In-situ preparation and properties of ultrafine cemented carbide through spark plasma sintering

VC and Cr3C2 grain growth inhibitors (GGIs) and WC ultrafine cemented carbides were synthesized in-situ by spark plasma sintering (SPS) with W, C, Co, V, and Cr as raw materials. The effects of sintering parameters and difference in the particle size (50/500 nm) of raw materials on the microstructure and performance of the alloys were evaluated. The hardness and toughness of the specimens prepared by sintering the raw material particles with equivalent spherical diameter of 500 nm and additive content of 1.2 wt% at 1350 degrees C and 35 MPa for 8 min were 1889.90 kgf/mm2 and K IC 9.98 MPa & sdot;m1/2, respectively. The results showed that the specimen has high hardness and toughness (2059.10 kgf/mm2, K IC 14.06 MPa & sdot;m1/2) prepared at 1400 degrees C for 8 min under a pressure of 35 MPa with the raw material particles having an equivalent spherical diameter of 50 nm, and an additive content of 0.8 wt%. With similar sintering parameters, reducing the particle size of the raw powders (500-50 nm) could effectively enhance the mechanical properties of the specimens,the Vickers hardness and density increased by 8.96% and 4.37%, respectively, and the fracture toughness is significantly improved by 40.88%. Both large and small grains are present in the sample, the small-size grains provide the sample with better hardness and the large-size grains endow the sample with excellent toughness. The preparation of ultrafine cemented carbide by in-situ synthesis is feasible, but it is susceptible to uneven grain size distribution and more defects. This can be solved by reducing the raw particle size and optimizing the sintering process appropriately. This study provides a feasible way for the in-situ preparation of high strength and toughness cemented carbides.