Faculty Publications
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Item Influence of Multi Axial Forging (MAF) on Microstructure and Mechanical Properties of Cu-Ti Alloy(Elsevier Ltd, 2018) Ramesh, S.; Shivananda Nayaka, H.S.; Gopi, K.R.Multi axial forging (MAF) is one among the severe plastic deformation (SPD) processes, where large strains are imposed into the component. In the present work, as-received Cu-1.5%Ti alloy was subjected to MAF for 2 and 4 cycles at room temperature. Microstructure showed grain refinement after 2 and 4 cycles. Average grain size obtained for MAF processed samples after 2 and 4 cycles are 120 μm and 40 μm, respectively compared to initial grain size of 800 μm. The Mechanical properties were analyzed for as-received and MAF processed samples. Tensile test showed increased ultimate tensile strength (493 MPa) for MAF 4-cycle sample compared to as-received (191 MPa) condition with accumulated strain of 2.18 for 4 cycles. Increase in hardness was observed for MAF processed sample of 143 Hv for 4-cycle compared to as-received sample of 67 Hv. © 2018 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 Investigation of Microstructure and Mechanical Properties of ECAP-Processed AM Series Magnesium Alloy(Springer New York LLC barbara.b.bertram@gsk.com, 2016) Gopi, K.R.; Shivananda Nayaka, H.S.; Sahu, S.Magnesium alloy Mg-Al-Mn (AM70) was processed by equal channel angular pressing (ECAP) at 275 °C for up to 4 passes in order to produce ultrafine-grained microstructure and improve its mechanical properties. ECAP-processed samples were characterized for microstructural analysis using optical microscopy, scanning electron microscopy, and transmission electron microscopy. Microstructural analysis showed that, with an increase in the number of ECAP passes, grains refined and grain size reduced from an average of 45 to 1 µm. Electron backscatter diffraction analysis showed the transition from low angle grain boundaries to high angle grain boundaries in ECAP 4 pass sample as compared to as-cast sample. The strength and hardness values an showed increasing trend for the initial 2 passes of ECAP processing and then started decreasing with further increase in the number of ECAP passes, even though the grain size continued to decrease in all the successive ECAP passes. However, the strength and hardness values still remained quite high when compared to the initial condition. This behavior was found to be correlated with texture modification in the material as a result of ECAP processing. © 2016, ASM International.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 Microstructural Evolution and Strengthening of AM90 Magnesium Alloy Processed by ECAP(Springer Verlag, 2017) Gopi, K.R.; Shivananda Nayaka, H.S.; Sahu, S.Equal-channel angular pressing (ECAP) was applied on AM90 magnesium alloy using processing route B C at 275?C up to four passes. Microstructural evolution and the corresponding modification in mechanical properties (strength, elongation and hardness) corresponding to the number of ECAP passes were evaluated using X-ray diffraction (XRD), electron backscatter diffraction, scanning electron microscopy, transmission electron microscopy, tensile test and microhardness test. Shear deformation was found to refine the microstructure by breaking it into smaller grains formed by dislocation reconstruction. Tensile strength and hardness were found to increase by ? 128 and 23%, respectively, for ECAP-processed 2-pass sample in comparison with that of the homogenized condition. After two passes, tensile strength and hardness started decreasing even though the grain size was still decreasing, which was found to be associated with texture modification during ECAP processing as observed by XRD analysis. © 2017, King Fahd University of Petroleum & Minerals.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 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.Item Effect of multiaxial cryoforging on microstructure and mechanical properties of a Cu-Ti Alloy(Institute of Physics Publishing helen.craven@iop.org, 2019) Ramesh, S.; Shivananda Nayaka, H.S.; Gopi, K.R.; Sahu, S.Cu-Ti alloy, processed by multiaxial forging (MAF) at cryogenic temperature with a cumulative strain up to 1.64, was investigated for microstructure and mechanical properties. The deformed microstructures were analyzed using optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The average grain size of 2 ?m was achieved in the deformed sample after 3 cycles of MAF. TEM studies indicated that the shear bands width of the deformed sample after 3 cycles reduced to 1 ?m. Tests for mechanical properties indicated an increase in tensile strength and hardness and it was found to be correlated with an increase in dislocation density and grain boundary strengthening mechanism. Ultimate tensile strength (UTS) of 390 MPa, 480 MPa, and 590 MPa was observed in MAF processed samples after 1, 2, and 3 cycles, respectively. Hardness increased from 65 Hv (as-received) to 240 Hv after 3 cycles of MAF. Fractography analysis showed that, with an increase in number of MAF cycles, dimple size reduced up to 1 cycle and percentage elongation increased after 2 cycles of MAF. © 2018 IOP Publishing Ltd.Item Impact of ECAP on wear performance of Al-Mn magnesium alloy(Institute of Physics Publishing helen.craven@iop.org, 2020) Gopi, K.R.; Shivananda, N.H.The current study examines the wear performance of deformed AM90 magnesium alloy using pin-on-disc wear test apparatus under varying load of 30 and 40 N with the sliding distance of 2500 m and 5000 m at constant sliding speed of 3 m s-1. The samples were processed through equal channel angular pressing were subjected to microstructural, wear studies and are characterized by optical and scanning electron microscopy. Vickers microhardness was carried out to evaluate the relation between the wear behavior of homogenized and ECAP processed samples. Increment in number of ECAP passes increased the grain refinement as observed in the microstructure with reduction in grain size from ?70 ?m (homogenized sample) to ?4 ?m (ECAP 4 pass sample). Increase in wear resistance and hardness were observed for processed samples and the worn faces are analyzed by scanning electron microscopy and energy-dispersive X-ray spectrometer. The worn surfaces revealed the occurrence of wear debris, delamination, ploughing in the direction of sliding and the predominant wear mechanism was considered to be the combination of oxidation and abrasive wear. © 2020 The Author(s). Published by IOP Publishing Ltd.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