Faculty Publications
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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 Microstructure and tribological behavior of plasma sprayed NiCrAlY/WC-Co/cenosphere/solid lubricants composite coatings(Elsevier B.V., 2018) Doddamani, M.; Mathapati, M.; Ramesh, M.R.Present investigation deal with NiCrAlY/WC-Co/Cenosphere/MoS2/CaF2, NiCrAlY/WC-Co/Cenosphere/MoS2/CaSO4 and NiCrAlY/WC-Co/Cenosphere coatings deposited on MDN 321 steel using atmospheric plasma spraying. Tribological properties of MDN 321 steel and coatings are evaluated from room temperature (RT) to 600 °C under dry lubrication conditions using a pin on disc high-temperature tribometer. Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) and Energy Dispersive Spectroscopy (EDS) are used to characterize the coatings. Presence of cenospheres in these coatings might effectively reduce wear acting as localized regions accumulating wear debris. The result shows that wear rate of all the coatings are lower as compared to MDN 321 substrate at all the test conditions. NiCrAlY/WC-Co/Cenosphere/MoS2/CaF2 and NiCrAlY/WC-Co/Cenosphere/MoS/CaSO4 coatings registered lower friction coefficient as compared to NiCrAlY/WC-Co/Cenosphere coating and MDN 321 substrate. Characterization of the NiCrAlY/WC-Co/Cenosphere/MoS2/CaF2 and NiCrAlY/WC-Co/Cenosphere/MoS2/CaSO4 coatings worn out surface suggests that MoS2 provides lubrication at 200 °C and formation of CaMoO4, MoO3 through tribo chemistry reaction at higher temperature provides lubrication at 600 °C. SEM micrograph of worn surface demonstrates that the main wear mechanism is plowing and delamination. © 2018 Elsevier B.V.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 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 Elevated temperature wear and friction performance of WC-CoCr/Mo and WC-Co/NiCr/Mo coated Ti-6Al-4V alloy(Elsevier Inc., 2024) Behera, N.; Ramesh, M.R.; Rahman, M.R.The effect of adding Mo to WC-based coatings on the microstructure and dry sliding wear performance at elevated temperatures is investigated. The WC-based coatings are deposited using a high-velocity oxy-fuel process on the titanium-31 substrate. The coating was characterized by microstructure, microhardness, porosity, surface roughness, density, and bond strength. The wear and friction behavior of coatings was evaluated using a ball-on disc tribometer at temperatures of 200, 400, 600, and 800 °C and loads of 20 and 30 N. SEM-EDS and an optical profilometer were utilized to evaluate the wear rate and mechanism. The microhardness and bond strength of WC-CoCr/10%Mo coating is more than that of WC-Co/20%NiCr/10%Mo coatings. The WC-CoCr, WC-CoCr/10%Mo, and WC-Co/20%NiCr/10%Mo coatings exhibited decreasing wear rates up to 600 °C, transitioning to an increase at 800 °C. The oxide phases of CoWO4 WO3 MoO3, CoMoO4, and NiMoO4, formed at 600 °C, aid in reducing the rate of wear and friction coefficient. However, the wear rate slightly increased at 800 °C due to vigorous oxidation and softness of coatings. The friction coefficient of WC-CoCr, WC-CoCr/10%Mo, and WC-Co/20%NiCr/10%Mo coating decreases with increasing temperatures due to the lubricating properties of oxide phases on the worn surface. The WC-CoCr/10%Mo coating demonstrates a lower friction and wear rate than the WC-CoCr and WC-Co/20%NiCr/10%Mo coating. At 200 °C, the predominant wear mechanisms were abrasive and fatigue wear, while at 800 °C, oxidative wear, abrasive wear, and adhesive wear were observed. © 2024Item Effect of molybdenum on high-temperature tribological performance in HVOF sprayed of WC-based coatings on superni-76(SAGE Publications Ltd, 2025) Behera, N.; Sarmah, P.; Chandramouli, T.V.; Ramesh, M.R.This study examines the effects of Mo on the high-temperature wear and friction behavior of HVOF-sprayed 70%WC-Co/25%Mo/5%C and 70%WC-CrC-Ni/30%Mo coatings on Superni-76. The ball-on-disc tribometer wear tests were conducted at different temperatures (300°C and 600°C) and loads (10 and 30?N) against counter body Al2O3 ball. Microstructures and phase formation were investigated using SEM/EDS and XRD. The characterization of coating microhardness, surface roughness, and coating density was examined. The 70%WC-Co/25%Mo/5%C coating showed lower surface roughness and higher microhardness values than the 70%WC-CrC-Ni/30%Mo coating. The wear rate of the substrate increases with an increase in temperature, whereas 70%WC-Co/25%Mo/5%C and 70%WC-CrC-Ni/30%Mo coatings decrease with temperature from 300°C to 600°C. The coefficient of friction of substrate and coating decreases with increasing temperatures. The worn surfaces of 70%WC-Co/25%Mo/5%C and 70%WC-CrC-Ni/30%Mo coating contain oxide phases (WO3, Cr2O5) and lubrication phases (M0.2W0.8O3, CoMoO4, and MoO3) at 600°C. These oxide phases reduced the coating wear rate and coefficient of friction at 600°C. The 70%WC-Co/25%Mo/5%C coating showed improved resistance to wear and lower friction coefficient than the substrate and 70%WC-CrC-Ni/30%Mo coating. At temperatures of 300°C, the main abrasive wear mechanism changes to oxidative wear when the temperature reaches 600°C for both coatings. © The Author(s) 2025.