Pressureless Sintering of Zirconium Diboride

Zirconium diboride (ZrB 2 ) 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, ZrB 2 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 μm. Four-point bend strength, elastic modulus, and Vickers' hardness were measured for sintered ZrB 2 and compared with values reported for hot-pressed materials. Vickers' hardness of sintered ZrB 2 was 14.5±2.6 GPa, which was significantly lower when compared with 23 GPa for hot-pressed ZrB 2 . Strength and elastic modulus of the ZrB 2 were 444±30 MPa and 454 GPa, which were comparable with values reported for hot-pressed ZrB 2 . The ability to densify ZrB 2 ceramics without hot pressing should enable near-net shape processing, which would significantly reduce the cost of fabricating ZrB 2 components compared with conventional hot pressing and machining.

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