Synergetic migration behavior of La and Ce and related microstructure character of Cr-V-RE co-doped WC-Co alloy

The as-sintered sinter skin and the polished section of WC-11Co-0.4Cr3C2-0.3VC-0.2RE (RE=mischmetal with La/Ce ratio of 0.65) alloy were analyzed. It was shown that the microstructures on the skin and in the inner part of the alloy were all characterized with a WC+β+M structure, where β was a cobalt-based binder phase and M represented a RE-containing phase. There existed an inward diffusion of S atoms, which caught and fixed the Ce atoms in the alloy and an outward diffusion of La atoms during the sintering process. Consequently, the M phase was characterized with the decreased La/Ce ratio (0.59) in the inner part and the increased La/Ce ratio (1.01) on the skin. The M phase on the skin was characterized with a γ-Ce2S3 type structure. To suppress the long range migration of rare earth to the skin, S in the sintering atmosphere had to be eliminated.