Existing states of lanthanum and cerium in WC-Co hardmetal

The microstructure and the sinter skin of high-activity mischmetal (RE, with La and Ce) doped WC-8% Co-0.8% RE hardmetal were observed by scanning electron microscopy. The element surface distribution analysis was used in the study of the combining states of La and Ce both in the alloy and on the sinter skin. It was shown that in the alloy, a fine La and Ce containing phase was distributed dispersedly, and La and Ce were in their initial combining state. Nevertheless, on the sinter skin, only Ce containing oxide phase which was in an irregular shape was detected, and the initial combining state of La and Ce was broken, indicating an unstable La and Ce combining state. The good interface combining strengths of the La and Ce containing phase with the WC hard phase and the binder phase were revealed by comparing the Palmqvist fracture toughness of the hardmetal with and without RE.