Hot Pressed HfB_2 and HfB_2-20 vol%SiC Ceramics Based on HfB_2 Powder Synthesized by Borothermal Reduction of HfO_2

摘要

Phase pure hafnium diboride (HfB_2) powder was synthesized by borothermal reduction of hafnium dioxide using amorphous boron at relatively low temperature (1600℃) 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_20 vol%SiC composite were hot pressed at 2000℃ 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 significandy higher than that of the HfB_2 monolithic and the reported values in literature.