B6O ceramics prepared by near-ambient and high pressure sintering technologies

With a hardness of up to 45 GPa and a fracture toughness of 4.5 MPa*m1/2 measured on single crystals [1], Boron suboxide (B6O1-x, x ≤ 0.28) is a suitable candidate for wear and cutting applications. However, although boron suboxide can be cost-effective synthesized near ambient pressures its commercial application is actually prevented by its poor sinterability beside a resulting low fracture toughness of polycrystalline B6O materials. Recent studies have shown that these shortcomings can be at least partially bypassed by the use of liquid forming sintering additives [2]. In this investigation, the densification, microstructure formation and mechanical properties of ceramic B6O1-x materials with/without sintering additives prepared by near-ambient (Field Assisted Sintering Technolo gy, FAST/SPS and Hot-isostatic Pressing, HIP) as well as high-pressure sintering techniques (cubic anvil press up to 8 GPa/1680 °C) were systematically evaluated and compared. Full densified B6O1-x materials were obtained from all sintering techniques whereas at the given sintering parameters at least minor amounts of additives are necessary for a full compaction by hot-isostatic pressing. The effect of the sintering equipment and varying amounts and compositions of oxide sintering additives on the microstructure and phase formation as well as the B6O1-x oxygen stoichiometry and mechanical properties is discussed. Highest hardness of up to 40 GPa (HV0.4) were obtained for the high-pressure densified materials whereas the highest measured values of fracture toughness (SEVNB), tensile streng th and Youngs modulus are derived for FAST/SPS and HIP materials and in the range of 3 4 MPa*m1/2, up to 500 MPa and 500 GPa, respectively.