Abstract: Boron suboxide (B₆O) is recognized as a superhard material with a low mass density, high resistance to chemical wear, and excellent wear resistance. Despite its desirable properties, the limited fracture toughness of B₆O restricts its application in industrial contexts. This study presents the structural and mechanical characterization of B₆O-SiC nanocomposites, which were synthesized via a high-pressure high-temperature sintering process of B₆O powders and SiC whiskers. The sintering process induced fragmentation of SiC whiskers, resulting in the homogenous distribution of SiC fragments within the B₆O matrix. An increase in SiC content was observed to decrease the composite's hardness, while initially reducing then enhancing its toughness. The nanocomposites containing 20 wt% and 30 wt% SiC whiskers exhibited significant improvements in fracture toughness, averaging 6.5 MPa m^1/2 and 7.0 MPa m^1/2, respectively—approximately threefold the toughness of polycrystalline B₆O—while sustaining high hardness values of 36.3 GPa and 35.6 GPa on average. Microstructural analyses revealed that the composites' superior mechanical performance is due to the presence of strong grain boundaries, as well as a high density of nanotwins and stacking faults. The findings demonstrate a viable method for producing B₆O-based nanocomposites with enhanced hardness and toughness, potentially expanding their industrial applicability.

Key words: B₆O, Ceramic nanocomposite, Mechanical properties, Microstructure