Protection against corrosion of iron alloys by aluminized coatings produced using two different processes
Aluminized coatings were produced on iron by means of two different processes: electron beam deposition under UHV of Al on iron samples previously covered with 57Fe films, and hot-dipping of iron samples in molten aluminium. Aluminized samples were submit
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riginally published in the journal Hyperfine Interactions, Volume 187, Nos 1–3, 1211–1216. DOI: 10.1007/s10751-008-9873-8 © Springer Science + Business Media B.V. 2008
Abstract Aluminized coatings were produced on iron by means of two different processes: electron beam deposition under UHV of Al on iron samples previously covered with 57 Fe films, and hot-dipping of iron samples in molten aluminium. Aluminized samples were submitted to thermal treatments in order to promote interdiffusion at the Fe–Al interface and favour the formation of Fe–Al intermetallic compounds of composition suitable to protect the underlying iron from oxidation. Phase composition, structure and morphology of both as deposited and thermally treated coatings were characterized by means of X-ray diffraction, Mössbauer spectroscopy and metallographic techniques. Significant differences among the effects of the Fe–Al interdiffusion occurring for Al layers produced with the two processes are pointed out and discussed. Keywords Aluminizing · Electron beam deposition · Hot-dipping · Fe–Al intermetallics
1 Introduction In the important field of surface treatments addressed to improve the resistance of iron alloys to corrosion, wear and fatigue, a considerable interest is given to aluminizing processes where layers of aluminium are thermally deposited onto widely used structural materials (e.g. steels) which, subsequently, are subjected to thermal treatments designed to obtain the formation of protective coatings of Fe– Al intermetallic compounds. In this regard, a new and important field of application
G. Palombarini (B) · A. Casagrande Department of Metals Science, Electrochemistry and Chemical Techniques, University of Bologna, Bologna, Italy e-mail: [email protected] M. Carbucicchio · R. Ciprian Department of Physics, University of Parma, Parma, Italy
N. S. Gajbhiye and S. K. Date, ICAME 2007. DOI: 10.1007/978-3-540-78696-2_166
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is represented by the protection of steels to be used in heavy liquid metal-cooled (HLM) nuclear reactors, where the base alloy in contact with HLM can undergo a considerable damage due to corrosion phenomena [1]. Aluminized coatings are expected to adequately resist the main corrosion processes: iron oxidation by oxygen in the melt, and dissolution into the melt of alloying elements in the steel, as it has been found in the case of austenitic stainless steels which undergo significant losses of Ni and Cr when kept in contact with liquid Pb or Pb-Bi eutectic alloy [2–4]. In the present work, aluminized coatings were produced on iron using two different procedures: (1) electron beam deposition under UHV of Al films on iron samples previously covered with 57 Fe films, and (2) hot-dipping of iron samples into molten aluminium. Aluminized samples were subjected to thermal treatments at various temperatures for different periods of exposure in order to favour the formation of Fe–Al intermetallic compounds of composition suitable to effectively protect the underlying metal. The effect
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