In situ formation of RE2S3 and RE2O2S phases on sinter skin of Cr–mischmetal co-doped WC—Co alloy

The as-sintered sinter skin of WC—11Co—0.71Cr3C2—0.06RE cemented carbide with WC+β microstructure was analyzed by scanning electron microscope, energy dispersive X-ray spectroscope and X-ray diffractometer. RE represents La-, Ce-, Pr- and Nd-containing mischmetal, and β is cobalt-based binder phase. It was discovered that La, Ce, Pr and Nd migrated directionally from the alloy to the sinter skin to combine with the impurity elements S and O from the sintering atmosphere during the sintering process. As a result, main dispersed phase RE2S3 and minor RE2O2S were formed in situ on the sinter skin. The mechanisms for the stimulation of the migration activity and the directional migration of RE atoms were discussed in terms of the thermodynamics stability of Cr3C2, solubility characteristic of Cr in Co and the polarization or ionization of RE atoms.