Investigation of mechanical characteristics of materials based on refractory borides

The object of research is the effect of sintering under pressure (10 MPa–4.1 GPa) on the formation of the structure and properties of ZrB2, HfB2, and composites on their bases. It has been found that high pressure consolidation results in an improvement of mechanical characteristics. In particular, the hardness and fracture toughness of the materials sintered under 4.1 GPa pressure are higher than those of the materials obtained under hot pressing conditions at 20–30 MPa and spark-plasma sintering at 50 MPa. High-pressure sintered HfB2 demonstrated hardness HV(9.8 N)=21.3±0.8 GPa, HV(49 N)=19.3±1.3 GPa, and HV(98 N)=19.2±0.5 GPa and fracture toughness K1C(49 N)=7.2 MPa·m0.5 and K1C(98 N)=5.7 MPa·m0.5. The HfB2 sintered by hot pressing at 1850 °C and 30 MPa demonstrated hardness: HV(9.8 N)=19.0 GPa, HV(49 N)=18.7 GPa, and HV(98 N)=18.1 GPa, K1C(9.8 N)=7.7 MPa·m0.5, K1C(49 N)=6.6 MPa·m0.5 and K1C(98 N)=5.3 MPa·m0.5. High pressure sintered ZrB2 (a=0.3167 nm, c=0.3528 nm, γ=6.2 g/cm3) demonstrated HV(9.8 N)=17.7±0.6 GPa, HV(49 N)=15.4±1.2 GPa, and HV(98 N)=15.3±0.36 GPa and K1C(9.8 N)=4.3 MPa·m0.5, K1C(49 N)=4.2 MPa·m0.5 and K1C(98 N)=4.0 MPa·m0.5. Addition of 20 wt. % of SiC to ZrB2 and sintering under high pressure (4.1 GPa) allowed essential increase of hardness to HV(9.8 N)=24.2±0.7 GPa, HV(49 N)=16.7±0.5 GPa, and HV(98 N)=17.6±0.4 GPa and fracture toughness to K1C(49 N)=7.1 MPa·m0.5, K1C(98 N)=6.2 MPa·m0.5; the material density was γ=5.03 g/cm3. Additions of SiC and Si3N4 to ZrB2 lead to some increase in fracture toughness (up to K1C(98 N)=9.2 MPa·m0.5). The developed ZrB2- and HfB2-based materials and composites can be used for aerospace applications, in cutting and refractory industries, etc