Boron suboxide ultrahard materials

B6O is a possible candidate as a superhard material with a hardness of 45 GPa measured on single crystals. The first dense superhard B6O-materials were produced under high pressure (1 GPa). However, recently it was found that different oxides can be utilized as an effective sintering additive allowing the reproducible densification at 50–80 MPa pressure at temperatures 1800–1900 °C. The resulting materials have similar hardness as the pure B6O materials but strongly increased fracture toughness. This article summarizes the state of the art of B6O materials — the densification, microstructure and resulting room and high temperature properties. It compares the B6O materials with boron carbide and cBN based materials.

► Sintering at temperatures between 1800-1900°C at low pressure. ► Significantly increased fracture toughness. ► Review of key mechanical properties of this material.