Abstract: The urgent demand for additive manufacturing (AM) cemented carbide parts with complex geometric structures has emerged. However, the powder bed fusion AM WC-Co cemented carbide exhibits poor mechanical properties due to cracks, pores, and abnormal WC grain growth caused by low formability, particularly in ultrafine-grained cemented carbide. We employed material extrusion (MEX) AM to prepare an ultrafine-grained WC-0.5Cr₃C₂-0.2CeO₂-9Co cemented carbide. MEX AM eliminated defects, inhibited abnormal WC grain growth, and increased residual α-Co content at room temperature by improving the W and C solubility in Co phase to increase the stacking fault energy. The ultrafine-grained cemented carbide achieved a relative density of 99.52 %, as well as an α-Co content of 16.5 vol. %, an average WC grain size of 384.6 nm, a adjacency of the WC phase of 0.58, and a mean free path of the Co phase of 208 nm, respectively. The synergistic effects of densification reinforcement, fine-grain strengthening, and residual α-Co phase toughening, simultaneously improved the mechanical properties of the cemented carbide, achieving a Vickers hardness of 2123 ± 11 HV₃₀, a transverse rupture strength of 3639 ± 28 MPa, and a fracture toughness of 13.13 ± 0.03 MPa m^1/2, respectively, which demonstrated significantly superior mechanical properties compared with the cemented carbide prepared via AM or traditional powder metallurgy reported. These findings effectively address the challenge of simultaneously enhancing the hardness and fracture toughness of ultrafine-grained cemented carbide and provide important guidance for the development of cemented carbide with excellent mechanical properties via AM.

Key words: Ultrafine-grain, WC-Co cemented carbide, Material extrusion, Additive manufacturing, Mechanical properties