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 degrees 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/cm(3), Vickers hardness of 39.8 GPa and fracture toughness of 8.1 MPa.m(1/2). 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 pullout of homogeneously dispersed diamond grains. Superhard second phase dispersion high-pressure sintering provides a new technical route to improve the properties of advanced composites.