Microstructure and mechanical properties of nanocrystalline WC-12Co consolidated by spark plasma sintering

Cemented carbide powders based on WC-12Co with a grain size of 40-250 nm were generated by high-energy ball milling. The powders with different extents of VC and (VC + Cr3C2) addition were consolidated to full density by spark plasma sintering (SPS). The density, microstructure, grain size and fracture toughness K-Ic of the SPS consolidated samples were measured and compared with samples made by liquid phase sintering. Dense samples with a pore rating < A02B00 were obtained by SPS at a temperature of 1100 degrees C (10 min). In contrast, a high sintering temperature of 1450 degrees C (45 min) was necessary to obtain similar density via liquid phase sintering. Addition of grain growth inhibitors VC reduced the final grain size both in SPS and in liquid phase sintering. But the addition also led to lower density, the effect being higher in SPS. Grain size distribution in all cases was narrower and the cobalt distribution more uniform in SPS than in liquid phase sintering. Hence, higher hardness was obtained in SPS. Fracture toughness was lower in SPS samples. VC addition resulted in improved fracture toughness in both SPS and liquid phase sintered samples. Replacement of part of the VC by Cr3C2 resulted in further improvement in toughness in SPS samples. The higher K-Ic values resulting from addition of VC or (VC + Cr3C2) has been attributed to porosity in the cobalt layer providing crack arrestors. (c) 2006 Elsevier Ltd. All rights reserved.