Browsing by Author "Paul, C.P."

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An Improved Finite Element Based Approach to Predict Single Track Geometry During Laser Directed Energy Deposition
(Springer Science and Business Media Deutschland GmbH, 2025) Chaurasia, J.K.; Gurugubelli, R.C.; Jinoop, A.N.; Bontha, S.; Paul, C.P.; Bindra, K.S.
This paper reports development of a two-dimensional transient finite element based numerical model to predict dimensions of deposited single track during laser directed energy deposition (LDED) of Inconel 625 (IN625) superalloys. The numerical model in the paper is based on two steps where first melt pool dimensions are determined using a transient thermal simulation. The second step accounts for the material addition, where the elements are activated based on the calculation of excess enthalpy. The numerical model is based on the fundamental principles of energy and mass balance. The numerical model also incorporates the fluid dynamics effects by multiplying the correction factor to the thermal conductivity of the material above melting temperature and also compares the track dimensions without considering the correction factor. A comparison of the track height and width obtained from the numerical model at Cfâ€‰=â€‰1 and 2.5 with experimental measurements was done. The maximum absolute percentage error in the numerical model considering the fluid dynamics effects (Cfâ€‰=â€‰2.5) is 5% in track height and 9% in track width. The percentage errors in the case of numerical model without fluid dynamics effects (Cfâ€‰=â€‰1) is 13% in track height and 16% in track width. The numerical model without considering the fluid dynamics effect is found to overpredict the track dimensions in all the cases. Â© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2025.
Development of thick SiC coating on thin wall tube of zircaloy-4 using laser based directed energy deposition technique
(Elsevier B.V., 2020) Rai, A.K.; Srinivasulu, B.; Paul, C.P.; Singh, R.; Rai, S.K.; Mishra, G.K.; Bontha, S.; Bindra, K.S.
In the present study, optimization of various laser-processing parameters for the deposition of thick SiC coating on zircaloy-4 (Zry-4) tube is studied in view of the development of accident tolerant fuel clad material for current and future nuclear reactors with the enhanced safety. The SiC coatings are deposited using laser directed energy deposition (LDED). It is found to be quite challenging to deposit desired SiC coating on a thin (~400 ?m) substrate of Zry-4 tubes due to either its excessive melting or damage. This is minimized largely by cooling the tube from inside by passing Ar gas (20 l min?1). It is observed that different processing parameters play a vital role on homogeneity, uniformity and defects-free SiC coatings as well as on the melting and oxidation of Zry-4 substrate. A uniform and homogeneous coating of SiC is deposited on Zry-4 at the optimized laser power density of 4.52 kW cm?2, powder feed rate of 2.71 g min?1and scan speed of 325 mm min?1. The interface between SiC coatings and substrate is characterized using different techniques such as optical microscopy, scanning electron microscopy and X-ray diffraction to access the homogeneity, uniformity, defects and to identify the different phases formed in the coated layer. Coated layer is found to be consisting of Zr(?), SiC, ZrSi2, ZrSi and ZrC types of phases and the same is also confirmed by the ThermoCalc(R) based ternary phase diagram. Further, the effect of processing parameters on substrate melting and the nature of SiC coating is explained by simulating the substrate temperature using COMSOL@ multi-physics. To the author's best knowledge, this would be the first study to report the laser directed energy deposition of SiC on Zry-4 alloy. © 2020 Elsevier B.V.
Effect of deposition strategy and post processing on microstructure and mechanical properties of serviced Inconel 625 parts repaired using laser directed energy deposition
(Elsevier Ltd, 2024) Chaurasia, J.K.; Jinoop, A.N.; Paul, C.P.; Bindra, K.S.; Balla, V.K.; Bontha, S.
In the present work, an attempt is made to understand and explore the repair capabilities of the Laser Directed Energy Deposition (LDED) process on Nickel based superalloy Inconel 625 (IN625). Samples were extracted from a wrought plate of IN625 and then were subjected to a fatigue test to mimic a component in service for repairing. Further, deposition was carried out on these fatigued tensile sample surfaces i.e., Top, Top & bottom, One side and Both sides. The samples were also solution-treated at 1200 °C for 90 mins. Microstructure and mechanical properties were evaluated and then compared between the different deposition strategies and sample heat-treatment conditions. Tensile properties were compared for all the three sample conditions viz. wrought alloy, as repaired and solution treated. Results indicate sound deposition with minimal porosity in all the four deposition strategies using the LDED process with a mean deposit height of 1.02 ± 0.25 mm. Microstructural analysis revealed mixed dendrite and columnar structure in the case of as-deposited samples whereas, solution treated samples exhibited recrystallized equiaxed grains with the presence of annealing twins. The as-deposited samples show a ductile mode of failure with a maximum ultimate strength of 830 MPa, yield strength of 350 MPa and elongation of 72%. For solution treated samples, a maximum ultimate tensile strength of 620 MPa, yield strength of 270 MPa and elongation of 73% were observed. The strength of the material was found to be highly influenced by the solution treatment. © 2023 Elsevier Ltd
Effect of Heat Treatment on Microstructure and Dry Sliding Wear Behavior of Laser Directed Energy Deposited Inconel 625
(Springer, 2025) Praharaj, A.K.; Chaurasia, J.K.; Suvin, P.S.; Narayanan, J.A.; Paul, C.P.; Balla, V.K.; Chakrapani, S.K.; Bontha, S.
Laser directed energy deposition (LDED) is a promising technology for manufacturing and repair of Inconel 625 (IN625) components used in critical sectors requiring enhanced tribological performance due to harsh operating environments. Hence, the current work focuses on the evaluation of the tribological performance of LDED-built IN625 with the implementation of different heat treatment methods, i.e., solution treatment (ST), direct aging (AG), and solution treatment + aging (ST + AG). A detailed microstructural analysis, hardness, and wear testing were performed for the as-deposited (AD) and heat-treated (HT) samples, and the results were compared. The analysis revealed coarser grains in the case of ST and ST + AG samples, whereas finer grains for AD and AG samples, indicating grain coarsening after solution treatment. Further, the brittle laves phase gets dissolved after ST, whereas the AG and ST + AG samples resulted in the precipitation of metal carbides and strengthening phases. The microhardness of the ST sample (193.2 HV) was lower compared to the AD (211.6 HV) sample, whereas the AG and ST + AG samples exhibited 25.6 and 9.3% higher hardness than the AD sample. Considering tribological performance, the AG sample illustrated a maximum reduction of 61.4% in the coefficient of friction (COF) and 36.5% in wear rate when compared to the AD sample. This could be attributed to the presence of finer grains and strengthening phases. © ASM International 2025.
Effect of Surface Modification on Erosion Behavior of Alumina-Samarium Strontium Aluminate Composite Thermal Barrier Coatings
(Springer, 2025) James J, F.; Arya, S.B.; Yadav, S.; Paul, C.P.
The mechanical and tribological characteristics of a thermal barrier coating are highly critical in gas turbine applications to resist high-temperature oxidation, corrosion, and solid particle erosion. In the present investigation, a composite coating with alumina and samarium strontium aluminate has been developed through a plasma spraying process. The as-coated composite top coat consisted of three phases ?-alumina, ?-alumina, and Sm2SrAl2O7. The as-coated surface is re-engineered with an Nd: YAG fiber laser to improve the mechanical and microstructural properties. The laser-treated samples showed a better erosion resistance than the as-coated samples. Despite the surface treatment, both the as-coated and the laser-treated samples showed a higher ‘average erosion value’ at an impact angle of 90° for the test temperatures of 200 and 800 °C. In addition, the as-coated and the laser-treated samples have a higher erosion rate at 800 than at 200 °C for the selected impact angles, with a mixed mode of material removal presenting both ductile and brittle failure mechanisms. © ASM International 2024.
Elucidating Corrosion Behavior of Hastelloy-X Built Using Laser Directed Energy Deposition-Based Additive Manufacturing in Acidic Environments
(Springer Science and Business Media Deutschland GmbH, 2021) Diljith, P.K.; Jinoop, A.N.; Paul, C.P.; Krishna, P.; Bontha, S.; Bindra, K.S.
This paper reports an investigation on the electrochemical corrosion behavior of laser directed energy deposition (LDED)-based additive manufacturing built Hastelloy-X (Hast-X) bulk samples for the first time in various acidic environments (2M HNO3, 2M HCl, and 2M H2SO4). Open-circuit potential results reveal that corrosion activity is more in HCl than the other two media. The corrosion rate (CR) estimated using the Tafel extrapolation method shows that the corrosion rate (CR) is the most in HCl and least in HNO3. Potentiodynamic studies reveal activeâ€“passive behavior of Hast-X in all the media and it is seen that the material stays in passivation for a longer potential range in HCl. Further, pitting potential is observed to be comparable in all three media. The cyclic polarization curve shows no loops, which points out the absence of pitting in the samples immersed in any of the media. The estimated CR for Hast-X in all the acidic environments under investigation comes within the acceptable CR for nickel-based alloys (4Â mpy). The morphology of the corroded surface is analyzed using stereo microscope and it confirms the absence of pitting in all the three samples. These observations confirm the suitability of LDED built Hast-X components for applications in investigated acidic environments. Â© 2021, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.
Experimental investigations on the milling characteristics of Cu alloys and additively manufactured CuCrZr
(Institute for Problems in Mechanical Engineering, Russian Academy of Sciences, 2025) Mundla, S.R.; Vendan, S.A.; Paul, C.P.; Shettigar, A.K.; Jambagi, S.C.
Copper is one of the widely used materials in various fields such as automotive, electronics, aviation, etc. The inherent property of copper makes it useful in wide variety of applications. The features on different components using the copper material can be made using different manufacturing techniques. However, post processing is one of the inevitable steps in any manufacturing process. Machining is one of the widely used post processing. There are multiple varieties of milling process. Among them, end milling process is widely used for making the slots. Three important process parameters in end milling process are depth of cut, cutting rate and feed rate. In this experimental approach, the copper is subjected to end milling operation by varying the aforementioned input parameters. In this fast-moving world, any manufacturing industry aims to produce the features with good dimensional accuracy with minimal amount of tool wear. Hence, the output responses selected are surface roughness and the tool wear. This research investigates the machining behavior of pure copper (Cu) and additively produced CuCrZr alloys to assess how fabrication methods affect processability. Pure copper, recognized for exceptional thermal / electrical conductivity, is compared against additively manufactured CuCrZr, which retains copper’s advantages while offering improved strength and wear resistance through alloy composition. During the milling process the following parameters such surface quality, cutting forces, tool degradation, and removal rates are reviewed through proper analysis. Compared to commercial copper, CuCrZr is more difficult to machine because it requires precise control over machining parameters to attain superior surface quality during milling. It is found that the CS and FR parameters balance material removal rate while controlling surface quality in both materials. As–built CuCrZr finds demand in high–performance applications such as heat exchangers, rocket engine components, and electrical contacts wherein strength, excellent thermal conductivity and additive manufacturability are critical. © S.R. Mundla, S. Arungalai Vendan, P. Paul, A.K. Shettigar, S.C. Jambagi, 2025.
Study of melt pool geometry and solidification microstructure during laser surface melting of Inconel 625 alloy
(Elsevier GmbH, 2021) Chaurasia, J.K.; Jinoop, A.N.; P, P.; Paul, C.P.; Bindra, K.S.; Bontha, S.
The present study aims to comprehend thermo-fluid conditions during laser surface melting (LSM) of Inconel 625 (IN625) alloy using experimental and numerical modelling approaches. Nine tracks were melted on an IN625 plate at different laser powers and scan speeds. Melt pool geometry and grain morphology were evaluated using microscopy techniques. A 3-D finite volume model based on heat conduction solidification equation (HCS model) was used to simulate LSM process. Further, HCS model was expanded to include effects of fluid dynamics (HCS-FD model). Both the numerical models were used to predict melt pool geometry, peak temperatures, temperature gradients and cooling rates. The error in predictions of melt pool geometry from the HCS-FD model was lower when compared to the HCS model. The velocity vectors show a strong surface tension driven flow which has resulted in narrow and deeper melt pools in agreement with the cross sectional images of the melted tracks. Further, solidification characteristics were interpreted to obtain inferences about grain size and morphology. © 2021 Elsevier GmbH
Understanding the corrosion behaviour of laser directed energy deposition-based additive manufacturing built Inconel 718 under acidic environments
(Springer Science and Business Media Deutschland GmbH, 2021) Diljith, P.K.; Jinoop, A.N.; Paul, C.P.; Krishna, P.; Bontha, S.; Bindra, K.S.
This paper presents an investigation on the electrochemical corrosion behaviour of Laser Directed Energy Deposition (LDED)-based additive manufacturing built Inconel 718 (IN718) for the first time in various acidic environments (2 M HNO3, 2 M HCl and 2 M H2SO4). Open circuit potential reveals that corrosion is more active in HCl, and Tafel extrapolation shows that the corrosion rate (CR) is maximum in HCl and minimum in HNO3. Potentiodynamic polarization studies conducted on the samples reveal active–passive behaviour of IN718 and show that pitting potential is maximum in HCl. Cyclic polarization studies reveal localized pitting behaviour in HCl, with no signs of pitting corrosion in HNO3 and H2SO4, which is further confirmed using Scanning Electron Microscopy. The estimated CR for IN718 is lower than the acceptable CR for nickel-based alloys (4 mpy) in all acidic environments under investigation. The study paves the way for potential deployment of LDED built IN718 components under various corrosive environments. © 2021, The Author(s), under exclusive licence to Springer Nature Switzerland AG.