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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
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 [en]
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: urn:nbn:se:hv:diva-9929ISBN: 978-91-87531-33-0 (print)ISBN: 978-91-87531-32-3 (print)OAI: oai:DiVA.org:hv-9929DiVA: diva2:972718
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
List of papers
1. A Comparative Study of Corrosion Resistance for HVAF-Sprayed Fe- and Co-Based Coatings
Open this publication in new window or tab >>A Comparative Study of Corrosion Resistance for HVAF-Sprayed Fe- and Co-Based Coatings
2016 (English)In: Coatings, ISSN 2079-6412, Vol. 6, no 2, 1-15 p.Article, review/survey (Refereed) Published
Abstract [en]

There is an increasing demand to replace Co-based coatings with cheap and environmentally friendly Fe-based coatings in corrosive environments. The main objective of this work was to evaluate whether Fe-based coatings could present a better corrosion performance than Co-based coatings. Therefore, two types of Fe-based and one type of Co-based coatings with chemical 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 corrosion behavior 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 underlying substrate better than the CoCrC coating, while the FeCrNi coating failed to hinder the penetration of corrosive ions. Electrochemical impedance spectroscopy (EIS) measurements revealed that thesolution penetrated into the coating through defects, however the corrosion process slowed down due to clogging of the interconnected defects by corrosion products. Increasing the in-flight average particle temperature from 1400 C to 1500 C led to a denser coating with fewer defects which seemed to improve the corrosion resistance of the FeCrNiC coating. The high-alloyed Fe-based coatings had the best corrosion protection performance and can thus be recommended as a potential alternative toCo-based coatings.

Place, publisher, year, edition, pages
Basel, Switzerland: MDPI, 2016
Keyword
Thermal spray coating, HVAF, corrosion, polarization, EIS
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-9294 (URN)10.3390/coatings6020016 (DOI)000378428700003 ()
Available from: 2016-04-07 Created: 2016-04-07 Last updated: 2016-12-28Bibliographically approved
2. A comparative study on Ni-based coatings prepared by HVAF, HVOF, and APS methods for corrosion protection applications
Open this publication in new window or tab >>A comparative study on Ni-based coatings prepared by HVAF, HVOF, and APS methods for corrosion protection applications
2016 (English)In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 25, no 8, 1604-1616 p.Article in journal (Refereed) Published
Abstract [en]

Selection of the thermal spray process is the most important step towards a proper coating solution for a given application as important coating characteristics such as adhesion, and microstructure, etc. are highly dependent on it. In the present work, a process-microstructure-properties-performance correlation study was performed in order to figure out the main characteristics and corrosion performance of the coatings produced by different thermal spray techniques such as high-velocity airfuel (HVAF), high-velocity oxy fuel (HVOF), and atmospheric plasma spraying (APS). Previously optimized HVOF and APS process parameters were used to deposit Ni, NiCr, and NiAl coatings and compare with HVAF-sprayed coatings with randomly selected process parameters. As the HVAF process presented the best coating characteristics and corrosion behavior, various process parameters,e.g., feed rate and stand off distance (SoD) were investigated to systematically optimize the HVAF coatings in terms of high density and corrosion properties. The coatings with lower porosity and better corrosion behavior were obtained at an average SoD of 300 mm for the Ni and NiAl coatings and a SoDof 250 mm for the NiCr coating. Increasing the feed rate to 150 g/min in the Ni and NiAl coatings decreased the coating pores and accordingly increased the Rp.

Place, publisher, year, edition, pages
Materials Park, OH: ASM International, 2016
Keyword
Thermal Spraying, Process optimization, Corrosion, OCP, Potentiodynamic polarization
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-9926 (URN)10.1007/s11666-016-0474-9 (DOI)000390041000016 ()2-s2.0-84994756460 (Scopus ID)
Note

Ingår i lic avhandling

Available from: 2016-09-22 Created: 2016-09-22 Last updated: 2017-04-20Bibliographically approved
3. Corrosion performance of bi-layer Ni/Cr2C3–NiCr HVAF thermal spray coating
Open this publication in new window or tab >>Corrosion performance of bi-layer Ni/Cr2C3–NiCr HVAF thermal spray coating
2016 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 369, 470-481 p.Article, review/survey (Refereed) Published
Abstract [en]

The corrosion behavior of three HVAF thermal spray coating systems (A: single-layer Ni, B: single-layer Cr2C3–NiCr coatings, and C: bi-layer Ni/Cr2C3–NiCr coating) was comparatively studied using immersion,salt spray, and electrochemical tests. Polarization and EIS results showed that the corrosion behavior of Cr2C3–NiCr coatings in 3.5 wt.% NaCl solution was significantly improved by adding the intermediate layer of Ni. It was illustrated that the polarization resistance of the bi-layer Ni/Cr2C3–NiCr and singlelayerCr2C3–NiCr coatings were around 194 and 38 k cm2, respectively. Microstructure analysis revealed that the bond coating successfully prevented the corrosion propagation toward the coating.

Place, publisher, year, edition, pages
Amsterdam: Elsevier, 2016
Keyword
Thermal spray, HVAF Corrosion, EIS, Polarization, Immersion test
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-9293 (URN)10.1016/j.apsusc.2016.02.002 (DOI)000374203000060 ()2-s2.0-84958787256 (Scopus ID)
Available from: 2016-04-07 Created: 2016-04-07 Last updated: 2016-12-16Bibliographically approved
4. Microstructural and electrochemical characterization of Ni-based bi-layer coatings produced by the HVAF process
Open this publication in new window or tab >>Microstructural and electrochemical characterization of Ni-based bi-layer coatings produced by the HVAF process
2016 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 304, 606-619 p.Article in journal (Refereed) Published
Abstract [en]

Bi-layer coating systems comprising a Cr3C2-NiCr coating with different underlying coatings of Ni, NiCr, NiCoCrAlY, and CoNiCrAlY were deposited on 304L stainless steel substrates using the high-velocity air fuel (HVAF) process. The corrosion behavior of the coating systems was studied using electrochemical and immersion tests in 3.5 wt% NaCl at 25 °C. The higher open-circuit potential (OCP) value of the NiCoCrAlY coating (− 120 mV/SCE) compared to the value of the Cr3C2-NiCr coating (− 230 mV/SCE) revealed that the underlying NiCoCrAlY coating was sacrificially protected by Cr3C2-NiCr coating. The polarization resistance (Rp) of the bi-layer coatings with the different underlying coatings of Ni, NiCr, NiCoCrAlY and CoNiCrAlY was approximately 77, 189, 487, and 74 kΩ·cm2 respectively, while the value was 101 kΩ·cm2 for the single-layer Cr3C2-NiCr coating and 30 kΩ·cm2 for the 304L substrate, which confirmed a higher corrosion protection of the NiCoCrAlY coating. The electrochemical impedance spectroscopy (EIS) results showed that the corrosion resistance of the 304L substrate was significantly improved by adding an intermediate layer of NiCoCrAlY to the Cr3C2-NiCr coating. Results of the immersion tests confirmed that the underlying coatings in the different bi-layer coating systems acted as protective barriers. Moreover, the NiCoCrAlY coating showed the best corrosion protection among the investigated underlying coatings.

Place, publisher, year, edition, pages
Lausanne: Elsevier Sequoia, 2016
Keyword
Thermal spray, HVAF, Corrosion, EIS, Polarization
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-9927 (URN)10.1016/j.surfcoat.2016.07.080 (DOI)000384775900069 ()2-s2.0-84979916804 (Scopus ID)
Available from: 2016-09-22 Created: 2016-09-22 Last updated: 2016-12-19Bibliographically approved
5. Microstructure effect of intermediate coat layer on corrosion behavior of HVAF-sprayed bi-layer coatings
Open this publication in new window or tab >>Microstructure effect of intermediate coat layer on corrosion behavior of HVAF-sprayed bi-layer coatings
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
Keyword
Thermal spray, HVAF, Corrosion, OCP, Polarization
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-9928 (URN)10.1007/s11666-016-0484-7 (DOI)000392060300024 ()
Note

Ingår i lic avhandling

Available from: 2016-09-22 Created: 2016-09-22 Last updated: 2017-05-15Bibliographically approved

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