Faculty Publications
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Item Tribological and corrosion properties of AM70 magnesium alloy processed by equal channel angular pressing(Cambridge University Press, 2017) Gopi, K.R.; Shivananda Nayaka, H.Wear and corrosion properties of AM70 magnesium alloy subjected to equal channel angular pressing (ECAP) were investigated using pin-on-disc dry sliding wear test and electrochemical impedance spectroscopy (EIS), respectively. Wear test was conducted with 30 and 40 N loads with sliding distance of 5000 m and at a constant speed of 3 m/s. Reduced coefficient of friction (COF) and wear mass loss of ECAP processed samples showed increased wear resistance. Worn surface analysis by scanning electron microscope (SEM) showed the presence of delamination, wear debris, and plowing. Energy dispersive X-ray spectrometer (EDS) revealed the occurrence of oxidation, and the wear mechanism was identified as abrasion and oxidation wear. EIS plots showed the improvement in corrosion resistance of ECAP processed magnesium alloy compared to initial condition due to grain refinement and homogeneous distribution of secondary particles. © Materials Research Society 2017.Item Corrosion Behavior of ECAP-Processed AM90 Magnesium Alloy(Springer Verlag, 2018) Gopi, K.R.; Shivananda Nayaka, H.; Sahu, S.Magnesium AM90 alloy was subjected to equal-channel angular pressing (ECAP) using route B C. Microstructural characterization revealed refined grains having average grain size ?3?m after ECAP 4 passes. Samples were subjected to electrochemical measurements to study the corrosion behavior. Potentiodynamic polarization test showed reduced corrosion current density (Icorr) for processed samples up to ECAP 3 pass due to grain refinement. Electrochemical impedance spectroscopy showed an increase in the diameter of the capacitive arcs and charge-transfer resistance (Rt) for ECAP-processed 3 pass sample indicating the reduction in corrosion rate. Increase in corrosion resistance is due to refined microstructure and uniform distribution of secondary particles forming a protective passivation layer (Mg (OH) 2) on the sample’s surface. Immersion test indicated lower hydrogen evolution from ECAP-processed samples compared to the unprocessed condition indicating decreased corrosion rate. © 2018, King Fahd University of Petroleum & Minerals.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 Investigation of Tribological and Corrosion Behavior of Cu-Ti Alloy Processed by Multiaxial Cryoforging(Springer, 2020) Ramesh, S.; Shivananda Nayaka, H.Wear and corrosion properties of Cu-3%Ti alloy subjected to multiaxial forging (MAF) under cryogenic conditions are estimated at room temperature. Wear study was performed using pin-on-disk dry sliding wear setup at 10 and 20 N loads with varying sliding distances (500-3000 m) under different sliding velocities (1 and 2 m/s). Coefficient of friction and wear mass loss decreases with an increase in MAF cycles, due to increases in hardness of samples. Wear resistance decreases with an increase in load and sliding velocity. Worn surface shows the plastic deformation regions, wear track, micro-cracks, micro-plowing groove and scratches. Potentiodynamic polarization test clearly shows that current density (Icorr) increases with an increase in MAF passes, because of grain refinement. Reduction in corrosion rate was evident from electrochemical impedance spectroscopy results which show increased diameter of the capacitive arc. An enhancement of corrosion resistance was revealed at higher MAF passes. © 2020, ASM International.Item Influence of Ball Burnishing Process on Equal Channel Angular Pressed Mg-Zn-Si Alloy on the Evolution of Microstructure and Corrosion Properties(Springer Science and Business Media B.V., 2021) Ramesh, S.; Anne, G.; Kumar, G.; Jagadeesh, C.; Shivananda Nayaka, H.In the present study, Mg-4Zn-1Si alloy was subjected to equal channel angular pressing (ECAP) up to 4 passes at 300 °C, followed by ball burnishing using 0.3 mm depth of press, 300 mm/min feed and 1 pass successfully. The effect of ECAP and ECAP + ball burnishing process on microstructure, mechanical properties (tensile and hardness) and corrosion behavior was systematically investigated. After 4 pass ECAP, initial coarse grains (210 ?m) were refined and average grain size is 6 ?m and after ball burnishing, the grain size is found to be 3.3 ?m. Microstructure evolution is discussed using optical images, scanning electron microscope images and transmission electron microscope images. For ECAP samples, maximum strength and hardness was recorded at 3 pass. Both strength and hardness decreased for 4 pass ECAP processed samples, even though grain size decreased, this is because of texture modification in the material. ECAP 4 pass + ball burnished samples exhibited 48.5% enhancement of microhardness as compared to 4 pass ECAP samples. Corrosion resistance of the samples decreased with increase in the number of ECAP passes, this is due to strain-induced grain refinement with more crystalline defects in samples. Combined process of ECAP and ball burnishing effectively reduces the Icorr and this consequently reduces corrosion rate of the Mg–4Zn-1Si alloy. © 2020, Springer Nature B.V.Item Effect of Equal Channel Angular Pressing on Properties Evaluation of Biodegradable Mg-Zn-Mn Alloy(Springer Science and Business Media Deutschland GmbH, 2021) Ramesh, S.; Kumar, G.; Jagadeesh, C.; Anne, G.; Shivananda Nayaka, H.Equal channel angular pressing (ECAP) was used to process Mg-4Zn-1Mn alloy at 300 °C using route Bc up to 4 pass with a cumulative strain of 3.2. Optical microscope (OM), microstructures results shows homogenized sample grain size was 260 µm, after 4 pass ECAP grain size was decreased to 6 µm. Electron back-scattered diffraction (EBSD) shows the misorientation angle converted from low-angle grain boundaries (LAGB) to high-angle grain boundaries (HAGB). Dislocation density and fine grains were observed from transmission electron microscope (TEM) images. Strength has been increased from 156 to 218 MPa and hardness increased to 68 Hv after 4 pass of ECAP. Fractography analysis revealed that dimple size decreases as ECAP passes increased. XRD analysis shows the peak broadening and intensity variation, because of grain refinement. The corrosion behavior of the homogenized and ECAP-processed samples were investigated by electrochemical tests using simulated body fluids (SBF) at 37 ± 1 °C. The lower corrosion resistance of ECAP-processed Mg-4Zn-1Mn alloy attributed to the strain-induced crystalline defects, subgrain boundaries and high-density dislocations. Enhanced strength and ductility combined with lower corrosion resistance of ECAP-processed Mg-4Zn-1Mn has greater potentials for biomedical implants. © 2021, The Author(s), under exclusive licence to Springer Nature Switzerland AG.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 EngineersItem 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.