Faculty Publications

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Author: search.filters.author.Bontha, S.Subject: search.filters.subject.Brinell Hardness

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    Effect of surface remelting on the characteristics of IN718 components fabricated using laser powder directed energy deposition
    (Institute of Physics, 2024) Thanumoorthy, R.S.; Jadhav, S.V.; Oyyaravelu, R.; Bontha, S.; Balan, A.A.S.
    Laser Powder Directed Energy Deposition (LP-DED) fabricated components exhibit poor surface finish, necessitating additional post-processing steps prior to their practical application. Enhancing the surface quality of additively manufactured IN718 specimens through conventional post-processing methods is particularly challenging, given the material’s poor machinability and the complexity of the fabricated components. The current study is centered on comprehending the impact of Laser Surface Remelting (LSR) on the surface properties of Laser Powder Directed Energy Deposited (LP-DED) IN718 material. To gain insights into how remelting influences surface characteristics, remelting was carried out using various sets of parameters. The remelted zone exhibited a refined grain structure, leading to increased hardness. Moreover, significant reductions in surface roughness and residual stress were observed in the remelted samples. Regression analysis indicated that laser power played a pivotal role, with positive impact on surface finish and depth of influence but a negative impact on residual stress and hardness. Therefore, considering all the comparison metrics, remelting using laser power of 150 W and a scan speed of 1140 mm min−1 were found to yield optimal surface conditions. © 2024 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.
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    The influence of laser direct energy deposition processing parameters on Al7075 alloy and Zr-modified Al7075 alloy
    (Springer Science and Business Media Deutschland GmbH, 2024) Balla, S.K.; Mallaiah, M.; Nagamuthu, S.; Gurugubelli, R.C.; Aranas, C.; Bontha, S.
    The Laser Directed Energy Deposition (LDED) technique in metal additive manufacturing (MAM) offers intricate geometries while maintaining material properties akin to cast and wrought components. However, challenges persist in fabricating high-strength aluminum alloys like 2xxx, 6xxx, and 7xxx series due to hot cracking during rapid solidification in LDED. This study addresses Al7075 hot cracking issue by introducing 1 wt% Zr. To evaluate this novel approach, the influence of process parameters on track geometry, porosity, microstructure, hardness, and tensile properties of both Al7075 and modified Al7075 (with 1 wt% Zr) was examined using an L27 orthogonal array of experiments. Findings indicate that increased laser power widens bead width and wetting angle. Conversely, higher scan speeds reduce bead height but marginally increase width, impacting wetting angle. Notably, the addition of Zr decreased porosity from 0.07 to 0.032%, indicating enhanced material quality. Microstructural analysis reveals Zr’s role in preventing solidification cracking by enhancing molten metal fluidity during solidification, transitioning the microstructure from columnar to equiaxed fine grain due to Al3Zr precipitates, and promoting grain refinement. This addition of Zr also improved hardness and tensile strength by 11% and 10%, respectively, attributed to Al3Zr precipitates’ role in grain refinement and precipitation strengthening within Al7075. In summary, incorporating 1 wt% Zr into Al7075 via LDED demonstrates promising improvements in microstructure, reducing porosity, enhancing mechanical properties, and mitigating solidification cracking, thereby offering potential enhancements in the fabrication of high-strength aluminum alloys. © The Author(s), under exclusive licence to Springer-Verlag London Ltd., part of Springer Nature 2024.
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    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.