High-pressure sintering of full-dense B6O ceramic with excellent hardness and fracture toughness

B6O is an extremely prospective hard material for industrial applications. Herein, the densification behavior, microstructure and mechanical properties of high-pressure sintered B6O ceramics at 6 GPa are investigated. As sintered B6O ceramics exhibit enhanced densification as the sintering temperature increases, and the ceramic sintered at 1700 °C possesses nearly full-dense characteristics with strong bonding at grain boundaries and exhibits outstanding mechanical properties (HV: 38.5 ± 0.7 GPa, HN: 45.7 ± 0.8 GPa, KIc: avg. 4.8 MPa·m1/2). At higher temperatures, however, the increase in sublimation pressure is counterproductive to densification. The enhanced fracture toughness of the full-dense B6O ceramics is mainly attributed to the high strength grain boundaries and the abundance of defects within the grains, which generate substantial crack bridging, crack deflection and grain pull-out.