Hardness and toughness control of brittle boron suboxide ceramics by consolidation of star-shaped particles by spark plasma sintering

The hardness and fracture toughness of boron suboxide ceramics synthesized under ambient pressure and consolidated by spark plasma sintering (SPS) are reported. The structure and characterization of ceramics with a hardness of up to 43 GPa under a 9.8 N load and almost 28 GPa under a load of 198 N are reported. It was shown that an increase in the stoichiometry of boron suboxide by promoting the occupancy of the 6c position in the rhombohedral cell is the effective for achieving both hard and tough pure B₆O ceramics. SPS consolidation preserved the unique fivefold symmetry of the boron suboxide grains and thus promoted additional toughening due to numerous crack deflections on fine 100 nm subgrains.