Faculty Publications
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Item Recent progress in in vivo studies and clinical applications of magnesium based biodegradable implants – A review(National Engg. Reaserch Center for Magnesium Alloys, 2021) Sekar, P.; Narendranath, N.; Desai, V.Biodegradable magnesium has regained great attention due to its ability to temporarily offer mechanical strength and degrade completely once the injured pathological tissue is healed. A few clinical applications of Mg-based implants were reported in the last century. However, the knowledge and experience is being gained continuously by studying the host response and degradation behavior of Mg implant in animal models and clinical trials. This led to the development of commercial products emerging from Europe and Asia very recently. The potential of Mg implants in repairing fractures at upper and lower limb of large, small animal models and humans is compared and discussed in detail. In addition the possible future Mg implants that might treat problems concerning to urology and gynecology are reviewed. © 2020Item 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 Enhancement of resistance to galvanic corrosion of ZE41 Mg alloy by equal channel angular pressing(Wiley-VCH Verlag info@wiley-vch.de, 2020) Sekar, P.; Sanna, N.; Desai, V.The galvanic corrosion behavior of as-received and ECAPed ZE41 Mg alloy coupled with Al7075 alloy is investigated using zero resistance ammeter in three different corrosive environments, 0, 0.1, and 1 M NaCl, to mimic the conditions experienced in engineering applications. The mechanism of galvanic corrosion for the ZE41 Mg–Al7075 aluminum alloy is explained. It is observed that a robust surface film containing a composite layer of oxide/hydroxide of magnesium and aluminum is established in deionized water (0 M). However, only a single layer of magnesium oxide/hydroxide is detected in chloride-containing environments. Equal channel angular pressing (ECAP) improved the resistance to galvanic corrosion by 58% and 54% when compared with the as-cast counterparts in 0 and 1 M NaCl solution, respectively. In contrast, galvanic corrosion resistance decreased by 26% in 0.1 M NaCl after ECAP while the as-received samples evinced pits unfavorable to be used in engineering applications. ECAP is a promising method to combat galvanic corrosion encountered by ZE41 magnesium alloy used in automobiles and components of military vehicles. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimItem Bio-corrosion impacts on mechanical integrity of ZM21 Mg for orthopaedic implant application processed by equal channel angular pressing(Springer, 2021) Sekar, P.; Nyahale, M.B.; Naik, G.M.; Narendranath, N.; Prabhu, A.; Rekha, P.D.The mechanical integrity of rolled ZM21 Mg was improved by equal channel angular pressing (ECAP) to function as a potential biodegradable bone screw implant. Electron backscattered diffraction (EBSD) revealed deformed grains of 45 µm observed in rolled ZM21 Mg. They were transformed to equiaxed fine grains of 5.4 µm after 4th pass ECAP. The yield strength of rolled and ECAPed ZM21 Mg alloys were comparable. In contrast, 4th pass ZM21 Mg exhibited relatively higher elongation when compared to rolled sample. The mechanical properties of rolled and ECAPed ZM21 Mg were dependant on both grain refinement and crystallographic texture. The rolled and 4th pass ECAPed tensile samples exhibited nonlinear deterioration of mechanical properties when tested after 7, 14, 21 and 28 days immersion in Hank’s solution. The evaluation signifies that regardless their processing condition, ZM21 Mg alloys are suitable for surgical areas that requires high mechanical strength. In addition, the 4th pass ECAP samples were viable to MG-63 cells proving themselves to be promising candidates for future in vivo studies. [Figure not available: see fulltext.] © 2021, The Author(s).Item A study on the influence of WEDM parameters on surface roughness, kerf width, and corrosion behavior of AZ31B Mg alloy(Elsevier Ltd, 2022) Chaitanya, V.H.; Sekar, P.; Narendranath, S.; Balaji, V.Wire electric discharge machining (WEDM) is a nontraditional machining process where the material is removed by the spark erosion technique. This technique is used to machine AZ31B, a biodegradable Magnesium alloy. In the present work impact of WEDM input parameters, namely pulse on time (Ton), pulse off time (Toff), servo voltage (SV), and wire feed (WF) on response characteristics is studied. The response characteristics considered are kerf width (KW), surface roughness (SR), and corrosion rate (CR). L9 orthogonal array by Taguchi's is employed as the design of experimentation. Taguchi's analysis implied that TON is the most influencing input parameter on the response characteristics. At a relatively lower TON setting (105 μs), comparatively lesser kerf width (335.894 μm), lower surface roughness (3.069 μm), and lower corrosion rate (0.95 mm/year) are exhibited by the machined specimens. From the main effects plots using signal-to-noise ratios, it is understood that the values of response characteristics increased with an increase in TON value. It is due to the increase in discharge at the more pulse on time duration. It is also understood that a surface with relatively better surface finish exhibited better corrosion resistance. With the help of regression equations, the relation between response characteristics and input parameters is built. © 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.Item Enhanced disinfection of E. faecalis and levofloxacin antibiotic degradation using tridoped B-Ce-Ag TiO2 photocatalysts synthesized by ecofriendly citrate EDTA complexing method(Springer Science and Business Media Deutschland GmbH, 2022) Sekar, P.; Sadanand Joshi, D.; Manjunatha, M.; Mahalingam, H.Since its use for photochemical water splitting reported first in 1972, TiO2 is one of the most extensively studied photocatalysts for a diverse range of applications. Monodoping or codoping of the catalyst is a proven strategy to enhance the functionality of TiO2 under solar or visible light. However, the use of three or more dopants in the development of more efficient and visible light active photocatalysts has not been investigated widely, especially for microbial disinfection. Boron/cerium/silver tridoped TiO2 photocatalysts with curated amounts of the dopants (B = 1, 2 at.%, Ce = 0.1 at.%, Ag = 0.06 at.%), synthesized by the ecofriendly EDTA-citrate method, were evaluated for the disinfection of water using Enterococcus faecalis under UV-A irradiation and degradation of levofloxacin antibiotic under solar light. The catalyst characterization revealed that the spherical nanoparticles had a crystallite size of ~ 13 nm and bandgap energy values of 2.8–2.9 eV. 2B-0.1Ce-0.06Ag-TiO2 is the best catalyst for microbial disinfection with a log reduction and kinetic rate constant ~ 30 and ~ 4.5 times higher than those values determined for the other codoped or monodoped catalysts, confirming an enhanced performance. Regarding levofloxacin degradation, the best performing catalyst is 1B-0.1Ce-0.06Ag-TiO2 with degradation of 99% and 83% COD reduction in 100 min. The tridoped photocatalysts are very effective in the inactivation of Enterococcus faecalis, thus solving the problem of antimicrobial resistance in waters containing antibiotic residues. Graphical abstract: [Figure not available: see fulltext.] © 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.Item Effect of Zinc and Bio-Glass Addition on Mechanical Properties and Corrosion Behavior of Magnesium-Based Composites for Orthopedic Application: A Preliminary Study(Springer, 2022) Moudgalya, K.V.S.; Sekar, P.; Hebbar, H.S.; Rahman, M.R.Magnesium is extensively researched as a biodegradable implant material. However, achieving a combination of biomechanical properties viz., controlled degradation, bio-transformability and osteoconductivity is highly challenging. Indeed, bio-composites developed by reinforcing bio-ceramics with metals are gaining research interest. In this current work, the suitability of a bio-composite developed by reinforcing 5, 10 and 15% of bioglass (BG) in Mg and Mg-3 wt.% Zn metal matrix is investigated. The bio-composites containing Mg, Mg-BG and Mg-Zn-BG are processed by vacuum sintering and tested for important mechanical and corrosion properties. Particle size analysis revealed that magnesium exhibited a larger mean particle size while zinc evinced the lowest average particle size. The density-porosity analysis showed that porosity was found to increase linearly with the addition of BG. In contrast, the compressive strength of Mg-BG and Mg-Zn-BG composites increased up to 10 wt.% BG and decreased drastically for 15 wt.% BG reinforcement. The addition of Zn and BG significantly enhanced the Vickers hardness, showing an increasing trend with the increase in BG reinforcement content. Immersion corrosion study in phosphate buffered saline revealed that 10 wt.% BG reinforced composite exhibited the least corrosion rate. Thus, composites developed by reinforcing BG in Mg-3Zn metal matrix showed enhanced mechanical and corrosion properties in the physiological environment. The possible corrosion mechanism of Mg, Mg-Zn and Mg-Zn-BG composites is also proposed and compared. © 2022, ASM International.Item Grinding parameters prediction under different cooling environments using machine learning techniques(Taylor and Francis Ltd., 2023) Prashanth, G.S.; Sekar, P.; Bontha, S.; Balan, A.S.S.Selection of optimum process parameters is vital for performing a sound grinding operation on Inconel 751 alloy. This paper co-relates the relationship between the most influential input parameters like cutting velocity, depth of cut, feed rate, and environmental conditions to the output parameters, namely, tangential grinding forces, normal grinding forces, temperature, and surface roughness. Three types of machine-learning (ML) algorithms such as support vector machine (SVM), Gaussian process regression (GPR), and boosted tree ensemble techniques are employed to develop a ML model for predicting the output variables during grinding operation of Inconel 751. In order to develop a better ML model, K-fold technique is employed on a total of 81 datasets which are extracted from experimental studies. ML models developed from different algorithms are compared based on performance metrics like R2 score and root-mean-square error (RMSE). GPR algorithm exhibits best results with relatively better R2 score and RMSE value in predicting grinding forces and temperature at wheel work interface. From analyzing the ML models, it is found that cooling environments determined the output grinding parameters to a greater extent when compared with the input grinding parameters. © 2022 Taylor & Francis.Item 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.Item 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.