HfB2-CNTs composites with enhanced mechanical properties prepared by spark plasma sintering

HfB2-x vol%CNTs (x=0, 5, 10, and 15) composites are prepared by spark plasma sintering. The influence of CNTs content and sintering temperature on densification, microstructure and mechanical properties is studied. Compared with pure HfB2 ceramic, the sinterability of HfB2-CNTs composites is remarkably improved by the addition of CNTs. Appropriate addition of CNTs (10 vol%) and sintering temperature (1800 degrees C) can achieve the highest mechanical properties: the hardness, flexural strength and fracture toughness are measured to be 21.8 +/- 0.5 GPa, 894 +/- 60 MPa, and 7.8 +/- 0.2 MPa m(1/2), respectively. This is contributed to the optimal combination of the relative density, grain size and the dispersion of CNTs. The crack deflection, CNTs debonding and pull-out are observed and supposed to exhaust more fracture energy during the fracture process.