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Chlorine-induced high temperature corrosion of HVAF-sprayed Ni-based alumina and chromia forming coatings
Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT). (PTW)ORCID-id: 0000-0002-7663-9631
The University of Nottingham, Faculty of Engineering, Nottingham, UK.
The University of Nottingham, Faculty of Engineering, Nottingham, UK.
Högskolan Väst, Institutionen för ingenjörsvetenskap, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT). (PTW)ORCID-id: 0000-0002-9578-4076
Vise andre og tillknytning
2018 (engelsk)Inngår i: Corrosion Science, ISSN 0010-938X, E-ISSN 1879-0496, Vol. 132, nr March, s. 170-184Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Chlorine-induced corrosion of HVAF-sprayed Ni21Cr and Ni5Al coatings was investigated in 5 vol.% O2 + 500vppm HCl + N2 with and without KCl at 600 °C up to 168 h. Both coatings were protective in the absence of KCl. With KCl, Ni21Cr degraded through a two-stage mechanism: 1) formation of K2CrO4 followed by diffusion of Cl− through the oxide grain boundaries to yield chlorine and a non-protective oxide, and 2) inward diffusion of chlorine though defects in the non-protective oxide, leading to breakaway oxidation. Cl−/Cl2 could not diffuse through the protective alumina scale formed on Ni5Al, hence the corrosion resistance increased.

sted, utgiver, år, opplag, sider
2018. Vol. 132, nr March, s. 170-184
Emneord [en]
Thermal spray coating, NiCr, NiAl, High-Velocity Air Fuel (HVAF), biomass-/waste-fired boiler, fireside corrosion
HSV kategori
Forskningsprogram
TEKNIK, Produktions- och materialteknik
Identifikatorer
URN: urn:nbn:se:hv:diva-11960DOI: 10.1016/j.corsci.2017.12.033ISI: 000424961000016Scopus ID: 2-s2.0-85039789597OAI: oai:DiVA.org:hv-11960DiVA, id: diva2:1169671
Forskningsfinansiär
Knowledge Foundation, DNR 20160201Tilgjengelig fra: 2017-12-29 Laget: 2017-12-29 Sist oppdatert: 2019-10-21bibliografisk kontrollert
Inngår i avhandling
1. Ni-based coatings for high temperature corrosion protection
Åpne denne publikasjonen i ny fane eller vindu >>Ni-based coatings for high temperature corrosion protection
2018 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
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.

sted, utgiver, år, opplag, sider
Trollhättan: University West, 2018. s. 78
Serie
PhD Thesis: University West ; 23
Emneord
Thermal Spray Coating; HVAF; High Temperature Corrosion Protection; Composition; Microstructure; Dispersed Oxide
HSV kategori
Forskningsprogram
Produktionsteknik; TEKNIK, Produktions- och materialteknik
Identifikatorer
urn:nbn:se:hv:diva-12277 (URN)978-91-87531-70-5 (ISBN)978-91-87531-69-9 (ISBN)
Disputas
2018-05-31, F104, Trollhättan, 10:15 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2018-05-04 Laget: 2018-05-03 Sist oppdatert: 2019-10-23

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