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 B 4 C. Vickers' hardness at 9.8 N was ~31 GPa for a ceramic containing 70 vol% TiB 2 , 15 vol% SiC, and 15 vol% B 4 C, increasing to ~33 GPa for a ceramic containing equal volume fractions of the three constituents. Hardness values for the ceramics containing ZrB 2 and HfB 2 were ~30% and 20% lower than the corresponding TiB 2 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 containing equal volume fractions of TiB 2 , SiC and B 4 C 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% TiB 2 , 15 vol% SiC, and 15 vol% B 4 C also displayed the highest flexural strength of ~1.3 GPa and fracture toughness of 5.7 MPa·m1/2, decreasing to ~0.9 GPa and 4.5 MPa·m1/2 for a ceramic containing equal volume fractions of the constituents. [ABSTRACT FROM AUTHOR]