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Autocatalytic duplex Ni-P/Ni-W-P coatings on AZ31B magnesium alloy

Selvi, Ezhil V and Chatterji, Purba and Subramanian, S and Balaraju, JN (2014) Autocatalytic duplex Ni-P/Ni-W-P coatings on AZ31B magnesium alloy. In: SURFACE & COATINGS TECHNOLOGY, 240 . pp. 103-109.

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Official URL: http://dx.doi.org/10.1016/j.surfcoat2013.12.022


Autocatalytic duplex Ni-P/Ni-W-P coatings were deposited on AZ31B magnesium alloy using stabilizer free nickel carbonate bath. Some of the coated specimens were passivated in chromate solution with and without heat treatment. Plain Ni-P coatings were also prepared for comparison. Coatings were characterized for their surface morphology, composition and corrosion resistance. Energy dispersive analysis of X-ray (EDX) showed that the phosphorous content in the Ni-P coating is 6 wt.% and for Ni-W-P it reduced to 3 wt.% due to the codeposition of tungsten in the Ni-P coating. Marginal increase in P and W contents was observed on passivated coupons along with Cr (0.18 wt.%) and O (2.8 wt.%) contents. Field emission scanning electron microscopy (FESEM) examination of these coating surfaces exhibited the nodular morphology. Chromate passivated surfaces showed the presence of uniformly distributed bright Ni particles along with nodules. Potenfiodynamic polarization and electrochemical impedance spectroscopy (EIS) studies were carried out in deaerated 0.15 M NaCI solution to find out the corrosion resistance of the coatings. Among the coatings developed, duplex-heat treated-passivated (duplex-HIP) coatings showed lower corrosion current density (i(corr)) and higher polarization resistance (R-p) indicating the improved corrosion resistance. The charge transfer resistance (R-ct) value obtained for the duplex-HIP was about 170 times higher compared to that for Ni P coating. (c) 2013 Elsevier B.V. All rights reserved.

Item Type: Journal Article
Additional Information: Copyright for this article belongs to the ELSEVIER SCIENCE SA, SWITZERLAND
Keywords: Magnesium alloy; Duplex Ni-P/Ni-W-P; Corrosion; EIS
Department/Centre: Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Date Deposited: 16 Apr 2014 10:39
Last Modified: 16 Apr 2014 10:40
URI: http://eprints.iisc.ac.in/id/eprint/48863

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