KCI-induced corrosion behavior of HVAF-sprayed Ni-based coatings in ambient air

• It is well known that the presence of KCl deposited on superheater tubes in biomass- and waste-fired boilers leads to a severe corrosion and premature damage. In order to protect such critical components which are routinely exposed to aggressive environments, thermal spray coatings are frequently proposed as a potential solution. By virtue of the techno-commercial benefits that provides as a direct outcome of its ability to cost-effectively deposit coatings virtually free of porosity and in situ formed oxides, the high velocity air-fuel (HVAF) process offers a particularly attractive approach. In the present work, the influence of KCl on the oxidation behavior of four HVAF-sprayed Ni-based coatings (Ni21Cr, Ni5AI, Ni21Cr7AI1Y, and Ni21Cr9Mo) has been investigated. The coatings were deposited onto specimens of 16Mo3 steel, a widely used boiler tube material. High temperature corrosion tests were carried out in ambient air at 600°C, with 0.1 mg/cm2 KCl being sprayed onto the samples prior to the exposure. Uncoated substrates and an identical test environment without KCl were used as reference. 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 damage to the coatings. It was further revealed that the alumina-forming NiAl coating was capable of forming a more protective oxide scale compared to other chromia and mixed-oxide scale forming coatings. In general, the oxidation resistance of the coatings based on the kinetic studies had the following ranking (from the best to the worst): NiAl >NiCr> NiCrAlY> NiCrMo. © Copyright 2017 by DVS Media GmbH. All rights reserved.

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

Alumina

Aluminum alloys

Aluminum oxide

Binary alloys

Boiler corrosion

Boilers

Chlorine compounds

Chromium alloys

Corrosion protection

Corrosive effects

Inorganic coatings

Molybdenum alloys

Oxidation resistance

Potassium compounds

Scale (deposits)

Sprayed coatings

Superheater tubes

Ternary alloys

Yttrium alloys

Aggressive environment

Biomass boiler

Corrosion behavior

Critical component

High velocity air fuels

Oxidation behaviors

Thermal spray coatings

Waste-fired boilers

Corrosion resistant coatings

Manufacturing and materials engineering

Produktions- och materialteknik

Production Technology

Produktionsteknik

Publikations- och innehållstyp

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