Browsing by Author "Bontha, S."

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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.
A Closed-Form Solution for the Effect of Free Edges on Melt Pool Geometry and Solidification Microstructure in Additive Manufacturing of Thin-Wall Geometries
(Springer Boston, 2016) Gockel, J.; Klingbeil, N.; Bontha, S.
Laser and electron beam-based additive manufacturing of Ti-6Al-4V are under consideration for application to aerospace components. A critical concern for these processes is the ability to obtain a consistent and desirable microstructure and corresponding mechanical properties of the deposit. Based on the Rosenthal solution for a moving point-heat source, recent work has developed simulation-based process maps for the thermal conditions controlling microstructure (grain size and morphology) in beam-based deposition of semi-infinite geometries, where a steady-state melt pool exists away from free edges. In the current study, the Rosenthal solution is modified to include the effects of free edges. This is accomplished by the superposition of two point-heat sources approaching one another, with the line of symmetry representing the free edge. The result is an exact solution for the case of temperature-independent properties. Dimensionless results for melt pool geometry are determined, and plotted as a function of distance from the free edge. Results are plotted on solidification maps to predict trends in microstructure for Ti-6Al-4V. Finite element analysis is used to verify results. Results suggest that melt pool geometry is more sensitive to free edges than solidification microstructure. © 2015, The Minerals, Metals & Materials Society and ASM International.
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.
A study on the effect of process parameters and scan strategies on microstructure and mechanical properties of laser directed energy deposited IN718
(Elsevier Ltd, 2023) Thanumoorthy, R.S.; Sekar, P.; Bontha, S.; Balan, A.S.S.
The present study focuses on understanding the effect of scan strategy on the microstructure and mechanical properties of LDED fabricated IN718 built at optimized process conditions from single track analysis. Initially, single track studies were conducted by varying laser power, scan speed, and feed rate (3 levels) to optimize process parameters for bulk deposition. Based on the dilution, aspect ratio, track continuity and melt pool shape, best process parameter were chosen for depositing bulk structures. Bulk rectangular specimens were fabricated using the LDED process for different infill rotation (0°, 45°, 67°, and 90°) at optimized process conditions. Infill rotation did not show any significant change in the density of the samples. However, grain size measurement from EBSD and SEM micrographs revealed a substantial difference in grain size between samples without infill rotation (0°) and samples with infill rotation (45°, 67°, and 90°). XRD and EDS mapping revealed higher the formation of secondary laves phases with infill rotation as a result of higher cooling rate. Similarly, melt pool shape and arrangement showed significant variation with different infill angles. Samples with 0° and 90° infill rotation exhibited strong crystallographic texture along the build direction. There was a significant variation in the microhardness and tensile strength of the build with variation in infill rotation. This variation in mechanical properties were attributed to grain size, LAGB's fraction, secondary phases, and crystallographic texture. © 2023 Elsevier B.V.
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.
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 Authors
An Experimental Investigation on Microstructure, Mechanical Properties and Corrosion Performance of CMT-Wire Arc Additively Manufactured Al-4043 Alloy
(Springer, 2023) Manjhi, S.K.; Kumar, B.S.S.; Rodrigues, J.P.; Sekar, P.; Bontha, S.; Balan, A.S.S.
The wire arc additive manufacturing process (WAAM) has drawn incredible potential to manufacture non-ferrous alloys such as Aluminium and Magnesium. The deposition of Aluminium using a conventional WAAM process resulted in various defects such as porosity, cracks and tensile residual stress owing to high heat input. Therefore, to address these challenges, cold metal transfer wire arc additive manufacturing process (CMT-WAAM) is used to deposit 4043 Al alloy. The microstructure, mechanical properties and corrosion performance of Al 4043 are evaluated to ascertain the quality of deposited parts. The XRD peak intensity and microstructure shows that the main phases are α-Al and MgSi2 eutectics distributed along the grain boundaries of the Al matrix. The grain size of the bottom section is relatively smaller than the middle and top sections due to the high thermal gradient at the beginning of the deposition. Therefore, the hardness increases from the bottom to the top section of the thin wall. In addition, variations in the fraction of secondary phases are also responsible for the variation in hardness. The average UTS and % EL of travel direction (TD) are 177 ± 5 MPa and 20 ± 0.3%, which are relatively higher than the average UTS (164 ± 2 MPa) and % EL (17 ± 0.5%) of build direction (BD). However, the differences are only 10 ± 3 MPa and 2 ± 0.3% EL, exhibiting isotropic mechanical properties. The corrosion rates of the bottom, middle and top sections are 0.172, 0.116 and 0.102 mm/year, which are comparable, exhibiting uniform corrosion resistance of the deposited thin wall. © 2023, The Indian Institute of Metals - IIM.
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.
Characterization and thermal analysis of laser metal deposited ?-TiAl thin walls
(Elsevier Editora Ltda, 2021) Mallikarjuna, B.; Bontha, S.; Krishna, P.; Balla, V.K.
The present work focuses on investigating the effect of process variables (power, travel speed, powder flow rate) on microstructure and mechanical properties of Laser Metal Deposited (LMD) ?-TiAl thin walls. To this end, LMD technique was used to deposit ?-TiAl thin walls at different processing conditions. Microstructures of as-deposited samples were investigated using both optical and scanning electron microscopy. X-ray diffraction (XRD) technique was used to determine the phases present. Microhardness measurements were carried out along both longitudinal and build directions. Microstructural analysis of as-deposited samples revealed a fine lamellar structure comprising of ? and ?2 phases. Colony size of 30–60 ?m and lamellar spacing between 0.1 and 0.7 ?m were observed. XRD analysis confirmed the presence of ? and ?2 phases. Comparison of elemental analysis results on both powder and as-deposited samples revealed a negligible loss of Al and no oxygen pick up in the deposited thin walls. Hardness values were found to decrease with an increase in wall height, and hardness values increased marginally (5%) with an increase in travel speed. Further, 3D transient thermal analysis was also carried out to complement the LMD of thin walls in terms of melt pools and cooling rates. It was found that the melt pool depth (MPDc = 0.266 mm) is smaller at the centre than the edge (MPDe = 0.513 mm) of the wall. A higher cooling rate of 1.05 × 105 °C/s near the wall substrate was found for 200–12. © 2021
A Closed-Form Solution for the Effect of Free Edges on Melt Pool Geometry and Solidification Microstructure in Additive Manufacturing of Thin-Wall Geometries
(2016) Gockel, J.; Klingbeil, N.; Bontha, S.
Laser and electron beam-based additive manufacturing of Ti-6Al-4V are under consideration for application to aerospace components. A critical concern for these processes is the ability to obtain a consistent and desirable microstructure and corresponding mechanical properties of the deposit. Based on the Rosenthal solution for a moving point-heat source, recent work has developed simulation-based process maps for the thermal conditions controlling microstructure (grain size and morphology) in beam-based deposition of semi-infinite geometries, where a steady-state melt pool exists away from free edges. In the current study, the Rosenthal solution is modified to include the effects of free edges. This is accomplished by the superposition of two point-heat sources approaching one another, with the line of symmetry representing the free edge. The result is an exact solution for the case of temperature-independent properties. Dimensionless results for melt pool geometry are determined, and plotted as a function of distance from the free edge. Results are plotted on solidification maps to predict trends in microstructure for Ti-6Al-4V. Finite element analysis is used to verify results. Results suggest that melt pool geometry is more sensitive to free edges than solidification microstructure. 2015, The Minerals, Metals & Materials Society and ASM International.
Comparative investigation of coating and friction stir processing on Mg-Zn-Dy alloy for improving antibacterial, bioactive and corrosion behaviour
(Elsevier B.V., 2021) Rokkala, U.; Jana, A.; Bontha, S.; Ramesh, M.R.; Balla, V.K.
Magnesium based alloys are well-known materials for temporary implant applications. However, failures due to early degradation and bacterial infection are limiting their applications. To overcome these problems, in the present work a Mg-Zn-Dy alloy based composite surface was prepared using coating and friction stir processing (FSP) techniques. Herein, hydroxyapatite (HA) and silver (Ag) particles were deposited on Mg-Zn-Dy alloy to obtain HA and Ag coated surface (C-HAg). Later, FSP was carried out on the C-HAg surface to develop a Mg-Zn-Dy alloy based composite surface (F-HAg). Field emission scanning electron microscope (FESEM) and energy dispersive X-ray analysis (EDS) confirm the mixing of HA and Ag particles with the Mg-Zn-Dy substrate. Antibacterial studies reveal that both C-HAg and F-HAg samples inhibit Escherichia coli and Staphylococcus aureus bacteria. In vitro cytotoxicity study indicates that the both samples are non-toxic in nature. Results of in vitro corrosion study reveal a significant reduction (72%) in corrosion rate of F-HAg sample when compared to C-HAg sample. The F-HAg samples showed simultaneous improvement in corrosion resistance and antibacterial properties with good biocompatibility. The results of this study indicate that the developed composite surface is a promising material for antibacterial and biodegradable implant applications. © 2021 Elsevier B.V.
Copper-graphene nanocomposite fabrication through LP-DED process: Powder preparation, characterization and printability studies
(Elsevier Ltd, 2024) Sharma, S.; Thanumoorthy, R.S.; Bontha, S.; Balan, A.S.S.
Copper and its alloys play a crucial role in various engineering applications due to their excellent conductive properties. However, their poor laser absorptivity and high conductivity make them a complex material to work with using laser additive manufacturing processes, hindering the ease of fabrication of precise and complex geometries. To overcome this challenge, graphene-reinforced copper powders were employed to enhance laser absorptivity. With graphene addition, there was a substantial increase in the laser absorptivity. The addition of graphene improved laser absorptivity from 15 % for pure copper to ~60 % in Gr-Cu composites. However, the flowability deteriorated at higher compositions, which could result from increased specific surface area due to graphene agglomeration and its nanoscale surface. The influence of graphene on the ease of fabrication employing laser powder-directed energy deposition was evaluated with a single-track and bulk deposition. A single-track study revealed that pure copper tracks were inconsistent and exhibited poor bonding due to their poor laser absorptivity. Meanwhile, graphene?copper composite tracks displayed stable melt pools and uniform tracks, which could result from enhanced absorptivity. Geometrically sound and defect-free Gr-Cu tracks were deposited using 750 W laser power with composite powders, while pure copper tracks at 950 W laser power deposition yielded defective tracks. However, a graphene percentage above 0.1 % resulted in the formation of keyhole porosity due to a significant enhancement in laser absorption (~60 %). A similar observation was made for bulk deposition, i.e., defect-free deposition for Gr-Cu composites ?0.1 % graphene and keyhole porosities in the deposition of 0.25Gr-Cu and 0.8Gr-Cu. © 2024 The Society of Manufacturing Engineers
Degradation, wettability and surface characteristics of laser surface modified Mg–Zn–Gd–Nd alloy
(Springer, 2020) K.r, R.; Bontha, S.; M.r, R.; Das, M.; Balla, V.K.
This work evaluates the effects of laser surface modification on Mg–Zn–Gd–Nd alloy which is a potential biodegradable material for temporary bone implant applications. The laser surface melted (LSM) samples were investigated for microstructure, wettability, surface hardness and in vitro degradation. The microstructural study was carried out using scanning and transmission electron microscopes (SEM, TEM) and the phases present were analyzed using X-ray diffraction. The in vitro degradation behaviour was assessed in hank’s balanced salt solution (HBSS) by immersion corrosion technique and the effect of LSM process parameters on the wettability was analyzed through contact angle measurements. The microstructural examination showed remarkable grain refinement as well as uniform redistribution of intermetallic phases throughout the matrix after LSM. These microstructural changes increased the hardness of LSM samples with an increase in energy density. The wetting behaviour of processed samples showed hydrophilic nature when processed at lower (12.5 and 17.5 J/mm2) and intermediate energy density (22.5 and 25 J/mm2), which can potentially improve cell-materials interaction. The corrosion rate of as cast Mg–Zn–Gd–Nd alloy decreased by ~83% due to LSM. [Figure not available: see fulltext.]. © 2020, Springer Science+Business Media, LLC, part of Springer Nature.
Development of thick SiC coating on thin wall tube of zircaloy-4 using laser based directed energy deposition technique
(Elsevier B.V., 2020) Rai, A.K.; Srinivasulu, B.; Paul, C.P.; Singh, R.; Rai, S.K.; Mishra, G.K.; Bontha, S.; Bindra, K.S.
In the present study, optimization of various laser-processing parameters for the deposition of thick SiC coating on zircaloy-4 (Zry-4) tube is studied in view of the development of accident tolerant fuel clad material for current and future nuclear reactors with the enhanced safety. The SiC coatings are deposited using laser directed energy deposition (LDED). It is found to be quite challenging to deposit desired SiC coating on a thin (~400 ?m) substrate of Zry-4 tubes due to either its excessive melting or damage. This is minimized largely by cooling the tube from inside by passing Ar gas (20 l min?1). It is observed that different processing parameters play a vital role on homogeneity, uniformity and defects-free SiC coatings as well as on the melting and oxidation of Zry-4 substrate. A uniform and homogeneous coating of SiC is deposited on Zry-4 at the optimized laser power density of 4.52 kW cm?2, powder feed rate of 2.71 g min?1and scan speed of 325 mm min?1. The interface between SiC coatings and substrate is characterized using different techniques such as optical microscopy, scanning electron microscopy and X-ray diffraction to access the homogeneity, uniformity, defects and to identify the different phases formed in the coated layer. Coated layer is found to be consisting of Zr(?), SiC, ZrSi2, ZrSi and ZrC types of phases and the same is also confirmed by the ThermoCalc(R) based ternary phase diagram. Further, the effect of processing parameters on substrate melting and the nature of SiC coating is explained by simulating the substrate temperature using COMSOL@ multi-physics. To the author's best knowledge, this would be the first study to report the laser directed energy deposition of SiC on Zry-4 alloy. © 2020 Elsevier B.V.
Eco-friendly lightweight filament synthesis and mechanical characterization of additively manufactured closed cell foams
(2019) Patil, B.; Bharath, Kumar, B.R.; Bontha, S.; Balla, V.K.; Powar, S.; Hemanth, Kumar, V.; Suresha, S.N.; Doddamani, M.
Environmentally pollutant fly ash cenospheres (hollow microballoons) are utilized with most widely consumed, relatively expensive high density polyethylene (HDPE) for developing lightweight eco-friendly filament for 3D printing of closed cell foams. Cenospheres (20, 40 and 60 by volume %) are blended with HDPE and subsequently extruded in filament to be used for 3D printing. Cenosphere/HDPE blends are studied for melt flow index (MFI) and rheological properties. MFI decreases with cenospheres addition. Complex viscosity, storage and loss modulus increase with filler loading. DSC results on the filament and printed samples reveal increasing crystallization temperature and decreasing crystallinity % with no appreciable change in peak melting temperature. Cooling rate variations exhibit crystallinity differences between the filament and the prints. CTE decreases with increasing cenosphere content resulting in lower thermal stresses and under diffusion of raster leading to non-warped prints. Micrography on freeze fractured filament and prints show cenospheres uniform distribution in HDPE. Intact cenospheres lower the foam density making it lightweight. Tensile tests are carried out on filaments and printed samples while flexural properties are investigated for 3D prints. Cenospheres addition resulted in improved tensile modulus and decreased filament strength. Tensile and flexural modulus of printed foams increases with filler content. Results are also compared with injection molded samples. Printed foams registered comparable tensile strength. Specific tensile modulus is noted to be increased with cenospheres loading implying weight saving potential of 3D printed foams. Property map reveals printed foams advantage over other fillers and HDPE composites synthesized through injection and compression molding. 2019 Elsevier Ltd
Eco-friendly lightweight filament synthesis and mechanical characterization of additively manufactured closed cell foams
(Elsevier Ltd, 2019) Patil, B.; Bharath Kumar, B.R.; Bontha, S.; Balla, V.K.; Powar, S.; Hemanth Kumar, V.H.; Suresha, S.N.; Doddamani, M.
Environmentally pollutant fly ash cenospheres (hollow microballoons) are utilized with most widely consumed, relatively expensive high density polyethylene (HDPE) for developing lightweight eco-friendly filament for 3D printing of closed cell foams. Cenospheres (20, 40 and 60 by volume %) are blended with HDPE and subsequently extruded in filament to be used for 3D printing. Cenosphere/HDPE blends are studied for melt flow index (MFI) and rheological properties. MFI decreases with cenospheres addition. Complex viscosity, storage and loss modulus increase with filler loading. DSC results on the filament and printed samples reveal increasing crystallization temperature and decreasing crystallinity % with no appreciable change in peak melting temperature. Cooling rate variations exhibit crystallinity differences between the filament and the prints. CTE decreases with increasing cenosphere content resulting in lower thermal stresses and under diffusion of raster leading to non-warped prints. Micrography on freeze fractured filament and prints show cenospheres uniform distribution in HDPE. Intact cenospheres lower the foam density making it lightweight. Tensile tests are carried out on filaments and printed samples while flexural properties are investigated for 3D prints. Cenospheres addition resulted in improved tensile modulus and decreased filament strength. Tensile and flexural modulus of printed foams increases with filler content. Results are also compared with injection molded samples. Printed foams registered comparable tensile strength. Specific tensile modulus is noted to be increased with cenospheres loading implying weight saving potential of 3D printed foams. Property map reveals printed foams advantage over other fillers and HDPE composites synthesized through injection and compression molding. © 2019 Elsevier Ltd
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.
Effect of Build Orientation on Anisotropy in Tensile Behavior of Laser Powder Bed Fusion Fabricated SS316L
(Springer, 2024) Thanumoorthy, R.S.; Chaurasia, J.K.; Anil Kumar, V.A.; Pradeep, P.I.; Balan, A.A.S.; Rajasekaran, B.; Sahu, A.; Bontha, S.
In the present study, Stainless steel 316L (SS316L) cylindrical specimens were fabricated at two different build orientations and two different laser powers using Laser powder bed fusion process (LPBF). Microstructural characterization such as XRD, SEM, EBSD analysis and tensile testing were carried out on fabricated specimens in stress relieved condition to understand the anisotropic behavior of LPBF printed specimens. Horizontally oriented specimens showed higher tensile strength when compared to vertically oriented specimens for both laser powers. XRD and EBSD phase maps did not reveal the presence of any secondary phases. However, build orientation and laser power affected the crystallite size of the samples. Bimodal grain structure comprising coarse columnar grains and fine equiaxed grains were observed from the micrographs. With variation in build orientation, there was a significant change in the average grain size of the specimens. High dislocation density was observed in horizontally oriented samples built at low laser power because of dislocation annihilation that can occur at high temperatures. However, EBSD analysis revealed random weak crystallographic texture which does not vary significantly with laser power or build orientation. Variation in grain size, grain morphology, sub-grain features and dislocation density are the reasons for the anisotropic tensile behavior observed in LPBF printed SS316L coupons in stress relieved condition. © ASM International 2023.
Effect of burnishing strategies on surface integrity, microstructure and corrosion performance of wire arc additively manufactured AZ31 Mg alloy
(KeAi Publishing Communications Ltd., 2025) Manjhi, S.K.; R, O.; Bontha, S.; Balan, A.S.S.
AZ31 Mg alloy is an emerging material that has received considerable attention in aerospace, automotive, and temporary biodegradable implant applications owing to its attractive properties, such as low density, high specific strength, and biodegradability. Nevertheless, some shortcomings in Mg alloys are their low ductility, which is associated with challenging its manufacturing, and poor corrosion resistance associated with unreliable components. Therefore, a cold metal transfer wire arc additive manufacturing (CMT-WAAM) process is used to manufacture AZ31 Mg alloy and achieved 29.4 % ductility by controlling the gas porosity, keyhole porosity, and internal cracks. Further, severe plastic deformation is induced on the surface of deposited parts by low plasticity burnishing (LPB) with parallel and cross-pattern burnishing to modulate their surface to slow down the kinetics of the corrosion damage. The average surface roughness (Sa) of the cross-burnishing pattern is 0.235 ?m, which is 123.6 % lower than the parallel burnished and 261.7 % lower than the milled specimens. The residual stress (RS) of WAAM is 40 MPa with a tensile nature; however, it is drastically reduced and develops compressive RS of 45 MPa under a parallel burnishing pattern and 62 MPa under a cross-burnishing pattern. Moreover, LPB with cross pattern deformed ?395 ?m depth of WAAMed AZ31 workpiece, which is ?45 % higher than deformed depth (?272 ?m) by parallel pattern burnishing. The electrochemical corrosion rate of the WAAM specimen is 9.71 mm/year, and it is reduced to 1.82 mm/year under LPB caused by compressive residual stress and grain refinement. © 2024 The Authors
Effect of CMT-WAAM Process Parameters on Bead Geometry, Microstructure and Mechanical Properties of AZ31 Mg Alloy
(Springer, 2024) Manjhi, S.K.; Sekar, P.; Bontha, S.; Balan, A.A.S.
Fabrication of Mg alloys using the additive manufacturing process is quite challenging owing to high oxidation and volatile nature at high temperatures. The present study investigates the effect of wire feed speed (WFS) and travel speed (TS) on single tracks of AZ31 Mg alloy fabricated using the cold metal transfer wire arc additive Manufacturing (CMT-WAAM) process. The WFS and TS of CMT-WAAM are optimized to achieve better deposition quality. An increase in WFS increased the width, height, penetration depth, and heat-affected zone of single tracks. In addition, increasing TS decreased the deposited tracks' contact angle and height. The average grain size at the interface zone, center and top portion of single tracks are 35, 42, and 60 μm. The x-ray diffraction results show only the presence of primary phase α-Mg; interestingly, the β-Mg17Al12 and η-Al8Mn5 secondary phases are identified by SEM + EDS and TEM images. The microhardness increased from the substrate to the top section of single tracks due to the increased volume fraction of secondary-phase particles. Based on the best-chosen process parameters obtained from single-track deposition, a multilayer AZ31 Mg thin wall is deposited. The UTS, YS, and % EL of the deposited thin wall in travel direction (TD) are 222 MPa, 102 MPa, and 18%, while in build direction are 202 MPa, 110 MPa, and 14%, respectively. The tensile strength and elongation % of TD and BD samples exhibited comparable properties and were higher than cast AZ31 Mg alloy. © ASM International 2023.