Synthesis of cBN-hBN-SiC(w) Nanocomposite with Superior Hardness, Strength, and Toughness

Nanocomposites with one-dimensional (1D) and two-dimensional (2D) phases can demonstrate superior hardness, fracture toughness, and flexural strength. Cubic boron nitride-hexagonal boron nitride-silicon carbide whiskers (cBN-hBN-SiC(w)) nanocomposites with the simultaneous containing 1D SiC(w) and 2D hBN phases were successfully fabricated via the high-pressure sintering of a mixture of SiC(w) and cBN nanopowders. The hBN was generated in situ via the limited phase transition from cBN to hBN. Nanocomposites with 25 wt.% SiC(w) exhibited optimal comprehensive mechanical properties with Vickers hardness of 36.5 GPa, fracture toughness of 6.2 MPa·m(1/2), and flexural strength of 687.4 MPa. Higher SiC(w) contents did not significantly affect the flexural strength but clearly decreased the hardness and toughness. The main toughening mechanism is believed to be a combination of hBN inter-layer sliding, SiC(w) pull-out, crack deflection, and crack bridging.