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KCl-Induced High Temperature Corrosion Behavior of HVAF-Sprayed Ni-Based Coatings in Ambient Air
Tarbiat Modares University, Department of Material Science and Engineering, Tehran, Iran.
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing. (PTW)ORCID iD: 0000-0002-7663-9631
Tarbiat Modares University, Department of Material Science and Engineering, Tehran, Iran.
M. H. Engineering AB, Karlskoga, Sweden .
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2018 (English)In: Journal of thermal spray technology (Print), ISSN 1059-9630, E-ISSN 1544-1016, Vol. 27, no 3, p. 500-511Article in journal (Refereed) Published
Abstract [en]

KCl-induced high temperature corrosion behavior of four HVAF-sprayed Ni-based coatings (Ni21Cr, Ni5Al, Ni21Cr7Al1Y, and Ni21Cr9Mo) under KCl deposit has been investigated in ambient air at 600°C up to 168h. The coatings were deposited onto 16Mo3 steel - a widely used boiler tube material.Uncoated substrate, 304L and Sanicro25 were used as reference materials in the test environment.SEM/EDS and XRD techniques were utilized to characterize the as-sprayed and exposed samples.The results showed that the small addition of KCl significantly accelerated degradation to the coatings. All coatings provided better corrosion resistance compared to the reference materials. The alumina-forming Ni5Al coating under KCl deposit was capable of forming a more protective oxide scale compared to the chromia-forming coatings as penetration of Cl through diffusion paths was hindered. Both active corrosion and chromate formation mechanisms were found to be responsible for Page 1 of 23ASM the corrosion damages. The corrosion resistance of the coatings based on the microstructure analysis and kinetics had the following ranking (from the best to worst): Ni5Al >Ni21Cr> Ni21Cr7Al1Y>Ni21Cr9Mo.

Place, publisher, year, edition, pages
Springer, 2018. Vol. 27, no 3, p. 500-511
National Category
Manufacturing, Surface and Joining Technology Metallurgy and Metallic Materials Composite Science and Engineering
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
URN: urn:nbn:se:hv:diva-11959DOI: 10.1007/s11666-017-0684-9ISI: 000425622500022OAI: oai:DiVA.org:hv-11959DiVA, id: diva2:1169666
Conference
International Thermal Spray Conference & Exposition, ITSC 2017, Düsseldorf, Germany, June 7-9, 2017
Funder
Knowledge Foundation, SCoPe: Dnr 20160201
Note

This article is an invited paper selected from presentations at the 2017 International Thermal Spray Conference, held June 7–9, 2017, in Düsseldorf, Germany, that has been expanded from the original presentation.

Available from: 2017-12-29 Created: 2017-12-29 Last updated: 2018-05-03Bibliographically approved
In thesis
1. Ni-based coatings for high temperature corrosion protection
Open this publication in new window or tab >>Ni-based coatings for high temperature corrosion protection
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Biomass/waste-fired boilers severely suffer from high temperature corrosion of critical load-bearing components, e.g. water-wall and superheater tubes, due to presence of Cl-containing corrosive species. Deposition of a dense and adherent Ni-based coating by high velocity air-fuel (HVAF) thermal spray technique is a promising approach to extend the component's lifetime and, hence, increase the thermal/electrical efficiency of the boilers. In this research, high temperature corrosion of candidate Ni-based coatings –Ni21Cr, Ni21Cr7AlY, Ni5Al, Ni21Cr9Mo, Ni21Cr9Mo-SiO2 – sprayed by HVAF has been investigated through detailed laboratory studies in ambient air, moisture and HCl-laden environments. The exposures were conducted at 600 °C for up to 168 h with and without presence of KCl salt. All coatings were highly protective in all environments in the absence of KCl due to formation of corresponding protective scales of alumina or chromia on the coating surface. When KCl was introduced, chromia-forming coatings degraded through a two-stage mechanism; 1) formation of K2CrO4 and Cl- followed by diffusion of Cl- through oxide grain boundaries, leading to formation of Cl2, metal chlorides as well as a nonprotective oxide, and 2) inward diffusion of the formed Cl2 through defects in the non-protective oxide, leading to metal chloride evaporation and breakaway oxidation. The corrosion behavior of the chromia-forming Ni21Cr coating was improved by addition of alloying elements such as Al and Mo. It was also shown that adding dispersed SiO2 further increased the corrosion resistance of the coatings. The oxide scale formed in the presence of SiO2 effectively suppressed Cl- ingress and lowered the corrosion rate, since the formed oxide was continuous, adherent andrich in Cr. The performance of the coatings in the complex Cl-containing environment was ranked as (from highest to lowest corrosion resistance); Ni21Cr9Mo-SiO2 > Ni21Cr7AlY > Ni5Al > Ni21Cr9Mo > Ni21Cr, confirming the enhanced corrosion protection of chromia-forming coatings in the presence of alloying elements and dispersed SiO2.

Place, publisher, year, edition, pages
Trollhättan: University West, 2018. p. 78
Series
PhD Thesis: University West ; 23
Keywords
Thermal Spray Coating; HVAF; High Temperature Corrosion Protection; Composition; Microstructure; Dispersed Oxide
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-12277 (URN)978-91-87531-70-5 (ISBN)978-91-87531-69-9 (ISBN)
Public defence
2018-05-31, F104, Trollhättan, 10:15 (English)
Opponent
Supervisors
Available from: 2018-05-04 Created: 2018-05-03

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Sadeghimeresht, EsmaeilMarkocsan, NicolaieJoshi, Shrikant V.

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