Journal Articles
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Item Evaluation of cyclic oxidation and hot corrosion behavior of HVOF-sprayed WC-Co/NiCrAlY coating(Springer New York LLC journals@springer-sbm.com, 2014) Somasundaram, B.; Kadoli, R.; Ramesh, M.R.Corrosion of metallic structural materials at an elevated temperature in complex multicomponent gas environments are potential problems in many fossil energy systems, especially those using coal as a feedstock. Combating these problems involves a number of approaches, one of which is the use of protective coatings. The high velocity oxy fuel (HVOF) process has been used to deposit WC-Co/NiCrAlY composite powder on two types of Fe-based alloys. Thermocyclic oxidation behavior of coated alloys was investigated in the static air as well as in molten salt (Na2SO4-60%V2O5) environment at 700 °C for 50 cycles. The thermogravimetric technique was used to approximate the kinetics of oxidation. WC-Co/NiCrAlY coatings showed a lower oxidation rate in comparison to uncoated alloys. The oxidation resistance of WC-Co/NiCrAlY coatings can be ascribed to the oxide layer of Al 2O3 and Cr2O3 formed on the outermost surface. Coated alloys extend a protective oxide scale composed of oxides of Ni and Cr that are known to impart resistance to the hot corrosion in the molten salt environment. © 2014 ASM International.Item High-Temperature Solid Particle Erosion Behavior of Partially Oxidized NiCrBSiFe/NiCr Plasma Spray Coatings(Springer, 2021) Medabalimi, S.R.; Ramesh, M.R.; Kadoli, R.This paper investigated the solid particle erosion behavior of partially oxidized NiCrBSiFe and NiCr coatings by varying temperature and impact angle. The challenge in the current situation is to process a new system of powders containing metallic and oxide phases. Partially oxidized powders containing metallic and oxide phases were processed by flame spraying the alloy powders into distilled water and allowing the oxide layer to form while keeping the core in the middle of the particle. Partially oxidized coatings were developed on MDN321 steel using the plasma spray technique with feedstock of partially oxidized powders. An air jet erosion test was carried out using Al2O3 erodent of grit size 50 µm at room temperature, 200, 400, 600, and 800°C by varying 30, 45, 60, 75, and 90° impact angles. Coatings were characterized concerning bond strength, porosity, micro-hardness, and density. The effect of temperature and impact angle on volumetric erosion loss was studied using SEM, EDS, and XRD analysis. Partially oxidized NiCrBSiFe coating exhibited better erosion resistance compare with partially oxidized NiCr coating. NiCr coating demonstrates maximum volumetric erosion loss at 45° impact angle, whereas NiCrBSiFe at 60° impact angle under all tested temperatures. © 2021, ASM International.Item Effect of Mechanical Alloying on the Microstructure of CoCrNiTiMo x High Entropy Alloy(Springer, 2022) Addepalli, S.N.; Joladarashi, S.; Ramesh, M.R.; Arya, S.B.The present research focuses on synthesizing nanocrystalline CoCrNiTiMox (x: molar ratio; x = 1, 1.5 at.%, respectively) high entropy alloy by mechanical alloying of pure metal powders for further application as feedstock in the atmospheric plasma spray process. The paper describes the phase evolution and microstructural transformation of milled powders with respect to the ball milling time and speed. A Retsch PM 100 ball mill with a ball to powder ratio of 10:1 and speeds of 200 and 300 rpm are used to synthesize the feedstock powder for plasma spraying. The ball milled powders were assessed for particle size, phase transformation and surface morphologies at regular intervals of 10, 20, 30, 40 and 50 h to optimize the ball mill process parameters. The particle morphology and chemical homogeneity studies were done by scanning electron microscope along with energy dispersive spectroscopy. The influence of Mo variation in the CoCrNiTiMox high entropy alloy in phase formation and crystal structure is studied using the x-ray diffraction technique. The results reveal that the CoCrNiTiMox high entropy alloy possesses two BCC solid solution phases and the powder milled for 10 h is selected as the feedstock powder for plasma spray due to its morphology and good homogeneity of mixing. © 2022, ASM International.Item Influence of Solid Lubricants on Microstructure and Tribological Performance of Nickel-Based Composite Coatings(Springer, 2022) Gudala, S.; Ramesh, M.R.; Siva Shanmugam, N.S.The present study investigates the microstructure and high-temperature tribological studies of solid lubricant encapsulated nickel alloy coatings developed by tungsten inert gas (TIG) cladding technique. The TIG current values of 90 A, 95 A, and 100 A were considered as process parameters. The microstructure of the coatings (coating A: NiCrSiB/WC/Ag/hBN, coating B: NiCrSiB/WC/MoS2/hBN) was characterized using the scanning electron microscopy, X-ray diffraction, X-ray energy dispersive spectroscopy and EBSD (electron backscatter diffraction) analysis. The dry sliding wear studies were conducted using a pin on disc apparatus, and the microhardness of the coating was assessed using Vicker’s indentation technique. The results show that coating A exhibited high hardness and excellent tribological properties than coating B. In particular, coating A presents the high average microhardness (950 HV), low coefficient of friction (0.34), and wear rate (2.96 × 1−3 mm3/N-m). Additionally, coating A showed three-fold higher hardness and a 2.43 times lower wear rate than the titanium substrate. The lubricant phases (Ag, BN, Mo2S3) and oxide phases (TiO, Ag2O, Ni (TiO3)) formed in both coatings were adequate to reduce the material loss. © 2022, ASM International.Item Combating corrosion degradation of turbine materials using HVOF sprayed 25% (Cr3C2-25(Ni20Cr)) + NiCrAlY coating(2013) Jegadeeswaran, N.; Ramesh, M.R.; Bhat, K.High velocity oxy fuel process (HVOF) is an advanced coating process for thermal spraying of coatings on to components used in turbines. HVOF process is a thermal spray coating method and is widely used to apply wear, erosion, and corrosion protective coatings to the components used in industrial turbines. 25% (Cr3C2-25(Ni20Cr)) + NiCrAlY based coatings have been sprayed on to three turbine materials, namely, Ti-31, Superco-605, and MDN-121. Coated and uncoated substrates were subjected to hot corrosion study under cyclic conditions. Each cycle consisted of 1 hour heating at 800°C followed by 20 minutes air cooling. Gravimetric measurements were done after each cycle and a plot of weight gain as a function of number of cycles is drawn. Parabolic rate constants were estimated for the understanding of corrosion behaviour. It was observed that coated Ti-31 and MDN-121 were more resistant compared to the uncoated ones. Uncoated superco-605 was undergoing sputtering during corrosion study and hence comparison between coated and uncoated superco-605 was difficult. The cross-sectional analysis of the corroded, coated samples indicated the presence of a thin layer of chromium oxide scale on the top of the coating and it imparted better corrosion resistance. Parabolic rate constants also indicated that coating is more beneficial to Ti-31 than to MDN-121. © 2013 N. Jegadeeswaran et al.Item Hot corrosion behaviour of HVOF sprayed stellite-6 coatings on gas turbine alloys(2014) Jegadeeswaran, N.; Ramesh, M.R.; Sampath, S.; Bhat, K.U.The coal burned natural gas in contact with gas turbine can contain impurities of sodium, sulfur, vanadium, silicon and possibly lead and phosphorous, induce accelerated hot corrosion during long term operation. Coatings are frequently applied on gas turbine components in order to restrict surface degradation and to obtain accurate lifetime expectancies. High velocity oxy-fuel thermal spraying has been used to deposit Stellite-6 alloy coatings on turbine alloys. Hot corrosion behavior of the coatings were investigated for 50 cycles of 1 h heating at 800 C followed by 20 min cooling in presence of Na 2SO4 + 50 % V2O5 measuring weight gain (or loss). X-ray diffraction and SEM/EDAX techniques were used to characterize the oxide scale formed. The superior performance of Stellite-6 coating can be attributed to continuous and protective thin oxide scale of CoO, Cr2O3 and SiO2 formed on the surface. The coating region beneath this thin oxide scale was partially oxidized. Uncoated SuperCo-605 and MDN-121 showed less weight gain than Stellite-6 coated samples, but they showed spalling or sputtering during cyclic oxidation. Stellite-6 coating was dense and pore free even after 50 cycles, indicating that it can resist the hot corrosion cycle. © 2013 Indian Institute of Metals.Item Hot Corrosion Behaviour of HVOF Sprayed (Cr3C2–35 % NiCr) + 5 % Si Coatings in the Presence of Na2SO4–60 % V2O5 at 700 °C(Springer, 2015) Somasundaram, B.; Kadoli, R.; Ramesh, M.R.The hot corrosion behavior of high velocity oxyfuel sprayed (Cr3C2–35 % NiCr) + 5 % Si coatings on three substrate alloys of SA213-T22, MDN-310 and Superfer 800 H was investigated. The as-sprayed coatings are characterized with respect to microstructure and mechanical properties. Thermocyclic hot corrosion studies were performed in a molten salt environment of Na2SO4–60 % V2O5 for 50 cycles at 700 °C. Thermogravimetric technique was used to establish the kinetics of hot corrosion of uncoated and coated steels. It was observed that the coated steel showed better hot corrosion resistance than the uncoated steels. The coated steels follow the parabolic rate law of oxidation and the parabolic rate constant values are appreciably lower in comparison to the uncoated steels. The coated steels showed slow oxidation kinetics which indicated that the reaction rate is diffusion limited. The oxides of Cr2O3 and SiO2 formed on the outermost surface of the coatings are found to be passive in the molten NaVO3 melt. © 2014, The Indian Institute of Metals - IIM.Item Improving Hot Corrosion Resistance of Cobalt Based Superalloy (Superco-605) Using HVOF Sprayed Oxide Alloy Powder Coating(Springer India sanjiv.goswami@springer.co.in, 2015) Jegadeeswaran, N.; Bhat, K.U.; Ramesh, M.R.Superco-605 is a cobalt based superalloy used widely in the hot section of gas turbines. During their operation, they are exposed to high temperature and molten salt environment, causing damage to the component due to hot corrosion. In this investigation, Superco-605 alloy was coated using a fused oxide alloy powder, $$ 10\,\% {\text{Al}}_{ 2} {\text{O}}_{ 3} + {\text{CoCrAlTaY}} $$10%Al2O3+CoCrAlTaY , using high velocity oxy-fuel process. Coating thickness was in the range of 260–280 µm and it was lamellar in nature. Uncoated and coated samples were subjected to cyclic hot corrosion tests at 800 °C in presence of molten salt environment of $$ {\text{Na}}_{ 2} {\text{SO}}_{ 4}{+}50\% {\text{V}}_{ 2} {\text{O}}_{ 5} $$Na2SO4+50%V2O5. Resistance to hot corrosion was investigated using thermogravimetric analysis, visual observations, X-ray diffractometry, scanning electron microscopy and energy dispersive X-ray spectroscopy. Both samples developed an oxide scale at the top. The uncoated Superco-605 exhibited intense spalling during hot corrosion cycles. The oxide scale on the coated substrate was thin compared to total thickness of the coating. There was a chromium depleted region close to the oxide top scale. An alumina rich layer at the interface of coating-substrate prevents penetration of oxygen into the substrate material. Based on the experimental results, it is concluded that the fused oxide alloy powder is effective in reducing hot corrosion tendency of Superco-605 alloy. © 2015, The Indian Institute of Metals - IIM.Item High temperature corrosion behaviour of HVOF sprayed WC-CrC-Ni coatings(Inderscience Publishers, 2016) Somasundaram, B.; Kadoli, R.; Ramesh, M.R.; RAMESH, C.S.The present work aims to study the hot corrosion resistance of high velocity oxy-fuel (HVOF) sprayed WC-CrC-Ni coating developed on three types of boiler tube materials such as SA213-T22, MDN-310 and Superfer 800 H steels. Hot corrosion studies were conducted in a molten salt environment of Na2SO4-60%V2O5 at 700°C and thermogravimetric analysis was used to establish kinetics of corrosion. Corrosion kinetics of coated steels followed nearly parabolic behaviour and showed a lower corrosion rate in comparison to uncoated alloys. It is concluded that corrosion is restricted to the external surface of the coating and the formation of thick scale composed of oxides of Cr, Ni and their spinel oxides, acts as a diffusion barrier to the transportation of corrosive species into the coating. The carbides of tungsten and chromium uphold the strength of the coating. © © 2016 Inderscience Enterprises Ltd.Item Processing of cenosphere/HDPE syntactic foams using an industrial scale polymer injection molding machine(Elsevier Ltd, 2016) Bharath Kumar, B.R.; Doddamani, M.R.; Zeltmann, S.E.; Gupta, N.; Ramesh, M.R.; Ramakrishna, S.Rapid production of high quality components is the key to cost reduction in industrial applications. The present work is the first attempt of manufacturing syntactic foams, hollow particle filled lightweight composites, using an industrial scale injection molding machine. High density polyethylene (HDPE) is used as the matrix material and fly ash cenospheres are used as the filler. Development of syntactic foams with cenospheres serves dual purpose of beneficial utilization of industrial waste fly ash and reduction in the cost of the component. The pressure and temperature used in the injection molding process are optimized to minimize fracture of cenospheres and obtain complete mixing of cenospheres with HDPE. The optimized parameters are used for manufacturing syntactic foams with 20, 40 and 60 wt.% cenospheres. With increasing cenosphere content, density and strength reduce and modulus increases. Surface modification of constituents results in rise in strength with increasing filler content. A theoretical model based on a differential scheme is used to estimate the properties of cenospheres by conducting parametric studies because of inherent difficulties in direct measurement of cenosphere properties. The potential for using the optimized injection molding process is demonstrated by casting several industrial components. © 2015 Elsevier Ltd.