Shrinkage, hardness and fracture toughness of ternary ZrB2-SiC-HfB2 composite with different amount of HfB2

Ternary ZrB2-SiC-HfB2 composites with different amount of 4, 8 and 12 vol% HfB2 were consolidated at 1800 degrees C, 9 min and 30 MPa SPS conditions. Microstructural evaluations were done by scanning electron microscopic (SEM). Densification was measured by Arashmidous method. Fracture toughness was determined by crack length measurement. Macro-hardness (Hv30.0) was measured by a Vickers indenter with 30 kg as applied load for 20 s on polished sections. The results showed with HfB2 ascent up to 8 vol%, fracture toughness was enhanced from 5.1 MPa m(0.5) up to 7.3 MPa m(0.5), but with more addition up to 12 vol%, fracture toughness was decreased to 6.2 MPa m(0.5). The maximum hardness, 17 GPa was obtained in composite which was consolidated at 1800 degrees C temperature for 9 min and under 30 MPa pressure with 8 vol% HfB2.