Hot Pressed HfB 2 and HfB 2 –20 vol%SiC Ceramics Based on HfB 2 Powder Synthesized by Borothermal Reduction of HfO 2 *

Phase pure hafnium diboride (HfB 2 ) powder was synthesized by borothermal reduction of hafnium dioxide using amorphous boron at relatively low temperature (1600°C) in vacuum. The synthesized HfB 2 powder had an average particle size of 1.37 μm with an equiaxed shape, and a low oxygen content of 0.79 wt%. Using the as‐synthesized HfB 2 powder and a commercial SiC, HfB 2 monolithic, and HfB 2 –20 vol%SiC composite were hot pressed at 2000°C to relative densities of 95.7% and 99.2%, respectively. With the addition of SiC, the grain size decreased and the fracture behavior changed from intergranular to a mixed mode, which resulted in a high flexural strength of 993±90 MPa for the composite. Fracture toughness of the composite was 6.29±0.65 MPa m 1/2 , which was significantly higher than that of the HfB 2 monolithic and the reported values in literature.