High-entropy monoborides: Towards superhard materials

• Published in: Scripta materialia Vol. 189; pp. 101 - 105
• Main Authors: Qin, Mingde, Yan, Qizhang, Wang, Haoren, Hu, Chongze, Vecchio, Kenneth S., Luo, Jian
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.12.2020
• Subjects: High-entropy ceramics; High-entropy monoborides; Reactive sintering; Superhard materials; Vickers hardness; Reactive sintering; High-entropy ceramics; Vickers hardness; High-entropy monoborides; Superhard materials
• ISSN: 1359-6462; 1872-8456
• DOI: 10.1016/j.scriptamat.2020.08.018

•First synthesis of high-entropy monoborides (HEMBs).•Vickers hardness values are ~22–26 GPa with an indentation load of 9.8 N.•Vickers hardness values are ~32–37 GPa with an indentation load of 0.98 N.•(V0.2Cr0.2Nb0.2Ta0.2W0.2)B is harder than (Ta, W)B and high-entropy metal diborides.•(V0.2Cr0.2Nb0.2Ta0.2W0.2)B shows comparable hardness with the superhard WB4. Single-phase high-entropy monoborides (HEMBs) of the CrB prototype structure have been synthesized for the first time. Reactive spark plasma sintering of ball milled mixtures of elemental precursor powders produced bulk (V0.2Cr0.2Nb0.2Mo0.2Ta0.2)B, (V0.2Cr0.2Nb0.2Mo0.2W0.2)B, and (V0.2Cr0.2Nb0.2Ta0.2W0.2)B HEMB specimens of ~98.3–99.5% relative densities. Vickers hardness was measured to be ~22–26 GPa at an indentation load of 9.8 N and ~32–37 GPa at 0.98 N. In particular, the load-dependent hardness of (V0.2Cr0.2Nb0.2Ta0.2W0.2)B is higher than those of ternary (Ta0.5W0.5)B (already considered as superhard) and hardest reported high-entropy metal diborides, and on a par with the classical superhard boride WB4. [Display omitted]