A new class of high-entropy M3B4 borides

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)(3)B-4 and (V0.2Cr0.2Nb0.2Ta0.2W0.2)(3)B-4 were fabricated via reactive spark plasma sintering of high-energy-ball-milled elemental boron and metal precursors. The sintered specimens were similar to 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.

Automated summary

A new class of high-entropy M3B4 borides with Ta3B4-prototyped orthorhombic structure has been synthesized in bulk form. The specimens were fabricated through reactive spark plasma sintering and showed high Vickers hardness values, expanding the family of reported high-entropy ceramics with different structures.