Faculty Publications

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Author: search.filters.author.Balla, V.K.Subject: search.filters.subject.Directed energy

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Now showing 1 - 6 of 6
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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
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    Laser directed energy deposited Ti-48Al-2Cr-2Nb alloy: An investigation of high temperature oxidation behavior
    (Elsevier B.V., 2024) Gurugubelli, R.C.; Balla, V.K.; Rajasekaran, B.; Krishna, P.; Bontha, S.
    This study investigates high-temperature oxidation behavior and kinetics of Laser Directed Energy Deposited (LDED) Ti-48Al-2Cr-2Nb (Ti-48-2-2) alloy at 750 °C, 850 °C, and 950 °C, for 30, 60 and 100 h. Results reveal that the oxide-scale consists of alternating bands of TiO2 and Al2O3 and its stability is strongly dependent on the oxidation temperature and duration. At 850 °C and 950 °C, the oxide-scale delaminated following 100-h exposure. LDED Ti-48-2-2 exhibited an oxidation rate constant of 0.984 mg2 cm−4 h−1 at 850 °C (100 h) and 2.09 mg2 cm−4 h−1 at 950 °C (100 h), and an activation energy of 83.7 kJ mol−1 (850°–950 °C). LDED Ti-48-2-2 exhibited poor oxidation resistance compared to conventionally processed Ƴ-TiAl alloys. This can be attributed to the absence of N-rich layer and the typical nano-scale α2/γ banded lamellar microstructure observed in other processing routes. Post-process heat treatments can be utilized to obtain the desired microstructural features. © 2024 Elsevier B.V.
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    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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    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 Ltd
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    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.
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    Investigation of high-temperature oxidation behavior of Ti-48Al-2Cr-2Nb fabricated using electron beam powder bed fusion and feature added with laser directed energy deposition
    (Elsevier B.V., 2025) Gurugubelli, R.C.; Balla, V.K.; Krishna, P.; Bontha, S.
    This study investigates the microstructure and high-temperature oxidation behavior of Ti-48Al-2Cr-2Nb (Ti-4822) alloy at 950°C processed using Electron Beam Powder Bed Fusion (EB-PBF) with feature addition using Laser Directed Energy Deposition (LDED). The EB-PBF substrates in As-Built (AB) and EB-PBF + Hot Isostatic Pressing (HIP) conditions were used for feature addition using LDED. Oxidation studies revealed oxide scales mainly comprising alternating bands of TiO2 and Al2O3. The oxidation rate constant of AB + LDED samples was 1.223 mg2 cm?4 h?1 and AB+ HIP + LDED samples was 0.874 mg2 cm?4 h?1. The oxide scale thickness on the LDED-feature side was higher than that observed on the AB, /AB + HIP side (of the AB+LDED, AB+HIP+LDED) samples suggesting their poor oxidation resistance. This can be attributed to the ultra-fine massive-like ?-TiAl microstructure in LDED compared to the nano-sized ?2/? lamellae seen in EB-PBF (AB/ AB+HIP). Delamination and spallation of the oxide scale were observed at the interface between the substrate and LDED feature owing to the difference in oxide-scale growth rates and the presence of ?2-Ti3Al. © 2025 Elsevier B.V.