Microstructure and Corrosion Properties of Multilayered CrAlN / SiNx Coatings

Abstract

The multilayers were deposited by radio-frequency reactive magnetron sputtering. In multilayers, the layer thickness varied from 0.3 to 1 nm, and the layer thickness ratios of CrAlN to were set to be 4:0.3, 13:1, and 4:1. The effects of the layer thickness on the crystalline behavior and microstructure of the multilayers were discussed by X-ray diffraction patterns, scanning electron microscopy, and high resolution transmission electron microscopy. In addition to transforming the structure from crystalline to amorphous with thickness increase from 0.3 to 1 nm, the films were changed from a columnar microstructure to a dense one. The corrosion resistance of the coatings in 3.5 wt % NaCl solution was investigated by Tafel measurement and electrochemical impedance spectroscopy. The multilayers refined the coarse columnar structure in single-layered CrAlN, leading to a denser microstructure, and revealed lower corrosion current density and higher corrosion impedance. Additionally, the multilayer with a thickness ratio of to was identified with a similar composition yet a denser microstructure compared to the one with an to thickness ratio of 4:0.3. The multilayer with the thickness ratio of to showed better corrosion resistance, suggesting that anticorrosion properties were dominated by microstructure rather than composition. Furthermore, the multilayer with the thickness ratio of to exhibited the densest microstructure and revealed the best corrosion resistance because the amorphous layers interrupted the columnar growth and then provided no direct diffusion paths.