Pressureless Sintering of Zirconium Diboride

TLDR

Zirconium diboride ceramics were sintered to ~98 % relative density without external pressure by heating between 1900–2150 °C, with isothermal holds at 2150 °C used to study time‑dependent densification and microstructure, and mechanical properties were subsequently measured and compared to hot‑pressed counterparts. At 2150 °C, a 540‑min isothermal hold produced 98 % theoretical density (6.02 g cm⁻³) with ~9 µm grains, while Vickers hardness (14.5 GPa) and strength (444 MPa) and modulus (454 GPa) were comparable to hot‑pressed ZrB₂, though hardness was lower, and the pressureless sintering route promises cost‑effective near‑net‑shape fabrication.

Abstract

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.