Faculty Publications
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Item Development and characteristics of accumulative roll bonded Mg-Zn/Ce/Al hybrid composite(Elsevier Ltd, 2017) Anne, G.; Ramesh, M.R.; Shivananda Nayaka, H.; Arya, S.B.; Sahu, S.Accumulative roll bonding (ARB) process have been used develop Mg-2%Zn/Ce/Al hybrid composite and microstructure, mechanical and corrosion properties were investigated. The electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) revealed that the grains are significantly reduced and reaches up to 1 ?m in Mg-2%Zn layer and 1.8 ?m in Al layer having high angle misorientation of grain boundaries after subjected to 5-passes of the ARB process. The Al17Mg12, AlMg4Zn11 and Al11Ce3 intermetallic phases were observed through the XRD analysis. Mechanical properties of the hybrid composite improved with increase in the number of ARB passes which is attributed to work hardening, grain refinement and uniform distribution of Ce particles. Presence of Ce in the hybrid composite restricts the phenomenon of dynamic recrystallization and prevents the grain growth during ARB process. The corrosion rate of Mg-Zn/Ce/Al hybrid composite (0.72 mm/y) improved about 3.3 times as compared to that of Mg-2%Zn alloy (2.37 mm/y). © 2017 Elsevier B.V.Item Effect of zinc and rare-earth element addition on mechanical, corrosion, and biological properties of magnesium(Cambridge University Press, 2018) Kottuparambil, R.R.; Bontha, S.; Ramesh, M.R.; Arya, S.; Jana, A.; Das, M.; Balla, V.K.; Amrithalingam, S.; Prabhu, T.R.The present work aims to understand the effect of zinc and rare-earth element addition (i.e., 2 wt% Gd, 2 wt% Dy, and 2 wt% of Gd and Nd individually) on the microstructure evolution, mechanical properties, in vitro corrosion behavior, and cytotoxicity of Mg for biomedical application. The microstructure results indicate that the Mg-Zn-Gd alloy consists of the lamellar long period stacking ordered phase. The electrochemical and immersion corrosion behavior were studied in Hanks balanced salt solution. Enhanced corrosion resistance with reduced hydrogen evolution volume and magnesium (Mg2+) ion release were estimated for the Mg-Zn-Gd alloy as compared to the other two alloy systems. At the early stage of corrosion, formation of the oxide film inhibited the corrosion propagation. However, at the later stages, the breaking of the oxide film leads to shallow pitting mode of corrosion. The ultimate tensile strength of Mg-Zn-Gd-Nd is better than the other two alloys due to the uniform distribution of the Mg12Nd precipitate phase. The moderate strength in the Mg-Zn-Gd alloy is due to the low volume fraction of the secondary phase. The MTT (methylthiazoldiphenyl-tetrazolium bromide) assay study was carried out to understand the cell cytotoxicity on the alloy surfaces. Studies revealed that all three alloys had significant cellular adherence and no adverse effect on cells. © 2018 Materials Research Society.Item Experimental Investigation on Effects of Wire Electro Discharge Machining of Ti50Ni45Co5 Shape Memory Alloys(Springer Netherlands rbk@louisiana.edu, 2018) Soni, H.; Narendranath, S.; Ramesh, M.R.TiNiCo shape memory alloy is most popular shape memory alloy for biomedical applications due to their outstanding properties such as shape memory effect, pseudoelasticity and transformation temperature. Machining of such kind of alloys is very difficult through conventional machining process is very difficult because they may affect their internal properties of these alloys. However conventional machining processes give poor surface quality during the machining hence non-conventional machining processes such as (wire electro discharge machining, water jet machining and electro discharge machining etc.) are more suitable for machining of such kind of alloy. From the literature it has been found that Wire electro discharge machining (WEDM) is more suitable non-conventional machining process for such kind of alloy. Present study exhibits the effects WEDM characteristics of Ti50Ni45Co5 shape memory alloy. L-9 orthogonal array has been created by using Taguchi as a design method for machining of selected alloy and machined surface characterization has been carried out at the optimized process parameters with respect to microstructures, surface topography, microhardness, XRD analysis and residual stresses. To find the optimum setting of the input process parameters a couple of optimization techniques are used, namely principal component analysis (PCA) and Gray relational analysis (GRA) technique. 125?s pulse on time (Ton), 35?s pulse off time (Toff) and 40V servo voltage (SV) were found as an optimal setting for the higher material removal rate (MRR) with better surface roughness (SR) in the present study. Moreover, characterization of the machined surface is performed with respect to microstructures, surface topography, microhardness analysis, XRD and residual stresses. Harder surface observed near the cutting edge and TiNio3 Tio2 and CuZn were noticed on the surface of machined component through XRD analysis. However, compressive residual stress has been noticed on the machined surface during WEDM process. © 2018, Springer Science+Business Media B.V., part of Springer Nature.Item Laser surface modification of Mg-Zn-Gd alloy: Microstructural, wettability and in vitro degradation aspects(Institute of Physics Publishing helen.craven@iop.org, 2018) Rakesh, K.R.; Bontha, S.; Ramesh, M.R.; Arya, S.; Das, M.; Balla, V.K.; Srinivasan, A.Mg-Zn-Gd have great potential for biomedical applications owing to excellent bioactivity and non-toxicity properties. In the present study, laser surface melting (LSM) was carried out on newly developed Mg-1Zn -2Gd (wt%) alloy. Effects of laser energy on microstructural evolution, corrosion properties, surface energy, and hardness have been investigated. The surface modified sample processed at different energy densities showed fine grain structure in the melt zone compared to the untreated substrate. Grain refinement in the laser melted region improved the hardness by 60%. The surface roughness was found to be increased with increasing laser energy density. At higher energy density, removal of materials from the surface is enhanced, resulting in deeper grooves and higher surface roughness. The wettability studies indicated that the variations in surface geometry, grain size and surface roughness of LSM samples strongly influence the surface energy and hydrophilicity. Improved wetting of LSM sample was achieved owing to grain refinement and low surface roughness. The corrosion resistance determined by immersion and electrochemical methods of laser melted sample in Hank's balanced salt solution improved considerably due to grain refinement, meltpool depth and uniform distribution of secondary phases. © 2018 IOP Publishing Ltd.Item Influence of Multidirectional Forging on Microstructural, Mechanical, and Corrosion Behavior of Mg-Zn Alloy(Springer New York LLC barbara.b.bertram@gsk.com, 2019) Ramesh, S.; Anne, G.; Shivananda Nayaka, H.S.; Sahu, S.; Ramesh, M.R.Multidirectional forging (MDF) was applied to Mg-6%Zn alloy up to 5 passes successfully at 280 °C. MDF-processed materials were characterized using optical microscope, scanning electron microscope, electron backscatter diffraction, transmission electron microscope, and x-ray diffraction. Obtained results showed a significant reduction in grain size (up to 3.8 ?m) having a large fraction of high-angle grain boundaries after 5 passes of MDF process. Maximum tensile strength of 230 MPa was achieved for 5-pass MDF-processed Mg-6%Zn alloy which is about ~ 2.0 times higher in comparison with that of homogenized alloy (117 MPa) and was attributed to higher dislocations density and grain refinement. Corrosion behavior of the alloy was investigated in 0.1 M NaCl solution using potentiodynamic polarization test, electrochemical impedance spectra analysis, and immersion tests. It was found that the corrosion rate of 5-pass MDF sample improved (0.34 mm/year) ~2.5 times in comparison with that of homogenized Mg-6%Zn alloy (0.86 mm/year) due to fine grain structure, which creates more grain boundaries that act as a corrosion barrier. © 2019, ASM International.Item Investigation of dry sliding wear properties of multi-directional forged Mg–Zn alloys(National Engg. Reaserch Center for Magnesium Alloys zhangdingfei@cqu.edu.cn, 2019) Ramesh, S.; Anne, G.; Shivananda Nayaka, H.S.; Sahu, S.; Ramesh, M.R.Effect of multi-directional forging (MDF) on wear properties of Mg–Zn alloys (with 2, 4, and 6 wt% Zn) is investigated. Dry sliding wear test was performed using pin on disk machine on MDF processed and homogenized samples. Wear behavior of samples was analyzed at loads of 10 N and 20 N, with sliding distances of 2000 m and 4000 m, at a sliding velocity of 3 m/s. Microstructures of worn samples were observed under scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and x-ray diffraction (XRD) and the results were analyzed. Mechanical properties were evaluated using microhardness test. After 5 passes of MDF, the average grain size was found to be 30 ± 4 µm, 22 ± 3 µm, and 18 ± 3 µm, in Mg–2%Zn, Mg–4%Zn, and Mg–6%Zn alloys, respectively, with significant improvement in hardness in all cases. Wear resistance was improved after MDF processing, as well as, with increment in Zn content in Mg alloy. However, it decreased when the load and the sliding distance increased. Worn surface exhibited ploughing, delamination, plastic deformation, and wear debris along sliding direction, and abrasive wear was found to be the main mechanism. © 2019Item Tailoring surface characteristics of bioabsorbable Mg-Zn-Dy alloy using friction stir processing for improved wettability and degradation behavior(Elsevier Editora Ltda, 2021) Rokkala, U.; Bontha, S.; Ramesh, M.R.; Balla, V.K.; Srinivasan, A.; Kailas, S.V.Magnesium (Mg) and its alloys are currently under consideration for use as temporary implants. However, early degradation and maintaining mechanical integrity is a significant concern. Surface modification techniques are used to improve mechanical and corrosion properties of Mg based alloys. In the present study, friction stir processing (FSP) was used to tailor the surface characteristics of Mg-1Zn-2Dy (wt.%) alloy for temporary implant applications. The FSPed alloy was characterized using EBSD to understand the influence of FSP on crystallographic texture, grain size and grain boundaries and thereby their effect on corrosion, wettability and hardness. Results showed that the grain size of stir zone (SZ) was refined to less than 3 ?m, as a result of dynamic recrystallization (DRX) during FSP and the FSPed alloy exhibited better wettability than as-cast alloy. An increase in the hardness (11.7%) and elastic modulus (6.84%) of FSPed alloy were also observed. Electrochemical corrosion and weight loss methods were conducted in Dulbecco's Modified Eagle's Medium (DMEM) with, 10% Fetal Bovine Serum (FBS) physiological solution. The lower degradation rate (0.72 mm/yr) of FSPed alloy has been attributed to the fine grains and evenly distributed secondary phase particles. Further, the influence of grain boundary characteristics and crystallographic texture on the corrosion behavior have been investigated. © 2021 The Author(s).Item 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.Item 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.Item Comparative Study of Plasma Spray and Friction Stir Processing on Wear Properties of Mg-Zn-Dy Alloy(Springer, 2024) Rokkala, U.; Gudala, S.; Ramesh, M.R.Mg alloys are becoming increasingly popular as lightweight materials in recent years. Wear resistance, on the other hand, is a severe issue with Mg alloys. Plasma spray and friction stir processing (FSP) are being investigated in this context for developing composite surfaces with improved surface characteristics. Scanning electron microscopy (SEM), energy dispersive spectroscopy, and x-ray diffraction are used to examine the microstructural changes and phase changes of all materials. After FSP, SEM analysis indicated that the coated particles were equally dispersed throughout the Mg matrix. The composite samples had the lowest wear rate as compared to other samples, according to the wear tests. In comparison to AC, the F-1 sample surface has much higher wear resistance. As a consequence, the findings of this investigation for the F-1 sample appear encouraging for biological wear resistant applications. © ASM International 2023.