Dense and core-rim structured B4C-TiB2 ceramics with Mo-Co-WC additive

B 4 C-TiB 2 ceramics (TiB 2 ranging 5~70 vol%) with Mo-Co-WC as the sintering additive were prepared by spark plasma sintering. In comparison with B 4 C-TiB 2 without additive, the enhanced densification was evident in the sintered specimen with Mo-Co-WC additive. Core-rim structured grain was observed around TiB 2 grains. The interface of the rim between TiB 2 and B 4 C phases demonstrated different feature: the inner borderline of the rim exhibited a smooth feature, whereas a sharp curved grain boundary was observed between the rim and the B 4 C grain. The formation mechanism is discussed: the epitaxial growth of (Ti,Mo,W)B 2 rim around the TiB 2 core may occur as a result of the solid solution and dissolution-precipitation between TiB 2 phase and the sintering additive. It was revealed that the fracture toughness increased as the content of TiB 2 content increased, alongside the decreased hardness. B 4 C-30 vol% TiB 2 specimen demonstrated the optimal combination of mechanical properties, reaching Vickers hardness of 24.3 GPa and fracture toughness of 3.33 MPa·m 1/2 .