Abstract :
Experiments were conducted by hot-pressing to
densify HfB2 commercial powders using HfSi2 (5 vol%) or
B4C (7 vol%) as sinter additives. The former was very
effective as sintering enhancer: 15 min at 1,600 C was a
sufficient condition to achieve near full density. The occurrence
of a liquid phase sintering, which substantially
enhanced densification during hot-pressing, was found out.
The HfB2–B4C powder mixture, hot-pressed at 1,900 C for
40 min, achieved a relative density of 94%. Aside the key
role of sintering enhancer, B4C also allowed the development
of a uniform microstructure, preventing an excessive growth
of the diboride matrix (2 lm mean size). On the contrary,
thanks to the liquid phase that sustained substantial transfer of
mass during heating, the HfSi2-doped composition had an
uneven and more obvious grain growth (4 lm mean size),
with faceted diboride grains up to 10 lm
