Synthesis, consolidation and characterization of monolithic and SiC whiskers reinforced HfB2 ceramics

Spark Plasma Sintering is used for the fabrication of highly dense HfB2 monolithic and HfB2-26vol.% SiCw composite. Reactive SPS from elemental reactants is preferred for the preparation of bulk HfB2 instead of classical sintering. The desired phase is rapidly formed through a solid-solid combustion synthesis mechanism, while full densification is achieved in 30min at 1350A when the applied pressure is switched from 20 to 50MPa after the synthesis reaction. A 99.4% dense whiskers-reinforced HfB2 ceramic matrix composite is also obtained in 30min by SPS (I=1350A, P=20MPa) using SHSed HfB2 powders and SiCw. Nevertheless, whiskers degradation into SiCp resulted under such conditions (temperature up to 1830°C). On the other hand, the presence of whiskers is clearly evidenced in 96% dense products obtained when the applied current was decreased down to 1200A (1700°C) while P was increased to 60MPa.