In Situ Analysis of the Thermal Evolution of Electrodeposited Fe-C Coatings

Fe-C coatings with a high amount of carbon were electrodeposited from an iron-sulfate electrolyte. Citric acid as an additive in the electrolyte not only served as a carbon source during electrodeposition but also caused the reproducible codeposition of oxygen and hydrogen. The various codeposited elements (C, O, H) result in the complex nature of the as-deposited coatings and allow for deliberate alterations of the coating properties by postdeposition annealing. The thermal evolution of electrodeposited Fe-C coatings was investigated in situ during isochronal annealing. In situ synchrotron diffraction analysis revealed temperature-dependent phase transformations, which were supplemented with in situ thermal analysis for investigating the evolution of codeposited elements and associated mass changes during annealing. Based on the determined activation energies of identified thermal events, the underlying mechanisms are discussed. The results clearly indicate the role of codeposited elements in the coatings and suggest that they partly exist in the form of organic compounds, which decompose during annealing. In addition to revealing the thermal stability of the coatings and quantifying the coatings’ thermal evolution, the complementary methods of in situ analysis considerably improved the understanding of the as-deposited Fe-C coatings—both are essential prerequisites for the successful application of the Fe-C coatings.