Faculty Publications

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Author: search.filters.author.Ramesh, M.R.Subject: search.filters.subject.Thermogravimetric analysis

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    Improving Hot Corrosion Resistance of Cobalt Based Superalloy (Superco-605) Using HVOF Sprayed Oxide Alloy Powder Coating
    (Springer India sanjiv.goswami@springer.co.in, 2015) Jegadeeswaran, N.; Bhat, K.U.; Ramesh, M.R.
    Superco-605 is a cobalt based superalloy used widely in the hot section of gas turbines. During their operation, they are exposed to high temperature and molten salt environment, causing damage to the component due to hot corrosion. In this investigation, Superco-605 alloy was coated using a fused oxide alloy powder, $$ 10\,\% {\text{Al}}_{ 2} {\text{O}}_{ 3} + {\text{CoCrAlTaY}} $$10%Al2O3+CoCrAlTaY , using high velocity oxy-fuel process. Coating thickness was in the range of 260–280 µm and it was lamellar in nature. Uncoated and coated samples were subjected to cyclic hot corrosion tests at 800 °C in presence of molten salt environment of $$ {\text{Na}}_{ 2} {\text{SO}}_{ 4}{+}50\% {\text{V}}_{ 2} {\text{O}}_{ 5} $$Na2SO4+50%V2O5. Resistance to hot corrosion was investigated using thermogravimetric analysis, visual observations, X-ray diffractometry, scanning electron microscopy and energy dispersive X-ray spectroscopy. Both samples developed an oxide scale at the top. The uncoated Superco-605 exhibited intense spalling during hot corrosion cycles. The oxide scale on the coated substrate was thin compared to total thickness of the coating. There was a chromium depleted region close to the oxide top scale. An alumina rich layer at the interface of coating-substrate prevents penetration of oxygen into the substrate material. Based on the experimental results, it is concluded that the fused oxide alloy powder is effective in reducing hot corrosion tendency of Superco-605 alloy. © 2015, The Indian Institute of Metals - IIM.
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    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.
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    Hot corrosion behaviour of HVOF sprayed Ni3Ti and Ni3Ti + (Cr3C2 + 20NiCr) coatings in presence of Na2SO4-40%V2O5 at 650 °c
    (IOP Publishing Ltd custserv@iop.org, 2019) Reddy, N.C.; Koppad, P.G.; Reddappa, H.N.; Ramesh, M.R.; Babu, E.R.; Varol, T.
    Ni3Ti and Ni3Ti + (Cr3C2 + 20NiCr) coatings were deposited on gas turbine based ASTM B265 titanium (Ti-15) and AISI 420 stainless steel (MDN-420) substrate materials using HVOF technique. Thermocyclic hot corrosion tests were carried out at 650 °C in molten salt environment of Na2SO4-40%V2O5 for about 50 cycles. Thermogravimetric analysis was carried out to study the hot corrosion kinetics of uncoated and coated titanium and stainless steel substrates. The weight gain per unit area showed that the coated substrate materials displayed better resistance to hot corrosion when compared with that of uncoated substrate materials. The surface morphology of uncoated and coated substrate materials were analysed using scanning electron microscopy and elemental analysis. The formation of different types of oxides and compounds were analysed using x-ray diffraction. The uncoated substrates surface showed microspalling at several regions while coated substrates surface were composed of protective oxide layers. The presence of ternary NiCr2O4 protective oxides on the surface of Ni3Ti + (Cr3C2 + 20NiCr) coated substrates leads to reduction in the diffusion of corrosive species inside the coating. © 2019 IOP Publishing Ltd.
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    High-Temperature Oxidation Studies of Plasma-Sprayed NiCrAlY/TiO2 and NiCrAlY/Cr2O3/YSZ Cermet Composite Coatings on MDN-420 Special Steel Alloy
    (Springer, 2021) Madhu Sudana Reddy, G.; Prasad, C.D.; Shetty, G.; Ramesh, M.R.; Rao, T.N.; Patil, P.
    The plasma spray process was used to form 70%NiCrAlY + 30%TiO2 and 70%NiCrAlY + 25%Cr2O3 + 5%YSZ cermet coatings on MDN-420 special steel alloy. Cyclic oxidation testing was conducted on coated and uncoated specimens at 700°C under a static air environment. Thermogravimetric analysis was applied to establish the oxidation kinetics. X-ray diffraction (XRD), scanning electron microscopy (SEM)/energy-dispersive x-ray spectroscopy (EDS), and electron probe microanalysis (EPMA) techniques were used to analyze the oxidized products. The NiCrAlY + Cr2O3 + YSZ coating was found to be most resistive when compared with the NiCrAlY + TiO2 coating in the aggressive oxidation environment. Net weight loss was observed for bare MDN-420 alloy due to sputtering. The oxidation resistance of the coatings was due to formation of Cr2O3, NiCr2O4, NiO, and Al2O3 phases. © 2021, ASM International.
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    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.
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    Mechanical characterization of 3D printed MWCNTs/HDPE nanocomposites
    (Elsevier Ltd, 2022) Kumar, S.; Ramesh, M.R.; Doddamani, M.; Rangappa, S.M.; Siengchin, S.
    The development of polymer nanocomposite blends using multi-walled carbon nanotubes (MWCNTs) and high-density polyethylene (HDPE) is presented in this paper. Fused Filament Fabrication (FFF) based 3D printer is used to realize MWCNT (0.5, 1, 3, and 5 by wt. %)/HDPE nanocomposite (NC) 3D printed samples. The addition of MWCNT increases TCryst, αCryst and TMelt. Thermogravimetric analysis (TGA) of neat HDPE and MWCNT/HDPE NCs is also carried out to check their thermal stability at higher working temperatures. The degradation temperature of MWCNT/HDPE NCs is observed to be higher than neat HDPE and increasing with MWCNT content. The filaments are tested for tensile, while specimens are tested for both tensile and flexural properties. It is observed that tensile and flexural modulus and strength improve with increasing MWCNT. Finally, the results of the tensile tested specimens are compared to those of various HDPE composites found in the literature. © 2022