Effect of Cr addition on solid state sintering of WC–Co alloys

• Cr addition delays the onset of shrinkage in WC–Co alloys.
• Cr addition delays Co spreading.
• The delaying effect is explained by the presence of Cr surface oxides.
• Cr addition enhances differential shrinkage in WC–Co alloys.

The effect of Cr addition and C content on densification and microstructural evolution of WC–Co alloys in the solid state was studied. Two alloys containing Cr and an excess of carbon or tungsten were investigated. They were compared with Cr free alloys. The intercept length distribution of the pore and binder phase was measured at several temperatures using image analysis. Cr addition delays the shrinkage whatever the C potential whilst better binder spreading and more effective rearrangement occur at lower temperature in the W rich alloy. When the temperature increases, the densification is accelerated in the C rich alloy. It is found that Cr addition has no significant effect on the solubility of W in the binder. The influence of Cr on the shrinkage behaviour is discussed putting emphasis on the grain boundary energies and on Cr oxides.