Electrochemical Corrosion Behavior of TiAlN/CrN Nanoscale Multilayer Coatings by Multi-Arc Ion Plating in 3.5% NaCl Solution

Multi-arc ion plating was used to deposit TiAlN/CrN multilayer coatings with different bilayer thicknesses on Type 316L stainless steel. The impacts of the bilayer thickness on the electrochemical performance of the TiAlN/CrN multilayer coatings were explored in a neutral saline (3.5% NaCl) solution. The fracture cross-sectional morphology of the as-deposited coatings were investigated by scanning electron microscope. The crystal structure and preferred orientation were analyzed by x-ray diffraction. The interface characteristic was detected by transmission electron microscopy. The potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were used for as-deposited coatings. Corroded surface morphology and EIS of the 15-day immersion coatings and substrate were examined to analyze the anticorrosion performance. EIS showed an increase of polarization resistance (Rp) and a decrease in constant-phase element (CPE) for multilayer coatings with a decrease in bilayer thickness. After 15 days of immersion, the EIS plot showed that the C3 coating (with 20 bilayers) had the lowest electrical double-layer capacitance (CPEdl) and highest charge transfer resistance (Rct) in all samples. The relative decay of the Rp of the C3 coating was the smallest compared with the as-deposited coatings, which shows a satisfactory corrosion resistance. The electrochemical tests and immersion corrosion morphology showed that the existence of a large number of interfaces between individual layers in a multilayer structure inhibits the pitting propagation significantly and enhances the corrosion resistance.