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Microstructure effect of intermediate coat layer on corrosion behavior of HVAF-sprayed bi-layer coatings
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. (PTW)ORCID iD: 0000-0002-7663-9631
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. (PTW)ORCID iD: 0000-0002-9578-4076
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. (PTW)ORCID iD: 0000-0001-7787-5444
2017 (English)In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 26, no 1-2, 243-253 p.Article in journal (Refereed) Published
Abstract [en]

The inherent pores and carbides of Cr3C2-NiCr coatings significantly reduce the corrosion resistance, the former by providing preferential paths for ion diffusion and the latter by forming cathodic sites in galvanic couples (between NiCr and Cr3C2). Adding a dense intermediate layer (intermediate coat layer) between the Cr3C2-NiCr coating (top coat) and substrate increases the corrosion protection of the coating if the layer acts as cathode in connection to the top coat. In the present work, NiCr, NiAl, and NiCoCrAlY layers were deposited by high-velocity air fuel(HVAF) process as intermediate coat layers for the Cr3C2-NiCr top coat. Effects of coating microstructure on corrosion behavior of single- and bi-layer coatings were studied by open circuitpotential (OCP) and polarization tests in 3.5 wt% NaCl at room temperature. A zero resistanceammeter (ZRA) technique was used to study the galvanic corrosion of the coupledtop and intermediate coat layers. Methods such as SEM and XRD were employed to characterize the as-sprayed and corroded coatings and investigate the corrosion mechanisms.The results showed that the NiCoCrAlY coating not only presented a more positive corrosion potential (Ecorr) than the Cr3C2-NiCr coating, but also provided a better passive layer than the single-phase NiCr and NiAl coatings.

Place, publisher, year, edition, pages
Materials Park, OH: ASM International, 2017. Vol. 26, no 1-2, 243-253 p.
Keyword [en]
Thermal spray, HVAF, Corrosion, OCP, Polarization
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
URN: urn:nbn:se:hv:diva-9928DOI: 10.1007/s11666-016-0484-7ISI: 000392060300024OAI: oai:DiVA.org:hv-9928DiVA: diva2:972708
Note

Ingår i lic avhandling

Available from: 2016-09-22 Created: 2016-09-22 Last updated: 2017-05-15Bibliographically approved
In thesis
1. Corrosion Behavior of HVAF-Sprayed Bi-Layer Coatings
Open this publication in new window or tab >>Corrosion Behavior of HVAF-Sprayed Bi-Layer Coatings
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In a variety of engineering applications, components are subjected to corrosive environment. Protective coatings are essential to improve the functional performances and/or extend the lifetime of the components. Thermal sprayingas a cost-effective coating deposition technique offers high flexibility in coatings' chemistry/morphology/microstructure design. However, the inherent pores formed during spraying limit the use of coatings for corrosion protection. The recently developed supersonic spray method, High-Velocity-Air-Fuel (HVAF), brings significant advantages in terms of cost and coating properties. Although severely reduced, the pores are not completely eliminated even with the HVAF process. In view of the above gap to have a high quality coating, bi-layer coatings have been developed to improve the corrosion resistance of the coatings. In a bi-layer coating, an intermediate layer is deposited on the substrate before spraying the coating. The electrochemical behavior of each layer is important to ensure a good corrosion protection. The corrosion behavior of the layers strongly depends on coating composition and microstructure, which are affected by feedstock material and spraying process. Therefore, the objective of the researchis to explore the relationships between feedstock material, spraying process, microstructure and corrosion behavior of bi-layer coatings. A specific motivationis to understand the corrosion mechanisms of the intermediate layer which forms the basis for developing superior protective coatings. Cr3C2-NiCr top layer and intermediate layers (Fe-, Co- and Ni-based) were sprayed by different thermal spraying processes. Microstructure analysis, as well as various corrosion tests, e.g., electrochemical, salt spray and immersion tests were performed. The results showed a direct link between the corrosion potential (Ecorr) of the intermediate layer and the corrosion mechanisms. It was found that the higher corrosion resistance of Ni-based coatings than Fe- and Co-based coatings was due to higher Ecorr of the coating in the galvanic couple with top layers. Inter-lamellar boundaries and interconnected pores reduced the corrosion resistance of intermediate layers, however a sufficient reservoir of protective scale-forming elements (such as Cr or Al) improved the corrosion behavior.

Place, publisher, year, edition, pages
Trollhättan: University West, 2016. 59 p.
Series
Licentiate Thesis: University West, 10
Keyword
Thermal spray coating, HVAF, Corrosion protection, Galvanic corrosion, Composition, Microstructure, EIS, Polarization, OCP
National Category
Production Engineering, Human Work Science and Ergonomics
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-9929 (URN)978-91-87531-33-0 (ISBN)978-91-87531-32-3 (ISBN)
Presentation
2016-09-30, C118, University West, Trollhättan, 10:15 (English)
Supervisors
Available from: 2016-09-30 Created: 2016-09-22 Last updated: 2016-09-30Bibliographically approved

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