Browsing by Author "Gurugubelli, R.C."

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An Improved Finite Element Based Approach to Predict Single Track Geometry During Laser Directed Energy Deposition
(Springer Science and Business Media Deutschland GmbH, 2025) Chaurasia, J.K.; Gurugubelli, R.C.; Jinoop, A.N.; Bontha, S.; Paul, C.P.; Bindra, K.S.
This paper reports development of a two-dimensional transient finite element based numerical model to predict dimensions of deposited single track during laser directed energy deposition (LDED) of Inconel 625 (IN625) superalloys. The numerical model in the paper is based on two steps where first melt pool dimensions are determined using a transient thermal simulation. The second step accounts for the material addition, where the elements are activated based on the calculation of excess enthalpy. The numerical model is based on the fundamental principles of energy and mass balance. The numerical model also incorporates the fluid dynamics effects by multiplying the correction factor to the thermal conductivity of the material above melting temperature and also compares the track dimensions without considering the correction factor. A comparison of the track height and width obtained from the numerical model at Cfâ€‰=â€‰1 and 2.5 with experimental measurements was done. The maximum absolute percentage error in the numerical model considering the fluid dynamics effects (Cfâ€‰=â€‰2.5) is 5% in track height and 9% in track width. The percentage errors in the case of numerical model without fluid dynamics effects (Cfâ€‰=â€‰1) is 13% in track height and 16% in track width. The numerical model without considering the fluid dynamics effect is found to overpredict the track dimensions in all the cases. Â© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2025.
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.
Influence of bulk post processing techniques on anisotropy of microstructural and tribological properties of L-DED produced Ti64 alloy
(Elsevier Ltd, 2025) Suresh, S.; Joshy, J.; Kuriachen, B.; Gurugubelli, R.C.; Kumar, V.; Bontha, S.
Laser-Direct Energy Deposited (L-DED) Ti64 alloy is known to have high anisotropy, and low wear resistance which reduce the longevity of artificial bone joints. Thus, the primary objective of this study is to compare and contrast the effect of bulk treatments to mitigate these inherent limitations. Keeping printing parameters constant, the printed samples were put through different post-treatments, namely, super-? annealing (1050 °C, 1 h) and deep cryogenic dipping (?196 °C, 48 h). Electron back scatter diffraction (EBSD) and x-ray diffraction (XRD) analysis revealed differences in grain morphology and phase distributions in the treated samples. A linear reciprocating wear test is conducted with Al2O3 as the counter body to mimic the artificial hip socket. The super-? annealing process reduced the anisotropy in wear rate from 76 % to 60 % but did not show an overall betterment. On the other hand, the cryo-treatment showed an 83 % reduction in wear and a slight reduction in anisotropy compared to the as-build sample. The coefficient of friction (COF) plots also displayed an increase for annealed samples (15.4%–31.5 % higher) while showing a major reduction in cryo-treated samples (42.8%–54.7 % reduction). © 2025 Elsevier B.V.
Influence of Process Parameters on Microstructural Properties of L-DED Produced Ti64 Alloy
(Springer Science and Business Media Deutschland GmbH, 2025) Suresh, S.; Kuriachen, B.; Kumar, V.; Bontha, S.; Gurugubelli, R.C.
Additive manufacturing (AM) techniques have revolutionized the manufacturing of complex and customized parts across various applications. However, they are known for producing titanium parts with high anisotropy and low ductility, due to high cooling gradient in the build direction and the presence of martensite phase in microstructure respectively. These are inherent problems which limit their application in critical engineering fields. Laserâ€”Direct Energy Deposition (L-DED) produced parts also have the same disadvantages. Thus, the primary objective of this paper is to identify the optimal combination of process parameters for L-DED that can mitigate these inherent limitations. Keeping the parameters such as powder size, orientation angle and hatch angle as constant, the laser power and scan speed are varied to fabricate 9 different sets of samples using L-DED. The research methodology includes an analysis of the microstructure, focusing on grain width, phase distribution, lath characteristics and presence of defects, if any. Microscopy and XRD techniques were used to observe the microstructure. Additionally, hardness studies were performed to evaluate the changes in material hardness. It was noticed thatÂ laser power significantly influences Î² width and Î±â€™ length while scan speed has a lesser dominant effect on both of them. The findings will contribute to the development of process-structure-property relations for L-DED-produced Ti64 and further, optimized manufacturing strategies for producing titanium parts with reduced anisotropy and increased ductility. Â© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2025.
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.
Isothermal oxidation behavior of As-deposited and HIPed Ti-48Al-2Cr-2Nb alloy processed using Electron Beam Powder Bed Fusion
(Elsevier Ltd, 2025) Gurugubelli, R.C.; Balla, V.K.; Rajasekaran, B.; Krishna, P.; Bontha, S.
This work focuses on oxidation behavior of Electron Beam Powder Bed Fusion (EB-PBF) processed Ti-48Al-2Cr-2Nb at elevated temperatures. Two different sample conditions were considered: As-deposited (AD) and post-processed by hot isostatic pressing (HIPed). The oxidation studies were carried out at 750 °C, 850 °C, and 950 °C for 30, 60, and 100 h. The oxidized samples were analyzed for oxide layer growth and kinetics using Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray Spectroscopy (EDS), Raman Spectroscopy, and X-ray Diffraction (XRD) techniques. Results indicate that oxide layers are composed of alternative bands of TiO2 and Al2O3. These oxide layers spalled at 850 °C and 950 °C after an exposure of 100 h. The HIPed samples exhibited superior oxidation resistance when compared to AD samples, with an oxidation rate constant of 0.134 mg2 cm4 h?1 at 950 °C (100 h). The presence of homogenized microstructure with large nano-scale lamellar colonies aided in uniform oxide layer growth. EB-PBF samples exhibit fine fully lamellar microstructure due to the rapid heating and cooling cycles. Hence EB-PBF (AD and HIPed) samples exhibited better oxidation resistance when compared to conventionally processed Ti-48Al-2Cr-2Nb. © 2025 Elsevier B.V.
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.
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.