Ultrafine-grained B6O-diamond composites with superb mechanical properties

We report here the high-pressure and high-temperature (HPHT) synthesis of well-sintered B6O-diamond composites from B6O and carbon black nanopowders. The carbon black was transformed into diamond nanograins at HPHT conditions, and simultaneously formed high-strength B6O-diamond interfaces. The ultrafine B6O and diamond nanograins and the high-strength B6O-diamond interfaces synergistically construct excellent mechanical properties for the synthesized composites. The B6O-diamond composites possess a hardness (avg. 52 GPa) comparable to that of polycrystalline diamond (40-60 GPa), whereas the fracture toughness (avg. 7.2 MPa m(1/2)) is increased several times compared to previously synthesized polycrystalline B6O ceramics (1.7-3.1 MPa m(1/2)) and B6O-based composites (3-4 MPa m(1/2)). Fracture behavior analysis demonstrates that the main toughening mechanisms in this B6O-diamond composite are nanotwin toughening, crack deflection, and crack bridging.

Automated summary

We report the high-pressure and high-temperature synthesis of B6O-diamond composites with excellent mechanical properties. The carbon black nanopowders were transformed into diamond nanograins and formed high-strength B6O-diamond interfaces. The composites exhibit a hardness comparable to that of polycrystalline diamond and significantly improved fracture toughness compared to previous materials.