High hardness and high fracture toughness B4C-diamond ceramics obtained by high-pressure sintering

The B4C-diamond composite with high hardness and toughness was first prepared by high-pressure sintering of B4C and diamond powders at 5 GPa and 1600 °C. The effect of the diamond fraction on the densification, microstructure and mechanical properties of B4C-diamond composite were investigated. The results indicated that the hardness of the as-prepared composite ceramics increased gradually with the increase in diamond content. The composite having 40 vol% diamond exhibited excellent comprehensive mechanical properties with a relative density of 98.3%, a density of 2.86 g/cm3, Vickers hardness of 39.8 GPa and fracture toughness of 8.1 MPa·m1/2. The use of superhard diamond enhanced the fracture toughness of the B4C while maintaining its lightweight and high hardness. The main toughening mechanisms were crack bridging, crack deflection and pull-out of homogeneously dispersed diamond grains. Superhard second phase dispersion high-pressure sintering provides a new technical route to improve the properties of advanced composites.