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Ni-P/Zn-Ni compositionally modulated multilayer coatings – part 2: corrosion and protection mechanisms

Bahadormanesh, B ; Sharif University of Technology | 2018

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  1. Type of Document: Article
  2. DOI: 10.1016/j.apsusc.2018.02.130
  3. Publisher: Elsevier B.V , 2018
  4. Abstract:
  5. The Ni-P/Zn-Ni compositionally modulated multilayer coatings CMMCs were electrodeposited from a single bath by switching the deposition current density. The corrosion resistance of the deposits was studied and compared with that of monolayers of Ni-P and Zn-Ni alloys via Tafel polarization, EIS and salt spray tests. Characterization of corrosion products by means of EDS and XRD revealed more details from the corrosion mechanism of the monolayers and multilayers. The corrosion current density of Ni-P/Zn-Ni CMMCs were around one tenth of Zn-Ni monolayer. The CMMC with incomplete layers performed lower polarization resistance and higher corrosion current density compared to the CMMC with complete layers. The electrical circuit that was proposed for modeling the corrosion process based on the EIS spectrum, proved that layering reduces the porosity and consequently improves the barrier properties. Although, layering of Zn-Ni layers with Ni-P deposits increased the time to red rust in salt spray test, the time for white rust formation decreased. The corrosion mechanism of both Zn-Ni and Ni-P (containing small amount of Zn) was preferential dissolution of Zn and the corrosion products were comprised of mainly Zn hydroxychloride and Zn hydroxycarbonate. Also, Ni and P did not take part in the corrosion products. Based on the electrochemical character of the layers and the morphology of the corroded surface, the corrosion mechanism of multilayers was discussed. © 2018 Elsevier B.V
  6. Keywords:
  7. Compositionally modulated multilayer coatings ; Ni-P/Zn-Ni ; Zn-Ni-P alloys ; Binary alloys ; Coatings ; Corrosion ; Corrosion inhibitors ; Corrosion resistance ; Corrosion resistant alloys ; Current density ; Deposits ; Electrochemical corrosion ; Electrodeposition ; Electrodes ; Monolayers ; Multilayers ; Nickel ; Nickel alloys ; Polarization ; Zinc ; Compositionally modulated multilayers ; Corrosion current densities ; Corrosion mechanisms ; Deposition current density ; Ni-P alloy ; Polarization resistances ; Preferential dissolution ; Protection mechanisms ; Zinc alloys
  8. Source: Applied Surface Science ; Volume 442 , 2018 , Pages 313-321 ; 01694332 (ISSN)
  9. URL: https://www.sciencedirect.com/science/article/pii/S0169433218304732