Enhanced Corrosion Resistance of TiZrN-Coated Additively Manufactured 8620 Low-Alloy Steel in Nitrate Salt Solution and Salt Bath

Abstract

In this study, corrosion resistance of TiZrN-coated additively manufactured (3D-printed) 8620 steel has been separately studied in a 60–40 wt% NaNO3 + KNO3 molten salt and in an aqueous nitrate salt environment. Microstructural characterization of the as-built bare 3D-printed 8620 sample revealed martensitic microstructures. High-temperature corrosion analysis in molten nitrate salt revealed improved film stability and corrosion resistance of the coating. The coated 3D-printed sample showed no scale of corrosion products, whereas the bare 3D-printed sample exhibited a layer of corrosion products of 2.62 ± 0.24 µm thickness. Potentiodynamic polarization and electrochemical impedance spectroscopy tests in aqueous nitrate salts at room temperature exhibited an ~8-fold decrease in corrosion current density and a ~7-fold increase in charge transfer resistance, indicating enhanced corrosion resistance of the coated 8620. The coated wrought 8620 showed comparable corrosion resistance to that of the coated 3D-printed sample. However, in aqueous solution, the bare 3D-printed sample exhibited localized corrosion, whereas the bare wrought revealed uniform corrosion on the surface.