Pressureless Sintering of Zirconium Diboride

Zirconium diboride (ZrB2) ceramics were sintered to a relative density of ∼98% without applied external pressure. Densification studies were performed in the temperature range of 1900°-2150°C. Examination of bulk density as a function of temperature revealed that shrinkage started at ∼2100°C, with significant densification occurring at only 2150°C. At 2150°C, isothermal holds were used to determine the effect of time on relative density and microstructure. For a hold time of 540 min at 2150°C, ZrB2 pellets reached an average density of 6.02±0.04 g/cm3 (98% of theoretical) with an average grain size of 9.0±5.6 μm. Four-point bend strength, elastic modulus, and Vickers\u27 hardness were measured for sintered ZrB2 and compared with values reported for hot-pressed materials. Vickers\u27 hardness of sintered ZrB2 was 14.5±2.6 GPa, which was significantly lower when compared with 23 GPa for hot-pressed ZrB2. Strength and elastic modulus of the ZrB2 were 444±30 MPa and 454 GPa, which were comparable with values reported for hot-pressed ZrB2. The ability to densify ZrB2 ceramics without hot pressing should enable near-net shape processing, which would significantly reduce the cost of fabricating ZrB2 components compared with conventional hot pressing and machining