In-situ formation of RE oxysulfide with self lubricating function during cutting process of cemented carbide tool

As-sintered high activity mischmetal (RE, with lanthanum and cerium) doped WC-8%Co-0.07%RE (mass fraction) cemented carbide inserts were tested for the turning of cast iron. The sinter skin, flank face, rake face and cutting edge of the inserts after testing were observed and analyzed by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffractometry. Asynchronous migration phenomenon of lanthanum and cerium from the inside to the working faces of the as-sintered insert during the turning process was observed. The results show that a rare earth oxysulfide phase with self lubricating function forms in-situ on the working faces of cemented carbide cutting tool. The mechanisms for the directional migration and formation of rare earth oxysulfide were discussed.