A Study on the Corrosion Inhibition of Fe-Based Amorphous/Nanocrystalline Coating Synthesized by High-Velocity Oxy-Fuel Spraying in an Extreme Environment

In this work, Fe-based (Fe-Cr-B-P-C) amorphous/nanocrystalline composite coatings were deposited by high-velocity oxy-fuel thermal spray method with varying powder feed rates and their behavior in saline environment was investigated. An SS316L coating with optimized parameters was also prepared for comparison purpose. The microstructural characterization of the composite coatings revealed the presence of embedded nanocrystalline phases in the amorphous matrix. The amorphicity of the coating increased, whereas the porosity content decreased gradually with the increment in feed rate during the spraying process. The combined effect of extent of devitrification and porosity content on the corrosion behavior of the various coatings was analyzed. Potentiodynamic polarization and electrochemical impedance spectroscopy studies revealed that the Fe-based composite coatings exhibited significantly lower corrosion current density and higher polarization resistance than that of the mild steel substrate as well as SS316L coating. The enhanced corrosion resistance of the composite coatings is ascribed to the combined effect of lower porosity content and retained amorphous phase. In addition, the formation of chromium hydroxide along with some of the oxides and hydroxides of iron in the post-corroded coating samples aids in impeding the corrosive solution penetration, thereby increasing the corrosion inhibition efficiency of the composite coatings. Graphic