A study on the synthesis and microstructure of WC–TiN superlattice coating

WC–TiN superhard coatings are formulated to form a nanoscaled superlattice by separate arc reactive evaporation of Ti and WC. The microstructure of WC–TiN films was identified to be a superlattice of TiN and β-WC1−x phases with modulation period (λ) of 5–13 nm and the lattice planes were continuous through the TiN and β-WC1−x layers. The residual stress of WC–TiN films was measured to be 7.9 GPa. This high stress was reduced to 2.2 GPa by introducing Ti or Ti–WC interlayers. Ti–WC interlayer also increased the film adhesion strength. In spite of almost the same residual stress of 2.2–2.3 GPa, Ti–WC/WC–TiN film showed a higher adhesion strength of 48.5 N than that of Ti/WC–TiN film. These results are attributed to the low residual stress and higher stiffness of the Ti–WC interlayer than the soft Ti interlayer. The microhardness of Ti–WC/WC–TiN film on cemented carbide was measured to be 40 GPa and the maximum hardness was obtained as the period (λ) was approximately 7 nm. This value is approximately 1.5 times higher than that of the TiN single layer film. Other WC–TiN superlattice coatings with Ti and WC interlayers showed a hardness range of 38–40 GPa. The ratio H3/E2 (plastic deformation resistance) of WC–TiN superlattice films with various interlayers was calculated to be in a range from 0.18 to 0.33. This paper reports the preparation of WC–TiN superlattice coatings on WC–Co and Si substrates using a multi-cathode arc ion-plating system. The microstructures and mechanical properties of WC–TiN superlattice films were investigated, too.