Preparation and annealing study of TaNx coatings on WC-Co substrates

To prevent Co diffusion from cemented carbides at high temperatures, we fabricated TaNx coatings by reactive direct current (d.c.) magnetron sputtering onto 6 wt.% cobalt cemented carbide substrates, to form diffusion barrier layers. Varying the nitrogen flow ratio, N2/(Ar + N2), from 0.05 to 0.4 during the sputtering process had a significant effect on coating structure and content. Deposition rate reduced as the nitrogen flow ratio increased. The effects of nitrogen flow ratio on the crystalline characteristics of the TaNx coatings were examined by X-ray diffraction. The TaNx coatings annealing conditions were 500, 600, 700, and 800 °C for 4 h in air. We evaluated the performance of the diffusion barrier using both Auger electron spectroscopy depth-profiles and X-ray diffraction techniques. We also investigated oxidation resistance of the TaNx coatings annealed in air, and under a 50 ppm O2-N2 atmosphere, to evaluate the fabricated layers effectiveness as a protective coating for glass molding dies.

► TaNx coatings served as diffusion barriers for Co during 500 and 600 °C annealing. ► The columnar structure provided fast channels for oxygen diffusion in air annealing. ► The in-diffusion of oxygen is restricted in a glass molding, 50 ppm O2-N2 atmosphere.