Boron Carbide-Zirconium BorideIn SituComposites by the Reactive Pressureless Sintering of Boron Carbide-Zirconia Mixtures

The heating of B 4 C–YTZP (where YTZP denotes yttria‐stabilized zirconia polycrystals) mixtures, under an argon atmosphere, generates B 4 C–ZrB 2 composites, because of a low‐temperature (<1500°C) carbide–oxide reaction. Composites derived from mixtures that include ≥15% YTZP are better sintered than monolithic B 4 C that has been fired under the same conditions. Firing to ∼2160°C (1 h dwell) generates specimens with a bulk density of ≥91% of the theoretical density (TD) for cases where the initial mixture includes ≥15% YTZP. Mixtures that include 30% YTZP allow a fired density of ≥97.5% TD to be attained. The behavior of the B 4 C–YTZP system is similar to that of the B 4 C–TiO 2 system. Dense B 4 C–ZrB 2 composites attain a hardness (Vickers) of 30–33 GPa.