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 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 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.