Ultrafine‐grained B₆O–diamond composites with superb mechanical properties

Abstract

We report here the high-pressure and high-temperature (HPHT) synthesis of well-sintered B 6 O-diamond composites from B 6 O and carbon black nanopowders. The carbon black was transformed into diamond nanograins at HPHT conditions, and simultaneously formed high-strength B 6 O-diamond interfaces. The ultrafine B 6 O and diamond nanograins and the high-strength B 6 O-diamond interfaces synergistically construct excellent mechanical properties for the synthesized composites. The B 6 O-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 B 6 O ceramics (1.7-3.1 MPa m 1/2 ) and B 6 Obased composites (3-4 MPa m 1/2 ). Fracture behavior analysis demonstrates that the main toughening mechanisms in this B 6 O-diamond composite are nanotwin toughening, crack deflection, and crack bridging.