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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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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Qin, M., Yan, Q., Liu, Y. et al. A new class of high-entropy M3B4 borides. J Adv Ceram 10, 166–172 (2021). https://doi.org/10.1007/s40145-020-0438-x
- high-entropy ceramics
- high-entropy borides
- reactive sintering
- spark plasma sintering
- Ta3B4-prototyped orthorhombic structure