Hard and tough boron suboxide based composites

Boron suboxide (B6O) powder was synthesized at temperatures of about 1400 °C from the reaction of amorphous boron powder with boric acid. The synthesized B6O powders were hot pressed at temperatures up to 1900 °C and at pressures of 50 MPa. Additionally to pure B6O materials, composites with aluminium were prepared. The microstructure and properties of the sintered compacts were investigated. The addition of aluminium in the composites results in the formation of an additional aluminium borate phase. The composites showed a similar hardness (∼30 GPa) as the pure B6O samples but increased fracture toughness (∼3.5 MPa m1/2).