Effect of N2 flow rate on microstructure and mechanical properties of PVD CrNx coatings for tribological application in seawater

The CrNx coatings were deposited on 316L stainless steel and silicon (100) wafer by multi-arc ion plating with different N2 flow rates. Composition, microstructures and mechanical properties of the as-deposited CrNx coatings were systematically investigated by X-ray photoelectron spectrometry (XPS), X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), nano-indentation and scratch tester. The friction and wear properties of CrNx coatings were investigated by a ball-on-disk tribometer in artificial seawater. The results showed that the coatings transformed from a mixture of Cr + Cr2N to single-phase Cr2N, and then Cr2N + CrN to pure CrN phase with the increase of N2 flow rate. The coatings were all dense except for the one deposited at 200 sccm, which clearly exhibited a typical columnar structure. With the increase of N2 flow rate, the friction coefficients first decreased to 0.196 at 100 sccm then slightly increased to 0.215 at 200 sccm in seawater. However, the depth of wear track and wear rate were lowest at 125 sccm, which could be attributed to the denser structure related to better corrosion resistance consisting of Cr2N and CrN phases.