Superhard refractory high-entropy diborides

Using first-principles calculations and companion experimental validations, we demonstrate that the valence electron concentration (VEC) can be used to self-consistently parameterize the bonding characteristics of high-entropy diborides (HEBs) and in turn predict their mechanical properties. When VEC is 10.0 per formula unit (f.u.), HEBs enter the superhard category where Hv>40GPa because bonding states are optimally filled to resist shear deformation. Conversely, above or below a VEC of 10.0, the hardness decreases due to the filling of antibonding or the emptying of bonding states of the HEBs, respectively. This result is supported by analyses of the electronic structure, bonding, antibonding, and electronic orbitals’ (metal d and B 2p) occupation as a function of VEC. To complement the first-principles calculations, four HEBs were synthesized using high power impulse magnetron sputtering to interrogate their crystalline structure and mechanical properties. All HEBs retain a single-phase AlB2-type hexagonal structure with highly dense nodular grain morphology. Hardness measurements reveal general agreement between theory and experiment. An HEB with VEC of 10.0/f.u. shows superhard characteristics, with micro- and nanoindentation hardness greater than 40 GPa. This combined entropy and VEC-based materials design formulation establishes a foundation for the discovery of high-entropy ceramics with enhanced thermomechanical properties, making them suitable for extreme engineering applications.

Duke Scholars

Author Stefano Curtarolo Thomas Lord Department of Mechanical Engineering and Materia ...

Author Hagen Eckert Thomas Lord Department of Mechanical Engineering and Materia ...

Author Simon Divilov Thomas Lord Department of Mechanical Engineering and Materia ...