Browsing by Author "Cadambi, S."

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An Assessment of Coating Thickness on the Microstructure and Mechanical Behavior of IN625 Coating on Ni-Based Superalloy Substrate Deposited by High Velocity Air Fuel Technique
(Springer, 2024) Prashanth, M.; Babu, N.; Kumari, S.; Maurya, S.S.; Keshri, A.K.; Cadambi, S.; Nand Gosvami, N.N.; Bhowmik, A.
High velocity air fuel (HVAF) technique, an innovative thermal spraying method, has proven more promising than traditional methods for both coating and repairing surfaces. This study focuses on the application of different thicknesses of IN625 superalloy coatings using HVAF to assess its potential for repair and cladding applications. Detailed coating characteristics of IN625 superalloy coating have been examined based on various techniques like nanoindentation, adhesion, micro-tensile and flexural strength of the coated samples. Within the coating, ? (NiCr rich), secondary peaks ?? and carbide phases were identified. Particle deformation under impact and rapid cooling resulting in the formation of ?? precipitates enhances the coating strength. However, the decrease in the adhesion strength with increasing coating thicknesses results from the defects formed at the coating–substrate interface and also influenced by thermal stresses and oxidation. Coating microstructure revealed a strong particle-to-substrate adhesion and varied splat morphologies dependent on degree of particle melting—at higher particle velocities in-flight oxidation of the powders was also minimal. Furthermore, the in-plane cohesive strength of the coating approaches 50% of the wrought alloy's yield strength, attributed to strain hardening from the peening effect. However, decrease in flexural strength as coating thickness increases due to compressive residual stress and coating delamination. The flexural strength of the as-sprayed coating exhibits up to 70% of the flexural strength of the wrought material with thicker coatings exhibiting lower strength. © ASM International 2024.
Determining the solidification characteristics of Manganese bronze (MAB) alloy using computer-aided cooling curve analysis
(Elsevier Ltd, 2022) Pranesh; Mohammed Anas, S.; Johnson, S.; Jose, R.; Sachin, B.; Cadambi, S.; Vijayan, V.; Karinka, S.
Computer-aided cooling curve analysis (CACCA), known for its reliability and simplicity was used to study the material properties of manganese bronze (MAB) alloy. MAB alloy, due to its high strength and corrosion resistance, is a staple material for marine applications. Since the alloy is difficult to machine, non-heat treatable, and complex to fabricate, casting is the only cost-effective process of producing products of the material. As the literature is scant on the MAB's high-temperature properties, this study is aimed at determining the thermo-physical properties of the alloy required for casting simulation by carrying out Newtonian and Fourier analysis of the recorded temperature of the solidifying alloy from liquidus state. Â© 2022 Elsevier Ltd. All rights reserved.
Effect of Humidity and Temperature on PVD TiAlN-Coating Wear
(Springer, 2025) Cadambi, S.; Dasari, B.P.; Jayaram, V.
Gas turbine blades and disks undergo wear at high temperatures at dovetail joints where tolerances are very small. Thin hard coatings are known to enhance the wear resistance of the superalloy components minimally influencing the tolerance levels. However, fundamental understanding of the coating’s wear mechanisms operating in these harsh conditions is not well understood. In this study, wear tests are performed to understand the wear mechanisms that operate in the temperature range from RT up to 800 °C for thin hard TiAlN coating using simple wear geometry eliminating any influence of wear debris. It is challenging to measure wear of thin hard coatings especially at elevated temperatures but important nevertheless. A coated ball on disk geometry with rough alumina as counterface is used for wear studies to understand exclusively the influence of humidity and temperature coating wear behavior. Cathodic arc evaporation, a physical vapor deposition technique is used to deposit TiAlN coatings on heat-treated IN718 substrates and characterized with, XRD, EPMA, TEM, SEM, nanoindentation, and FIB. The wear at room temperature shows scatter which has been ascribed to seasonal fluctuations in relative humidity. Further, wear results are shown to correlate with Young’s equation for capillary condensation. Wear below 50 pct RH is essentially dry and constant up to 600 °C above which wear increases marginally upto 800 °C. The coefficient of friction shows a maximum at 400 °C, below which friction reduces due to increased adsorption of water vapor, while above 400 °C, TiO2 forms on the surface to reduce the friction. The wear rate at 3 N load in the range of 50–800 °C is ~ 1 × 10?6 mm3/m/N. For 5 N load, the wear rate is same as for 3 N load upto 600 °C but doubles above 700 °C. The average contact pressure through the test is ~ 550 and 650 MPa which is almost twice the design contact pressure. The wear debris gets richer in Ti with increase in temperatures. The Al-rich TiAlN coatings deposited by cathodic arc evaporation (CAE) technique show a low and constant wear behavior over a wide range of temperatures and are ideally suited for the protecting the dovetail joints in gas turbines. © The Minerals, Metals & Materials Society and ASM International 2024.
Failure analysis of a fire water jockey pump shaft
(Elsevier Ltd, 2022) Padasale, B.; Kulkarni, G.S.; Rakshan Kumar, J.K.; Cadambi, S.; Hegde, S.R.
This work presents failure investigation of a fire water jockey pump shaft that is installed in the fire-station of a petrochemical plant. The jockey pump is driven by a 130 kW motor at about 1480 RPM whose shaft and the coupling key are made of 40C8 steel and 55C8 steel respectively. The drive-shaft of one of the pumps fractured after running for approximately 110 h, while its twin remained functional. The failure analysis involves visual inspection, hardness measurements, metallography, fractography, analytical design calculations, and numerical stress analysis. The analysis concludes that usage of square-ended key in the round-ended keyway is the primary cause, and usage of dissimilar materials for the shaft and the key is the secondary cause for the premature failure. The present work recommends a modified key design and use of the same grade of steel for both the shaft and the key to avoid such failures in the future. © 2022 Elsevier Ltd
Failure Analysis of Cooling Tower Fan-Arm
(Springer, 2020) Padasale, B.; Kumar, J.K.R.; Sondar, P.R.; Cadambi, S.; Hegde, S.R.
This work presents failure investigation of cooling tower fan-arms commissioned in a chemical processing plant. The analysis aims at understanding the mechanism and root-cause of the failure. The investigation involves site visits, microstructural analysis, fracture surface analysis, hardness measurements, numerical stress analysis and experimental simulation. Work concludes that the fan-arms failed due to the lack of post-weld heat treatment, which caused localized stress-corrosion and pitting at critical locations that served as crack initiation sites. Fatigue loading condition and presence of residual stresses at the weld enabled easy propagation of cracks that led to recurring premature failure. Based on the root-cause and the mechanism identified in this analysis, proper pre-heating and post-weld heat treatment is recommended to relieve the residual stresses at the critical locations and thus to avoid/minimize such recurring failures in future. © 2020, ASM International.
Failures Investigation of Marine Propellers in Corrosive Environments
(Springer Nature, 2021) Mirashi, V.U.; Johnson, S.; Hegde, S.; Vijayan, V.; Cadambi, S.
Marine corrosion failure of fishing boat propellers made of cast Nickel Aluminium Bronze were investigated. Specimens extracted from the corroded propellers were characterized by optical microscopy, scanning electron microscopy, and energy dispersive spectroscopy. The alloy comprises several Fe3Al (κ1, κ2, κ4), NiAl (κ3) type intermetallic precipitates and β’ martensite embedded in Cu-rich α-matrix. Transverse sections of the corroded region showed two distinct zones; a non-uniform top oxide layer and a partially corroded zone with selective corrosion of the β’ martensite which run parallel to the κ3 precipitates. From the microstructural analysis it is adjudged that the aggressive local corrosion of the matrix is preceded by cracking of the oxide by erosion, cavitation, etc., A slow growth of the oxide layer follows that reduces the corrosion rate. However, the corrosion cycle repeats on erosion or cracking of the oxide layer when the propeller is used in marine waters. Coupon specimens immersed in actual marine conditions is presented that supports the above theory. © 2021, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.
High Velocity Air Fuel Spraying for Surface Restoration of Worn-out IN718
(Springer, 2025) Sreerag, M.P.; Abhijith Vijay, V.; Babu, N.N.; Ali, S.S.; Cadambi, S.; Rajasekaran, B.
This study explores the efficacy of high velocity air fuel (HVAF) spraying for repairing worn-out IN718 thrust collars used in the chemical industry. We investigated the characteristics and application potential of thick IN718 depositions for surface restoration, focusing on their adhesion. To evaluate microstructure and adhesion, approximately 2-mm-thick IN718 layers were deposited onto IN718 wrought coupons. The HVAF-sprayed layers were notably dense (99.5%) and exhibited excellent hardness, reaching 450 HV0.3, which suggests superior mechanical properties compared to the bulk material. A three-point bending test was conducted to assess the adhesion strength of these thick deposits. The results demonstrated excellent adhesion in both compressive (1281 MPa with > 2% strain) and tensile bending. Trusting in these promising substrate-layer interfacial adhesion characteristics, the investigation was extended to demonstrate the refurbishment of an actual worn-out industrial IN718 thrust collar. A 2-mm-thick IN718 deposition was applied to the entire worn area, and excess material was subsequently machined to achieve the desired surface finish for reuse. Overall, HVAF spray technology shows significant promise for developing thick metallic layers with excellent interfacial adhesion, providing a robust and viable solution for effectively refurbishing heavily worn metallic components and extending their service life. © ASM International 2025.
Hot corrosion behaviour of HVAF coatings deposited on Fe[sbnd]25Cr[sbnd]20Ni support hanger material
(Elsevier B.V., 2024) Ramanathan, P.; Gandimani, L.; K, S.; Cadambi, S.; Hegde, S.R.
Fe[sbnd]25Cr[sbnd]20Ni cast alloy is used as the material of construction for support hangers in fired heaters of oil refineries. These hangers support heater tubes in the fired heaters and are susceptible to hot corrosion due to Na2SO4 and V2O5 containing corrosive ash, especially when low-grade fuels are burnt. API recommends 50Cr[sbnd]50Ni cast-alloy for constructing the support hangers in highly corrosive atmospheres which, is highly expensive as well as brittle. To overcome this problem, in this work, coatings of 50Cr[sbnd]50Ni and 20Cr[sbnd]80Ni were applied on Fe[sbnd]25Cr[sbnd]20Ni substrates by HVAF process. The coatings were characterized by: Optical Microscopy, SEM-EDS Analysis, XRD Analysis, and Raman Spectroscopy. To study the hot corrosion behaviour of these coated specimens, a cyclic hot-corrosion test was carried out at 700 °C using 20 % Na2SO4–80 % V2O5 salt slurry. Along with the coated specimens, cast specimens of Fe[sbnd]25Cr[sbnd]20Ni and 50Cr[sbnd]50Ni were also subjected to the hot-corrosion test. Thus, Type-II hot corrosion behaviour of all four specimens were analyzed comparatively by weight-change measurements, cross-sectional metallography, SEM-EDS, XRD, and Raman-Spectroscopy. The Fe[sbnd]25Cr[sbnd]20Ni cast specimen displayed the least corrosion resistance. The corrosion resistance of the 50Cr[sbnd]50Ni coated specimen and the 50Cr[sbnd]50Ni cast specimen was found to be intermediate and quite comparable. 20Cr[sbnd]80Ni coated specimen recorded the best corrosion resistance. The corrosion mechanism and beneficial effects of high nickel-containing HVAF coatings against hot corrosion are presented. © 2024 Elsevier B.V.
Hot corrosion behaviour of mullite thermal barrier coatings for marine diesel engines
(Elsevier Ltd, 2024) K, S.; Babu, N.; Cadambi, S.; Arya, S.B.
Mullite's inherent qualities have made it a potential material for the application of thermal barrier coatings (TBCs) for diesel engine components. Hot corrosion at 600–800 °C can cause TBC degradation, thus significantly affecting the performance of engine components and reducing their service life. This work examines the hot corrosion behaviour of atmospheric plasma-sprayed (APS) mullite coating over NiCrAlY bond coat on mild steel substrates. The coated specimen surface was covered with a mixture of Na2SO4 (sodium sulphate) and V2O5 (vanadium pentoxide) in the form of paste and heated in a muffle furnace at 700 °C for up to 300 h. SEM, EDS, and XRD characterisations were used to investigate the mechanism of hot corrosion. Coatings remained intact after corrosion tests; however, it had reacted with corrosive salts, particularly sodium sulphate. This was evidenced by the removal of amorphous silica, followed by the formation of nosean as a major phase. During the reaction between sodium sulphate and mullite coating, vanadium pentoxide was found to be acting as a flux and mineraliser. © 2023 Elsevier Ltd and Techna Group S.r.l.
Mechanical and Tribological Properties of High Velocity Air Fuel-Sprayed IN625 and IN718 Coatings
(Springer, 2025) Kumari, S.; Raj, S.; Babu, N.; Prashanth, M.; Junaid, S.; Cadambi, S.; Mondal, C.; Nand Gosvami, N.N.; Bhowmik, A.
This study explores the mechanical and tribological behavior of IN625 and IN718 coatings deposited on Ni-based IN718 alloy substrates using the high-velocity air fuel, HVAF technique. Microstructural analysis revealed that the IN625 coating exhibited more visible splats, weaker bonding, and a greater presence of unmelted and partially melted regions than IN718. Both IN625 and IN718 coatings retained the original constituent phases from the powder. The IN718 coating, however, demonstrated superior mechanical properties, with its hardness and adhesion strength surpassing those of IN625 by 56% and 30%, respectively. Notably, the adhesion strength was highest in a 0.5 mm thick IN718 coating, reaching 63 MPa. At room temperature, both the coatings had significant coefficient of friction (COF) values, while the wear volume loss for IN718 was reduced by 52% compared to IN625, although IN625 showed wider wear scars with more pits, deeper grooves, and peeling. IN718 formed a glaze layer, enhancing its wear resistance. These findings suggest that optimally thick IN718 HVAF coatings hold significant promise for improving performance in various repair and cladding applications. © ASM International 2025.
Microstructural, Mechanical, and Tribological Evaluation of HVAF-Sprayed Inconel 718 Coatings
(Springer, 2025) Babu, N.N.; Kumar, S.; Cadambi, S.
This study evaluates the mechanical and wear properties of IN718 coating on IN625 substrates deposited using the HVAF-spraying technique. The deposited coating was characterized by SEM, EDS, EBSD, Raman, nanoindentation, and microhardness. The integrity and adhesion of the coating were assessed using scratch tests aided by acoustic emission spectroscopy. The tribological evaluation was performed using a dry sliding wear test with a ball-on-coated disc configuration using alumina as the counterface. The coating microstructure comprises mostly unmelted particles with a small fraction of melted, with a porosity level < 1.5% and about 8.4% oxidation. Both the microhardness and nanoindentation show the anisotropy in the coating. The elastic modulus is at the same level as bulk IN718 when measured perpendicularly to the thickness direction, but it is lower when measured along the thickness. The average compressive stress of 608 MPa and the Bauschinger effect influence the anisotropy observed in the coatings. ISO 27307 scratch tests reveal that coatings have good cohesion and adhesion strength. Wear tests were performed at room temperature, 400 °C and 600 °C. The room temperature wear is high and abrasive, while the high-temperature wear was lower and determined to be oxidative. Porosity is detrimental to the abrasive wear at room temperatures, which leads to localized chipping. © ASM International 2025.
Synergistic effects of iron and hexagonal-Boron Nitride additions in copper-based composites for braking application
(SAGE Publications Ltd, 2022) Cadambi, S.; K, K.; Lamture, N.; Kale, S.S.; Prabhu, T.
This paper explores the addition of h-BN and iron to Cu-based brake pads on the performance benefits. It also investigates the effect of graded layering by synthesizing three and four-layer brake pads by powder compaction and sintering route. The top one or two layers are made of Cu-based composite containing Fe, h-BN, and W, while the middle layer is pure Cu and, bottom steel plate. Two different compositions were explored for the composites by varying Fe content. From the two composite compositions, brake pads with single-layer composite or two-layer composite were synthesized. Characterization of brake pad specimens was carried out using density measurements, optical microscopy, scanning electron microscopy, energy dispersive spectroscopy. The brake pads were subjected to simulated braking tests at braking energy/cycle of 60, 96, and 136 K Joules. Wear rate, coefficient of friction, stopping distance, stopping time, and hardness were measured and compared among other brake pads. The brake pad containing single-layer Fe rich Cu composite showed the best performance in the simulated braking tests. EDS analysis of wear debris shows the formation of iron (boride, nitride, oxide) complex which is indicative of a surface with superior dry lubricating properties. This surface is a result of synergetic interaction between h-BN and Fe particles. The iron particles which are scattered in the Cu matrix composite act as low friction regions on the brake pad surface that interrupt the high friction regions on the Cu matrix, thus reducing the local and bulk temperature rise. The two-layer composite brake-pad showed performance intermediate to the two single-layer brake pads. No advantage due to higher thermal conductivities in Fe deficient composite was observed as the two composite layers, showed similar Fe contents in their matrix phases. © IMechE 2021.