Enhancing the Vickers hardness, melting point and thermodynamic properties of hafnium dodecaboride

Abstract

Although HfB12 is a promising surperhard material because of the boron cuboctahedron cage, the Vickers hardness of HfB12 remains controversial. We apply first-principles calculations to investigate the influence of a transition metal on the structural stability, Vickers hardness and thermodynamic properties of HfB12. The Vickers hardness of HfB12 is 39.3 GPa. In particular, the Vickers hardness of TM-doped HfB12, which are novel superhard materials, is larger than 40 GPa. The Vickers hardness of Re-doped HfB12 is up to 47.6 GPa. The improvement of Vickers hardness is that the introduction of an alloying element improves the localized hybridization between B and Hf, and then enhances the bond strength of the B-B covalent bond and the Hf-B bond. In addition, these alloying elements enhance the melting-point and Debye temperature of the HfB12. Therefore, we believe that alloying is an effective method to improve the Vickers hardness and thermodynamic properties of HfB12 superhard material.