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Influence of KCl and HCl on high temperature corrosion of HVAF-sprayed NiCrAlY and NiCrMo coatings
University West, Department of Engineering Science, Division of Subtractive and Additive Manufacturing.ORCID iD: 0000-0002-7663-9631
The University of Nottingham, Faculty of Engineering, Nottingham, United Kingdom.
The University of Nottingham, Faculty of Engineering, Nottingham, United Kingdom.
M. H. Engineering AB, Karlskoga, Sweden.
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2018 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 148, p. 17-29Article in journal (Refereed) Published
Abstract [en]

The oxidation performance of NiCrAlY and NiCrMo coatings thermally sprayed by high velocity air-fuel (HVAF) technique has been investigated in a chloridizing-oxidizing environment, with and without a KCl deposit, at 600 °C for up to 168 h. Both coatings protected the substrate in the absence of KCl due to formation of a dense Cr-rich oxide scale. In the presence of KCl, Cl−/Cl2 diffused through a non-protective and porous NiCr2O4 scale formed on NiCrAlY, leading to formation of volatile CrCl3. On the other hand, Mo in NiCrMo stimulated the formation of a more protective Cr-rich oxide scale which increased the corrosion resistance by reducing Cl−/Cl2 diffusion.

Place, publisher, year, edition, pages
Elsevier Ltd , 2018. Vol. 148, p. 17-29
Keywords [en]
Air; Aluminum corrosion; Boiler corrosion; Chromium compounds; Corrosion protection; Corrosion resistance; High temperature corrosion; Potassium compounds; Scale (deposits); Sprayed coatings; Ternary alloys, Fireside corrosion; High velocity air fuels; NiCrAlY; NiCrMo; Thermal spray coatings, Chlorine compounds
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
URN: urn:nbn:se:hv:diva-12245DOI: 10.1016/j.matdes.2018.03.048ISI: 000430079200003Scopus ID: 2-s2.0-85044482024OAI: oai:DiVA.org:hv-12245DiVA, id: diva2:1196243
Note

Available online 22 March 2018.

Available from: 2018-04-09 Created: 2018-04-09 Last updated: 2018-05-14Bibliographically 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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