Pressureless Sintering of Zirconium Diboride: Particle Size and Additive Effects

Zirconium diboride (ZrB 2 ) was densified by pressureless sintering using <4‐wt% boron carbide and/or carbon as sintering aids. As‐received ZrB 2 with an average particle size of ∼2 μm could be sintered to ∼100% density at 1900°C using a combination of boron carbide and carbon to react with and remove the surface oxide impurities. Even though particle size reduction increased the oxygen content of the powders from ∼0.9 wt% for the as‐received powder to ∼2.0 wt%, the reduction in particle size enhanced the sinterability of the powder. Attrition‐milled ZrB 2 with an average particle size of <0.5 μm was sintered to nearly full density at 1850°C using either boron carbide or a combination of boride carbide and carbon. Regardless of the starting particle size, densification of ZrB 2 was not possible without the removal of oxygen‐based impurities on the particle surfaces by a chemical reaction.