Faculty Publications
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Item High temperature corrosion behaviour of HVOF sprayed WC-CrC-Ni coatings(Inderscience Publishers, 2016) Somasundaram, B.; Kadoli, R.; Ramesh, M.R.; RAMESH, C.S.The present work aims to study the hot corrosion resistance of high velocity oxy-fuel (HVOF) sprayed WC-CrC-Ni coating developed on three types of boiler tube materials such as SA213-T22, MDN-310 and Superfer 800 H steels. Hot corrosion studies were conducted in a molten salt environment of Na2SO4-60%V2O5 at 700°C and thermogravimetric analysis was used to establish kinetics of corrosion. Corrosion kinetics of coated steels followed nearly parabolic behaviour and showed a lower corrosion rate in comparison to uncoated alloys. It is concluded that corrosion is restricted to the external surface of the coating and the formation of thick scale composed of oxides of Cr, Ni and their spinel oxides, acts as a diffusion barrier to the transportation of corrosive species into the coating. The carbides of tungsten and chromium uphold the strength of the coating. © © 2016 Inderscience Enterprises Ltd.Item Hot corrosion behavior of plasma sprayed FeCrNiC and FeCrNiC/Cenosphere coatings on ASTM-SA213-T22 steel(Elsevier Ltd, 2022) Hanumanthlal, S.; Siddaraju, C.; Ramesh, M.R.; Thirtha Prasada, H.P.; Somasundaram, B.The steel alloys tubes used to manufacture boilers which are used in high temperature environment in thermal power plants are often subjected to high temperature corrosion. Therefore, to protect the surface of boiler tubes, protective coatings are used to counter the corrosion. In this work FeCrNiC and FeCrNiC/Cenosphere coatings deposited on T22 boiler tube steel using atmospheric plasma spraying. Thermocyclic hot corrosion studies were examined in a liquid salt condition of Na2SO4-60%V2O5 for 17 cycles of 51 h at 600 °C on uncoated and coated steel. Thermogravimetric practice was utilized to build up the kinetics of hot corrosion of uncoated and coated steel. As-coated samples are studied for microstructure and microhardness. The X-ray diffraction(XRD), Scanning electron microscopy(SEM)/Energy dispersive spectroscopy(EDX), and X-ray mapping characterization techniques were used to analyse the corrosion products. It was observed that FeCrNiC/Cenosphere coated steel showed better hot corrosion resistance than the uncoated steels. Parabolic rate constant values of coated steel are lower in comparison to the uncoated steels. Better resistance is provided by high-temperature stability of mullite, alumina, defensive glassy oxide layer of silicon, titanium and spinels of chromium and carbon that is formed at elevated temperatures. © 2021Item High Temperature Corrosion Behavior of High Velocity Oxy Fuel Sprayed NiCrMoFeCoAl-30%SiO2 and NiCrMoFeCoAl-30%Cr2O3 Composite Coatings on ASTM SA213-T22 Steel in a Coal-fired Boiler Environment(Materials and Energy Research Center, 2022) Patil, V.G.; Somasundaram, B.; Kandaiah, S.; Ramesh, M.R.; Patil, S.High-velocity oxy fuel (HVOF) sprayed coatings can improve the corrosion resistance of bare ASTM SA213-T22 boiler steel. In this report, we have investigated the NiCrMoFeCoAl-30%SiO2 and NiCrMoFeCoAl-30%Cr2O3 composite coatings were deposited on bare ASTM SA213-T22 boiler steel for corrosion protection. High-temperature corrosion studies were conducted in a molten salt (Na2SO4-60%V2O5) environment at 700ºC under thermo-cyclic conditions. The as-sprayed composite coatings are characterized for microstructure and mechanical properties. The thermo-gravimetric method was utilized to understand the kinetics of corrosion. Characterization of the corrosion products was examined by using scanning electron microscope (SEM)/ Energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) techniques. The obtained results suggest both the composite coatings are favorable to corrosion resistance over the bare ASTM SA213-T22 boiler steel. The NiCrMoFeCoAl-30%Cr2O3 composite coating was concluded to present a superior corrosion resistance in the high-temperature corrosion environment because of the uniform distribution of the composite coating matrix and the development of protective protection Cr2O3 in the scale. The molten salt heat-treated chromium oxide containing coating shows good corrosion stability than the silica composite. This could be attributed to the high temperature assisted formation metal chromates, chromites and oxide layers. © 2022 Materials and Energy Research Center. All rights reserved.Item Cyclic Oxidation and Hot-Corrosion Behavior of HVOF-Sprayed NiCrAl Coating on Industrial Boiler Tube Steels(Springer, 2024) Ramesh, M.R.; Medabalimi, S.; Rupanagudi, R.S.; Prasad, C.D.; Sollapur, S.B.At high temperatures, coatings provide a protective scale development on surfaces to maintain long-term stability. In the current study, ASTM-SA210-Grade A1 (GrA1) and ASTM-SA213-T-11 (T11) boiler tube steels were coated with NiCrAl alloy with high-velocity oxy-fuel (HVOF) to prevent oxidation and hot corrosion. For hot corrosion and oxidation, 50 cycles at 900°C were taken into account. Additionally, tests of hot-corrosion behavior were conducted in an atmosphere containing molten salt (Na2SO4-60%V2O5), while tests of oxidation behavior were conducted in static air. The kinetics of oxidation were calculated using the thermogravimetric method. Using XRD, EPMA, and SEM/EDAX methods, the produced oxide scales were characterized. The oxidation rate of NiCrAl-coated steels was found to be lower than that of uncoated steels. The coated steels subjected to oxidation in air exhibit slow scale growth kinetics and oxides of α-Al2O3 and Cr2O3 on the outermost surface, while accelerated oxidation caused by the molten salt exhibits metastable Al2O3. Along the nickel-rich splat boundary, Cr and Al were formed a preferential oxidation, which prevents other oxygen from entering the coating via pores and voids, resulting in steady-state oxidation. © The Minerals, Metals & Materials Society 2024.