B6O powders were produced from the reaction between boric acid and amorphous boron powders at the reaction temperatures between 300 and 1400 o C for 6 hours. The powders produced were characterized in terms of particle size, phase analysis and composition, product yield as well as morphology. Increase in temperature increases both the yield as well as the particle size of the produced powders. XRD pattern obtained also showed improved crystallinity of the produced powder as the temperature increases. SEM image obtained at higher temperature clearly showed improved crystallinity (star-like crystals) as the reaction temperature was increased. The B6O powders synthesised at 1300 o C for 6 hours had the optimum yield of over 95%.

This study investigated and compared the mechanical properties of boron suboxide (B6O) with and without chromium bromide (CrB2) additive, hot pressed at 1900 o C and 1850 o C and for 20 minutes, with applied pressures of 50 and 80 MPa respectively. The theoretical density attained for these materials was More than 96%. The phase relationship, microstructures and mechanical properties of these materials were examined and good combination of mechanical properties was obtained with the B6O-CrB2 material (HV 32.1 GPa, KIC 4.5 MPa.m 0.5 ) compared to pure B6O material. Mixing with a small amount (1.7 wt.%, equivalent of 0.4 vol.%) of CrB2 additive resulted in a pronounced improvement in both the hardness and fracture toughness values. The improvement in the fracture toughness was attributed to the introduction of the second phase and the toughening mechanism is presumed to be by crack bridging and deflection due to bimetallic stress.

The basis of this study is that the mechanical properties of Boron suboxide (B6O) materials, especially fracture toughness are greatly influenced by the composition of the grain boundary phase and the grain size of the phases in the sintered material. Therefore, in this work, effort has been directed towards improving the fracture toughness and densification of this material by incorporating potential rare-earth oxide phases and tailoring the microstructure to the desired properties. Boron suboxide (B6O) powder was synthesized from the reaction of amorphous boron and boric acid powders. The powder was hot pressed at 1900 degrees C and 50 MPa. Additionally to pure sintered B6O, materials with rare-earth oxides were prepared at 1850 degrees C. The microstructure, phase composition and properties were investigated. More than 95% of the theoretical density was attained and fracture toughness up to 5.6 +/- 0.2 MPam(1/2) was obtained for the materials. Although the pure B6O sample was brittle, fracture toughness was strongly improved in the materials.

Fully densified in-situ reinforced (TiB + TiC)-Ti matrix composites have been produced from TiH2-B4C mixtures using pressure less sintering or hot pressing technique. With increasing content of reinforcing components the sintering is retarded. The materials with more than 20 - 30 vol. % were only completely densified by hot pressing technique. Hardness values of the Ti matrix composites produced are up to 5 times higher than that of the sintered pure Ti produced from TiH2. This is caused beside the higher hardness of the inclusions also by hardening the matrix due to solubility of B and C in the titanium.