Comparative Study on Microstructure and Mechanical Properties of Coarse-grained WC-based Cemented Carbides Sintered with Ultrafine WC or (W plus C) as Additives

The effects of ultrafine WC (WCUF, 0.5 mu m) or W (1 mu m) and C (0.3 mu m) (W+C)UF additives on the densification, microstructure and mechanical properties of coarse-grained cemented carbides were compared systematically. Overall, the cemented carbides with WCUF/(W+C)UF additives are almost fully densification to be higher than 99%, and the average grain size is kept above 2.8 mu m. The WCUF additive assists grains to (truncated) trigonal prism shape by two dimensional (2D) growth, whereas the (W+C)UF additive assists grains to rounded shape by three dimensional (3D) growth, lowers WC contiguity and increases face-centered-cubic Co. The hardness and bending strength of (75WCC-15WCUF)-10Co are 86.6 HRA and 2 272 MPa, respectively, both higher than those of (75WCC-15(W+C)UF)-10Co, which could be ascribed to the enhanced densification and unblemished grains. However, the fracture toughness of the (75WCC-15(W+C)UF)-10Co is 23.5 MPa center dot m1/2, higher than that of the (75WCC-15WCUF)-10Co due to the uniform WC-Co structure and flexible binder phase.