Synthesis, Sintering, and Oxidative Behavior of HfB2–HfSi2 Ceramics

The self-propagating high-temperature synthesis (SHS) of (1 – x)­HfB2–xHfSi2 (x from 0 to 1) ceramics is successfully performed in this work starting from elemental reactants. The presence of HfSi2 in the composite system progressively reduces the exothermic character of the synthesis reaction. Bulk ceramics are then obtained after consolidation by spark plasma sintering (SPS) of the SHS crashed products. It is found that the HfB2–xHfSi2 composite powders synthesized in a single step by SHS require milder sintering conditions as compared to the mixtures consisting of the ceramic constituents obtained separately by the same route. In addition, 15 vol % is the minimum percentage of HfSi2 required to achieve the complete densification of the starting powders, under the SPS conditions investigated in the present work (I = 1350 A, P = 50 MPa, 30 min total time). Thermogravimetric analysis experiments performed in air flow up to 1450 °C clearly indicate that the introduction of HfSi2 plays a beneficial role for protecting the obtained material from oxidation.