Microstructures and tribological properties of CrN/ZrN nanoscale multilayer coatings

Nanoscale multilayer CrN/ZrN coatings with bilayer thicknesses ranging from 11.7 to 66.7 nm were prepared by reactive magnetron sputtering techniques. The structure of the thin films was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). X-ray diffraction results showed that CrN individual layers presented a preferred orientation in the multilayer coatings. The diffraction peaks of CrN shifted continuously to low diffraction angle with decreasing bilayer thickness. TEM observations showed that the multilayer did not form a superlattice structure instead of the coexistence of nanocrystalline CrN and ZrN layers. Columnar growth for all the coatings was observed by cross-sectional SEM. Nanoindentation tests showed that the multilayer coatings had almost a constant nanohardness of 29 GPa in spite of the variations of bilayer thickness. Pin-on-disk tests indicated that both the friction coefficients and wear rates increased when decreasing bilayer thickness. However, in comparison with the monolayer coating, the multilayer coatings exhibited excellent wear resistance.