Faculty Publications
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Item Additive Manufacturing of Lattice Structures for Heat Transfer Enhancement in Pipe Flow(Springer Science and Business Media Deutschland GmbH info@springer-sbm.com, 2021) Koneri, R.; Mulye, S.; Ananthakrishna, K.; Hota, R.; Khatei, B.; Bontha, S.Additive manufacturing has added a new dimension to manufacturing technology. The Design for Additive Manufacturing (DFAM) principles provide guidelines for successful 3D printing. Several industrial applications utilize the cellular structures in AM for design improvement by light weighting, topology optimization, etc. Self-supporting behavior is the most desired characteristic for DFAM of cellular structures. In the present work, gyroid, star kagome and BCC cellular structures are evaluated for self-supporting behavior using Materialize Magics software. The lattice designs of different sizes are 3D printed and visually examined for defects. The lattice designs are introduced into a smooth circular pipe. Conjugate heat transfer analysis is done for different Reynolds numbers (1193–10736) using FloEFD to study heat transfer and pressure drop characteristics. All the lattice designs show heat transfer enhancement and higher pressure drop with respect to smooth pipe. Among all lattice designs, gyroid shows the highest heat transfer enhancement and highest pressure drop. © 2021, The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.Item A brief review of titanium (Ti)-based bioimplants fabricated using various additive manufacturing methods(CRC Press, 2024) Praharaj, A.K.; Suvin, P.S.; Bontha, S.In recent years, a noticeable growth has been observed in the research and development of manufacturing methods for biomedical implants. Extensive research has been conducted for orthopedic and dental implants due to their huge market size worth 4.5 billion dollars. Titanium (Ti) and its alloys are the most widely acknowledged biomaterials used in the production of orthopedic and dental implants due to their intriguing physical and biological properties including higher mechanical strength, excellent corrosion resistance, and biocompatibility. Apart from pure titanium (CP-Ti) and Ti-6Al-4V alloy, β-titanium has recently emerged as one of the important biomaterials for specific orthopedic applications due to its harmless chemical composition and low modulus. Over the years, Ti-based bioimplants were manufactured by conventional machining techniques which were less economical. With the growing demand across the world for the fabrication of customized biomedical implants, researchers were focusing on the development of new approaches and techniques for these implants. Recently, additive manufacturing (AM) has emerged as a potential fabrication method for biomedical implants due to its ability to produce customized products in less time with higher precision and flexibility. In addition, AM-fabricated bioimplants have shown improved osseointegration when compared to conventionally processed implants. In this chapter, various AM methods used for the fabrication of Ti-based implants were summarized with a special focus on the process parameters, microstructure, and related mechanical properties of the end product. Further, the effect of porous structures on the performance of Ti-based bioimplants was highlighted. This study will be helpful in identifying the pros and cons of AM methods in the manufacturing of bioimplants and leads to the advancement of research direction in biomedical sectors. © 2025 selection and editorial matter, Abhilash P M, Kishor Kumar Gajrani and Xichun Luo.Item Effect of Process Parameters on Track Geometry and Porosity in Laser Direct Energy Deposition of High Strength Aluminum Alloy(Springer, 2024) Balla, S.K.; Manjaiah, M.; Selvaraj, N.; Bontha, S.Laser Directed Energy Deposition (LDED) is a metal Additive Manufacturing (Metal AM) process that has attracted significant attention due to its ability to produce complex geometries with material properties comparable to cast and wrought parts. High-strength aluminum alloys especially 2xxx, 6xxx, and 7xxx series are difficult to fabricate using LDED process since these alloys are prone to hot cracking due to rapid solidification during the LDED process. The focus of this work is to evaluate the effect of LDED process parameters on track geometry and porosity of Al7075 powder. The effects of process parameters such as laser power, scan speed, and powder flow rate on track geometry and porosity, were investigated using a Formalloy LDED machine via L27 orthogonal array of experiments. Increasing the laser power resulted in an increase in bead width and wetting angle, whereas increasing the scan speed led to a decrease in bead height and wetting angle and a minor increase in width. The results also showed a linear increase in wetting angle and bead height with increased powder flow rate, while the width of the bead remained relatively constant. Furthermore, it was also observed that increasing the laser power to 750 W resulted in a decrease in the cross-sectional porosity of the bead due to the availability of sufficient energy density thereby facilitating proper melting. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024.Item Effect of ECAP on sliding wear behaviour of Mg-Zn-Gd-Zr alloy(Elsevier Ltd, 2020) Patil, A.; Bontha, S.; Ramesh, M.R.Magnesium is a lightweight, recyclable, and biocompatible material. However, the extensive commercial use of Magnesium and its alloys is hindered by their poor wear behaviour and mechanical properties. Equal Channel Angular Pressing (ECAP) is a severe plastic deformation technique which improves the material properties through grain refinement. In the present study, wear behaviour of ECAP processed Mg-Zn-Gd-Zr alloy was investigated. ECAP process was carried out up to 3 passes at a temperature of 380 °C. Wear testing of as-cast and ECAP processed alloy were carried out using dry sliding wear method on a pin on disk tribometer by varying loads. The wear mechanism was analysed using Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). Average Coefficient of Friction (COF) increased after each pass of ECAP. Wear rate increased with the applied load. Despite severe plastic deformation, wear resistance of ECAP processed samples was found to be lower than that of as-cast samples at higher loads. Abrasive and oxidation wear mechanisms were found in both as-cast and ECAP processed samples. © 2019 Elsevier Ltd. All rights reserved.Item Elucidating Corrosion Behavior of Hastelloy-X Built Using Laser Directed Energy Deposition-Based Additive Manufacturing in Acidic Environments(Springer Science and Business Media Deutschland GmbH, 2021) Diljith, P.K.; Jinoop, A.N.; Paul, C.P.; Krishna, P.; Bontha, S.; Bindra, K.S.This paper reports an investigation on the electrochemical corrosion behavior of laser directed energy deposition (LDED)-based additive manufacturing built Hastelloy-X (Hast-X) bulk samples for the first time in various acidic environments (2M HNO3, 2M HCl, and 2M H2SO4). Open-circuit potential results reveal that corrosion activity is more in HCl than the other two media. The corrosion rate (CR) estimated using the Tafel extrapolation method shows that the corrosion rate (CR) is the most in HCl and least in HNO3. Potentiodynamic studies reveal active–passive behavior of Hast-X in all the media and it is seen that the material stays in passivation for a longer potential range in HCl. Further, pitting potential is observed to be comparable in all three media. The cyclic polarization curve shows no loops, which points out the absence of pitting in the samples immersed in any of the media. The estimated CR for Hast-X in all the acidic environments under investigation comes within the acceptable CR for nickel-based alloys (4 mpy). The morphology of the corroded surface is analyzed using stereo microscope and it confirms the absence of pitting in all the three samples. These observations confirm the suitability of LDED built Hast-X components for applications in investigated acidic environments. © 2021, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.Item 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 Cf = 1 and 2.5 with experimental measurements was done. The maximum absolute percentage error in the numerical model considering the fluid dynamics effects (Cf = 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 (Cf = 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. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2025.Item 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. Laser—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 that laser power significantly influences β width and α’ 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. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2025.Item Laser Surface Melting of Cold Metal Transfer Wire Arc Directed Energy Deposited AZ31 Mg Alloy(Springer Science and Business Media Deutschland GmbH, 2025) Manjhi, S.K.; Bontha, S.; Balan, A.S.S.The deposition of Mg alloy using an additive manufacturing process is challenging due to its volatile nature at high temperatures and difficult handling of Mg powder during fabrication. Therefore, the cold metal transfer wire arc additive manufacturing (CMT-WAAM) process deposits AZ31 Mg alloy because of its tremendous potential to fabricate heat-sensitive materials due to comparatively low heat input and wire as a feed material. However, the mechanical properties of CMT-WAAMed AZ31 Mg alloy are still poor due to pores, microcracks, and poor surface finish. Therefore, deposited components cannot be directly used in the application. Machining is required to make the surface smooth and flat before application. However, microcracks and burrs are the primary issues during milling operation, further reducing the mechanical properties and corrosion performance of deposited parts. Therefore, this study uses the laser surface melting (LSM) process to enhance surface properties by minimizing the microcracks and other CMT-WAAMed AZ31 Mg alloy defects. The obtained results of the 3D profilometer show that the surface roughness (Ra) of machined samples was 3.34 μm, which is reduced to 2.279 μm after laser surface melting treatment. In addition, optical microscope (OM) results exhibited a huge reduction of grain refinement after LSM from 45 ± 3 μm to less than 1 μm with dendrites microstructure. Consequently, the hardness of the surface increased from 60 ± 2 to 143 ± 10 HV due to grain refinement and the formation of secondary phase particles. The grain refinement and uniform distribution of secondary phase particles act as a barrier to Cl−1 corrosive ions, enhancing corrosion resistance after the SLM process. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2025.Item Additive manufacturing of magnesium alloys: Characterization and post-processing(KeAi Publishing Communications Ltd., 2024) Manjhi, S.K.; Sekar, P.; Bontha, S.; Balan, A.S.S.Magnesium and its alloys remain perilous in the framework of light weighting and advanced devices structure such as rockets and satellites. However, the utilization of Magnesium (Mg) is increasing every year, revealing growing demands in manufacturing industries. Manufacturing of Mg components is challenging because of their HCP crystal structure and limited ductility. In this context, additive manufacturing (AM) provides the flexibility to manufacture complex shape components with excellent dimensional stability. It also provides a new possibility for utilizing novel component structures that increase the applications for Mg alloy. This review herein pursues to holistically explore the additive manufacturing of Mg alloy with a synopsis of processes used and microstructure, mechanical properties, corrosion behaviour and postprocessing of AMed Mg alloy. The challenges and future scope of AMed Mg alloys are critically explored. © 2023 The AuthorsItem Microstructure and corrosion behavior of laser processed NiTi alloy(Elsevier Ltd, 2015) Marattukalam, J.J.; Singh, A.K.; Datta, S.; Das, M.; Balla, V.K.; Bontha, S.; Kalpathy, S.K.Abstract Laser Engineered Net Shaping (LENS™), a commercially available additive manufacturing technology, has been used to fabricate dense equiatomic NiTi alloy components. The primary aim of this work is to study the effect of laser power and scan speed on microstructure, phase constituents, hardness and corrosion behavior of laser processed NiTi alloy. The results showed retention of large amount of high-temperature austenite phase at room temperature due to high cooling rates associated with laser processing. The high amount of austenite in these samples increased the hardness. The grain size and corrosion resistance were found to increase with laser power. The surface energy of NiTi alloy, calculated using contact angles, decreased from 61 mN/m to 56 mN/m with increase in laser energy density from 20 J/mm2 to 80 J/mm2. The decrease in surface energy shifted the corrosion potentials to nobler direction and decreased the corrosion current. Under present experimental conditions the laser power found to have strong influence on microstructure, phase constituents and corrosion resistance of NiTi alloy. © 2015 Elsevier B.V.