Effect of C content on the microstructure evolution during early solid state sintering of WC–Co alloys

• C excess delays the spreading of Co on WC particles when heating WC–Co alloys.
• C excess results in a more uniform Co distribution when heating in the solid state.
• C excess leads to a more uniform porosity reduction during solid state sintering.
• W excess favours the formation of WC/Co interfaces with low energy configurations.

The densification of WC–10Co (wt %) alloys is studied in relation with interface formation, below the melting temperature of the Co base binder phase. Two alloys containing an excess of carbon or tungsten are investigated. The evolution of the pore and Co phase size distribution is quantified at several temperatures using image analysis. While shrinkage and Co spreading start earlier in the W rich alloy, the reduction of porosity and Co spreading is more uniform in the C rich alloy. Preferential orientation relationships are frequently found at WC basal facets for WC/Co interfaces especially in the W rich alloy. A WC1-x film is also sometimes observed at randomly oriented WC/Co interfaces whatever the C content. The formation of low energy interfaces may explain the early spreading of the binder phase and the onset of densification in the solid state.