Faculty Publications
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Item 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.Item Role of thermally grown oxide and oxidation resistance of samarium strontium aluminate based air plasma sprayed ceramic thermal barrier coatings(Elsevier B.V., 2017) Baskaran, T.; Arya, S.B.Samarium Strontium Aluminate (SSA) based ceramic oxide was synthesized and coated on a bond coated (NiCrAlY) Inconel 718 superalloy by air plasma spray (APS) process. Thermally grown oxide (TGO) thicknesses were controlled at different pre-oxidation times of 10, 20 and 30 h at 1050 °C in the argon atmosphere, the highest TGO thickness being found for 30 h pre-oxidized samples. The percentage elastic recovery of pre-oxidized samples increased (45, 48, and 50%) with an increasing pre-oxidation time at 1050 °C. The isothermal oxidation test was performed on pre-oxidized samples at 1100 °C for 15 h in air. The parabolic oxidation rate constant decreased from 6.08 × 10? 5 to 3.90 × 10? 5 mg2 cm? 4 s? 1 (from 10 to 20 h) and then increased up to 4.55 × 10? 5 mg2 cm? 4 s? 1 for 30 h pre-oxidized SSA samples at 1100 °C. SSA based TBCs showed 65% lower weight gain as compared to conventional YSZ TBCs after oxidation at 1100 °C in air. Cross-sectional SEM results revealed that the threshold TGO thickness of SSA TBCs is about 5.3 to 5.8 ?m. Failure of SSA TBCs was observed at the interface of TGO and ceramic top coat due to the formation of SmAlO3 along with spinel oxides. © 2017Item 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.Item Nonlinear bending and free vibration response of SUS316-Al2O3 functionally graded plasma sprayed beams: theoretical and experimental study(SAGE Publications Inc. claims@sagepub.com, 2018) Malik, P.; Kadoli, R.Functionally graded SUS316-Al2O3 beams with ceramic content varying from 0 to 40% were prepared by a plasma spraying technique. Nonlinear finite element analysis was used to obtain the static deflection and free vibration of a clamped-free functionally graded beam. Von Kármán geometric nonlinearity and power law variation in material gradation through the beam thickness are considered in the analysis. The maximum error between the experimental and nonlinear finite element results for deflection is 6.68% and 14.31% on the fundamental frequency. Numerical results have also been attempted using ANSYS 3D solid element and they compare more closely with the experimental results. © 2016, © The Author(s) 2016.Item 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.Item 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.Item 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.Item Hot corrosion resistance of air plasma sprayed ceramic Sm2SrAl2O7 (SSA) thermal barrier coatings in simulated gas turbine environments(Elsevier Ltd, 2018) Baskaran, T.; Arya, S.Samarium strontium aluminate (Sm2SrAl2O7-SSA) and Yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) were developed on NiCrAlY bond coated Inconel 718 superalloy substrate using air plasma spray process. The hot corrosion study was conducted in simulated gas turbine environments (molten mixtures of 50 wt% Na2SO4 + 50 wt% V2O5 and 90 wt% Na2SO4 + 5 wt% V2O5 + 5 wt% NaCl) for two different temperatures of 700 and 900 °C. A developed SSA TBCs showed about 8% and 22% lower lifetime at 700 and 900 °C, respectively than YSZ TBCs in 50 wt% Na2SO4 + 50 wt% V2O5 (vanadate). The hot corrosion life of SSA TBCs being found about 13% and 39% lower than YSZ TBCs in 90 wt% Na2SO4 + 5 wt% V2O5 + 5 wt% NaCl (chloride) at 700 and 900 °C, respectively. X-ray diffraction results showed the formation of SmVO4, SrV2O6, and SrSO4 as a major hot corrosion product in 50 wt% Na2SO4 + 50 wt% V2O5 and 90 wt% Na2SO4 + 5 wt% V2O5 + 5 wt% NaCl environments respectively for SSA TBCs. Similarly, YSZ TBCs also showed YVO4 as hot corrosion product in vanadate and chloride environments. Both the TBCs suffer a more severe hot corrosion attack in chloride environment at 900 °C. The leaching of Sr2+ and Y3+ ions from SSA and YSZ respectively play a vital role in the destabilization of coating in vanadate and chloride environments at 700 and 900 °C. In both SSA and YSZ TBCs, the leaching of ion has significantly low influence as compared to attack by chloride ions at the bond coat-top coat interface in the presence of chloride environment. The hot corrosion resistance of SSA TBCs was improved three times higher in the presence of MgO and NiO inhibitor in vanadate environment at 900 °C mainly due to the formation of a stable Ni3V2O8 phase at the surface. © 2018 Elsevier Ltd and Techna Group S.r.l.Item 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.Item 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.