Microstructures and mechanical properties of the bilayer functionally graded WC-TiC-Ni/Co cemented carbides

Abstract The nitridation of the WC-TiC-Ni/Co cemented carbides successfully yielded a bilayer-graded structure that consists of face center cubic-rich outer and coarse grain intermediate layers. The sintered carbides were nitrided at 1723 K under 4 MPa N2 for 90 min. The bilayer gradient showed a unique microstructure combination of element distribution and grain features. The graded microstructures contributed to the hardness and fracture toughness of the outer layer, intermediate layer, and inner region. The fracture mode of the intermediate layer was mainly a transgranular fracture, which increased the fracture toughness of the intermediate layer. The fracture mechanism of the inner region was a combination of the intergranular and transgranular fractures; however, the primary mechanism was intergranular fracture. The correlations among the binder phase composition, microstructure, and mechanical properties were investigated to determine the gradient structure characterization of the bilayers of the functionally graded cemented carbides.