Faculty Publications

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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
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.
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.

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