Pressureless sintering of zirconium diboride

Zirconium diboride (ZrB2) ceramics were sintered to a relative density of similar to 98% without applied external pressure. Densification studies were performed in the temperature range of 1900 degrees-2150 degrees C. Examination of bulk density as a function of temperature revealed that shrinkage started at similar to 2100 degrees C, with significant densification occurring at only 2150 degrees C. At 2150 degrees 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 degrees C, ZrB2 pellets reached an average density of 6.02 +/- 0.04 g/cm(3) (98% of theoretical) with an average grain size of 9.0 +/- 5.6 mu m. Four-point bend strength, elastic modulus, and Vickers' hardness were measured for sintered ZrB2 and compared with values reported for hot-pressed materials. Vickers' 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.