Faculty Publications
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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 Wear Properties of ECAP-Processed AM80 Magnesium Alloy(Springer New York LLC barbara.b.bertram@gsk.com, 2017) Gopi, K.R.; Shivananda Nayaka, H.; Sahu, S.AM80 magnesium alloy was subjected to equal-channel angular pressing (ECAP), and microstructural evolution was studied using scanning electron microscope (SEM). Grain size was found to decrease up to 3 µm after four passes. An increase in number of ECAP passes led to a corresponding increase in hardness of the processed samples. Unprocessed and ECAP-processed samples were subjected to wear test using pin-on-disk wear test machine to study the wear behavior. Effects of varying loads (30 and 40 N) with sliding distances (2500 and 5000 m) were studied. The results showed reduction in wear mass loss for the ECAP-processed samples in comparison with unprocessed condition. Coefficient of friction (COF) was studied for different loads, and improvement in COF values was observed for ECAP-processed samples compared to unprocessed condition. Worn surfaces were studied using SEM and energy-dispersive x-ray spectrometer, and they exhibited plastic deformation, delamination, plowing, wear debris and oxidation in the sliding direction. X-ray diffraction analysis was conducted on the worn surfaces to identify the phases. It revealed the presence of magnesium oxide and magnesium aluminum oxide which led to oxidation wear in the sliding direction. Wear mechanism was found to be abrasive and oxidation wear. © 2017, ASM International.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 Strength enhancement of magnesium alloy through equal channel angular pressing and laser shock peening(Elsevier B.V., 2020) Praveen, T.R.; Shivananda Nayaka, H.; Swaroop, S.; Gopi, K.R.AM80 magnesium alloy was processed by Equal Channel Angular Pressing up to 2 passes under route BC and C, to study the effect of change in microstructure. Microstructures were examined under optical microscope. Samples processed by route BC showed heterogeneous grain structure with good tensile strength compared to that processed by route C. Tensile tests of 2-pass equal channel angular pressed samples showed high tensile strength under route BC. Laser shock peening without coating was carried out on route BC sample for further grain refinement on the surface. Laser pulses with power density of 8 GW cm?2, under different percentages of cover, were used to peen the surface at high strain rate. Microstructures were analysed through scanning and transmission electron microscope, and fine grains of less than 100 nm were observed. Tensile tests indicated that the laser shock peened samples had increased strength and ductility. Fracture details from tensile tested specimens, were examined under SEM. Mixed mode of brittle and ductile fractures was observed in ECAP processed samples. Fracture surface of Laser shock peening without coating treated on equal channel angular pressed samples showed small dimples near the peened surface and intensity of dimples increased with increase in percentage of cover. Wear test was carried out on before and after Laser shock peening without coating processed samples, on pin-on-disc wear test machine. Increase in friction coefficients and wear rate was observed due to roughness induced by peening effect and it decreased after increase in sliding distance due to increase in hardness. Nano indentation experiments were carried out to examine the mechanical characterization at nano level, and it expose the effect of LSPwC in terms of increase in hardness at peened region. © 2020