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A new class of high-entropy M3B4 borides of the Ta3B4-prototyped orthorhombic structure has been synthesized in the bulk form for the first time. Specimens with compositions of (V0.2Cr0.2Nb0.2Mo0.2Ta0.2)3B4 and (V0.2Cr0.2Nb0.2Ta0.2W0.2)3B4 were fabricated via reactive spark plasma sintering of high-energy-ball-milled elemental boron and metal precursors. The sintered specimens were ~98.7% in relative densities with virtually no oxide contamination, albeit the presence of minor (4-5 vol%) secondary high-entropy M5B6 phases. Despite that Mo3B4 or W3B4 are not stable phase, 20% of Mo3B4 and W3B4 can be stabilized into the high-entropy M3B4 borides. Vickers hardness was measured to be 18.6 and 19.8 GPa at a standard load of 9.8 N. This work has further expanded the family of different structures of high-entropy ceramics reported to date.


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A new class of high-entropy M3B4 borides

Show Author's information Mingde QINQizhang YANYi LIUJian LUO( )
Department of NanoEngineering, Program of Materials Science and Engineering, University of California, San Diego, La Jolla, CA, 92093, USA

Abstract

A new class of high-entropy M3B4 borides of the Ta3B4-prototyped orthorhombic structure has been synthesized in the bulk form for the first time. Specimens with compositions of (V0.2Cr0.2Nb0.2Mo0.2Ta0.2)3B4 and (V0.2Cr0.2Nb0.2Ta0.2W0.2)3B4 were fabricated via reactive spark plasma sintering of high-energy-ball-milled elemental boron and metal precursors. The sintered specimens were ~98.7% in relative densities with virtually no oxide contamination, albeit the presence of minor (4-5 vol%) secondary high-entropy M5B6 phases. Despite that Mo3B4 or W3B4 are not stable phase, 20% of Mo3B4 and W3B4 can be stabilized into the high-entropy M3B4 borides. Vickers hardness was measured to be 18.6 and 19.8 GPa at a standard load of 9.8 N. This work has further expanded the family of different structures of high-entropy ceramics reported to date.

Keywords:

high-entropy ceramics, high-entropy borides, reactive sintering, spark plasma sintering, Ta3B4-prototyped orthorhombic structure
Received: 18 September 2020 Revised: 29 October 2020 Accepted: 09 November 2020 Published: 08 December 2020 Issue date: February 2021
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Publication history
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Publication history

Received: 18 September 2020
Revised: 29 October 2020
Accepted: 09 November 2020
Published: 08 December 2020
Issue date: February 2021

Copyright

© The Author(s) 2020

Acknowledgements

This work is partially supported by an office of Naval Research MURI Program (Grant No. N00014-15-1-2863). Qizhang YAN and Jian LUO also acknowledge partial support from the Air Force Office of Scientific Research (Grant No. FA9550-19-1-01327) for the microscopy work.

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