Faculty Publications

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Publications by NITK Faculty

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Author: search.filters.author.Sekar, P.Subject: search.filters.subject.Corrosion resistance

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    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, Weinheim
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    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.
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    Effect of equiaxed grains and secondary phase particles on mechanical properties and corrosion behaviour of CMT- based wire arc additive manufactured AZ31 Mg alloy
    (Elsevier Ltd, 2023) Manjhi, S.K.; Sekar, P.; Bontha, S.; Balan, A.S.S.
    Wire arc additive manufacturing (WAAM) has drawn tremendous attention for manufacturing large and complex components of lightweight material at a moderate cost due to its high deposition rate and energy efficiency. Generally, WAAM-Mg alloy comprises columnar and columnar dendrite grains due to high cooling rates and thermal gradients responsible for anisotropic mechanical properties. To overcome this challenge, in this work, CMT-WAAM, which generally uses comparatively low heat input (33% lower than conventional WAAM), was used to deposit AZ31 Mg thin wall. The metallurgical characterization of the deposited thin wall of the top (T), middle (M) and bottom (B) sections reveals equiaxed grains of average sizes ∼ 58, ∼ 63 and ∼ 38 µm, respectively. In addition, TEM results exhibit the formation of secondary phase particles, i.e., β-Mg17Al12 and ɳ-Al8Mn5. Further, the ultimate tensile strength (UTS) and % elongation (% EL) in the travel direction (UTS = 224 MPa, % EL= 23.47%) are superior to that obtained in the build direction (UTS = 217 MPa, % EL = 20.82%). The corrosion resistance of WAAMed AZ31 Mg alloy is higher than wrought (cold rolled) AZ31 Mg alloy in Hank's balanced salt solution (HBSS). The results of this study reveal the potential of CMT-WAAM to deposit different grades of Mg with desired microstructure, mechanical properties and corrosion resistance. © 2023 CIRP
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    On the microstructure, texture and electrochemical properties of severely deformed and artificially aged lightweight AA2050 Al-Cu-Li alloy
    (Institute of Physics, 2024) Jagadeesh, C.; Shivananda Nayaka, H.; Sekar, P.; Ramesh, S.; Anne, G.
    Lightweight 3rd generation Al-Cu-Li alloy AA2050 was severely deformed via Multi Axial Forging (MAF) at 170 °C followed by artificial aging at 150 °C. Effect of MAF and post MAF aging on microstructure and precipitation was investigated using transmission electron microscopy (TEM). Formation of deformation bands and large dislocation cells were evident on MAF processed samples. Post MAF peak aging resulted in the distribution of fine T1 precipitates in grain interiors with reduction in grain boundary precipitation. Bulk texture studies reveal the formation of strong Goss and S texture components upon MAF processing. Further, low temperature artificial aging doesn’t exhibit significant changes in texture characteristics, either in terms of texture intensities or texture components. Polarization studies showed that peak aged samples exhibited better corrosion resistance compared to un-aged samples. Overall, 12 pass MAF processed and peak aged samples showed higher corrosion resistance. Further, corrosion surface morphologies examination revealed the change in corrosion mechanisms with thermomechanical treatments. Improved corrosion resistance after MAF and peak aging widens the requirements in aerospace and aircraft applications for such engineering alloys. © 2024 The Author(s). Published by IOP Publishing Ltd.
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    Effect of Wire-EDM textures on corrosion performance of Bio-Degradable Mg alloy
    (Elsevier B.V., 2024) Aswith Babu, I.; Kumar Manjhi, S.; Sekar, P.; Narendranath, S.; Balan, A.S.S.
    Magnesium (Mg) is the most suitable material for biodegradable implant applications owing to its nontoxic behaviour and comparable Young's modulus to human bone. However, poor corrosion resistance limits its application. Therefore, surface texturing can be a more suitable and cost-effective technique to mitigate these issues. Hence, wire electric discharge machining (WEDM) is used to create various textures (wavy texture, microchannels, and micro-pillars) and investigate their influence on the corrosion resistance of Mg-Zn-Ca alloy. The results revealed that micropillar texture exhibited significantly lower surface roughness (Ra = 1.049 µm) and a higher contact angle indicative of hydrophobicity (130.3°), resulting in superior corrosion resistance (corrosion rate: 0.816 mm/year) compared to other textures and standard WEDM surfaces. These findings suggested that textured surfaces generated through WEDM hold the potential for enhancing the corrosion resistance of biodegradable Mg implants. © 2024 Elsevier B.V.