Thermal stability of ZrN–Ni and CrN–Ni superhard nanocomposite coatings

This paper reports on the thermal stability of ZrN–Ni and CrN–Ni nanocomposite coatings with a nickel content between approximately 0.5 and 8 at.%, which were prepared by DC reactive magnetron sputtering at a substrate temperature of 300 and 200°C, respectively, and a negative bias between −30 and −200 V for ZrN–Ni and −200 V for CrN–Ni. The films were characterised by X-ray diffraction (XRD), Vickers hardness measurements and X-ray photoelectron spectroscopy (XPS). Upon isochronal annealing in a forming gas (90 vol.% N2, 10 vol.% H2) between 400 and 650°C for 30 min, the hardness and lattice parameter of crystal planes parallel to the substrate decreased, indicating that the hardness enhancement is due to a high biaxial compressive stress in the coatings. No hardness enhancement could be attributed to the formation of a nanocomposite structure.