Faculty Publications
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Item Effect of Rolling Reduction on Microstructure and Mechanical Properties Cu-3%Ti Alloy(Pleiades journals, 2019) Singh, P.; Ramesh, S.; Anne, G.; Shivananda Nayaka, H.Cu-3%Ti alloy is cold rolled with different reduction ratios and the microstructures and mechanical properties are compared with that of as-cast Cu-3%Ti alloy. Microstructure was analyzed using optical microscope and scanning electron microscope. Optical microscopy revealed significant grain refinement that occurred during the rolling process. Tensile test results indicate that the UTS is increased by a significant amount up to 80% rolling reduction. A significant amount of tensile strength increased up to 812 MPa is about 1.69 times that of the cast Cu-3%Ti alloy. Hardness of the rolled Cu-3%Ti increased as % reduction increased. Dimples were revealed on the fracture surface of the rolled Cu-3%Ti specimens indicating a ductile nature of the fracture. © 2019, Springer Nature Singapore Pte Ltd.Item Microstructure and mechanical properties of magnesium alloy processed by equal channel angular pressing (ECAP)(Elsevier Ltd, 2017) Gopi, K.R.; Shivananda Nayaka, H.Equal Channel Angular Pressing (ECAP) with different passes was carried out for Mg-Al-Mn (AM) series magnesium alloy to investigate the microstructure and mechanical properties. ECAP process was carried up to 4 passes using route BC, where the samples are rotated by 90° in the same direction between consecutive passes. Microstructures were studied using optical microscope (OM) and scanning electron microscope (SEM) and it was observed that the grain size was reduced from 100 μm to 1 μm after 4 passes. Tensile test was conducted and the ultimate tensile strength (UTS) increased up to 2 passes but decreased with higher passes, even though grain size became finer with increase in ECAP passes. Microhardness was carried out and it was observed that the hardness was increased up to 2 passes of ECAP and decreased with higher passes. © 2017 Elsevier Ltd.Item Electrochemical Behaviour of ECAP-Processed AM Series Magnesium Alloy(Springer International Publishing, 2019) Gopi, K.R.; Shivananda Nayaka, H.Equal channel angular pressing (ECAP) is a technique for inducing high strain into the material to achieve ultrafine grain refinement. AM80 magnesium was processed by ECAP with processing route BC. ECAP-processed samples were tested for microstructural studies and electrochemical measurements. Potentiodynamic polarization test revealed decrease in corrosion current density due to uniform refined microstructure of the processed samples. Increment in charge transfer resistance (Rt) was observed for ECAPed samples with increase in capacitive arc diameters in Nyquist plots showing increased corrosion resistance in comparison with as-cast condition. The increment in corrosion resistance is because of grain refinement and uniform dispersal of intermetallic particles, which improved development of protective layer and bonding due to increased grain boundary density by ECAP process. © 2019, The Minerals, Metals & Materials Society.Item Effect of equal channel angular pressing on AZ31 wrought magnesium alloys(National Engg. Reaserch Center for Magnesium Alloys zhangdingfei@cqu.edu.cn, 2013) Muralidhar, A.; Narendranath, S.; Shivananda Nayaka, H.AZ31 wrought magnesium alloys are light weight materials which play an important role in order to reduces the environmental burdens in modern society because of its high strength to weight ratio, corrosion resistance, and stiffness and machinability. Applications of this material are mainly in structural component i.e., in constructions, automobile, aerospace, electronics and marine industries. In the present work, the microstructure characterization of the AZ31 alloys up to four ECAP passes at temperature of 573 K was observed for route Bc. Average grain size of the material was reduced from 31.8 ?m to 8 ?m after four ECAP passes. Mechanical properties of the alloy improved with increase in number of ECAP passes. Moreover, X-ray diffraction analysis was carried out for as received and ECAP processed material. © 2013 National Engineering Research Center for Magnesium Alloys of China, Chongqing University.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 Development and properties evaluation of Mg-6% Zn/Al multilayered composites processed by accumulative roll bonding(Cambridge University Press, 2017) Anne, G.; Ramesh, M.R.; Shivananda Nayaka, H.; Arya, S.B.; Sahu, S.Accumulative roll bonding (ARB) process was used to develop Mg-6% Zn/Al and Mg-6% Zn/anodized-Al multilayered composites. Microstructural characterization was done using scanning electron microscopy, energy-dispersive X-ray spectroscopy, electron backscattered diffraction, and transmission electron microscopy. An average grain size measured in the roll-bonded layers of Al, anodized Al, and Mg-2% Zn was found to be 1.8 ?m, 1.6 ?m, and 0.6 ?m, respectively. Phases Al17Mg12, AlMg4Zn11, and Al2O3 after 5-pass of ARB were confirmed by X-ray diffraction analysis. The Mg-6% Zn/Al and Mg-6% Zn/anodized Al composites exhibited tensile strengths ?252 MPa and ?256 MPa, respectively, after a 5-pass ARB process. Hardness of the individual layers of composite increased linearly with an increase in the number of ARB passes. Fractographs of the multilayered composite illustrated the ductile failure in Al and anodized Al layers and transgranular brittle fracture in Mg-6% Zn layers. © Materials Research Society 2017.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 Numerical Simulation of Shot Peening Process on Equal Channel Angular Pressed Magnesium Alloy(Springer Netherlands rbk@louisiana.edu, 2018) Praveen, T.R.; Gopi, K.R.; Shivananda Nayaka, H.This paper presents the numerical simulation of inducing residual stresses on equal channel angular pressed (ECAP) magnesium alloy by shot peening process. Mg-Al-Mn (AM) series magnesium alloy was ECAP processed up to 4 passes using route BC. Microstructures were analysed and grain size reduced from 100 µm for the as-received sample to 3 µm for ECAP 4 pass sample. Tensile test was carried out and maximum tensile strength was found in ECAP 2 pass sample and decreased with higher ECAP passes. Grain refinement was characterized by optical microscopy, electron backscatter diffraction analysis (EBSD) and X-ray diffraction (XRD). Material (tensile) behaviour of 2 pass sample was implemented for finite element modelling. A finite element method was used to estimate the intensity of residual stresses developed due to shot peening in ECAP processed AM80 alloy. Simulation was done with different boundary condition such as impact velocity, geometry of shot-peen media, angle of impact and multiple impacts. The results are presented and the relationship between process parameters and the intensity of residual stresses are discussed. Increase in velocity of shot peening media showed an increase in the magnitude of residual stresses. Change in geometry of shot media altered the contact area between target and shot media during impact which influenced the magnitude of residual stresses and coverage area. The magnitude of residual stresses varied with the angle of impact and the multiple repeated impacts showed that the effective depth of residual stresses increased with the number of impacts. © 2018, Springer Science+Business Media B.V., part of Springer Nature.Item Investigation of microstructure and mechanical properties of the Cu-3% Ti alloy processed by multiaxial cryo-forging(Cambridge University Press, 2018) Ramesh, S.; Shivananda Nayaka, H.; Gopi, K.R.; Sahu, S.; Kuruveri, U.B.A Cu-3%Ti (wt%) alloy was processed by multiaxial forging (MAF) at cryogenic temperature up to 3 cycles, imposing a total strain of 1.6. Microstructure and mechanical properties of the unprocessed and cryo-forged samples were analyzed. X-ray diffraction results showed deviation in peak broadening and peak intensity of the cryo-forged samples in comparison to that of unprocessed, which are due to texture modification caused by grain refinement during the MAF process. Microstructural analysis showed reduction in grain size from 80 m in the as-received condition to 250 nm after 3 cycles. Electron backscatter diffraction results indicated the transformation of high angle grain boundaries to low angle grain boundaries in all 3 cycles when compared to the as-received condition. Reduction in ductility was observed after 1 cycle, but with an increase in the number of cycles, both strength and ductility increased. After 3 cycles, ultimate tensile strength and hardness reached 1126 MPa and 427 Hv as compared to 528 MPa and 224 Hv for the as-received condition. Fractography analysis showed decrement in dimple size after 1 cycle, in comparison to that of the as-received condition. However, it kept on increasing for higher number of cycles. © © Materials Research Society 2018.