Microstructure, Mechanical and Tribological Properties of NbN/Ni Coatings

Abstract

The NbN/Ni coatings were deposited by co-sputtering on Si (100) substrates. The structure, hardness and tribological properties were characterized by X-ray diffraction (XRD), atomic force microscope (AFM), scanning electron microscopy (SEM), nanoindentation test and ball-on-disc tribometer. XRD revealed that the NbN/Ni coatings exhibited a NaCl-type NbN structure but no sign of any nickel phase. For the coatings with various nickel powers ranged from 20 W to 40 W, the shrinkage of the lattice parameter of NbN indicated that Ni atoms might be incorporated into the NbN lattice with a substitution of Nb atoms by the smaller Ni atoms. Further increasing of Ni powers, the degree of crystallinity of the coatings became worse. The NbN coating doped with a certan power of Ni (40 W) exhibited the best degree of crystallinity among all samples. It also displayed a maximum microhardness of 25 GPa combined with a better resistance to plastic deformation, which could attribute to the grain refinement and the solid solution strengthening. Tribilogical properties of NbN/Ni coatings were also found to be depentent on nickel powers significantly. For the pure NbN coating, the coefficient of friction (CoF) was 0.7 approximately, while it decreased to 0.54 when the power of Ni increased to 40 W. Simultaneously, the wear resistance of the NbN/Ni coatings was improved due to the spontaneous oxidation of the wear track surfaces caused by the addition of a certain amount of nickel to the niobium nitride coatings.