Superhard high-entropy AlB2-type diboride ceramics

Hardness was measured for six different nominally pure and single-phase high-entropy diboride ceramics with the AlB2 structure that were produced by a two-step process. Most of had relative densities greater than 99.5%. Vickers hardness average values ranged from 21.0 GPa to 25.4 at load 9.81 N, while increased range 33.1 48.3 0.49 N. Among compositions, highest N 48.3±2.3 (Cr0.2Hf0.2Ta0.2Ti0.2Zr0.2)B2 45.8±5.3 (Hf0.2Ta0.2Ti0.2W0.2Zr0.2)B2, both which are high enough be considered superhard. The present study demonstrated new class superhard materials.