Electrodeposition of Iron with Co-deposition of Carbon: On the Nature of Nanocrystalline Fe-C Coatings
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TRODUCTION
ELECTROCHEMICAL deposition of iron from iron-sulfate baths was developed a century ago and implies the advantages of a cheap electrolyte, low operating temperature, and low susceptibility to oxidation of the electrolyte.[1] Originally, electrodeposition of iron was mainly used for short-term restoration of worn or damaged surfaces of machine components[2,3] as for these applications, the ease of site-specific deposition and attractive mechanical properties of the coatings were of main interest. More recently, the intended co-deposition of other elements (e.g., tungsten, nickel, phosphorous, and zinc) from advanced electrolytes inspired a revival of the original interest in iron-based coatings.[4] Of particular interest is the co-deposition of carbon and iron, and iron-carbon (Fe-C) coatings have been synthesized not only by electrochemical deposition[5–13] but also by physical vapor deposition.[14–17] Although different morphologies and structures of Fe-C coatings ranging from amorphous to crystalline and different carbon concentrations are reported for the
JACOB OBITSØ NIELSEN, PER MØLLER, and KAREN PANTLEON are with the Department of Mechanical Engineering, Technical University of Denmark, Produktionstorvet, Building 425, 2800 Kongens Lyngby, Denmark. Contact e-mail: [email protected] Manuscript submitted November 20, 2018. Article published online June 5, 2019 METALLURGICAL AND MATERIALS TRANSACTIONS A
various deposition processes, all Fe-C coatings possess very high hardness, being similar to the hardness of martensite in steels. Despite that similarity, the peculiarities of the growth of Fe-C coatings suggest essential differences to traditional hardening of steel and, hence, a different origin of microstructure and properties. Despite a general consistency in the literature regarding the good mechanical properties of Fe-C coatings, their growth characteristics and, in particular, the role of carbon in the coatings are aspects that not fully are understood yet. This, however, is essential for the promising application of Fe-C coatings as a novel type of hard and wear-resistant surfaces, which both enables straightforward repairing of worn surfaces by site-specific deposition and the large-scale deposition on components exposed to mechanical loading during operation. Electrodeposited Fe-C coatings have a huge potential for surface engineering, including tailoring of the deposition parameters to optimize the growth characteristics and additional modifications during post-deposition treatments of the coatings. Understanding the correlation between the applied deposition conditions and the resulting microstructure is a prerequisite for the successful transfer of knowledge obtained on laboratory scale into a reliable, reproducible, large-scale production.[18,19] In addition to the type of electrolyte and the process parameters, like current density and temperature, both nucleation and growth of electrodeposits are further affected by the nature of the substrate, which influences the size, shape, crystallographi
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