Anti-corrosive yet color-tunable AlN/Si multilayer hard coatings on 304 stainless steel by magnetron sputtering

AlN based coatings are widely used to protect metal substrates from corrosion. However, synthesizing anti-corrosive yet color-tunable AlN based coatings is challenging. In this study, the AlN/Si multilayer coating was deposited on 304 stainless steel by embedding nine film layers of Si in an AlN monolayer coating using magnetron sputtering. The effects of embedded Si thin layers on the morphology, structure, composition, hardness, friction, optical and corrosion resistance of the AlN coatings were investigated. With the embedding of Si thin layers, the surface pinhole defects and columnar structure of the AlN monolayer coatings were significantly suppressed, and the surface particle size was reduced from 200 to 40 nm, and the average grain size of AlN was reduced from 19.7 to 12.9 nm. The hardness increased from 8.9 to 12.2 GPa, and the friction coefficient decreased from 0.96 to 0.75. The corrosion current density decreased from 6.81 × 10−8 to 2.57 × 10−10 A/cm2 in 3.5 wt% NaCl solution, and from 3.76 × 10−6 to 4.69 × 10−8 in 1 mol/L H2SO4 solution, which is about 4 orders of magnitude lower than the 304 steel. When the thickness of the AlN top layer was controlled to 220, 200, 185, 170, 160, 150 and 140 nm, the colors of the AlN/Si multilayer coatings were red, orange, yellow, green, blue, indigo and violet, respectively. The mechanism of anti-corrosion enhancement and color tunability of AlN/Si multilayer coatings was revealed in detail.