Abstract
The CrAlN/ SiN x multilayers were deposited by radio-frequency reactive magnetron sputtering. In multilayers, the SiN x layer thickness varied from 0.3 to 1 nm, and the layer thickness ratios of CrAlN to SiN x were set to be 4:0.3, 13:1, and 4:1. The effects of the SiN x 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 SiN x 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 l CrAlN to l SiN x =13:1 was identified with a similar composition yet a denser microstructure compared to the one with an l CrAlN to l SiN x thickness ratio of 4:0.3. The multilayer with the thickness ratio of l CrAlN to l SiN x =13:1 showed better corrosion resistance, suggesting that anticorrosion properties were dominated by microstructure rather than composition. Furthermore, the multilayer with the thickness ratio of l CrAlN to l SiN x =4:1 exhibited the densest microstructure and revealed the best corrosion resistance because the amorphous SiN x layers interrupted the columnar growth and then provided no direct diffusion paths. © 2010 The Electrochemical Society.