Densification and Mechanical Behavior of HfC and HfB 2 Fabricated by Spark Plasma Sintering

Hafnium diboride (HfB 2 )‐ and hafnium carbide (HfC)‐based materials containing MoSi 2 as sintering aid in the volumetric range 1%–9% were densified by spark plasma sintering at temperatures between 1750° and 1950°C. Fully dense samples were obtained with an initial MoSi 2 content of 3 and 9 vol% at 1750°–1800°C. When the doping level was reduced, it was necessary to raise the sintering temperature in order to obtain samples with densities higher than 97%. Undoped powders had to be sintered at 2100°–2200°C. For doped materials, fine microstructures were obtained when the thermal treatment was lower than 1850°C. Silicon carbide formation was observed in both carbide‐ and boride‐based materials. Nanoindentation hardness values were in the range of 25–28 GPa and were independent of the starting composition. The nanoindentation Young's modulus and the fracture toughness of the HfB 2 ‐based materials were higher than those of the HfC‐based materials. The flexural strength of the HfB 2 ‐based material with 9 vol% of MoSi 2 was higher at 1500°C than at room temperature.