The nanostructure and mechanical properties of PVD CrCu (N) coatings

Coatings with a nanocomposite structure have been identified as offering excellent wear resistant properties. This paper presents results on the CrCu (N) system, in which the immiscibility of Cr (with low N concentration) and Cu offers the potential of a predominantly metallic (and therefore tough) nanocomposite, composed of small Cr (N) grains interdispersed in a (minority) Cu matrix. A range of CrCu (N) compositions have been deposited using a twin-target (Cr and Cu) unbalanced magnetron sputtering system. The stoichiometry and nanostructure have been characterised by X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and electron energy loss spectroscopy (EELS). The hardness and elastic modulus have been determined by nanoindentation. The phase composition of the coatings is generally based on Cr2N with the additional presence of Cr and CrN depending on the elemental composition. Cu was found to be incorporated in the Cr based phases. The formation of this metastable structure is attributed to the relatively low deposition temperature employed (∼200 °C). The coating with the best mechanical properties, CrCu0.07N0.48 exhibited a hardness of 20 GPa.