-fabricated (Hf0.28Zr0.28Ta0.28W0.15)B2 samples are predicted to possess superior oxidation resistance at 1473–1773 K through the oxidation depth quantitative analysis obtained by machine learning, which is attributed to the reason that the moderate WO3 can effectively inhibit the volatilization of B2O3. Furthermore, a four-layered structure is found in the generated product layers at 1773 K, which is due to the preferential oxidation of Hf and Zr elements at low oxygen partial pressure and the different diffusion activation energies of oxide products. The preferential oxidation of Hf and Zr elements is further demonstrated by the computational phase stability diagrams, and oxygen adsorption energies and charge transfer between oxygen atoms and different metal adsorption sites via first-principles calculations. Such superior performance endows (Hf0.28Zr0.28Ta0.28W0.15)B2 with potential applications as ultrahigh-temperature structural materials.