Faculty Publications

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    Lightweight and sustainable materials for coating applications
    (Elsevier, 2023) Mathapati, M.; Ramesh, M.R.; Doddamani, M.
    This chapter deals with the development of Cr3C2-25NiCr/cenosphere/MoS2/CaF2, Cr3C2-25NiCr/cenosphere/MoS2/CaSO4, and Cr3C2-25NiCr coatings through plasma spraying on MDN 321 steel substrate. Methods such as X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersive spectroscopy (EDS) are used for coating phase composition and microstructure analysis. Sliding wear behavior of substrate and coatings is tested at 200°C-600°C by utilizing a pin-on-disk tribometer. Owing to the existence of cenospheres and action of solid lubricants, frictional coefficient and wear rate of fly ash cenosphere-based Cr3C2-25NiCr/MoS2/CaF2 and Cr3C2-25NiCr/MoS2/CaSO4 compositions are reduced in comparison with Cr3C2-25NiCr coating and substrate at all test parameters. The characterization of the coatings’ worn-out surface reveals lubrication at 200°C by MoS2. At elevated temperature, CaF2 with CaMoO4 formed through tribochemistry further aids lubrication. Micrographs of worn surfaces demonstrate plowing and delamination as the main wear mechanism. © 2023 Elsevier Ltd. All rights reserved.
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    Scratch adhesion strength of plasma sprayed carbon nanotube reinforced ceramic coatings
    (Elsevier Ltd, 2017) Jambagi, S.C.
    This report investigates the effect of both mechanical and thermal properties of Carbon nanotube (CNT) on scratch adhesion strength of ceramic coatings. Micro sized alumina and titania with 1 wt% CNT powders were prepared by three routes: dry/wet milling (with alcohol) and heterocoagulation. First, degree of CNT dispersion in the coatings was analysed. Heterocoagulated coatings displayed homogeneous dispersion of CNT. Next, the effect of homogeneous dispersion on phase transformation was studied. Higher thermal conductivity of CNT and its degree of dispersion seemed to affect the melting of powders and thus the phase transformations in the coatings. A higher fraction of stable phase was detected in the coatings. In addition, CNT/ceramic interface was analysed for the reaction layer. A stable phase layer was found covering the entire CNT surface, protecting it from thermal degradation. Finally, the scratch adhesion strength was quantified for both CNT reinforced and unreinforced coatings. The scratch resistance of heterocoagulated coatings improved by ?36–176%. Improvement in strength was attributed to: a) a higher stable phase fraction in the coatings, b) Strong wettability at CNT/ceramic interface, c) improvement in elastic moduli of the coatings has also led to the improvement in the work of adhesion of the coatings, and d) a toughening mechanism, CNT bridging. © 2017 Elsevier B.V.
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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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    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. © 2017
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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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    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.
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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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    Influence of ceramic top coat and thermally grown oxide microstructures of air plasma sprayed Sm2SrAl2O7 thermal barrier coatings on the electrochemical impedance behavior
    (Elsevier B.V., 2018) Baskaran, T.; Arya, S.B.
    Electrochemical impedance spectroscopy (EIS) technique is used to examine the top coat and thermally grown oxide (TGO) microstructures of Samarium Strontium Aluminate (SSA) thermal barrier coatings (TBCs) after exposed to pre-oxidation and oxidation at 1050 and 1100 °C, respectively. EIS spectra showed that the three relaxations frequencies in Bode plot corresponded to SSA top coat, TGO, and TGO-bond coat interface. A significant reduction in polarization resistance of SSA top coat and increase in capacitance for different pre-oxidation times of 10, 20 and 30 h are being found due to increasing the defects (pores and cracks) of about 13, 29 and 45%, respectively at 1050 °C. The reduction in bi-axial residual stresses was calculated to be about 57% as a consequence of decrement in top coat resistance. The growth of SSA TGO was found from 10 to 20 h of pre-oxidation treatment caused to decrease the capacitance which indicates the presence of highly enriched ?-Al2O3 at the bond coat-top coat interface. The highest charge transfer resistance and lowest capacitance were found to be about 0.48 × 106 ? cm2 and 1.1 nF cm?2 respectively for 20 h of pre-oxidation which could reflect the overall impedance kinetics of TBC system (SSA top coat and TGO) at the TGO-bond coat interface. The impedance responses of SSA top coat, TGO, and TGO-bond coat interface were reduced drastically after oxidation at 1100 °C for 10 h pre-oxidized specimen as compared to 20 and 30 h due to the compositional change of pure ?-Al2O3 based TGO into more conductive NiCr2O4. The lowest diffusion coefficient, DCr3+ in the NiO lattice which reduced the formation of metal ion vacancies at the TGO-top coat interface caused to exhibit higher TGO resistance for 20 h pre-oxidized specimens over 10 and 30 h after oxidation at 1100 °C. © 2018 Elsevier B.V.