Faculty Publications

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    Evolutionary algorithm based structure search for hard ruthenium carbides
    (Institute of Physics, 2015) Harikrishnan, G.; Ajith, K.M.; Chandra, S.; Valsakumar, M.C.
    An exhaustive structure search employing evolutionary algorithm and density functional theory has been carried out for ruthenium carbides, for the three stoichiometries Ru1C1, Ru2C1 and Ru3C1, yielding five lowest energy structures. These include the structures from the two reported syntheses of ruthenium carbides. Their emergence in the present structure search in stoichiometries, unlike the previously reported ones, is plausible in the light of the high temperature required for their synthesis. The mechanical stability and ductile character of all these systems are established by their elastic constants, and the dynamical stability of three of them by the phonon data. Rhombohedral structure is found to be energetically the most stable one in Ru1C1 stoichiometry and hexagonal structure , the most stable in Ru3C1 stoichiometry. RuC-Zinc blende system is a semiconductor with a band gap of 0.618 eV while the other two stable systems are metallic. Employing a semi-empirical model based on the bond strength, the hardness of RuC-Zinc blende is found to be a significantly large value of ?37 GPa while a fairly large value of ?21GPa is obtained for the RuC-Rhombohedral system. The positive formation energies of these systems show that high temperature and possibly high pressure are necessary for their synthesis. © 2015 IOP Publishing Ltd.
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    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.
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    Temperature-Dependent Conformational Evolution of SARS CoV-2 RNA Genome Using Network Analysis
    (American Chemical Society, 2021) Singh, O.; Venugopal, P.P.; Mathur, A.; Chakraborty, D.
    Understanding the dynamics of the SARS CoV-2 RNA genome and its dependence on temperature is necessary to fight the current COVID-19 crisis. Computationally, the handling of large data is a major challenge in the elucidation of the structures of RNA. This work presents network analysis as an important tool to see the conformational evolution and the most dominant structures of the RNA genome at six different temperatures. It effectively distinguished different communities of RNA having structural variation. It is found that at higher temperatures (348 K and above), 80% of the RNA structure is destroyed in both the SPC/E and mTIP3P water models. The thermal denaturation free energy change ??Gvalue calculated for the long-lived structure at higher temperatures of 348 and 363 K ranges from 2.58 to 2.78 kcal/mol for the SPC/E water model, which agrees well with the experimentally reported thermal denaturation free energy range of 2.874 kcal/mol of SARS CoV-NP at normal pH. At higher temperatures, the stability of RNA conformation is found to be due to the existence of non-native base pairs in the SPC/E water model. © 2021 American Chemical Society
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    High-Temperature Tribological Studies on Hot-Forged Al6061–TiB2 In Situ Composites
    (Springer Science and Business Media Deutschland GmbH, 2022) Venkategowda, C.; Hanumanthappa, H.; Prasad, C.D.; Shanmugam, B.K.; Sreenivasa, T.N.; Kumar, M.S.R.
    The present investigation deals with the tribological behavior of high-temperature hot-forged Al6061–TiB2 in situ composites. Three samples of Al6061–TiB2 in situ composites were prepared with the variation in the in situ TiB2 particles. An in situ technique forms TiB2 particles by facilitating a reaction between Al–3%B and Al–10%Ti parent metals in the Al6061 melt at 800 °C. Further, approximately 5 wt% and 10 wt% TiB2 particles were created in the Al6061 composite using suitable quantities of parent alloys. At 500 °C, the Al6061 and its in situ composites were subjected to hot forging, and about 50% reduction is employed. The scanning electron microscope (SEM) and optical microscopy analysis were conducted to check the TiB2 particle dispersion and worn surfaces in the in situ composites. The TiB2 particle dispersion is found to be fairly uniform throughout the Al6061 matrix with minimal clustering. The results indicate that the friction coefficient increases initially when the temperature increases and then declines due to the oxides in the debris released from the top surfaces of the samples. The results show that the increase in the TiB2 content in the Al6061–TiB2 composites increases the composite wear rate. © 2022, The Author(s), under exclusive licence to Springer Nature Switzerland AG.
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    Thermal expansion of Crofer 22 APU steel used for SOFC interconnect using in-situ high temperature X-ray diffraction
    (Elsevier Ltd, 2023) Manjunath, N.; Santhy, K.; Rajasekaran, B.
    Crofer 22 APU is ferritic stainless steel extensively used as metallic interconnect material in Solid Oxide Fuel Cell (SOFC) applications. The interconnects are exposed to both oxidizing and reducing atmospheres at high temperatures. As SOFCs are operated above 700 °C, understanding the thermal expansion behavior of the interconnect material with other components (anode, cathode, electrolyte) of the fuel cells is essential. Metallic interconnects should have a matchable thermal expansion to other ceramic materials such as anode, cathode, and solid electrolyte used in SOFCs. The present study evaluates the thermal expansion of Crofer 22 APU steel from 25 to 950 °C in a controlled atmosphere (10-4 mbar pressure) using in-situ high-temperature X-ray diffraction (XRD). The XRD patterns were analyzed using the ‘High Score Plus Software’ attached to the system, and the phases were identified using the standard Crystallographic Open Database (COD). The coefficient of thermal expansion (CTE) was determined based on the change in lattice parameter/peak shift to a lower 2θ value as a function of temperature. The normal XRD data showed no oxide formation on the Crofer steel after heating until 950 °C in in-situ high-temperature conditions. The peak shift to the lower 2θ degree observed in the XRD data was due to the relaxation of residual stress upon heating. The isothermal section and phase fraction of Crofer 22 APU alloys are analyzed with the help of thermo-calc with the iron database of TCFE7. The Fe-rich bcc phase was found to be stable up to high temperatures. The major phases are the Fe-rich bcc, Cr-rich BCC, and sigma phase in the solid state. The minor phases are FCC, M3P, TiC, Laves, and Ti4C2S2. The calculated lattice parameter of the Fe-rich BCC phase matches with the experimentally calculated data using XRD. The thermal expansion of Crofer 22 APU was found to be 11.9181 × 10-6 /°C at 950 °C. The in-situ high-temperature XRD technique has been an effective methodology for determining the thermal expansion behavior of the as-received Crofer steel. © 2023
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    High temperature erosion performance of NiCrAlY/Cr2O3/YSZ plasma spray coatings
    (Taylor and Francis Ltd., 2023) Reddy, G.M.S.; Prasad, C.D.; Patil, P.; Shetty, G.; Naresh, N.; Ramesh, M.R.
    The current investigation's objective was to assess the air jet erosion tester's ability to measure the erosive behaviour of plasma sprayed coatings on titanium-15 alloy. 65% NiCrAlY, 30% Cr2O3, and 5% YSZ make up the coating's chemical composition. A study of microstructure and phases was carried out. Microhardness and adhesive strength have both been measured in this work. With impact angles of 30° and 90° at 300°C, 500°C, and 700°C, Al2O3 erodent was utilised in a solid particle erosion test. An optical profilometer was used to calculate the erosion volume loss. The coating erosion resistance was found to be higher than the substrate sample for the test temperature that was employed, and this was more obvious at higher impact angles and higher temperatures The ductile character of the coating is seen in the contour of the deteriorated coating surface. © 2023 Institute of Materials Finishing Published by Taylor & Francis on behalf of the Institute.
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    Influence of wire-electric discharge machining process parameters on surface integrity of Ni-rich Ni-Ti-Hf alloys
    (Institute of Physics, 2023) Balaji, V.; Narendranath, S.
    Ni-Ti-Hf Shape memory alloys (SMAs) have shown promising results in high-temperature applications in aviation, space and energy exploration, actuators, etc. In the past decade, extensive work has been carried out to understand the behavior of High-Temperature SMAs (HTSMAs). NiTi-based SMAs are grouped as hard-to-machine materials, and machining these materials through traditional methods leads to high tool wear, dimensional inaccuracy, degradation of Shape Memory properties, etc. Therefore, Non-Conventional machining processes are a better choice for machining these alloys. It is evident from previous studies that Wire Electric Discharge Machining (WEDM) yields better results compared to other processes. The current study investigates the effect of WEDM input variables such as servo gap voltage (SV), spark-ON duration (TON), wire electrode feed rate (WF), and spark-OFF duration (TOFF) on the machining of Ni-Ti-Hf HTMSAs. The surface integrity of the machined samples was analyzed by investigating characteristics like machined surface morphology, machined surface quality, subsurface microhardness, and recast layer thickness. TON emerged as the most critical parameter for surface roughness and Material Removal Rate. Various defects like micro-cracks, micro-pores, craters, and globules were found on the machined surfaces, and approximately 30% harder surface was found near the machined region. The average thickness of the recast layer observed for Hf-15 and Hf-20 samples was around 12 μm and 50 μm for samples with lower and higher discharge energies, respectively. © 2023 IOP Publishing Ltd.
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    Effect of thermal expansion on the high temperature wear resistance of Ni-20%Cr detonation spray coating on IN718 substrate
    (Elsevier B.V., 2023) Purushotham, N.; Parthasarathi, N.L.; Babu, P.S.; Govindarajan, G.; Rajasekaran, B.
    The temperature-dependent materials properties on the dry sliding wear resistance of the detonation sprayed Ni-20%Cr coating have been studied. In-situ high-temperature X-ray diffraction (HT-XRD) was used to investigate high-temperature properties such as stress relieving, recrystallization, and thermal expansion. The dry sliding wear test was performed by using a ball-on-disc tribometer by sliding velocities (0.1 m/s), varying loads (6 N and 10 N), and temperatures (25 °C and 850 °C) against alumina (Al2O3) ball. The phase evolution, thermal expansion, crystallite size, and lattice strain were determined by the Williamson-Hall method. Field emission scanning electron microscopy and a non-contact optical profilometer was used to characterize the wear scar and calculate the wear rate. The wear test results demonstrated that the as-deposited coatings coefficient of friction (CoF) and wear rate (ω) continuously decreased as the temperature increased. The primary wear mechanism changed from abrasive and surface fatigue to adhesive and oxidative wear. The impact of stress relieving, recrystallization, and forming a composite tribolayer (Cr2O3, NiO) at elevated temperatures reduced the friction and enhanced the wear resistance. The effect of stress relieving, recrystallization, thermal expansion, and oxidation on the wear resistance of the coating has been discussed with a suitable mechanism. © 2023 Elsevier B.V.
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    Effect of Microwave Hybrid Heating on High-Temperature Adhesive Wear Behavior of High-Velocity Oxygen Fuel-Sprayed WC-CrC-Ni and WC-Co/NiCrFeSiB Coatings
    (Springer, 2023) Medabalimi, S.; Ananthu, M.R.; Gudala, S.; Ramesh, M.R.
    HVOF-processed coatings are chemically inhomogeneous and are not metallurgically bonded to the substrate. As a result, components coated with HVOF experience considerable material degradation during sliding wear. Microwave hybrid heating (MHH) is a novel surface modification technique for modifying the as-sprayed properties of the coating. Hence, this paper investigates and compares the wear and frictional behavior of HVOF as-sprayed coatings against MHH samples of WC-CrC-Ni and WC-Co/NiCrFeSiB coatings at elevated temperatures. MHH had a significant impact on wear rate and coefficient of friction by optimizing the porosity, integrated oxide phases and intersplat cohesion strength of the coatings. A modified domestic oven was used to perform MHH on HVOF-coated samples for 5 min at 1200 °C. Wear tests were performed using a pin-on-disk tribometer from room temperature to 200, 400, and 600 °C with Al2O3 disk as a counterface. SEM/EDS and XRD were utilized to examine the microstructural characterization of the coatings and substrate. Both the coatings showed higher wear resistance than the substrate at all temperatures. The WC-Co/NiCrFeSiB coating produced an oxide layer on the worn surfaces and integrated WC, CoWO4, and Fe2SiO4 splats, enhancing wear resistance. The MHH WC-CrC-Ni coating formed Cr2O3 and NiWO4 phases on the worn surfaces, increasing the intersplat cohesion strength between matrix and carbide splats, lowering the overall wear rate. After MHH, the wear rate of a substrate and WC-CrC-Ni coating was 3.5 and 1.12 times more at room temperature and 8.07 and 2.92 times more at 600 °C than WC-Co/NiCrFeSiB coating. © 2022, ASM International.
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    Investigation of the effect of NiCrAlY/Cr2O3/YSZ plasma coatings on erosion performance of MDN 420 steel at high temperature
    (Inderscience Publishers, 2023) Reddy, G.M.S.; Prasad, C.D.; Patil, P.; Shetty, G.K.; Kakur, N.; Ramesh, M.R.
    The purpose of the current study was to use an air jet erosion tester to examine the erosive behaviour of plasma sprayed coatings on MDN-420 that were composed of 70% NiCrAlY, 25% Cr2O3, and 5% YSZ. Microstructure and phase studies were performed. Measurements were made on the microhardness and adhesion strength. Al2O3 erodent was used in a solid particle erosion test with impact angles of 30° and 90° at 300°C, 500°C, and 700°C. The erosion volume loss was measured using an optical profilometer. For the test temperature used, it was found that the coating’s erosion resistance was greater than that of the substrate and that it was more pronounced at higher impact angles and higher temperatures. The shape of the degraded coating surface reflects the coating’s ductile nature. © © 2023 Inderscience Enterprises Ltd.