Pressureless sintering of zirconium diboride: Particle size and additive effects

Zirconium diboride (ZrB2) was densified by pressureless sintering using < 4-wt% boron carbide and/or carbon as sintering aids. As-received ZrB2 with an average particle size of similar to 2 mu m could be sintered to similar to 100% density at 1900 degrees 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 similar to 0.9 wt% for the as-received powder to similar to 2.0 wt%, the reduction in particle size enhanced the sinterability of the powder. Attrition-milled ZrB2 with an average particle size of < 0.5 mu m was sintered to nearly full density at 1850 degrees C using either boron carbide or a combination of boride carbide and carbon. Regardless of the starting particle size, densification of ZrB2 was not possible without the removal of oxygen-based impurities on the particle surfaces by a chemical reaction.