Abstract
The metal borides: YReB4, YCrB4 (YCrB4 structural type), Y2ReB6, Sc2ReB6 (Y2ReB6), Y3ReB7, Y3MoB7, and Y3WB7 (Y3ReB7), and YMo3B7 (YMo3B7) structural types, and their solid-solutions: YRe1–xCrxB4, Y1–xScxCrB4, Y2–2xSc2xReB6, Y2Re1–xCrxB6, and YMo1–xWxB7 were analyzed using powder X-ray diffraction and energy-dispersive X-ray spectroscopy, and studied for their mechanical properties. These metal borides possess unique crystal structures, not found in any other type of borides: alternating metal and boron layers with boron being arranged in 5-, 6-, and 7-member rings (YCrB4, Y2ReB6), corrugated cages of 5- and 13-member boron rings (Y3ReB7), as well as stacked layers of ribbons of hexagonal boron atoms 6 rings wide (YMo3B7). Although none of these borides in pure form possess high hardness, their solid solutions are superhard (Vickers hardness above 40 GPa): 42.48 ± 2.13 GPa for an alloy with a nominal composition of (YRe0.5Cr0.5):4B, 42.02 ± 2.05 GPa for (Y0.5Sc0.5Cr):4B and 41.33 ± 2.18 GPa for (YScRe):6B...
Published Version
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