Pressureless densification of HfB2-based ceramics using HfB2 powders by borothermal reduction

Abstract Using boron and SiC as additives, the pressureless densification of HfB2 powders synthesized by borothermal reduction with water-washing process was studied. The water-washing HfB2 powders showed good sinterability (relative density: 96.2%), due to the small grain size with the in-situ boron impurities, whereas the microstructure of the sintered sample was coarsened with average grain size of 10.19 ± 4.12 μm. After adding 5 wt% boron, the relative density was improved (98.7%) and the grain size was reduced (4.68 ± 1.17 μm). In order to further inhibit the grain growth, enhance densification and mechanical properties, 20 vol% SiC was added. Finally, fully dense HfB2-based ceramics (relative density: 99.9%) with small grain size of 3.45 ± 0.88 μm were fabricated by the combination of boron and SiC. The Vickers’ hardness and fracture toughness of HfB2 with additions of boron and SiC were 18.27 ± 1.95 GPa and 3.33 ± 0.16 MPa m1/2, respectively.