NbC as grain growth inhibitor and carbide in WC-Co hardmetals

WC-NbC-12 wt%Co hardmetals with 0.45-60 wt%NbC were prepared by solid state pulsed electric current sintering (PECS), also known as spark plasma sintering (SPS), for 2 min at 1240 degrees C and conventional sintering (CS) for 1 h at 1420 degrees C. The role of NbC as grain growth inhibitor and major carbide addition was investigated in terms of the densification behaviour, the microstructure and mechanical properties. Experimental work revealed that the addition of more than 5 wt%NbC inhibits pressure assisted solid-state densification compared to WC-Co based hardmetals. The addition of NbC limits WC grain growth during PECS and conventional sintering, whereas substantial (Nb, W)C grain growth was observed in the hardmetals with >= 0.9 wt%NbC addition. The influence of the NbC content on the hardness, strength and toughness of the WC-NbC-12 wt%Co hardmetals was explained in terms of WC grain growth inhibition and the formation of coarse (Nb, W)C grains. (C) 2007 Elsevier Ltd. All rights reserved.