Superhard Boride-carbide Particulate Composites

Particulate composites composed of boride and carbide ceramics were found to have remarkably high hardness values. Two different compositions were produced by hot-pressing commercially available ZrB2, SiC, and B4C powders. Using a Vickers' indentation load of 9.8 N, measured hardness was ∼20 GPa for a ceramic containing 70 vol% ZrB2, 15 vol% SiC, and 15 vol% B4C, but increased to ∼29 GPa for a ceramic containing equal volume fractions of the three constituents. Hardness values also increased as indentation load decreased due to the indentation size effect. at an indentation load of 0.49 N, the hardness of the ceramic containing equal volume fractions of the three constituents was ∼43 GPa, which was higher than the hardness values reported for so-called “superhard” ceramics at comparable indentation loads.