Faculty Publications
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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 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 Effects of combined multiaxial forging and rolling process on microstructure, mechanical properties and corrosion behavior of a Cu-Ti alloys(Institute of Physics Publishing helen.craven@iop.org, 2019) Ramesh, S.; Anne, G.; Shivananda Nayaka, H.; Sahu, S.; Arya, S.Combined multiaxial forging (MAF) and rolling was performed on Cu-3% Ti (wt%) alloy at room temperature with emphasis on microstructural evolution, improvement in mechanical properties, and corrosion resistance. Microstructural changes were confirmed from various characterization techniques, and co-related with mechanical properties. TEM analysis revealed high shear band density in the 3 pass MAF + 90% rolled sample appearing due to high strain. EBSD analysis revealed transformation to low angle grain boundaries from high angle grain boundaries. Maximum microhardness and UTS reached to 340 HV and 960 MPa, respectively in the processed samples. Significant grain refinement was observed in MAF processed Cu-3%Ti alloy, and after combined MAF + rolling, higher dislocation density and refinement of shear bands were observed. In addition, potentio-dynamic polarization test was used to study the corrosion behavior of the alloy. Scanning electron microscope (SEM) was used to analyze the corroded surface morphology. © 2019 IOP Publishing Ltd.Item Influence of Multiaxial Cryoforging on Microstructural, Mechanical, and Corrosion Properties of Copper-Titanium Alloy(Springer, 2019) Ramesh, S.; Shivananda Nayaka, H.S.; Sahu, S.; Gopi, K.R.; Shivaram, M.J.; Arya, S.Multiaxial forging (MAF) was used to process Cu-4.5%Ti (wt.%) alloy at cryogenic temperature up to three cycles with a cumulative strain of 1.64. Microstructures, mechanical, and corrosion properties of as-received and deformed samples were analyzed. Microstructural analysis showed that average grain size decreased from 70 µm to 200 nm, and electron backscattered diffraction (EBSD) analysis revealed the transformation of high-angle grain boundaries (HAGBs) to low-angle grain boundaries (LAGBs). Variations in intensity of peaks were observed by x-ray diffraction (XRD) technique. Microstructural investigation showed elongated grains with shear bands having width ~ 200 nm for 3-cycle sample. Tensile testing and micro-hardness tests showed improvements in ultimate tensile strength (UTS), yield strength (YS), and micro-hardness, with the increase in MAF cycles. Ultimate tensile strength and hardness increased from 605 MPa and 252 HV (for as-received) to 1284 MPa and 428 HV for three cycles of MAF-processed sample, respectively. Improvement in strength and hardness was attributed to refined grain structure. Corrosion study was carried out for different cycles of MAF-processed samples using potentiodynamic polarization, and corroded surfaces were analyzed using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) analysis. © 2019, ASM International.Item Surface modification of multi-directional forged biodegradable Mg-Zn alloy by ball burnishing process: Modeling and analysis using deep neural network(Elsevier Ltd, 2021) Ramesh, S.; Anne, G.; Bhat, N.; Aithal, G.; Shivananda Nayaka, H.; Arya, S.This research investigates the feasibility of improving surface integrity of the Mg-2%Zn alloy via a novel combined process of multidirectional forging (MDF) with ball burnishing technique. Mg-2%Zn alloy was subjected to multidirectional forging up to 5 passes at 280 °C and same sample is ball burnished with depth of press of 0.3 mm, feed of 300 mm/min and force of 250 N for 1 pass. Microstructure (optical and transmission electron microscope), phases (X ray diffraction), roughness (atomic force microscope) and mechanical properties (microhardness and tensile) were analyzed for cast, MDF processed and MDF + ball burnished samples. The study also defines a new reliability simulation framework to predict the roughness and hardness of the MDF + ball burnished samples using Deep Neural Network (DNN) approach. For the analysis, depth of press, feed and number of passes served as inputs for the DNN model. After configuring and training procedure of the model, the predicted roughness and microhardness of the MDF + ball burnished were compared with the results of experimental data. A large increase of microhardness was observed for MDF-5 + BB-1 (5 pass MDF processed Mg-2%Zn alloy + Ball burnished sample), found to be 98 Hv and surface roughness of 306 nm was achieved. According to the results, the obtained R-squared value is very close to the 99.5 percentage from the model for predicting roughness and hardness which is a promising result. Corrosion behavior of the AS-1, MDF-5 and MDF-5 + BB-1 was evaluated in Hank's balanced salt solution. Corrosion rate of the MDF-5 + BB-1 samples were found to be 0.87 mm/y which is 7 times better than that of AS-1 samples (6.10 mm/y). Grain refinement and residual stresses were higher in the MDF-5 + BB-1 sample, which helped significantly to enhance corrosion resistance. © 2021 The Society of Manufacturing Engineers