Faculty Publications
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Item Hot corrosion stability of double perovskite and pyrochlore in suphate solution of vanadates or chlorides at 900 °C(Trans Tech Publications Ltd ttp@transtec.ch, 2015) Baskaran, T.; Sreedhar, G.; Arya, S.B.Double perovskites, pyrochlores are having matching thermal expansion co-efficient with bond coat and may act as candidate materials for an intermediate layer between bond coat and top coat in Thermal Barrier Coatings. Hot corrosion stability of double perovskites and pyrochlores is also important for enhanced thermal cycle life. Based on these issues, systematic studies were conducted to find the hot corrosion stability of double perovskites and pyrochlores. The results revealed that, double perovskites and pyrochlores were undergone destabilization in the Na2SO4+50 wt.% V2O5 and Na2SO4+10 wt.% NaCl environments at 900 °C. The implications of these findings addresses the key issues related hot corrosion mechanisms and give a pathway to developing newer materials. This study clearly indicates the destabilization of both double perovskites and pyrochlores in vanadium and chloride environments at 900 °C. © (2015) Trans Tech Publications, Switzerland.Item Fabrication of samarium strontium aluminate ceramic and deposition of thermal barrier coatings by air plasma spray process(EDP Sciences edps@edpsciences.com, 2018) Baskaran, T.; Arya, S.B.Thermal barrier coatings (TBC) with the metallic NiCrAlY bond coat are often used in many aircraft engines to protect superalloy components from high-temperature corrosion thereby to improve the life of gas turbine components. The search for new TBC material has been intensified in recent years due to lack of thermo-physical properties of conventionally used Yttria stabilized Zirconia (YSZ) TBCs. Recently, the rare earth containing Samarium Strontium Aluminate (SSA) based ceramic was proposed as a new TBC material due to its matching thermo-physical properties with the substrate. The present work focused on the synthesis of SSA ceramics for TBCs application and its coatings development on Ni-based superalloy Inconel 718 substrate by air plasma spray process. The X-ray photoelectron spectroscopy (XPS) result confirmed the formation of single phase SSA ceramic after synthesis. The surface morphology of SSA TBCs is mainly composed of melted splats, semi and un-melted particles. The cross-sectional SEM micrographs did not show any spallation at the interface which indicated good mechanical interlocking between the bond coat and ceramic top coat. The Young's modulus and hardness of SSA TBCs were found to be 80 and 6.1 GPa, respectively. The load-depth curve of SSA TBC showed good elastic recovery about 47 %. © The Authors, published by EDP Sciences, 2018.Item Erosion behavior of Al2O3 + Sm2SrAl2O7 composite thermal barrier coatings(Elsevier Ltd, 2022) James J, F.; Arya, S.; Tailor, S.Thermal barrier coatings (TBC) are applied in gas turbines to protect the components from critical operating conditions at high temperatures. Foreign object damage is a major failure cause of turbine components due to erosion of the topcoat ceramic layer of the TBC system. In the present study, Samarium Strontium Aluminate (Sm2SrAl2O7) powders have been synthesized in the laboratory through molten salt synthesis, and thermal barrier coatings were developed using Atmospheric Plasma Spray (APS) technique on an Inconel substrate with NiCrAlY as a bond coat. The erosion behavior of the composite TBC system at temperatures of 200 °C and 800 °C at 30° and 90° impingement angles was analyzed using alumina erodent with a grit size of 50 µm. The erosion weight loss was measured in regular intervals and plotted against erodent mass. The samples exhibited a higher volumetric erosion at 90° and 800 °C. The morphological analysis of developed 70% Al2O3 + 30% Sm2SrAl2O7 composite coatings and eroded areas were performed using XRD, SEM, and surface profilometer. Erosion scars and surrounding deformed areas have been identified in the samples. The microstructure of the eroded areas in the samples showed micro-cutting and plowing as the major material removal mechanisms. Detailed phase analysis of the eroded locations in samples has been reported. © 2022Item Comparative analysis of steady state heat transfer in a TBC and functionally graded air cooled gas turbine blade(2010) Coomar, N.; Kadoli, R.Internal cooling passages and thermal barrier coatings (TBCs) are presently used to control metal temperatures in gas turbine blades. Functionally graded materials (FGMs), which are typically mixtures of ceramic and metal, have been proposed for use in turbine blades because they possess smooth property gradients thereby rendering them more durable under thermal loads. In the present work, a functionally graded model of an air-cooled turbine blade with airfoil geometry conforming to the NACA0012 is developed which is then used in a finite element algorithm to obtain a non-linear steady state solution to the heat equation for the blade under convection and radiation boundary conditions. The effects of external gas temperature, coolant temperature, surface emissivity changes and different average ceramic/metal content of the blade on the temperature distributions are examined. Simulations are also carried out to compare cooling effectiveness of functionally graded blades with that of blades having TBC. The results highlight the effect of including radiation in the simulation and also indicate that external gas temperature influences the blade heat transfer more strongly. It is also seen that graded blades with about 70% ceramic content can deliver better cooling effectiveness than conventional blades with TBC. © 2010 Indian Academy of Sciences.Item Effect of specimen crack lengths on stress intensity factor for Al6061-TiC composites using experimental and 3D numerical methods(Emerald Group Publishing Ltd. Howard House Wagon Lane, Bingley BD16 1WA, 2017) Raviraj, M.S.; Sharanaprabhu, C.M.; Mohan Kumar, G.C.Purpose-The purpose of this paper is to present the determination of critical stress intensity factor (KC) both by experimental method and three-dimensional (3D) finite element simulations. Design/methodology/approach-CT specimens of different compositions of Al6061-TiC composites (3wt%, 5wt% and 7wt% TiC) with variable crack length to width (a/W0.3-0.6) ratios are machined from as-cast composite block. After fatigue pre-cracking the specimens to a required crack length, experimental load vs crack mouth opening displacement data are plotted to calculate the KC value. Elastic 3D finite element simulations have been conducted for CT specimens of various compositions and a/W ratios to compute KC. The experimental results indicate that the magnitude of KC depends on a/W ratios, and significantly decreases with increase in a/W ratios of the specimen. Findings-From 3D finite element simulation, the KC results at the centre of CT specimens for various Al6061-TiC composites and a/W ratios show satisfactory agreement with experimental results compared to the surface. Originality/value-The research work contained in this manuscript was conducted during 2015-2016. It is original work except where due reference is made. The authors confirm that the research in their work is original, and that all the data given in the article are real and authentic. If necessary, the paper can be recalled, and errors corrected. © Emerald Publishing Limited.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 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.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 Investigation of thermally sprayed NiCrAlY/TiO2and NiCrAlY/Cr2O3/YSZ cermet composite coatings on titanium alloys(Institute of Physics, 2022) Madhu Sudana Reddy, G.; Prasad, C.D.; Patil, P.; Shetty, G.; Ramesh, M.R.; Nageswara Rao, T.The present work investigates the hot corrosion behavior of thermally sprayed 65 pct NiCrAlY + 35 pct TiO2 and 65 pct NiCrAlY + 30 pct Cr2O3 + 5 pct YSZ coatings on titanium 15 alloys. The coatings on the titanium 15 alloy substrates exhibit a near-uniform, dense, and adherent microstructure with a porosity of 2.7 to 2.9%. Thermogravimetric studies are made to examine the hot corrosion performance of coatings in a molten salt environment of Na2SO4 + 60%V2O5 at the temperature of 700 °C for 50 cycles. One cycle is carried out by heating for a period of one hour and cooling the sample at ambient conditions. The corrosion products are analyzed based on scanning electron microscopy, energy dispersive analysis, and X-ray diffraction techniques to study the morphology, phase composition, and abundance of the high-temperature corrosion constituents. The bare titanium-15 alloy, 65 pct NiCrAlY + 35 pct TiO2 coating and 65 pct NiCrAlY + 35 pct Cr2O3 + 5 pct YSZ coating produced a weight gain of 307.92 mg cm-2, 42.16 mg cm-2 and 44.02 mg cm-2 respectively after the period of 50 cycles. The effective resistance of the coatings is due to the formation of Ni3V2O8, NiCr2O4, Cr2O3 & AlV2O4 phases. © 2022 IOP Publishing Ltd.Item Hot corrosion behavior of Al2O3 + Sm2SrAl2O7 composite thermal barrier coatings(John Wiley and Sons Inc, 2022) Joseph, F.J.; Arya, S.B.; Tailor, S.Rare earth-based samarium strontium aluminate (Sm2SrAl2O7) powder has been synthesized in the laboratory through molten salt synthesis and Al2O3 + Sm2SrAl2O7 (SSA) thermal barrier coatings have been developed on an Inconel 718 superalloy substrate by atmospheric plasma spraying technique. The microstructures and surface morphologies of the samples before and after the hot corrosion tests in 50 wt% Na2SO4 + 50 wt% V2O5 (aviation atmosphere) and 90 wt% Na2SO4 + 5 wt% V2O5 + 5 wt% NaCl (marine atmosphere) at 700°C and 900°C were examined. It is observed that samples exposed to marine conditions exhibited 14.5% and 11.6% lower lifetime than the samples exposed to aviation conditions at 700°C and 900°C, respectively, due to significant chlorides attack. © 2022 Wiley-VCH GmbH.