Faculty Publications
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Item Hybrid additive manufacturing of ER70S6 steel and Inconel 625: A study on microstructure and mechanical properties(Elsevier Ltd, 2023) Rodrigues, J.P.; Thanumoorthy, R.S.; Manjhi, S.K.; Sekar, P.; Arumuga Perumal, D.A.; Bontha, S.; Balan, A.S.S.Hybrid Additive Manufacturing (HAM) is currently being explored because of its potential to achieve trade-off between build capacity and feature resolution. The present study aims at fabricating ER70S6-Inconel 625 (IN625) bimetallic clad using hybrid Wire Arc Additive Manufacturing (WAAM) and Laser Directed Energy Deposition (LDED) processes. Microstructure evaluation was performed at the cross section of bimetallic clad for distinct materials as well as the interface. WAAM built ER70S6 revealed equiaxed ferritic grains, whereas laser deposited IN625 region showed columnar dendrites with under developed secondary arms. However, the first layer of IN625 exhibited columnar dendrite with secondary arms due to the influence of diffused Fe from the base ER70S6 steel under the action of concentrated laser heat source, which was revealed by energy dispersive spectroscopy (EDS) maps. The measured microhardness across the cross section of the deposit showed values corresponding to inherent material system. The interface did not reveal presence of any intermetallic phases which was confirmed by hardness results and X-Ray diffraction. Shear test revealed superior bond strength between the two materials, maintaining average strength of 452 MPa. The fractography images exhibited fine dimples along with cleavages indicating mixed fracture characteristics. This additive manufacturing method explores a new dimension in multi-material fabrication which, when customized for different materials, serve critical areas in the aerospace and defence sector. © 2023 Elsevier LtdItem Process parameter optimization for laser directed energy deposition (LDED) of Ti6Al4V using single-track experiments with small laser spot size(Elsevier Ltd, 2024) Gonnabattula, A.; Thanumoorthy, R.S.; Bontha, S.; Balan, A.A.S.; Anil Kumar, V.A.; Kanjarla, A.K.Single-track experiments are routinely used in the optimization of process parameters in additive manufacturing processes. Most of the process parameter optimization studies use a laser spot size of 1 mm or more. Since laser spot size affects the input energy density and in turn the efficiency of the deposition process, it is important to develop process maps every time a laser of different spot sizes is used. In this work, we determine the process maps for a laser of 0.6 mm spot size. By combining the process maps and the metallographic inspection, we estimate the optimum process parameters (laser power, scan speed, powder feed rate) for building Ti6Al4V components using powder-based laser-directed energy deposition(LDED). Single-tracks corresponding to 64 different parameter combinations are deposited. After eliminating the process parameter combinations resulting in defective tracks, the optimum process parameters of 300 W laser power and 720 mm min−1 scan speed is established by considering the relationship between the process parameters and the geometrical features of the deposit. The experimental results are then used to calibrate the modeling parameters of a three-dimensional finite element model for simulating the deposition process. © 2024 Elsevier LtdItem 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.Item Surface Characteristics of Low Plasticity Burnished Laser Directed Energy Deposition Alloy IN718(Springer, 2024) Mohanraj; Thanumoorthy, R.S.; Sekar, P.; Muthuchamy, A.; Bontha, S.; Balan, A.S.S.The research work focuses on a novel post-processing sequence to improve the surface integrity and residual stress characteristics of as-printed Inconel718 (IN718) samples. The as-printed IN718 samples are subjected to solution treatment at 1050 °C, two-step precipitation hardening (@ 720 °C for 8 h and @ 620 °C for 8 h), and low plasticity burnishing. Two different sequences were attempted. Sequence-1 involves solutionizing ? low plasticity burnishing followed by precipitation hardening, and sequence-2 includes solutionizing ? precipitation hardening followed by low plasticity burnishing. The experimental observations and detailed investigations revealed that the samples processed via sequence 2 exhibited a better surface finish. The microhardness of the samples of sequence 2 is 10% higher than their counterparts in sequence 1. The maximum residual stress of ?1375.33 MPa is obtained in sequence 1 as compared to the residual stress of ?1100.67 MPa in sequence 2. The influence of the processing sequences on the surface properties has been discussed in detail using the XRD and microstructural characterization supported with EBSD analysis. Graphic Abstract: (Figure presented.) © The Indian Institute of Metals - IIM 2024.Item Effect of age hardening precipitates on the corrosion performance of laser Powder-Directed energy deposited CuNi2SiCr(Elsevier B.V., 2024) Urs, S.S.; Thanumoorthy, R.S.; Aswith Babu, I.; Doddamani, M.; Bontha, S.; Balan, A.S.S.This study explores Laser Powder ? Direct Energy Deposition (LP-DED) processing of CuNi2SiCr and the effect of heat treatment on corrosion behavior. The findings pave the way to increasing the life of the components and the possibility of refabrication upon failure. LP-DED manufactured CuNi2SiCr was subjected to solution treatment followed by age-hardening at 500? for 1,3,5 and 7 h. The microstructure analysis showed the formation of Cr3Ni precipitates due to a higher cooling rate in the LP-DED process. Upon aging, Ni3Si, Ni2Si, and CrSi2 precipitates evolved. Due to the Orowan phenomenon, microhardness increases with the aging time as the number of precipitates along the grain boundary increases with the aging time. The 5-hour aged sample exhibited the best corrosion resistance due to precipitation coherency in the matrix and the medium-sized precipitates with uniform precipitation-free zones (PFZ) in the grain boundary. © 2024 Elsevier B.V.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 A novel NiCrAlY-Cu based bond coat for rocket nozzle applications through LP-DED process(Elsevier Ltd, 2025) Thanumoorthy, R.S.; Vijay, A.; Bontha, S.; Balan, A.S.S.This study explores the development of a novel bond coat for copper-based substrates with the goal of minimizing thermal expansion mismatch and enhancing thermal life in rocket nozzle applications. The effect of copper (Cu) addition on the microstructure, phase evolution, and thermo-mechanical behavior of NiCrAlY clads fabricated via laser powder-directed energy deposition (LP-DED) is systematically investigated to optimize their performance. SEM and elemental mapping reveal a shift from columnar to cellular substructures with Cu additions up to 20 wt%, while higher Cu contents lead to coarse dendritic growth and Cu segregation at grain boundaries, inducing localized strain and crack formation. XRD and DFT analyses indicate that Cu suppresses the ?-NiAl phase and stabilizes the ?-Ni matrix due to its limited solubility in ? and preferential partitioning into ?. High-temperature XRD and EDS analyses show that while pure NiCrAlY forms a continuous alumina scale, Cu-enriched clads develop fragmented and crack-prone thermally grown oxides (TGOs), compromising the oxidation resistance. KAM analysis suggests reduced lattice strain at 10 wt% Cu, followed by increased dislocation density at higher concentrations. Thermal expansion measurements indicate a significant increase in the coefficient of thermal expansion (CTE) at 10 wt% Cu, improving compatibility with Cu-based substrates. However, further Cu additions yield minimal CTE benefits while degrading mechanical strength. Microhardness declines from ?406 Hv (0 % Cu) to ?251 Hv (40 % Cu) due to solid solution softening and ?-phase suppression. A radar plot comparing key metrics identifies 10 wt% Cu as the optimal composition, offering a balanced property set for regeneratively cooled rocket nozzle systems. © 2025 Elsevier B.V.