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 MICROSTRUCTURE AND TRIBOLOGICAL PERFORMANCE OF SELF-LUBRICATE CLADDING PRODUCED BY TUNGSTEN INERT GAS AND MICROWAVE HYBRID HEATING TECHNIQUES(World Scientific, 2022) Gudala, S.; Ramesh, M.R.; Siva Shanmugam, N.S.; Srinath, M.S.The wear reduction of moving components is highly desirable because wear limits their reliability and service life, mainly at elevated temperatures. This study produced thick clads of NiCrSiB/WC/MoS2/BaF2 by tungsten inert gas (TIG) and microwave hybrid heating (MHH) cladding techniques, which were compared for microstructural and high-temperature tribological properties. The clad samples were subjected to sliding contact using a pin on disc tribometer at 200°C, 400°C, 600°C under 20 and 40N load. The worn surface was analyzed using FESEM, XRD and three-dimensional (3D) profilometer. The experimental results revealed a significant effect of the TIG current and MHH exposure time on the microhardness value, which predominantly depends on the morphological characteristics. The average hardness of TIG clads was found to be 1.2 times higher than the MHH clad. Because of the MoS2 and BaF2 encapsulation, the continuous lubricant layer formation compensated for improved wear resistance with good reliability and longer service life. This work provides significant insights into the wear behavior of TIG and MHH clads at elevated temperatures and the prospective applications in turbines, where inadequate wear resistance of titanium alloy is the major concern for its use. © 2022 World Scientific Publishing Company.Item Microstructure and Wear Behavior of Self-Lubricating Microwave Clads Deposited on Titanium Alloy(Springer, 2022) Gudala, S.; Ramesh, M.R.; Srinath, M.S.In this work, composite clads (NiCrSiB/WC/Ag/hBN and NiCrSiB/WC/MoS2/hBN) have been successfully developed using microwave cladding technique on titanium 31 substrate. The clads were characterized by field emission scanning electron microscope (FESEM), electron backscatter diffraction (EBSD), x-Ray diffraction (XRD) analysis. The developed clads were free from porosity, defects, and other thermal distortion effects. Furthermore, due to the uniform distribution of hard phases, clads achieved uniform hardness across the clad depth. The convective currents of the molten pool improved metallurgical bonding with the substrate. Because of the volumetric heating, the deviation of microhardness values in the clad was found to be low. The tribological properties of the clads were tested against an Al2O3 counterbody using a pin on disc tribometer. The results showed that incorporating solid lubricants (Ag/hBN and MoS2/hBN) into the nickel-based alloy significantly improved tribological properties. The wear rate and coefficient of friction decreased as the temperature increased from 200 to 600 °C. It was demonstrated that anti-wear and lubricating capability of both clad could be improved at elevated temperatures by doping Ag, MoS2, and hBN solid lubricants. © 2022, ASM International.Item 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.Item Phase evolution and high-temperature wear behavior of non-equiatomic metastable CoCrNiTiMox HEA coatings fabricated by high-velocity oxy-fuel technique(Elsevier Ltd, 2023) Addepalli, S.N.; Joladarashi, S.; Ramesh, M.R.The current research aims to enhance the tribological performance of maraging steels at high temperatures by surface modification techniques. CoCrNiTiMox (x; molar fraction, x = 0.5, 1.5) high-entropy alloy (HEA) coatings with dense lamellar microstructures were deposited onto maraging steels using high-velocity oxy-fuel spray (HVOF). In order to achieve a uniform distribution of constituent elements for thermal spray deposition, mechanical alloying was employed to synthesize the HEA feedstock. The phases and microstructure of the synthesized HEA powder, as-sprayed coatings, and worn surfaces were examined using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The as-sprayed HEA coatings exhibited metastability, with a BCC phase solid solution, NiTiO3 spinel, and an intermetallic MoNi phase for CoCrNiTiMo0.5 and Co2Mo3 phase for CoCrNiTiMo1.5. The average microhardness of CoCrNiTiMo0.5 and CoCrNiTiMo1.5 HEA coatings were 841 ± 62 HV0.3 and 952 ± 23 HV0.3, respectively. The specific wear rate and friction coefficients of CoCrNiTiMox HEA coatings exhibited a decreasing trend with an increase in temperature, owing to the formation of tribofilms on the worn surface. X-ray diffraction studies revealed the formation of NiMoO4 spinel for CoCrNiTiMo0.5 and MoO2, Co3O4 phases for CoCrNiTiMo1.5 HEA at a wear temperature of 600 °C. The investigation of worn surfaces showed a transformation in wear mechanisms from abrasive wear at room temperature to oxidative wear with mild fatigue at elevated temperatures. © 2023 Elsevier LtdItem 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.Item Effect of dilution on the microstructure and high-temperature wear resistance of self-lubricating nickel alloy claddings(SAGE Publications Inc., 2024) Gudala, S.; Rokkala, U.; Rao Medabalimi, S.; M.r, R.; Konovalov, K.S.In this study, the impact of substrate dilution on the microstructure and tribological properties of tungsten inert gas (TIG)-deposited self-lubricating claddings was investigated. The dilution of Ti content on cladding increased as the TIG current increased, and the microhardness of the cladding decreased. The content of intermetallic phases such as TiNi and TiC increased with the increase in TIG current. The tribological studies revealed that coating dilution at higher TIG currents has prominent effects on wear behaviour at elevated temperatures. In both clads, the percentage decrease in hardness from higher TIG current to lower TIG current was noted as 31%. The higher dilution of Ti content in the cladding was found to be beneficial in tribological studies performed, especially at higher temperatures (≥400). Also, solid lubricants such as MoS2 and BaF2 encapsulation in the nickel alloy were found to be beneficial at both low and high temperatures. © The Author(s) 2024.Item Investigation on high-temperature tribological performance of laser directed energy deposited Inconel 625 for aerospace applications(Elsevier Ltd, 2025) Praharaj, A.K.; Bontha, S.; Balla, V.K.; Chakrapani, S.K.; Suvin, P.S.Laser directed energy deposition (LDED) is an emerging technique for fabricating superalloy based aero engine components. Hence, the current work investigates the tribological performance of LDED processed IN625 at room temperature (RT) and high temperature (HT) conditions of 850 °C to replicate the operating environment of aero engine components. The comparison with conventionally processed (CP) sample confirmed that as-deposited (AD) sample showed similar friction behavior to the CP sample but slightly improved wear performance. The COF and wear rate of AD sample reduced significantly at HT compared to RT due to the evolution of stable oxide layer. NiO, Fe2O3, and Cr2O3 were the major phases in oxide layer. The work indicates suitability of LDED to fabricate wear resistant surfaces. © 2024 Elsevier LtdItem Microstructure and elevated temperature wear behavior of HVOF-sprayed SS304L stainless-steel coating(Springer Nature, 2025) Medabalimi, S.; Gudala, S.; Rokkala, U.; Hebbale, A.M.; Ramesh, M.R.The paper aims to investigate the performance of the SS304L stainless steel coating on wear properties by varying load, temperature and velocity. Stainless-steel coatings were fabricated by high-velocity oxy-fuel spraying (HVOF) on superfer800. Surface morphology, elemental distribution and phase analysis were expressed by SEM, EDS, and XRD, respectively. The porosity, average surface roughness, and average microhardness of HVOF stainless steel coating are 2%, 7 µm, and 1167 ± 54 HV0.3, respectively. The wear rate of stainless-steel coating is 0.5 × 10?3 mm3/m at 600 °C with 20 N loads, which is about 16 times lower than the substrate. Adhesion and abrasion are the main wear mechanisms of HVOF stainless steel coatings during high-temperature tests. Comparing to superfer800 substrate, stainless steel coatings showed superior wear resistance at all the loads, temperature and velocities. © The Author(s) 2025.