The combined effects of Cu and Ag on the nanostructure and mechanical properties of CrCuAgN PVD coatings

• Nitrogen-containing Cr coatings with additions of both Cu and Ag were produced and investigated.
• Nitrogen-free CrCuAg coatings showed strong preferential orientation, and the orientations changed with sample position.

In order to study the combined effects of the noble, low miscibility metals, Cu and Ag, on the nanostructure and mechanical properties of nitrogen-containing Cr coatings, CrCuAgN coatings were prepared using unbalanced magnetron sputtering. An optimised semi-orthogonal closed-field target configuration was used to obtain coatings with similar thicknesses and distributed Cu + Ag concentrations across different stainless steel sample positions in the deposition chamber. The coating cross-sections and surface morphologies were investigated using Scanning Electron Microscopy (SEM), and the chemical compositions were analysed using Energy Dispersive X-ray (EDX) spectrometry. Phase compositions were analysed using X-Ray Diffraction (XRD), and the hardness and elastic modulus were measured using nanoindentation. The (Cu + Ag)/Cr concentration ratios of coatings were found to be strongly correlated to deposition rate (and thus coating thickness). In the nitrogen-free control group, coatings showed strong preferential orientation for both metallic Cr and Ag, with the orientations changing depending on the sample position relative to the sputter target. The introduction of nitrogen resulted in the formation of coatings showing a high-degree of solubility of Cu in metallic Cr and Cr2N nitride, or even an amorphous phase containing all four elements. A coating with moderately high hardness of 14.1 GPa and H/E ratio of 0.072, with combined Cu + Ag concentration approaching 15 at.% was obtained, which could be promising in prolonging the lifetime of solid-lubrication tribological coatings.