Corrosion mechanism investigation of TiAlN/CrN superlattice coating by multi-arc ion plating in 3.5 wt% NaCl solution

Abstract

This study focuses on effects of layered design method on the corrosion resistance of the coatings. The different corrosion behaviors could be extracted from the microstructure and electrochemical properties for nanoscale multilayer coating (TiAlN/CrN) and single layer coatings (TiAlN and CrN). Based on the analysis of microstructure characterization, electrochemical response and corrosion morphology, it may provide a reference for the development of new anti-corrosive films. The three different coatings were prepared by the process of multi-arc ion plating on 316 stainless steel. In the deposition of TiAlN/CrN multilayer coating, the almost 150 nm Cr film was first deposited as a transition layer, and then CrN and TiAlN individual layers were alternately deposited with a single layer thickness of 10 nm. The influences of the layered construction on the electrochemical performance of the multilayer and single layer coatings were investigated in a neutral saline solution (3.5 wt% NaCl), for which potentiodynamic polarization and electrochemical impedance spectroscopy were employed. The 316 stainless steel was regarded as comparative group. The surface and cross-sectional morphology of the as-deposited coatings were investigated by scanning electron microscope (SEM). The crystal structure and preferred orientation were analyzed by X-ray diffraction (XRD). The interface characteristic of the multilayer TiAlN/CrN coating was detected by transmission electron microscope (TEM). After the 15 days immersion corrosion test, the surface morphology of the samples were observed by the means of SEM and laser scanning confocal microscope (LSCM). The results showed that all the coatings exhibited a face centered cubic structure (fcc) and the multilayer coating presented (200) preferred orientation and coherent interface. In comparison with polarization curves of the substrate and the TiAlN and CrN single layer coatings, the corrosion potential of the TiAlN/CrN multilayer coating shifted positively to −0.36 V, the corrosion current density decreased to 0.047 μAcm−2 and the polarization resistance is 124.69 kΩ cm2. In terms of EIS, the TiAlN/CrN multilayer coating possessed the low value of CPE (10.9 × 10−6 Ω−1 cm−2 sn) and high value of n (0.9) in all samples. Furthermore, the corrosion morphology of the TiAlN/CrN multilayer coating was more close to the morphology of as-deposited coating. Therefore, the TiAlN/CrN multilayer coating exhibited superior corrosion resistance compared with 316 stainless steel and the single coatings. The roles of the layered design in enhancing the corrosion resistance can be summarized as: multilayer design can change the original growing mode of the coating, block the pinholes, reduce the inherent defects and form passive coating with compactness.