Faculty Publications
Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736
Publications by NITK Faculty
Browse
7 results
Search Results
Item 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 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 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 Improving Surface Finish of Laser Additively Manufactured Curvilinear Surfaces Via Electropolishing and Electroless Coating(American Society of Mechanical Engineers (ASME), 2025) Praharaj, A.K.; Kambikath, N.V.; Suvin, P.S.; Bontha, S.Laser-directed energy deposition (LDED) is a very useful additive manufacturing technique for repairing and manufacturing complex-shaped parts compared to traditional manufacturing techniques. However, the inadequate surface quality of the LDED fabricated components limits their direct utilization in different sectors. In addition, improving the surface finish of the curvilinear surfaces (useful for cooling channels and fuel nozzles) is also challenging. Hence, the current study focuses on surface modification of LDED fabricated SS 316L hollow cylindrical samples by combining electropolishing and electroless coating. We have performed electropolishing (two different currents, 8 A and 15 A) on the as-deposited (AD) sample with and without the application of the grinding process. The electropolishing reduced the roughness of the AD sample from 3.2 ?m to 0.85 ?m and 0.74 ?m for 8 A and 15 A, respectively. The reduction in roughness was more at a higher current value due to the rapid anodic dissolution of the surface peaks. A further reduction in roughness was observed when grinding was performed before electropolishing. However, grinding resulted in higher material removal from the deposited surfaces and reduction in roughness was also minimal. Hence, only the electropolishing sample was selected for the next step, in which Ni-P electroless coating was performed on the surface to form a protective layer. After electroless coating, the coefficient of friction and wear-rate were reduced by 9.5% and 25.6% compared to the AD sample. Delamination and severe plastic deformation were the major wear mechanisms for the AD sample, whereas abrasion was dominant for the coated sample. The current work proposes a combined surface modification approach of electropolishing and electroless coating for the LDED processed components with curvilinear surfaces. © © 2024 by ASME.Item 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.Item Mechanical and chemical post-treatments for enhancement in tribological performance of laser powder directed energy deposited Inconel 625(Elsevier B.V., 2025) Praharaj, A.K.; Byregowda, T.; Bontha, S.; Suvin, P.S.Laser powder-directed energy deposition (LP-DED) technique has shown tremendous potential to fabricate high-performance superalloy parts for real engineering applications. However, certain disadvantages like poor surface quality and incompetent mechanical and wear properties limit its practical usage. Hence, the current work investigates the effect of different post-processing techniques, including laser shock peening (single shot) (LSP1), laser shock peening (three shots) (LSP2), shot peening (high pressure) (SP1), shot peening (low pressure) (SP2), glass bead blasting (GB), sand blasting (SB), and electroless coating (EC) on the surface quality, hardness, and wear resistance of Inconel 625 (IN625) samples fabricated by LP-DED technique. EC sample resulted in the least surface roughness value (0.09 µm), whereas LSP2 sample exhibited the highest increase of 32.4 % in hardness compared to the as-polished (AP) sample. This can be attributed to grain refinement and the plastic deformation in the samples. Further, the wear test confirmed that LSP2 sample resulted in the lowest coefficient of friction (0.6) and wear rate (0.58 × 10-4 mm3/N.m) among the post-processed samples. © 2025 Elsevier B.V.