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.
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