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A Comparative Study of Corrosion Resistance forHVAF-Sprayed Fe- and Co-Based Coatings
University West, Department of Engineering Science, Research Environment Production Technology West. Amirkabir University of Tehran, Tarbiat Modares University of Tehran. (Thermal Spray)ORCID iD: 0000-0002-7663-9631
University West, Department of Engineering Science, Division of Manufacturing Processes.ORCID iD: 0000-0002-9578-4076
University West, Department of Engineering Science, Research Enviroment Production Technology West. (PTW)ORCID iD: 0000-0001-7787-5444
2016 (English)In: Coatings, ISSN 2079-6412, Vol. 6, no 2Article, review/survey (Refereed) Published
Abstract [en]

There is an increasing demand to replace Co-based coatings with cheap andenvironmentally friendly Fe-based coatings in corrosive environments. The main objective of thiswork was to evaluate whether Fe-based coatings could present a better corrosion performancethan Co-based coatings. Therefore, two types of Fe-based and one type of Co-based coatings withchemical compositions (in wt %) of Fe-28Cr-16Ni-1.85C (FeNiCrC), Fe-17Cr-12Ni (FeNiCr), andCo-28Cr-1C (CoCrC) were produced by High Velocity Air Fuel (HVAF) spraying. The corrosionbehavior of the coatings was studied comparatively by electrochemical tests in 3.5 wt % NaCl solutionat 25 C. The polarization test results showed that the FeCrNiC coating protected the underlyingsubstrate better than the CoCrC coating, while the FeCrNi coating failed to hinder the penetrationof corrosive ions. Electrochemical impedance spectroscopy (EIS) measurements revealed that thesolution penetrated into the coating through defects, however the corrosion process slowed downdue to clogging of the interconnected defects by corrosion products. Increasing the in-flight averageparticle temperature from 1400 C to 1500 C led to a denser coating with fewer defects which seemedto improve the corrosion resistance of the FeCrNiC coating. The high-alloyed Fe-based coatings hadthe best corrosion protection performance and can thus be recommended as a potential alternative toCo-based coatings.

Place, publisher, year, edition, pages
MDPI , 2016. Vol. 6, no 2
Keyword [en]
Thermal spray coating; HVAF; corrosion; polarization; EIS
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
URN: urn:nbn:se:hv:diva-9294DOI: 10.3390/coatings6020016OAI: diva2:917625
Available from: 2016-04-07 Created: 2016-04-07 Last updated: 2016-09-22Bibliographically 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.
Licentiate Thesis: University West, 10
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
urn:nbn:se:hv:diva-9929 (URN)978-91-87531-33-0 (Printed version) (ISBN)978-91-87531-32-3 (Electronic version) (ISBN)
2016-09-30, C118, University West, Trollhättan, 10:15 (English)
Available from: 2016-09-30 Created: 2016-09-22 Last updated: 2016-09-30Bibliographically approved

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