Influence of starting powder on the microstructure of WC–Co hardmetals obtained by spark plasma sintering

WC–Co hardmetals using different starting powders were densified by spark plasma sintering (SPS). Sintering cycles were performed at 1240 °C for the WC–12 wt.% Co–0.45 wt.% VC grade and 1280 °C for the WC–6 wt.% Co grade, applying a pressure of 60 MPa in combination with a heating rate of 100 °C/min. The influence of the carbon content and homogeneity of the starting powders on the final microstructure and mechanical properties was investigated. A thin graded surface layer is observed in case of slightly carbon deficient starting powder. Co agglomerates were observed in the SPS materials obtained from lower energetically multi-directionally mixed WC–Co powder, whereas a homogeneous microstructure was obtained when using attritor-milled or chemically synthesized WC–Co starting powder with adjusted carbon balance. The observed microstructures are related to the measured mechanical properties.