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The in-situ reduction and carbonization reactions were used to synthesize the WC-Co composite powder with nanoscale particle sizes. The nanocrystalline WC-Co cemented carbides bulk material was prepared by spark plasma sintering (SPS). Results show that the particle size of the grain growth inhibitor VC has a significant effect on the microstructure, grain size and properties of the prepared nanocrystalline WC-Co bulk material. When the VC particle size is below 100 nm, the prepared nanocrystalline WC-Co bulk has a mean grain size of about 70 nm. It has a high density, pure phase constitution, homogeneous grain size distribution and excellent mechanical properties, with a Vickers hardness of 19.84 GPa and a fracture toughness of 12.10 MPa×m1/2