Hardness measurements for high-pressure prepared TaB and nano-TaC ceramics

The Vickers hardness of the bulk TaB and nano-TaC ceramics sintered at high pressure and high temperature were measured by using a diamond indentation method. Our tests gave a maximum Vickers hardness of 13.9 GPa for TaB, and 19.2 GPa for nano-TaC ceramics under a load of 29.4 N. The hardness of nano-TaC-5 wt% Co composites was also measured under the same load for comparison, which was found to be much lower than that of TaB and nano-TaC. The relative densities calculated by the Archimedes method are 13.5 g/cm 3 for TaB and 13.6 g/cm 3 for nano-TaC. The averaged fracture toughness is 6.8 ± 0.3 MPa m 1/2 for TaB and 5.0 ± 0.2 MPa m 1/2 for nano-TaC. Our results show that the hardness of the TaB may not be as high as previous reports.