Multi-layer structure of Inconel 625 coatings prepared by magnetron sputtering.

The coating/substrate interface and oxide layers of the Inconel 625 film may have significant impacts on its material properties, especially the corrosion behavior of the film. However, since the interface and oxide layer can be very thin and experimental toolbox to characterize them is limited, the detailed vertical structure of Inconel 625 coatings remains poorly understood. In this study, a multi-layer structure in Inconel 625 film prepared by magnetron sputtering is revealed using X-ray reflectometry (XRR) and neutron reflectometry (NR) techniques. Thickness and major composition of each layer are obtained. The results indicate that there exists a ~2 nm-thick Cr-rich Inconel sublayer underneath the main Inconel 625 film. An oxide layer mainly consisting of NiO with thickness of ~2 nm is found on the surface of the main Inconel 625 film. In addition, we identified a ~2 Å contamination layer between sapphire substrate and Inconel film even after argon ion sputtering cleaning. We also found that the thickness of the main Inconel 625 film grows linearly with the deposition time, with thicknesses of other layers remaining constant. Our findings provide insight into the multi-layered structures of Inconel 625 coatings with atomic-scale spatial resolution and give directions for future study to improve the corrosion resistance of Inconel 625 coatings.