Effects of N2 content and thickness on CrNx coatings on Mg alloy by the planar DC reactive magnetron sputtering

The CrNx (0 < x = N/Cr < 1) coatings on Mg alloy were prepared by DC reactive planar magnetron sputtering at a mixed atmosphere containing Ar and N2. The effects of N2 content and thickness on the CrNx coatings were characterized by the X-ray photoelectron spectrometry (XPS), X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM). The experimental results show that the N atomic concentration increases exponentially and N1s spectrum shifts downward with the increase in N2 content (φ(N2)), and the deposition rate decreases exponentially. The morphologies evolution of CrNx coatings shows that the growth structure changes from fibre growth to columnar growth with the increase in φ(N2). Based on evolution of phase and structure, a SZM model is summarized, indicating that the change of structure and phase is consistent; ZT and sub-ZT correspond to Cr2N + Cr and CrN + Cr2N, respectively. The in-plane mean grain size linearly increases and the Root Mean Square roughness WRMS increases exponentially with coating thickening, and grain size obeys Gaussian distribution.