Processing, microstructure, and mechanical properties of large-grained zirconium diboride ceramics

Zirconium diboride ceramics produced using commercial ZrB2 powders, and milled with zirconium diboride grinding media, were fabricated by hot-pressing at temperatures of 2100-2200 °C with hold times of 30-120 min. This ZrB2 exhibits no additional impurities typically introduced by milling with grinding media of differing composition. Microstructure analysis revealed grain sizes ranging from ~25 to ~50 µm along with ~3 vol% porosity. Flexure strength ranged from 335 to 400 MPa, elastic modulus from 490 to 510 GPa, fracture toughness from 2.7 to 3.2 MPa m½, and hardness from 13.0 to 14.4 GPa. Strength limiting flaws were identified as surface grain pullout induced by machining. Elastic modulus and hardness were found to increase with decreasing porosity. Compared to the fine grained ceramics typically reported, large grain zirconium diboride ceramics exhibit higher than expected room temperature strengths.