Structure And Property Of Cr-based Coatings On Mg Alloy By Magnetron Sputtering

It will be one of the prevalent structure materials in future for Mg alloy, which need to be treated due to soft surface and lower ability of corrosion resistance. Although the surface treatment technologies applied in Mg alloy have improved surface performance, adhesion force, frictional wear and mechanical property can not satisfy demand which Mg alloy is applied in key parts area. At present magnetron sputtering is one of the mainstream PVD (physical phase deposition) technologies, and the coating deposited demonstrated high adhesion force and density at lower deposition temperature. So, it proposed a method that the hard coatings were deposited by magnetron sputtering.In present research, the CrNx and CrNxOyCz coatings on Mg alloy were deposited by planner magnetron sputtering and the structure property of coatings were characterized by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), respectively. The CrTiAlN coatings were deposited by closed field unbalanced magnetron sputtering ion plating (CFUBMS), and the structure, frictional wear and mechanical property were characterized by transmission electron microscope (TEM), frictional wear tester (ST3001) and microhardness tester, respectively. Moreover, the growth of columnar crystal and evolution of surface profile were discussed, the main results are as follows:①Structure property of CrNx coatings depends on the technological parameters which include subastrate temperature, N2 content, current density of target and bias voltage of substrate. Deposition rate shows the quadratic increasing function of current density, while it demonstrates exponentially decay with increasing N2 content. The CrNx coatings on Mg alloy tend to form columnar crystal with open boundary with increasing in N2 content.②Deposition of CrNx coatings is related to bridged Cr layer, transition CrNx layer and atomic CrN layer. The columnar growth of Cr film on Mg alloy originates from meshy growth. Growth of CrN coating on Mg alloy includes shadow and merger growth. The in-plane average diameter and variance of grain size (σ2) indicate linear growth with thickness increasing, and surface roughness presents exponential growth.③Surface profile of coating which was affected by substrate surface depends on coating thickness, and tends to smooth with coating thickening if the roughness of in-phase is omitted. Surface roughness increases with film thickness thickening for in-phase roughness, and the increased bias power will result in decrease of surface roughness. It shows linear function between surface roughness of CrNx coatings and N atomic concentration, and exponential relationship between one and thickness.④The CrNxOyCz coatings deposited in reactive atmosphere reveals columnar growth, several different species occur, including CrN, Cr2N, Cr3C2, Cr2O3, CrO2 and CrNxOy. The profile concentration Oxygen and Carbon atoms obey first order exponential decay function, and Cr3C2 and Cr2N belongs to unstable phase. The frictional wear property of CrNxOyCz coating is worse than that of CrNx coatings.⑤The special wear rate (SWR) of AZ31 arrives at 1055×10-15m3·N-1·m-1, while that of CrTiAlN coatings on Mg alloy is 2.4×10-15m3·N-1·m-1. The adhesion force of CrTiAlN coatings at bias voltage (Vb) -50V reaches to 10N.⑥The SWR of CrTiAlN coatings and WC-Co6% ball are the smallest at Vb=-55V and medium N2, and friction coefficient can stabilize at 0.2-0.3. Frictional wear property of CrTiAlN/MoS2 coating outperforms CrTiAlN coating, cycle index of sliding friction reaches to 70000, and friction coefficient can stabilize at 0.2-0.35.