Faculty Publications

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Author: search.filters.author.Bontha, S.Subject: search.filters.subject.As-cast

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    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.
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    Influence of friction stir processing on microstructure, mechanical properties and corrosion behaviour of Mg-Zn-Dy alloy
    (Springer, 2023) Rokkala, U.; Bontha, S.; Ramesh, M.R.; Balla, V.K.
    In the present study, friction stir processing (FSP) was carried out on as-cast Mg-Zn-Dy alloy to tailor grain size and texture which alter the mechanical properties and corrosion behaviour. The grain size of the as-cast alloy was reduced from 60 ± 2 µm to 3 ± 0.1 µm after FSP due to dynamic recrystallization. The effect of grain size, crystallographic orientation and fine precipitates on mechanical properties were investigated using field emission scanning electron microscope (FESEM) and electron back scattered diffraction (EBSD). The ultimate tensile strength, yield strength, % elongation and hardness of FSPed alloy improved by 55%, 60%, 53% and 46% when compared to as-cast alloy. The FSPed Mg-Zn-Dy alloy exhibited a 79% decrease in corrosion rate when compared to as-cast alloy which can be attributed to grain refinement, uniform distribution of secondary precipitates and strong basal texture. The surface of FSPed sample after immersion corrosion exhibited calcium phosphate rich minerals which help in apatite formation on the sample surface. Cytotoxicity studies using MTT assay revealed more than 80% cell viability for both as-cast and FSPed alloy illustrating non-toxic nature of both the samples. The results of this study indicate that FSPed Mg-Zn-Dy alloy is a potential material for biodegradable implants due to its high strength, corrosion resistance and biocompatibility. Graphical Abstract: [Figure not available: see fulltext.]. © 2023, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
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    Microstructural Evolution of Mg-Zn-Gd Alloy Using Equal Channel Angular Pressing to Enhance Mechanical and Corrosion Properties
    (Springer, 2025) Rokkala, U.; Patil, A.; Bontha, S.; Ramesh, M.R.; Balla, V.K.; Srinivasan, A.
    Equal channel angular pressing (ECAP) was used on the Mg-Zn-Gd alloy in this study to improve its corrosion and mechanical properties. Microstructural and phase analysis reveal that, after ECAP, a substantial grain refinement occurred, and secondary phases were observed. The grain size of the as-cast (AC) sample is reduced from 20 ± 1 to 0.88 ± 0.6 µm, attributed to dynamic recrystallization. The mechanical properties of the ECAP sample were significantly improved when compared to the AC sample. An improvement in the microhardness (43%), ultimate tensile strength (73%), yield strength (76%), and ductility (50%) were observed for the ECAP sample. A decrease in the corrosion rate was observed for ECAP sample (9 ± 1 mm/year) compared to the AC (16 ± 2 mm/year) sample. The grain refinement and crystallographic orientation of the ECAP samples contributed to the enhancement of corrosion resistance. © ASM International 2025.