Faculty Publications
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Item Inconel 625 Coatings on AISI 304 Steel using Laser Cladding: Microstructure and Hardness(Dr D. Pylarinos, 2023) Vijeesh, V.P.; Ramesh, M.R.; Anoop, A.D.Nickel-base super alloys such as Inconel 625 are preferred in high-temperature and corrosive environments. Since Inconel 625 is expensive and often difficult to machine, it is advantageous to deposit a protective coating of this alloy on a less costly and easily machinable substrate material such as stainless steel. In the present work, coatings were produced on AISI 304 steel substrate by depositing Inconel 625 powder using the laser cladding technique. As-received powder particles of Inconel 625 alloy were characterized using X-Ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM). After laser cladding, it becomes important to carry out the microstructural analysis of the cross-sectional areas of the coating and the substrate/coating interface region, for further understanding of the structure-property correlations. In this study, the microstructural features of the coatings and substrate/coating interface were examined using an FESEM equipped with X-ray elemental analysis. The phase analysis of the coating was carried out using XRD. In the coating region, the growth of planar, cellular, columnar dendritic, and equiaxed grains was noticed. It was observed that small amounts of Laves phase were precipitated. Furthermore, the laser-clad Inconel 625 coating showed superior microhardness over the stainless steel substrate. © 2023, Dr D. Pylarinos. All rights reserved.Item Hybrid additive manufacturing of ER70S6 steel and Inconel 625: A study on microstructure and mechanical properties(Elsevier Ltd, 2023) Rodrigues, J.P.; Thanumoorthy, R.S.; Manjhi, S.K.; Sekar, P.; Arumuga Perumal, D.A.; Bontha, S.; Balan, A.S.S.Hybrid Additive Manufacturing (HAM) is currently being explored because of its potential to achieve trade-off between build capacity and feature resolution. The present study aims at fabricating ER70S6-Inconel 625 (IN625) bimetallic clad using hybrid Wire Arc Additive Manufacturing (WAAM) and Laser Directed Energy Deposition (LDED) processes. Microstructure evaluation was performed at the cross section of bimetallic clad for distinct materials as well as the interface. WAAM built ER70S6 revealed equiaxed ferritic grains, whereas laser deposited IN625 region showed columnar dendrites with under developed secondary arms. However, the first layer of IN625 exhibited columnar dendrite with secondary arms due to the influence of diffused Fe from the base ER70S6 steel under the action of concentrated laser heat source, which was revealed by energy dispersive spectroscopy (EDS) maps. The measured microhardness across the cross section of the deposit showed values corresponding to inherent material system. The interface did not reveal presence of any intermetallic phases which was confirmed by hardness results and X-Ray diffraction. Shear test revealed superior bond strength between the two materials, maintaining average strength of 452 MPa. The fractography images exhibited fine dimples along with cleavages indicating mixed fracture characteristics. This additive manufacturing method explores a new dimension in multi-material fabrication which, when customized for different materials, serve critical areas in the aerospace and defence sector. © 2023 Elsevier LtdItem 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 LtdItem Enhanced tribological performance of laser directed energy deposited Inconel 625 achieved through laser surface remelting(Elsevier B.V., 2024) Praharaj, A.K.; Chaurasia, J.K.; Gurugubelli, R.C.; Bontha, S.; Suvin, P.S.Inconel 625 (IN625) is an essential material for the manufacture of turbine blades and seals, aircraft ducting systems, engine components, and pressure valves. Laser Directed Energy Deposition (LDED) process has shown the potential to fabricate IN625 parts with superior mechanical properties and higher corrosion resistance when compared to those fabricated using conventional manufacturing techniques. However, the poor surface quality limits the practical application of LDED fabricated parts, especially in sectors that demand high tribological performance. To this end, this study focuses on improving the surface quality and tribological performance of LDED fabricated IN625 components using Laser Surface Remelting (LSR) as a postprocessing operation. The tribological performance was evaluated using a linear reciprocating ball-on-flat wear test setup. The surface roughness, remelting depth (RD), microstructure, hardness, and tribological performance (coefficient of friction and wear rate) of the remelted (RM) samples were compared with that of as-deposited (AD) samples. Microstructural characterization revealed that LSR resulted in grain refinement, reduced dendrite size, and primary dendritic arm spacing (PDAS). Laser scanning speed effects RD, dendrite size and PDAS via its effect on cooling rates. SEM + EDS analysis confirmed the presence of Laves phase in both AD and RM samples. XRD analysis of RM samples showed an increase in the amount of Laves phase. The refinement in microstructural features and the increased amount of Laves phase among the RM samples led to improvement in microhardness when compared to AD samples. Wear test results revealed a reduction in the coefficient of friction (COF) and wear rate after LSR with wear mechanism being either abrasive or delamination. Reduction in the size of dendrites and refinement in grain size are attributed to the enhanced tribological performance after LSR. © 2023 Elsevier B.V.Item Characterization of Inconel 625-SS 304 Weldments Developed by Selective Microwave Hybrid Joining Technique for Promising Applications(Springer, 2024) Kamble, D.L.; Sahu, R.K.; Narendranath, S.Production of dissimilar weldments using microwave hybrid heating is currently gaining immense impetus in the field of advanced welding. This is because such heat source could provide benefits like cost-effectiveness, rapid, volumetric, uniform and selective heating, and efficient throughput which would be significant to various industries. Till-date researchers have carried out joining of dissimilar general purpose engineering materials using microwave hybrid heat source. But attention has not been paid on the joining and characterization of dissimilar exotic-general purpose materials using the aforementioned heat source and the promising applications of the weldments. Therefore, the present article is focused on the joining of dissimilar materials- Inconel 625 and SS 304 alloys using selective microwave hybrid joining (SMHJ) technique. In SMHJ, nickel-based powder is used as a filler material, Silicon carbide (SiC) block and SiC powder are used as susceptor to increase the initial temperature. The developed weldments through SMHJ are characterized using various physico-chemical diagnostic methods. The results reveal the average micro-hardness of joint was found to be 303 ± 17 HV owing to the presence of various carbides and nitrides phase like NbC, Cr23C6, Cr2Ni3, Ni8Nb, and Fe3Ni2 in the joint zone which is evident from XRD. The average UTS of the joints found to be 448.6 MPa with an elongation of 10.93% and flexural strength observed to be 435 MPa. Further, fractography study reveals, the joint regions have mixed mode of failure. The failure was attributed to the existence of secondary phases in the joint zone. © ASM International 2023.Item 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.Item Tailoring the Microstructure and Mechanical Properties of Laser Powder-Directed Energy-Deposited Inconel 625 Using Scan Strategies(Springer, 2025) Aromal, S.S.; Malathesh, P.B.; Thanumoorthy, R.S.; Agasti, S.K.; Praharaj, A.K.; Anil Kumar, V.A.; Sudarshan Rao, G.S.; Bontha, S.The current study is focused on the influence of different scan strategies on the microstructural evolution, crystallographic texture, and mechanical properties of the Inconel 625 (IN625) fabricated using the laser powder-directed energy deposition (LP-DED) process. Prior to the deposition of the bulk specimens, an optimized set of process parameters (laser power (P), scan speed (v), and feed rate (f)) was selected through analysis of single-track deposits. The single tracks were thoroughly analyzed based on the aspect ratio, track stability, dilution, and shape of the melt pool. Further, six rectangular blocks of IN625 with different scan strategies (unidirectional ? 0°, bidirectional ? 0°, 45°, 67°, 90°, and spiral) were fabricated using the optimized process parameters for deposition. Samples with a 0° unidirectional scan strategy exhibited higher yield strength values but lower ductility. Notably, the sample with a scan orientation of 67° exhibited superior isotropic properties that are required to bear intense multi-axial loads when compared to other samples. The results indicated that the sample with a 67° scan orientation has the best combination of both strength and ductility. This can be attributed to finer cells/grains, which occur due to fragmentation of cells/grains during their growth across the successive layers, a higher fraction of low-angle grain boundaries (LAGBs), and variation of vector length within a layer. EBSD analysis revealed that samples with a 67° scan orientation exhibited a random crystallographic texture (MUD = 2.2), which suggests isotropic behavior compared to other samples. © ASM International 2025.Item Optimization of measured mechanical characteristics of selective microwave hybrid heating processed Inconel 625/ SS 304 weldments using multi-objective JAYA algorithm coupled with multi-attributes decision making R-method(Elsevier B.V., 2025) Singha, B.; Kamble, D.L.; Sahu, R.K.; Narendranath, S.; Badiger, R.I.This work focuses on the joining of Inconel-625/SS-304 using selective microwave hybrid heating (SMHH) technique. Input power, filler powder particle size, separator, and susceptor size are considered for experimentation according to the Definitive Screening Design. The multi-objectives measured are UTS, FS, and microhardness. XRD results show the intermetallic/secondary phases, and FESEM micrographs show the metallurgical bonding occurs between base metal and filler. The joint and interface region had an average microhardness of 204 ± 10 HV and 342 ± 18 HV, respectively. The UTS and FS of the weldments measured to 550 MPa and 805 MPa. MOJAYA technique is utilized for multi-objective optimization, and R-method determined the optimal process parameters. The optimal process parameters found to 2.2 kW, 25 ?m powder, 120 grit and 0.804 mm separator. The confirmation test reveals UTS ? 566 MPa, FS ? 903 MPa, and microhardness ? 365 HV, which closely matched with predicted observations. © 2024 Elsevier LtdItem Investigation on high-temperature tribological performance of laser directed energy deposited Inconel 625 for aerospace applications(Elsevier Ltd, 2025) Praharaj, A.K.; Bontha, S.; Balla, V.K.; Chakrapani, S.K.; Suvin, P.S.Laser directed energy deposition (LDED) is an emerging technique for fabricating superalloy based aero engine components. Hence, the current work investigates the tribological performance of LDED processed IN625 at room temperature (RT) and high temperature (HT) conditions of 850 °C to replicate the operating environment of aero engine components. The comparison with conventionally processed (CP) sample confirmed that as-deposited (AD) sample showed similar friction behavior to the CP sample but slightly improved wear performance. The COF and wear rate of AD sample reduced significantly at HT compared to RT due to the evolution of stable oxide layer. NiO, Fe2O3, and Cr2O3 were the major phases in oxide layer. The work indicates suitability of LDED to fabricate wear resistant surfaces. © 2024 Elsevier LtdItem Microstructure - corrosion performance correlation of laser directed energy deposited Inconel 625(Elsevier Ltd, 2025) Praharaj, A.K.; Bontha, S.; Balla, V.K.; Chakrapani, S.K.; Suvin, P.S.The primary objective of the current work is to understand the influence of process parameters on the corrosion performance of laser directed energy deposited Inconel 625 (IN625). In this regard, IN625 bulk samples were deposited using optimized laser power and three different scanning speeds. The as-deposited (AD) samples are named as AD-L, AD-M, and AD-H corresponding to low, medium, and high scanning speeds, respectively. Comprehensive microstructural characterization, microhardness evaluation, and electrochemical corrosion testing (medium: 3.5 wt% NaCl solution) were performed to correlate the process parameters with the microstructural features and corrosion performance. The results revealed that average grain size of the AD-H sample was lowered by 22.8 % and 19 %, respectively than the AD-L and AD-M samples, resulting in an enhancement of 8.4 % and 3.3 % in microhardness. Electrochemical corrosion tests indicated that AD-H sample possessed a higher corrosion potential (Ecorr) and a lower corrosion current density (Icorr) when compared to other samples, confirming the corrosion resistance of the samples in the order of AD-H > AD-M > AD-L. The higher scanning speed resulted in finer grains, high dislocation density, and lowered volume fraction of secondary phases, which are attributed to superior corrosion resistance of the AD-H sample. Surface analysis of the corroded samples suggested a greater susceptibility to localized corrosion over pitting corrosion. The current work provides valuable insights to the correlation between process parameters, microstructure, and corrosion performance of LDED fabricated IN625, confirming notable influence of scanning speed on the corrosion behavior. © 2025 Elsevier B.V.