Effect of traceable nitrogen from low-pressure plasma nitriding on diamond growth over WC-co cemented carbides

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Cemented tungsten carbide alloys with 6% and 12% Co were plasma-nitrided at 600 °C in a 6 Pa vacuum in different working gases using a hot filament ion source. Diamond was directly coated onto the nitrided specimens. Surface morphologies and microstructures of the nitrided and diamond-coated specimens were characterized using scanning electron microscopy, electron probe microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. The adhesion between the coating and the substrate was evaluated using Rockwell indentation and the standard DIN-VDI 3198. Selective ion-etching of the surface Co during the low-pressure plasma nitriding introduced roughness and craters on the nitrided surface and created a surface conversion layer with a fixed structure. The nitrided surface is covered with a thin Co4N layer that produces a traceable amount of N and can effectively depress the graphitization catalysis of Co species. Diamond coating with adhesion level HF 2–4 can be deposited onto the 6% and 12% WC-Co alloys without chemical etching after the nitriding process.