Faculty Publications
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Item Corrosion Behaviour and Characterization of Thermal Sprayed Coating of Nickel Chromium Cermet on Low Carbon Steel(Elsevier Ltd, 2018) Amudha, A.; Shashikala, H.D.; Nagaraja, H.S.Corrosion is the major problem faced by Navy, especially when pumps, ship impellers and other components have to work in harsh environments like sea water. Therefore, high corrosion resistant metal ceramic matrix 75Cr3C2- 25 (NiCr) cermet has been one of the good choices for coating. In this study, we are discussing the HVOF (High Velocity Oxy Fuel) coating of 75Cr3C2-25(NiCr) on the low carbon steel substrate, IS 2062 grade B. The as coated samples were annealed at 600°C for 1 hour, 2hour and 3hours. The electrochemical tests were conducted for corrosion evaluation. Structural analysis was done by using X-Ray diffraction technique. Microstructure and thickness of the coating was studied using Scanning Electron Microscopy (SEM). Density measurement studies were done on as-coated and annealed coupons. © 2017 Elsevier Ltd.Item Electrochemical corrosion behaviour of nickel chromium-chromium carbide coating by HVOF process(American Institute of Physics Inc. subs@aip.org, 2018) Amudha, A.; Nagaraja, H.S.; Shashikala, H.D.To overcome the corrosion problem in marine industry, coatings are one of the most economical solutions. In this paper, the corrosion behaviour of 25(NiCr)-75Cr3C2 cermet coating on low carbon steel substrate by HVOF process is studied. Different phases such as Cr7C3 and Cr3C2, along with Ni and chromium oxide(Cr3O2) constituents present in the coating were revealed by X-Ray Diffraction (XRD) analysis. The morphology of the coating obtained by scanning electron microscope (SEM) gave confirmation for the XRD analysis. Electrochemical corrosion techniques such as Linear Polarization Resistance (LPR) and Electrochemical Impedance Spectroscopy (EIS) were used to study the corrosion behaviour of the cermet in 3.5wt% NaCl electrolyte solution. The corrosion current density of the coated sample and substrate were found to be 6.878μA/cm-2 and 21.091μA/cm-2 respectively. The Nyquist Impedance spectra were used to derive an equivalent circuit to analyze the interaction between the coating and electrolyte. The Bode Impedance plots obtained by EIS for the coating showed a typical passive material capacitive behaviour, indicated by medium to low frequency with phase angle approaching -60o, suggesting that a stable film is formed on the tested material in the electrolyte used. © 2018 Author(s).Item Plasma-sprayed graphene oxide reinforced alumina composite coatings on low carbon steel with improved fracture toughness, brittleness index, and microhardness(Elsevier Ltd, 2020) Amudha, A.; Nagaraja, H.S.; Shashikala, H.D.In this work, the mechanical properties of atmospheric plasma-sprayed Al2O3and Al2O3-xGO (x = 0.5, 1.0, 1.5, and 2.0 wt%) coatings on low carbon steel was evaluated using the Vickers indentation technique, and the effects of GO addition in microhardness brittleness index and fracture toughness were investigated. The Fourier-transform infrared (FTIR) spectroscopy and Field Emission Scanning Electron Microscopy (FE-SEM) techniques were employed to analyze the microstructural characterization of the plasma-sprayed coatings and to confirm the retention of GO in the Al2O3-xGO composite after the plasma spray. It was found that the Vicker's microhardness of as-sprayed Al2O3is 4.148 GPa and it decreased with the increase in the addition of GO and for Al2O3-2.0GO, it is 3.305 GPa. The fracture toughness of Al2O3is 4.86 (MPa m1/2) whereas for Al2O3-2.0GO is 16.85 (MPa m1/2). The fracture toughness has increased whereas the brittleness index has decreased as the weight percentage of GO addition is increased in the Al2O3-GO composite. Thus, the plasma-sprayed Al2O3and Al2O3-xGO coatings suggest that 2 wt% GO addition helps in the improvement of brittleness, fracture toughness, and the microhardness. © 2020 Elsevier Ltd. All rights reserved.Item Electrochemical impedance behaviour of SS-309Mo and inconel 625 weld overlay on carbon steel at different applied voltages(American Institute of Physics Inc. subs@aip.org, 2020) Amudha, A.; Nagaraja, H.S.; Shashikala, H.D.The electrochemical impedance spectroscopy (EIS) is one of the non-destructive methods to study the impedance behaviour of the coatings. In the present work, carbon steel coated with SS309Mo stainless steel. and the Inconel625, as first and second layers respectively using weld cladding process are subjected to EIS. The EIS under different applied potentials are studied. The EIS results are fitted to get the best equivalent circuit for the two coatings. The protective nature of the passive films essentially related to its electrochemical circuit parameters such as capacitor and charge transfer resistance are obtained. The charge transfer resistance under different applied potentials revealed good corrosion resistance properties of the coatings. © 2020 Author(s).Item Effect of graphene oxide loading on plasma sprayed alumina-graphene oxide composites for improved anticorrosive and hydrophobic surface(IOP Publishing Ltd custserv@iop.org, 2019) Amudha, A.; Shashikala, H.D.; Asiq Rahman, O.S.; Keshri, A.K.; Nagaraja, H.S.Alumina is a widely used anticorrosive coating material for protection of metal surfaces. The graphene oxide (GO)-Alumina composite coatings can enhance the anticorrosion property of carbon steel surfaces used in an industrial scale. In the present work, the spray dried graphene oxide nanoplatelets of 0, 0.5, 1, 1.5 and 2 wt% reinforced alumina (?-Al2O3) were deposited on the low carbon steel substrate by Atmospheric Plasma Spray (APS) technique. The GO-Alumina nanocomposite coatings are characterised using XRD, FE-SEM, HR-TEM and Raman Spectroscopy. The electrochemical corrosion behaviour of the coatings on carbon steel has been examined using three electrode electrochemical method in 3.5 wt% NaCl electrolyte. A remarkable improvement in the corrosion resistance (with a corrosion current density of 0.01 nAcm-2) of about six orders with respect to pristine alumina was observed. The wettability tests revealed that, with 1.5 and 2 wt% graphene oxide nanoplatelets addition, the surface coating turned out to be hydrophobic with contact angle of 127°, from hydrophilic with contact angle 36°, which complements the anticorrosion results. The in situ reduction of GO to r-GO by APS deposition and bridging of alumina splats by the GO sheets accounts for observing the superior performance of the composite coatings. © 2019 IOP Publishing Ltd.Item Dual electrochemical application of r-GO wrapped ZnWO4/Sb nanocomposite(Institute of Physics Publishing helen.craven@iop.org, 2019) Brijesh, K.; Bindu, K.; Amudha, A.; Nagaraja, H.S.ZnWO4/Sb nanorods and r-GO-ZnWO4/Sb nanocomposite have been prepared using a single step solvothermal method. The prepared nanocomposites have been characterized using x-ray diffractometer (XRD), Scanning Electron Microscope (SEM), High Resolution Transmission Electron Microscope (HR-TEM), Raman and Brunauer-Emmett-Teller (BET). The x-ray photoelectron spectroscopy (XPS) technique was used to determine the elemental composition of ZWS-5 (5 mg r-GO-ZnWO4/Sb) composite. The XRD reveals the monoclinic wolframite structure of ZnWO4/Sb and r-GO-ZnWO4/Sb. SEM and HRTEM confirms that the ZnWO4/Sb has been decorated on the r-GO sheets. The electrochemical performance of the prepared samples towards the Hydrogen Evolution Reaction (HER) and dopamine sensing has been tested using electrochemical techniques. Onset potential of 265 mV @10 mA cm-2, lower Tafel slope (95 mV dec-1), high electrochemical surface area (1383.216 m2g-1) and high specific site density (18.551 06 × 1021 g-1) of ZWS-5 reveals the high electrocatalytic activity of the composite towards HER. Chronoamperometric dopamine sensing shows that ZWS-5 has the superior sensing performance with highest specific sensitivity (723 ?A ?M-1 ?g-1), lowest limit of detection (0.9624 ?M), along with a good selectivity. Results suggest that the r-GO-ZnWO4/Sb nanocomposite is a good candidate for the HER and electrochemical dopamine sensor. The incorporation of r-GO nanosheets with ZnWO4/Sb (ZWS) nanorods enhances the specific and electrochemical surface area, which accounts for the high electrocatalytic activity of the composite. © 2019 IOP Publishing Ltd.Item Finite element analysis of thermal residual stresses in SS-309Mo and Inconel-625 multilayer weld deposition on low carbon steel(Elsevier Ltd, 2019) Amudha, A.; Nagaraja, H.S.; Shashikala, H.D.ANSYS Finite Element Analysis is adopted for simulation of SS-309Mo and Inconel-625 deposition in single and double layers, on IS-2062 Grade-B low carbon steel base metal. The Von-Mises residual stress distribution is obtained for twelve different combinations of weld deposition techniques and weld materials. Aim is to obtain a combination with minimum residual stress, using a technique of alternate skip weld deposition and base metal preheating. Also, the effect of change in the thickness of the base metal on coating residual stress is studied. The best model has 18 MPa surface residual stress. The very low values of residual stress obtained in the top layer of the multilayer deposition is helpful in preventing corrosion problems like stress corrosion cracking and corrosion fatigue, resulting in lower equipment downtime and losses to industry. © 2019 Elsevier LtdItem Enhanced corrosion resistance of atmospheric plasma-sprayed zirconia–GNP composite by graphene oxide nanoplatelet encapsulation(Springer, 2020) Amudha, A.; Hosakoppa S, N.; Holavanahalli Doraiswamy, S.The unique natural diffusion barrier property of graphene plays a crucial role in protecting the carbon steel substrates from corrosion, particularly using graphene oxide nanoplatelets (GNP)–zirconia (ZrO2) composites. In the present work, atmospheric plasma spraying (APS) technique has been used to coat both the spray-dried pristine ZrO2 and ZrO2–(0.5, 1.0, 1.5 and 2) wt% GNP composite on the carbon steel substrate. The retention of GNPs in the coating was confirmed using XRD, Raman spectroscopy, TEM, FE-SEM, and EDAX techniques. The corrosion properties of the coatings in 3.5 wt%NaCl electrolyte were studied using linear polarization resistance and electrochemical impedance spectroscopy technique. This reveals the enhanced charge transfer resistance, decreased corrosion current density and corrosion rate of ZrO2–GNP composite. Further, the corrosion rate of ZrO2–2 wt% GNP coating is 130 times less than the plasma-sprayed ZrO2. Compared to 0.5, 1.0 and 1.5 wt% GNP added zirconia coatings, ZrO2–2 wt% GNP displayed the highest stability up to 14 days in 3.5% NaCl electrolyte. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.Item Mechanical and wetting properties of 25%NiCr-75%Cr2C3 cermet coated on low carbon steel using HVOF thermal spray technique(Elsevier B.V., 2021) Amudha, A.; Nagaraja, H.S.; Shashikala, H.D.The hydrophobic ceramic–metal composites with enhanced mechanical properties will have longer durability because of the embedded liquid-repellent properties, with low water and salt absorption. In this work, the 25%NiCr-75%Cr2C3 cermet powder has been coated on low carbon steel substrate, using High Velocity Oxy-fuel thermal spray technique. The SEM is employed to analyse the morphological characterization of the coating. The mechanical properties of the 25%NiCr-75%Cr2C3 coating is evaluated using the Vickers micro-indentation technique. The micro-hardness, fracture toughness and brittleness index of the coatings are obtained. Also, the wetting property of the coating in 3.5% NaCl salt solution is investigated using the contact angle measured by sessile drop method. The contact angle of the coating is observed to be hydrophobic in nature with a contact angle of 98.14?. Thus, 25%NiCr-75%Cr2C3 hydrophobic coatings helps in the improvement of brittleness, fracture toughness, and the microhardness. © 2020 Elsevier B.V.Item Mesoporous NiWO4@rGO nanoparticles as anode material for lithium-ion battery(Taylor and Francis Ltd., 2023) Brijesh, B.; Amudha, A.; Mukesh, M.P.; Sagar, L.; Moolayadukkam, S.; Nagaraja, H.S.Herein, we have tried to explore the charge storage properties of mesoporous NiWO4 as an anode in lithium-ion batteries (LIB). A one pot-solvothermal synthesis is used to tweak the properties of mesoporous NiWO4 nanoparticles with reduced graphene oxide (rGO) for the first time and explored the LIB anode applications. Materials are well characterised using structural and morphological characterisations to corroborate the relation between the electrochemical properties and the graphene addition. At 100 mA g−1, the NiWO4@rGO (NWZC) exhibits initial discharge capacity of 1439 mAh g−1, which is more than that of NiWO4 (NWZ). Both NWZ and NWZC display initial coloumbic efficiency of 91.65% and 62.1%. After 500 cycles, the coloumbic efficiency of the NWZ and NWZC is above 99%. The improved lithium-ion storage characteristics of the NWZC may be from the synergetic effect between NiWO4 and r-GO. © 2023 Informa UK Limited, trading as Taylor & Francis Group.