Hot pressed HfB₂ and HfB₂-20 vol%SiC ceramics based on HfB₂ powder synthesized by borothermal reduction of HfO₂

Phase pure hafnium diboride (HfB2) powder was synthesized by borothermal reduction of hafnium dioxide using amorphous boron at relatively low temperature (1600°C) in vacuum. The synthesized HfB2 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 HfB2 powder and a commercial SiC, HfB2 monolithic, and HfB2-20 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 m1/2, which was significantly higher than that of the HfB2 monolithic and the reported values in literature. © 2009 The American Ceramic Society.