Experimental investigations and DICTRA simulations on formation of diffusion-controlled fcc-rich surface layers on cemented carbides

Wear resistant fcc-rich surface layers were produced on cemented carbides by nitridation of W–Ti–Ta–Nb–Co–C compositions at 1400 °C in nitrogen atmosphere. A 15 ± 3 μm thick (Ti,Ta,Nb,W)(C,N) top-layer formed on the surface of the cemented carbides. The driving force for formation of the fcc-rich layers was the difference in nitrogen activity between the sintering atmosphere and the cemented carbide bulk, which promoted in-diffusion of nitrogen and out-diffusion of Ti, Ta and Nb. The diffusion-controlled process was modeled by DICTRA considering that all diffusion occurred in the liquid binder phase of a dispersed system model with a labyrinth factor of λ(f) = f. Good agreement between experimental and simulations regarding layer thickness, phase fraction distribution and element profiles was obtained for the presented model.