Rare earth enrichment phenomenon during sintering process of grainy hardmetal

The sinter skin (exterior) of rare earth doped WC–Co grainy hardmetal was observed and analyzed by SEM and EDX to study the behavior of rare earth elements in hardmetal during sintering process. The addition forms of rare earth elements are mischmetal (mainly containing lanthanum and cerium) and cobalt pre-alloyed powder and La(NO3)3 dissolved in acetone which are added during the ball-milling of hardmetal. The results show that when rare earth elements are added in the form of mischmetal–cobalt pre-alloyed powder, during vacuum sintering process, lanthanum and cerium as well as the impurity elements mainly from the sintering atmosphere get enriched on the sinter skin of grainy hardmetal with an average diameter of less than 200 μm, forming a new phase containing La, Ce, W, C, S, Ca and O; however, when rare earth element is added in the form of La (NO3)3, lanthanum has not been detected on the sinter skin, suggesting that the activity of the rare earth additive affects the behavior of rare earth in hardmetal. The existence of rare earth-enrichment phase on the sinter skin can play a role of suppressing the formation of binder-enrichment structure on the sinter skin.