Faculty Publications
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Item 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.Item Developing partially oxidized NiCr coatings using the combined flame spray and plasma spray process for improved wear behaviour at high temperature(Elsevier Ltd, 2021) Medabalimi, S.R.; Ramesh, M.R.; Kadoli, R.The powders of NiCrBSiFe and NiCr are partially oxidized using a flame spray process and are deposited on MDN321 steel substrate using a plasma spray process. The effect of partial oxidization on microstructure, microhardness, density, bond strength, and porosity of the coatings is analyzed. The friction and wear behaviour of the coatings was assessed using a pin-on-disc tribometer by varying loads (10, 20 and 30 N), sliding velocities (1, 2 m/s) and temperatures (RT, 200, 400 and 600 °C). Worn surfaces of NiCrBSiFe and NiCr coatings consist of oxide phases of SiO2, NiO, Cr2O3 and NiCr2O4 at elevated temperatures. These phases contributed to reducing the wear rate by five folds in coated steels compared to uncoated steels at 600 °C. The wear rate in coating decreases with an increase in temperature. The coefficient of friction was reduced gradually with the temperature in coatings and substrate. The wear rate coefficient of NiCr coating was 1.7 times higher than the NiCrBSiFe coating. © 2021 Elsevier B.V.Item High-Temperature Oxidation Studies of Plasma-Sprayed NiCrAlY/TiO2 and NiCrAlY/Cr2O3/YSZ Cermet Composite Coatings on MDN-420 Special Steel Alloy(Springer, 2021) Madhu Sudana Reddy, G.; Prasad, C.D.; Shetty, G.; Ramesh, M.R.; Rao, T.N.; Patil, P.The plasma spray process was used to form 70%NiCrAlY + 30%TiO2 and 70%NiCrAlY + 25%Cr2O3 + 5%YSZ cermet coatings on MDN-420 special steel alloy. Cyclic oxidation testing was conducted on coated and uncoated specimens at 700°C under a static air environment. Thermogravimetric analysis was applied to establish the oxidation kinetics. X-ray diffraction (XRD), scanning electron microscopy (SEM)/energy-dispersive x-ray spectroscopy (EDS), and electron probe microanalysis (EPMA) techniques were used to analyze the oxidized products. The NiCrAlY + Cr2O3 + YSZ coating was found to be most resistive when compared with the NiCrAlY + TiO2 coating in the aggressive oxidation environment. Net weight loss was observed for bare MDN-420 alloy due to sputtering. The oxidation resistance of the coatings was due to formation of Cr2O3, NiCr2O4, NiO, and Al2O3 phases. © 2021, ASM International.Item Evolution of Microstructure and High-Temperature Tribological Performance of Self-Lubricating Nickel-Based Composite Tungsten Inert Gas Coatings(Springer, 2021) Gudala, S.; Ramesh, M.R.; Siva Shanmugam, S.S.The present study aims to assess the effect of Ag/BaF2 solid lubricant encapsulation in the nickel-based composite coatings for high-temperature tribological applications. The composite coatings (NiCrSiB/WC and NiCrSiB/WC/Ag/BaF2) have successfully been fabricated on the titanium 31 substrate by tungsten inert gas (TIG) cladding technique. The influence of the TIG processing current on the microstructure, microhardness, and fracture toughness was investigated. Mechanical characteristics of the coatings were further correlated with the microstructural morphologies. The coating fabricated at 70 A exhibited significantly higher hardness than other coatings. The tribological performances of the NiCrSiB/WC/Ag/BaF2 composite coatings were superior to those of the NiCrSiB/WC coatings at both low (200 °C) and high (600 °C) temperatures. The synergistic lubrication effect of the Ag/BaF2 solid lubricant combination provided lubrication at a wide range of temperatures. The addition of these solid lubricants in the nickel-based coating helped achieve the low coefficient of friction of 0.2 and lower wear rates. Particularly, oxide phases (such as NiO, TiO, Ni3Ti3O, and W3O) formed on the worn surface at 600 °C, and the lubricant phases (Ag, Ag2F, and Ba (TiO3)) provided excellent resistance to wear. © 2021, ASM International.Item Development of Self-lubricating Nickel Based Composite Clad using Microwave Heating in Improving Resistance to Wear at Elevated Temperatures(Korean Institute of Metals and Materials, 2022) Gudala, S.; Ramesh, M.R.; Srinath, M.S.This paper reports on a study of the high-temperature tribological performance of self-lubricating nickel-based composite clad. A porous and crack free clad containing matrix, reinforcement, and lubricant phase is developed on titanium 31 alloy using microwave irradiation. The microstructure of both NiCrSiB/WC and NiCrSiB/WC/Ag/BaF2 clad revealed very good metallurgical bonding with the substrate. The average microhardness of NiCrSiB/WC and NiCrSiB/WC/Ag/BaF2 clad is 710.58 HV and 650.25 HV respectively, is comparatively higher than the titanium 31 substrate (320 HV). The addition of Ag and BaF2 solid lubricants in the clad endowing clad to operate at a broad temperature range. Compared with the NiCrSiB/WC clad, solid lubricant encapsulate clad has shown very low friction coefficient and wear rates. The sliding wear characteristics of the clad were investigated by varying load and temperatures. The results revealed that oxide phases (NiO and Cr3O) and lubricant phases (Ag and BaWO4) formed at low and high temperatures are adequate to reduce delamination and material loss. Graphical abstract: [Figure not available: see fulltext.] © 2021, The Korean Institute of Metals and Materials.Item Green synthesis of fe/ni/cr oxide nanoparticles using costus pictus plant extract: Microstructure and biological properties(World Scientific, 2024) Kumar, P.; Ramesh, M.R.; Doddamani, M.; Suresh, J.Superior qualities to bulk material and larger surface area to volume ratio are some of the primary reasons that account for the wide use of nanoparticles (NPs) in biological applications. Advancements in molecular-level engineering and environmental and health concerns are driving factors in the green synthesis of NPs. Plant-based NP synthesis provides a good alternative compared to hazardous physical and chemical techniques of synthesis of NPs. An experimental study is carried out on the green synthesis of Fe/Ni/Cr oxide NPs using Costus pictus extract. The study encompassed an array of characterization techniques, including UV-visible spectroscopy for absorption properties, X-ray diffraction (XRD) for crystallinity assessment, and Fourier-transform infrared (FTIR) spectroscopy to probe the presence of phenolic groups in flavonoids that influence NP formation. Surface morphology and composition were elucidated using scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS), while transmission electron microscopy (TEM) affirmed the NPs' size (approximately 20 nm). The surface area of the NPs, 96.806 m2/g, was determined through BET analysis. Furthermore, the antibacterial potential of the NPs against various bacterial strains, including S. mutans, E. coli, P. aeruginosa, and S. aureus, was investigated using the agar well diffusion method. The NPs showed good antibacterial potential against bacterial species E. coli and P. aeruginosa. © 2024 World Scientific Publishing Company.Item Microstructural evolution and cyclic oxidation behavior of HVOF-sprayed NiCrSi and NiCrC coatings on T11 steel(Elsevier Inc., 2024) Medabalimi, S.; Hebbale, A.M.; Singh, R.; Desai, V.; Ramesh, M.R.This study analyzes NiCrSi and NiCrC coatings developed on low alloy ferritic stainless steel (grade T11) through the HVOF spraying technique. The coatings were characterized by their phase constitution, microstructure, cyclic oxidation behavior, and hardness. X-ray diffraction (XRD) analysis confirmed the presence of the NiCr solid solution matrix as the primary phase in both coatings. Moreover, the microstructure of the NiCrSi coating included the hard intermetallic compounds like Cr?Si and Ni?Si and the NiCrC coating contained the hard phases like Cr?C? and Ni?C which improved the hardness and the wear resistance of the coatings. Microhardness measurements revealed that the coatings had an average hardness of 300 ± 50 HV, significantly greater than the substrate hardness of 225 ± 25 HV. Cyclic oxidation tests were carried out at 700 °C revealed that both the coatings showed a lower weight gain than the uncoated substrate, suggesting enhanced oxidation resistance. This was because the protective oxide layers like Cr?O? and SiO? in the NiCrSi coating and Cr?O? and NiO in the NiCrC coating were formed. X-ray analysis establish ed. the presence of these oxides, which inhibited oxygen penetration through the coatings and provided additional protection against oxidation. Therefore, the study revealed that both NiCrSi and NiCrC coatings have good mechanical and oxidation resistance properties, which make them suitable for high-temperature applications where there is a need for improved durability, wear resistance, and protection against oxidation. © 2024