Transition metal diboride-silicon carbide-boron carbide ceramics with super-high hardness and strength

Three phase boride and carbide ceramics were found to have remarkably high hardness values. Six different compositions were produced by hot pressing ternary mixtures of Group IVB transition metal diborides, SiC, and B4C. Vickers' hardness at 9.8 N was-31 GPa for a ceramic containing 70 vol% TiB2, 15 vol% SiC, and 15 vol% B4C, increasing to-33 GPa for a ceramic containing equal volume fractions of the three constituents. Hardness values for the ceramics containing ZrB2 and HfB2 were-30% and 20% lower than the corresponding TiB2 containing ceramics, respectively. 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 previously reported ceramic con-taining equal volume fractions of TiB2, SiC and B4C was-54 GPa, the highest of the ceramics in the present study and higher than the hardness values reported for so-called "superhard" ceramics at comparable indentation loads. The previously reported ceramic containing 70 vol% TiB2, 15 vol% SiC, and 15 vol% B4C also displayed the highest flexural strength of-1.3 GPa and fracture toughness of 5.7 MPa center dot m1/2, decreasing to-0.9 GPa and 4.5 MPa center dot m1/2 for a ceramic containing equal volume fractions of the constituents.