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 are reactive evaporation of Ti and WC. The microstructure of WC-TiN films was identified to be a superlattice of TiN and beta -WC1-x phases with modulation period (lambda) of 5-13 nm and the lattice planes were continuous through the TiN and beta -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 (X) 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 H-3/E-2 (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 are ion-plating system. The microstructures and mechanical properties of WC-TiN superlattice films were investigated, too. (C) 2000 Elsevier Science B.V. All rights reserved.