Isothermal oxidation of HVAF-sprayed Ni-based chromia, alumina and mixed-oxide scale forming coatings in ambient air

• The power generation industry has been progressively shifting towards higher operating steam temperatures and pressures to increase efficiency and reduce CO2 emissions. However, higher operating temperatures lead to more aggressive oxidation of the boiler components. A promising route to improve the durability of degradation-prone components is through deployment of high-performance coatings. In the present work, four Ni-based coatings - Ni21Cr, Ni5Al, Ni21Cr9Mo, and Ni21Cr7Al1Y - thermally sprayed by the high-velocity air fuel (HVAF) technique on boiler steel (16Mo3) substrates were investigated. The isothermal oxidation behavior of the coatings was studied in ambient air environment at 600 °C for different time intervals i.e. 1, 5, 10, 24, 48, 96, and 168 h. The oxidation behavior of the as-sprayed and polished coatings was compared. The protective α-Al2O3 was not detected on the exposed alumina-forming NiAl coating. On the other hand, Cr2O3 along with a small amount of NiO were the main oxidation products on the surface of the NiCr and NiCrMo coatings, and were found to be relatively less protective. The mixed-oxide scale forming NiCrAlY coatings showed the best oxidation resistance due to the formation of a thin and slow-growing Al2O3 scale along with Ni(Al,Cr)2O4 and Cr2O3. The polished coatings were found to significantly reduce the oxidation rate in each case as the protective scale-forming elements were more uniformly supplied to the surface oxide scale by removing the surface asperities. © 2017 Elsevier B.V.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Materialteknik -- Bearbetnings-, yt- och fogningsteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Materials Engineering -- Manufacturing, Surface and Joining Technology (hsv//eng)

Nyckelord

Air; Aluminum; Aluminum coatings; Black coatings; Boilers; Carbon dioxide; Coatings; Inorganic coatings; Isotherms; Nickel; Oxidation; Scale (deposits); Sprayed coatings; Thermal spraying

High performance coatings; High velocity air fuels; Isothermal oxidations; Ni-based coatings; Operating temperature; Oxidation behaviors; Power generation industries; Scale-forming elements

Alumina

Manufacturing and materials engineering

Produktions- och materialteknik

Publikations- och innehållstyp

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