Corrosion resistance of duplex and gradient CrNx coated H13 steel

The electrochemical behavior of H13 steel coated with duplex and gradient CrNx coatings deposited by cathodic arc deposition has been studied. The substrate material was coated with CrN by cathodic arc deposition technique. Duplex layers of CrNx, which normally include an interlayer approximately 100–200 nm of Cr under the main CrN coating, were prepared; gradient CrNx coating were produced with continuous elevated nitrogen pressure. The X-ray photoelectron spectroscopy (XPS) was applied to characterize the chemical composition, and the glancing angle X-ray diffraction (GAXRD) was used to examine the crystallographic structure. The potentiodynamic polarization was examined by Zahner IM6e electrochemical workstation in a 0.5 M H2SO4 solution at ambient temperature, and the corrosive surface was detected by scanning electron microscopy (SEM). It was shown that the gradient coating could enhance the corrosion performance of CrNx coated H13 steel. The corrosion resistance improvement was not only attributed to the increase in thickness, but also to the internal microstructure and phase composition. Gradient CrNx coating produced in this work was proved to be particularly promising in terms of corrosion resistance, owing to its incontinuous pinholes and different composition: Cr, Cr2N in inner part and CrN in surface. The results showed that the gradient coating had an improved electrochemical performance than duplex CrN coating.