Microstructure and material properties of PECS manufactured WC-NbC-CO and WC-TiC-Ni cemented carbides

• PECS resulted in higher hardness and lower K1C than LPS, due to finer WC grains and poor binder pool distribution.
• Rapid WC grain growth in the nano and ultrafine grades occurred during PECS due to coalescence mechanism.
• Additions of NbC to WC-Co and Mo2C to WC-Ni necessitated higher sintering temperatures to achieve good density.
• High NbC (≥ 20 wt%) additions to WC-Co reduce the mechanical properties.
• Mo2C improved hardness and elastic modulus, without significantly changing fracture toughness.

The effects of grain size, NbC, TiC and Mo2C additions on the microstructure and mechanical properties of pulse electric current sintered (PECS) cemented carbides with Co and Ni binders were investigated using scanning electron microscopy (SEM) in the backscattered electron mode, high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), hardness and elasticity measurements. For WC-0.5Cr3C2-10Co (wt%) cemented carbides, increasing NbC content changed the shape of the WC grains at the WC/NbC interface, from faceted to more rounded. Cobalt was mainly between the WC grains and rarely between the NbC grains, found by SEM and STEM mapping. The reduction in hardness and fracture toughness with increased NbC was due to the lower hardness of NbC than WC, and reduction in WC-Co volume fraction. The addition of 5 wt% Mo2C to WC based cemented carbide containing 6.25 wt% TiC and 9.3 wt% Ni produced smaller (Ni) binder pools that were better distributed between the WC grains, leading to increased hardness and modulus of elasticity. Through PECS and optimised additions of NbC, TiC and Mo2C, higher hardness, comparable K1C and modulus of elasticity to the LPS WC-0.5Cr3C2-10Co (wt%) sample were obtained for the WC-Co and WC-Ni samples.