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 HfB₂–26 vol.% SiC_w 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 30 min at 1350 A when the applied pressure is switched from 20 to 50 MPa after the synthesis reaction. A 99.4% dense whiskers-reinforced HfB₂ ceramic matrix composite is also obtained in 30 min by SPS (I = 1350 A, P = 20 MPa) using SHSed HfB₂ powders and SiC_w. Nevertheless, whiskers degradation into SiC_p 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 1200 A (1700 °C) while P was increased to 60 MPa.