Faculty Publications

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Author: search.filters.author.Ramesh, M.R.Subject: search.filters.subject.Plasma jets

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Now showing 1 - 10 of 19
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    High temperature erosion behavior of plasma sprayed NiCrAlY/WC-Co/cenosphere coating
    (Elsevier B.V., 2017) Mathapati, M.; Ramesh, M.R.; Doddamani, M.
    High temperature erosive behavior of plasma sprayed NiCrAlY-25WC-Co/cenosphere coating deposited on MDN 321 steel is investigated in the present work. Coating is characterized using Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). Microhardness, porosity, adhesion strength, fracture toughness and ductility of the coating are quantified. Solid particle erosion test is conducted at 200, 400 and 600 °C with 30 and 90° impact angles using alumina erodent. Optical profilometer is used to evaluate erosion volume loss. Erosion resistance of the coating is observed to be higher than the substrate for the test temperatures chosen and noted to be more prominent at lower impact angle and higher temperature. High temperature stability of mullite, alumina and oxide layer assists in increasing erosion resistance of coating. The eroded coating surface morphology reveals the brittle mode of material removal. © 2017 Elsevier B.V.
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    Elevated Temperature Solid Particle Erosion Performance of Plasma-Sprayed Co-based Composite Coatings with Additions of Al2O3 and CeO2
    (Springer New York LLC barbara.b.bertram@gsk.com, 2017) Nithin, H.S.; Desai, V.; Ramesh, M.R.
    In this paper, investigation into solid particle erosion behavior of atmospheric plasma-sprayed composite coating of CoCrAlY reinforced with Al2O3 and CeO2 oxides on Superni 76 at elevated temperature of 600 °C is presented. Alumina particles are used as erodent at two impact angles of 30° and 90°. The microstructure, porosity, hardness, toughness and adhesion properties of the as-sprayed coatings are studied. The effects of temperature and phase transformation in the coatings during erosion process are analyzed using XRD and EDS techniques. Optical profilometer is used for accurate elucidation of erosion volume loss. CoCrAlY/CeO2 coating showed better erosion resistance with a volume loss of about 50% of what was observed in case of CoCrAlY/Al2O3/YSZ coating. Lower erosion loss is observed at 90° as compared to 30° impact angle. The erosion mechanism evaluated using SEM micrograph revealed that the coatings experienced ductile fracture exhibiting severe deformation with unusual oxide cracks. Reinforced metal oxides provide shielding effect for erodent impact, enabling better erosion resistance. The oxidation of the coating due to high-temperature exposure reforms erosion process into oxidation-modified erosion process. © 2017, ASM International.
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    High-Temperature Erosive Behavior of Plasma Sprayed Cr3C2-NiCr/Cenosphere Coating
    (Springer New York LLC barbara.b.bertram@gsk.com, 2018) Mathapati, M.; Doddamani, M.; Ramesh, M.R.
    This research examines the deposition of Cr3C2-NiCr/cenosphere and Cr3C2-NiCr coatings on MDN 321 steel through the process of plasma spray. In this process, the solid particle erosion test is established at 200, 400, 600 °C with 30° and 90° impact angles. Alumina erodent is adopted to investigate the erosive behavior of the coating at higher temperatures. The properties of the Cr3C2-NiCr/cenosphere coating are established based on the microhardness, the adhesive strength, the fracture toughness, and the ductility. To quantify volume loss as a result of erosion, an optical profilometer is used. At higher temperature, decrease in the erosion volume loss of Cr3C2-NiCr/cenosphere and Cr3C2-NiCr coatings is observed. The erosion-resistive property of Cr3C2-NiCr/cenosphere coating is higher than that of MDN 321 steel by 76%. This property is influenced by high-temperature stability of mullite, alumina, and protective oxide layer that is formed at elevated temperatures. The morphology of eroded coating discloses a brittle mode of material removal. © 2018, ASM International.
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    Elevated temperature solid particle erosion behaviour of carbide reinforced CoCrAlY composite coatings
    (Institute of Physics Publishing helen.craven@iop.org, 2018) Nithin, H.S.; Desai, V.; Ramesh, M.R.
    CoCrAlY+WC-Co and CoCrAlY+Cr3C2-NiCr coatings are deposited on nickel based alloy using atmospheric plasma spray technique. Mechanical properties such as microhardness, adhesion strength and fracture toughness of coatings are evaluated. Elevated temperature solid particle erosion behaviour of these coatings are investigated at 600 °C using alumina erodent at 30 and 90° impact angle. Coatings are characterized utilizing Scanning electron microscope (SEM), x-ray diffraction (XRD) and Energy dispersive spectroscopy (EDS). CoCrAlY+WC-Co coating shows higher hardness, adhesion strength and fracture toughness than CoCrAlY+Cr3C2-NiCr coating. CoCrAlY+WC-Co coating exhibited approximately 3 times higher erosion resistance than CoCrAlY+Cr3C2-NiCr coating at 90° and 30° impact angles. SEM images of eroded surfaces of coatings reveals the combination of ductile and brittle fracture. CoCrAlY+Cr3C2-NiCr coating shows severe cracks, craters, carbide pull out and chipping than CoCrAlY+WC-Co coating. High temperature erosion is a combination of simultaneous building up of material by oxidation and removal of material by erosion process. Thus reforming the erosion process to oxidation modified erosion process. © 2018 IOP Publishing Ltd.
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    Cyclic Oxidation and Hot Corrosion Behavior of Plasma-Sprayed CoCrAlY + WC-Co Coating on Turbine Alloys
    (Springer New York LLC barbara.b.bertram@gsk.com, 2018) Nithin, H.S.; Vijay, D.; Ramesh, M.R.
    Components in energy-producing systems suffer a variety of degradation processes such as oxidation and molten salt-induced corrosion as a consequence of complex multi-component gaseous environment. Coatings provide a composition that will grow the protective scale at high temperatures having long-term stability. Plasma spraying was used to deposit CoCrAlY + WC-Co composite coatings on turbine alloys of Hastelloy X and AISI 321. The thermocyclic oxidation behavior of coated alloys was investigated in static air and in molten salt (Na2SO4-60%V2O5) environment at 700 °C. The thermogravimetric technique was used to approximate the kinetics of oxidation in 50 cycles, each cycle consisting of heating and cooling. X-ray diffraction and SEM/EDAX techniques are used to characterize the oxide scale formed. Coated alloys showed a lower corrosion rate as compared to uncoated alloys. The coatings subjected to oxidation and hot corrosion showed slow scale growth kinetics. Preferential oxidation of Co, Cr, W and its spinel blocks the transport of oxygen and corrosive species into the coating by providing a barrier, thereby making the oxidation rate to reach steady state. As compared to the substrate alloys, coatings show better hot corrosion resistance. © 2018, ASM International.
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    Microstructure and tribological behavior of plasma sprayed NiCrAlY/WC-Co/cenosphere/solid lubricants composite coatings
    (Elsevier B.V., 2018) Doddamani, M.; Mathapati, M.; Ramesh, M.R.
    Present investigation deal with NiCrAlY/WC-Co/Cenosphere/MoS2/CaF2, NiCrAlY/WC-Co/Cenosphere/MoS2/CaSO4 and NiCrAlY/WC-Co/Cenosphere coatings deposited on MDN 321 steel using atmospheric plasma spraying. Tribological properties of MDN 321 steel and coatings are evaluated from room temperature (RT) to 600 °C under dry lubrication conditions using a pin on disc high-temperature tribometer. Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) and Energy Dispersive Spectroscopy (EDS) are used to characterize the coatings. Presence of cenospheres in these coatings might effectively reduce wear acting as localized regions accumulating wear debris. The result shows that wear rate of all the coatings are lower as compared to MDN 321 substrate at all the test conditions. NiCrAlY/WC-Co/Cenosphere/MoS2/CaF2 and NiCrAlY/WC-Co/Cenosphere/MoS/CaSO4 coatings registered lower friction coefficient as compared to NiCrAlY/WC-Co/Cenosphere coating and MDN 321 substrate. Characterization of the NiCrAlY/WC-Co/Cenosphere/MoS2/CaF2 and NiCrAlY/WC-Co/Cenosphere/MoS2/CaSO4 coatings worn out surface suggests that MoS2 provides lubrication at 200 °C and formation of CaMoO4, MoO3 through tribo chemistry reaction at higher temperature provides lubrication at 600 °C. SEM micrograph of worn surface demonstrates that the main wear mechanism is plowing and delamination. © 2018 Elsevier B.V.
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    Plasma sprayed Cr3C2-NiCr/fly ash cenosphere coating: Cyclic oxidation behavior at elevated temperature
    (Institute of Physics Publishing helen.craven@iop.org, 2018) Doddamani, M.; Mathapati, M.; Ramesh, M.R.
    Oxidation is one of the major degradation phenomena observed in components subjected to higher temperatures like in thermal power plants (boiler tubes), steam and gas turbines blades etc. Developing protective coatings for such components mitigate oxidation. In the present study, plasma spray technique is utilized to deposit the Cr3C2-NiCr/Cenospheres coating on MDN 321 steel substrate. Thermo cyclic oxidation test is conducted at 600 °C (20 cycles) on both the coating and MDN 321 steel substrate. The thermogravimetric methodology is employed to estimate the oxidation kinetics. Energy Dispersive Spectroscopy (EDS), x-ray Diffraction (XRD), Scanning Electron Microscope (SEM) and x-ray mapping technique is employed to characterize the oxidized samples. Cr3C2-NiCr/Cenosphere coating displayed lower rate of oxidation as compared to substrate implying its suitability in high-temperature applications. Protective oxides like Al2O3, Cr2O3, and NiCr2O4 are observed on the uppermost layer of the coating lowering the oxidation rate in the developed coating. © 2018 IOP Publishing Ltd.
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    Microstructure and tribological characteristics of APS sprayed NiCrBSi/flyash cenosphere/Cr2O3 and NiCrBSi/flyash cenosphere/Mo composite coatings at elevated temperatures
    (Institute of Physics Publishing helen.craven@iop.org, 2019) Nagabhushana, N.; Rajanna, S.; Mathapati, M.; Ramesh, M.R.; Koppad, P.G.; Reddy, N.C.
    In the present investigation NiCrBSi/flyash/Cr2O3 and NiCrBSi/flyash/Mo composite coatings are developed using atmospheric plasma spray technique on superni 76 alloy. Coatings are characterized in terms of microstructure, phase analysis, and microhardness. Tribological properties of the coatings are evaluated using a pin on disc tribometer. Test is conducted under dry sliding conditions at room temperature, 200 °C, 400 °C, and 600 °C respectively. Microstructure and worn surfaces of the coatings are analyzed by utilizing Scanning Electron Microscope (SEM) where in phase analysis is carried out using x-ray diffractometer (XRD). XRD results revealed the presence of ?-Ni as primary phase along with Ni3B, Cr7C3, SiO2 and Al2O3 as minor phases in both the NiCrBSi/flyash/Cr2O3 and NiCrBSi/flyash/Mo coatings. Among the two coatings, Mo composite coating exhibited lower porosity and higher microhardness. The friction coefficient of both the coatings decreased with increasing temperature. The wear rate is found to decrease at lower temperatures but increased at a higher temperature (>400 °C) for Cr2O3 composite coating wherein Friction coefficient is decreased with increase in the temperature for Mo composite coatings. The worn surface analysis conducted revealed abrasive wear at lower temperatures while the transition from abrasive to adhesive is observed at higher temperatures. © 2019 IOP Publishing Ltd.
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    High-temperature wear and frictional behavior of partially oxidized Al with NiCr composite coating
    (Institute of Physics Publishing helen.craven@iop.org, 2019) Medabalimi, S.R.; Ramesh, M.R.; Kadoli, R.
    The influence of composite coating in improving wear and frictional behavior from room temperature to 600 °C was investigated. Partially oxidized Al powder was prepared with a flame spray process by spraying pure Al powder into distilled water. The composite powder is the mixture of 30 weight percent of partially oxidized Al and 70 weight percent of NiCr alloy powder. The composite powder was subsequently coated on MDN321 steel by air plasma spray process. The composite coatings are characterized with respect to adhesion strength, porosity, micro-hardness, and density. Wear and frictional behavior of coatings are evaluated under disc speed of 1 and 2 m s-1, loads of 10, 20 and 30 N and 3000 m sliding distance. The test results indicated that at room temperature, frictional heat generated due to applied load produce three-body abrasion at the interface caused to increase the wear and friction in the coating. The oxide film formed at high temperature due to plastic deformation avoids surface degradation at the interface and reduce the wear and friction. The worn surfaces at 600 °C consist phases of ?-Al2O3, NiO, and Cr3O. These phases are contributing to improving the wear resistance of the coating more than 4-times compared to uncoated steels under varying load and sliding velocities. The coefficient of friction reduced with increase in temperature due to generated oxides act as lubricants at the interface. © 2019 IOP Publishing Ltd.
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    Microstructural Characterization and Hot Corrosion Behavior of Plasma-Sprayed Fe17Cr2Ni0.18C/Fly Ash Cenosphere-Based Composite Coating
    (SAE International, 2021) Hanumanthlal, S.; Siddaraju, C.; Ramesh, M.R.; Thirtha Prasada, H.P.; Somasunder, B.; Virupakshappa, L.
    The current investigation studies the microstructure and high-temperature hot corrosion behavior of plasma-sprayed coatings. The composition of Fe17Cr2Ni0.18C and fly ash cenosphere powder is maintained in the 0%, 5%, 10%, and 15% ratio by weight percent, respectively. Both powder mixtures were thoroughly blended correspondingly and coated on T22 boiler steel tubings. 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 bare and coated steels. Thermogravimetric practice was used to establish the kinetics of hot corrosion of uncoated and coated steels. As-coated samples are studied for microstructure and microhardness. X-ray diffraction (XRD), scanning electron microscopy (SEM)/energy-dispersive spectroscopy, and X-ray mapping characterization techniques have been utilized for structural analysis of the as-coated and hot-corroded samples. It was observed that FeCrNiC/cenosphere-coated steels showed better hot corrosion resistance than the uncoated steels. The coated steels follow the parabolic rate law of oxidation, and parabolic rate constant values are lower in comparison to the uncoated steels. Better resistance is provided by the high-temperature permanence of mullite, alumina, and defensive oxide layer of silicon that is formed at elevated temperatures. ©