Faculty Publications

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    Tribological Performance of Fe-Based Composite Coatings Under Elevated Temperature Conditions
    (Springer, 2025) Chandramouli, T.V.; Joladarashi, S.; Ramesh, M.R.
    The present study investigated the tribological performance of Fe-based coatings reinforced with carbides onto a maraging steel substrate using the HVOF spray technique. These materials are widely used in manufacturing various components in the aerospace and energy sectors. Commercially available SS316L and 17-4PH are reinforced with WC–Co feedstock powders to deposit these composite coatings on maraging steel substrate. The dry sliding wear tests were conducted using the ball-on-disc tribometer at varying temperatures (25 and 300 °C) with 10 N normal load using an alumina ball (Al2O3) as the counter body. The study includes micro-hardness, porosity, density, bond strength, and surface roughness of the coatings. The samples subjected to wear testing were analyzed using SEM/EDS and XRD techniques, and the wear scar volume was measured using a 3D profilometer to calculate the volume metric loss. The wear rate of SS316L30%WC–Co is 64.46% lower than that of 17-4PH30%WC–Co at room temperature and 67.33% lower at 300 °C under a load of 10 N. At room temperature, the worn surface exhibited abrasive wear, while at 300 °C, adhesive wear and oxidative wear were observed owing to the formation of protective layers. Therefore, SS316L-30%WC–Co demonstrates superior wear resistance compared to 17-4PH-30%WC–Co and offers enhanced mechanical strength, particularly in challenging environments. The deposition of these coatings effectively protects the maraging steel substrate. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2025.
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    Corrosion Behaviour and Characterization of Thermal Sprayed Coating of Nickel Chromium Cermet on Low Carbon Steel
    (Elsevier Ltd, 2018) Amudha, A.; Shashikala, H.D.; Nagaraja, H.S.
    Corrosion is the major problem faced by Navy, especially when pumps, ship impellers and other components have to work in harsh environments like sea water. Therefore, high corrosion resistant metal ceramic matrix 75Cr3C2- 25 (NiCr) cermet has been one of the good choices for coating. In this study, we are discussing the HVOF (High Velocity Oxy Fuel) coating of 75Cr3C2-25(NiCr) on the low carbon steel substrate, IS 2062 grade B. The as coated samples were annealed at 600°C for 1 hour, 2hour and 3hours. The electrochemical tests were conducted for corrosion evaluation. Structural analysis was done by using X-Ray diffraction technique. Microstructure and thickness of the coating was studied using Scanning Electron Microscopy (SEM). Density measurement studies were done on as-coated and annealed coupons. © 2017 Elsevier Ltd.
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    Comparative investigation of HVOF and flame sprayed CoMoCrSi coating
    (American Institute of Physics Inc. subs@aip.org, 2020) Prasad, C.D.; Joladarashi, S.; Ramesh, M.R.
    Present studies deals with comparison of high velocity oxy fuel and flame spray coating process by developing CoMoCrSi (Tribaloy T400) coating on a titanium grade-15 substrate. Prior to coating, feedstock is processed to obtain higher fraction intermetallics through high energy ball milling technique under controlled atmosphere. Processed feedstock material is sprayed on a Ti-15 substrate through HVOF and Flame spray process. The coated specimens are subjected to metallurgical and mechanical characterization using optical microscope, scanning electron microscope, energy dispersive spectroscopy, x-ray diffraction, Vickers mico hardness tester and bond strength using pull off test method. HVOF sprayed coating exhibits superior properties compared to Flame sprayed coating in terms of surface roughness, porosity, micro hardness and adhesion strength. The detailed studies of two coating systems is discussed. © 2020 Author(s).
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    Hot Corrosion Behaviour of HVOF Sprayed (Cr3C2–35 % NiCr) + 5 % Si Coatings in the Presence of Na2SO4–60 % V2O5 at 700 °C
    (Springer, 2015) Somasundaram, B.; Kadoli, R.; Ramesh, M.R.
    The hot corrosion behavior of high velocity oxyfuel sprayed (Cr3C2–35 % NiCr) + 5 % Si coatings on three substrate alloys of SA213-T22, MDN-310 and Superfer 800 H was investigated. The as-sprayed coatings are characterized with respect to microstructure and mechanical properties. Thermocyclic hot corrosion studies were performed in a molten salt environment of Na2SO4–60 % V2O5 for 50 cycles at 700 °C. Thermogravimetric technique was used to establish the kinetics of hot corrosion of uncoated and coated steels. It was observed that the coated steel showed better hot corrosion resistance than the uncoated steels. The coated steels follow the parabolic rate law of oxidation and the parabolic rate constant values are appreciably lower in comparison to the uncoated steels. The coated steels showed slow oxidation kinetics which indicated that the reaction rate is diffusion limited. The oxides of Cr2O3 and SiO2 formed on the outermost surface of the coatings are found to be passive in the molten NaVO3 melt. © 2014, The Indian Institute of Metals - IIM.
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    Improving Hot Corrosion Resistance of Cobalt Based Superalloy (Superco-605) Using HVOF Sprayed Oxide Alloy Powder Coating
    (Springer India sanjiv.goswami@springer.co.in, 2015) Jegadeeswaran, N.; Bhat, K.U.; Ramesh, M.R.
    Superco-605 is a cobalt based superalloy used widely in the hot section of gas turbines. During their operation, they are exposed to high temperature and molten salt environment, causing damage to the component due to hot corrosion. In this investigation, Superco-605 alloy was coated using a fused oxide alloy powder, $$ 10\,\% {\text{Al}}_{ 2} {\text{O}}_{ 3} + {\text{CoCrAlTaY}} $$10%Al2O3+CoCrAlTaY , using high velocity oxy-fuel process. Coating thickness was in the range of 260–280 µm and it was lamellar in nature. Uncoated and coated samples were subjected to cyclic hot corrosion tests at 800 °C in presence of molten salt environment of $$ {\text{Na}}_{ 2} {\text{SO}}_{ 4}{+}50\% {\text{V}}_{ 2} {\text{O}}_{ 5} $$Na2SO4+50%V2O5. Resistance to hot corrosion was investigated using thermogravimetric analysis, visual observations, X-ray diffractometry, scanning electron microscopy and energy dispersive X-ray spectroscopy. Both samples developed an oxide scale at the top. The uncoated Superco-605 exhibited intense spalling during hot corrosion cycles. The oxide scale on the coated substrate was thin compared to total thickness of the coating. There was a chromium depleted region close to the oxide top scale. An alumina rich layer at the interface of coating-substrate prevents penetration of oxygen into the substrate material. Based on the experimental results, it is concluded that the fused oxide alloy powder is effective in reducing hot corrosion tendency of Superco-605 alloy. © 2015, The Indian Institute of Metals - IIM.
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    High temperature corrosion behaviour of HVOF sprayed WC-CrC-Ni coatings
    (Inderscience Publishers, 2016) Somasundaram, B.; Kadoli, R.; Ramesh, M.R.; RAMESH, C.S.
    The present work aims to study the hot corrosion resistance of high velocity oxy-fuel (HVOF) sprayed WC-CrC-Ni coating developed on three types of boiler tube materials such as SA213-T22, MDN-310 and Superfer 800 H steels. Hot corrosion studies were conducted in a molten salt environment of Na2SO4-60%V2O5 at 700°C and thermogravimetric analysis was used to establish kinetics of corrosion. Corrosion kinetics of coated steels followed nearly parabolic behaviour and showed a lower corrosion rate in comparison to uncoated alloys. It is concluded that corrosion is restricted to the external surface of the coating and the formation of thick scale composed of oxides of Cr, Ni and their spinel oxides, acts as a diffusion barrier to the transportation of corrosive species into the coating. The carbides of tungsten and chromium uphold the strength of the coating. © © 2016 Inderscience Enterprises Ltd.
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    Erosion behaviour of HVOF sprayed (CR3C2-35%NICR) +5%Si coatings
    (IAEME Publication, 2017) Somasundaram, B.; Jegadeeswaran, N.; Madhu, G.; Ramesh, M.R.
    In the present study, (Cr3C2-35%NiCr) +5%Si cermet coatings were deposited on a Fe based T22 steel substrate to reduce the damage caused by erosion boiler applications. Erosion studies were conducted on uncoated as well as HVOF coated steels. The erosion experiments were carried out using an air-jet erosion test rig according to ASTM G-76 standard at a velocity of 30 m/s and at different impingement angles of 30°, 60° and 90°. Silica sand particles of size ranging between 150 to180 ?m were used as erodent. Analysis of weight-loss data and volumetric steady state erosion rates for different coatings and substrate alloys are evaluated. The bare T22 steel followed ductile erosion mode where as (Cr3C2-35%NiCr) +5%Si coating exhibited mixed behaviour respectively.
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    Influence of microwave hybrid heating on the sliding wear behaviour of HVOF sprayed CoMoCrSi coating
    (Institute of Physics Publishing helen.craven@iop.org, 2018) Prasad, C.D.; Joladarashi, S.; Ramesh, M.R.; Srinath, M.S.; Channabasappa, B.H.
    CoMoCrSi superalloy powder (Tribaloy-T400) consists of intermetallic laves phase and primary eutectic phase of Co-rich solid solution. Processing of Tribaloy-T400 powder is carried out through high-energy ball milling (HEBM) technique to obtain a higher volume fraction of intermetallic laves phases. The feedstock is sprayed using high-velocity-oxy-fuel (HVOF) process on titanium grade-15 substrate. The coating microstructure is homogenized by microwave hybrid heating technique. Characterization of feedstock, as-sprayed and microwave fused coatings is done by using Scanning Electron Microscopy (SEM), Energy dispersive spectroscopy (EDS) and x-ray Diffraction (XRD). Porosity, surface roughness, microhardness, and bond strength are measured. Adhesive wear behavior of the coatings under the dry sliding condition is evaluated at an applied load of l0 and 20 N and temperature of 200, 400 and 600 °C Fused coating exhibit higher wear resistance than the as-sprayed coatings and substrate. The hard intermetallic laves phases which are amorphous (bulk metallic glass) in nature strengthen the coating at high temperatures. © 2018 IOP Publishing Ltd.
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    Effect of microwave heating on microstructure and elevated temperature adhesive wear behavior of HVOF deposited CoMoCrSi-Cr3C2 coating
    (Elsevier B.V., 2019) Prasad, C.D.; Joladarashi, S.; Ramesh, M.R.; Srinath, M.S.; Channabasappa, B.H.
    This research reports the improvement of high-temperature sliding wear resistance of a grade 15 titanium alloy protected by an HVOF sprayed CoMoCrSi-Cr3C2 coating. The coatings have been tested in as-sprayed condition and after a post-deposition microwave heating step. The powder feedstock has been manufactured by high energy ball milling. X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) equipped with the Energy Dispersive Spectroscopy (EDS) methods were used for coatings characterization. Surface roughness, microhardness, adhesion strength, and porosity of coatings were also measured. The wear test was conducted at an applied load of l0 N and 20 N with varying temperatures of 200 °C, 400 °C, and 600 °C under dry sliding conditions. Co3Mo2Si, Co7Mo6, Mo3Si, Co3Mo, and Co2Mo3 were the intermetallic laves phases generated in the CoMoCrSi feedstock during HEBM process. The microwave-fused coating exhibited metallurgical bonding, homogeneous structure, less porosity, and greater hardness as compared to as-sprayed coating. Microwave-treated coating revealed better wear property than an as-sprayed coating. This was mainly due to the intermetallic formation and metallurgical bonding in coatings. The fused coatings exhibit tribo-oxide layers during sliding action which was the main phenomenon of improving the wear resistance of the fused composite coatings. © 2019 Elsevier B.V.
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    Comparison of Microstructural and Sliding Wear Resistance of HVOF Coated and Microwave Treated CoMoCrSi-WC + CrC + Ni and CoMoCrSi-WC + 12Co Composite Coatings Deposited on Titanium Substrate
    (Springer Science and Business Media B.V. editorial@springerplus.com, 2020) Prasad, C.D.; Joladarashi, S.; Ramesh, M.R.; Srinath, M.S.; Channabasappa, B.H.
    CoMoCrSi-WC + CrC + Ni and CoMoCrSi-WC + 12Co composite coatings are coated on titanium substrate by high velocity oxygen fuel method (HVOF). Prior to spraying, CoMoCrSi feedstock are processed through high energy ball milling (HEBM) in order improve the intermetallic laves phases and to reduce its particle size. The processed feedstock exhibits amorphous nature by improving laves phases and particle size of 60.12 ?m. Microwave heating energy is utilized as post heat treatment technique to improve the mechanical and metallurgical properties of as-sprayed coatings. Fused coatings reveals better properties in terms of surface roughness, porosity, microhardness and adhesion strength compared to as-sprayed coatings. Metallurgical bonding is observed in case of fused coatings due to diffusion of substrate elements. Frictional and wear behaviors have been investigated by a pin on disc apparatus at temperatures of 200 °C, 400 °C, and 600 °C under normal loads of 10 N and 20 N. Both wear trace and friction coefficients of the fused coatings are smaller than as-sprayed coatings and substrate at all test temperatures. The wear traces of fused coatings decreased with increasing the surface temperature due to the lubricant effect of cobalt oxides formed on the sliding surface. As a result, cobalt based cermet coatings are highly recommended as a durability improvement coating for the protection of sliding surface, such as high speed spindle. © 2020, Springer Nature B.V.