Effects of N 2 content and thickness on CrN x coatings on Mg alloy by the planar DC reactive magnetron sputtering

Abstract

The CrN x (0 < x = N/Cr < 1) coatings on Mg alloy were prepared by DC reactive planar magnetron sputtering at a mixed atmosphere containing Ar and N 2. The effects of N 2 content and thickness on the CrN x 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 N 2 content ( φ(N 2)), and the deposition rate decreases exponentially. The morphologies evolution of CrN x coatings shows that the growth structure changes from fibre growth to columnar growth with the increase in φ(N 2). 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 Cr 2N + Cr and CrN + Cr 2N, respectively. The in-plane mean grain size linearly increases and the Root Mean Square roughness W RMS increases exponentially with coating thickening, and grain size obeys Gaussian distribution.