Fabrication of dual-grain structure WC-Co cemented carbide by in-situ carbothermal reduction of WO3 and subsequent liquid sintering

Abstract

In this study, WC-Co cemented carbides with dual-grain structure were prepared via in-situ carbothermal reduction of WO3, followed by liquid sintering in a single thermal cycle, utilizing carbon black, Co, WO3 and coarse WC as raw powders. Densification behavior, phase formation, and microstructure evolution of the obtained materials were characterized through XRD, SEM, and EDX. It was demonstrated that carbothermal reduction of WO3 was finished under 800 °C, and microstructures of cemented carbide were composed of small WC grains with nearly round granular morphology as well as coarse WC grains with morphology of equilibrium triangle prism columns. Coarse WC grains were evenly encircled by small WC grains, showing an apparent dual-grain structure. This dual-grain structured cemented carbide exhibited similar hardness to cemented carbides fabricated by the mixtures of fine WC, coarse WC and Co powders. Fracture toughness was significantly improved because of crack deflection, transgranular fracture, and crack bridging. Cemented carbides with dual-grain structures prepared through this method exhibited good mechanical properties with a Rockwell hardness of 89.8 ± 0.2 HRA, a transverse rupture strength of 3415 ± 89 MPa, and a fracture toughness of 13.5 ± 0.4 MPa m1/2, respectively.