Faculty Publications
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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 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 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 Influence of Multidirectional Forging on Microstructural, Mechanical, and Corrosion Behavior of Mg-Zn Alloy(Springer New York LLC barbara.b.bertram@gsk.com, 2019) Ramesh, S.; Anne, G.; Shivananda Nayaka, H.S.; Sahu, S.; Ramesh, M.R.Multidirectional forging (MDF) was applied to Mg-6%Zn alloy up to 5 passes successfully at 280 °C. MDF-processed materials were characterized using optical microscope, scanning electron microscope, electron backscatter diffraction, transmission electron microscope, and x-ray diffraction. Obtained results showed a significant reduction in grain size (up to 3.8 ?m) having a large fraction of high-angle grain boundaries after 5 passes of MDF process. Maximum tensile strength of 230 MPa was achieved for 5-pass MDF-processed Mg-6%Zn alloy which is about ~ 2.0 times higher in comparison with that of homogenized alloy (117 MPa) and was attributed to higher dislocations density and grain refinement. Corrosion behavior of the alloy was investigated in 0.1 M NaCl solution using potentiodynamic polarization test, electrochemical impedance spectra analysis, and immersion tests. It was found that the corrosion rate of 5-pass MDF sample improved (0.34 mm/year) ~2.5 times in comparison with that of homogenized Mg-6%Zn alloy (0.86 mm/year) due to fine grain structure, which creates more grain boundaries that act as a corrosion barrier. © 2019, ASM International.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 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 Effect of Multi-directional Forging on the Evolution of Microstructural and Mechanical Properties of Lightweight Al-Cu-Li Alloy AA2050(Springer, 2023) Jagadeesh, C.; Shivananda Nayaka, H.S.; Ramesh, S.; Praveen, T.R.Microstructural evolution and the mechanical properties of recently developed lightweight AA2050 Al-Cu-Li alloy have been presented. A processing route of multi-directional forging (MDF) at 170 °C followed by artificial aging at 150 °C was employed. Systematic EBSD analysis revealed significant grain refinement with grain size reducing from 74.3 ± 12 to 22.1 ± 2.8 µm after 12 passes of MDF. Transformation of deformation bands into subgrains with dynamic recrystallization has led to grain refinement. TEM results show the presence of large dislocation clusters and deformation bands in MDF processed samples with a large number of fine precipitates in peak aged MDF processed samples. XRD analysis shows variation in peak intensities and occurrence of peak shifts due to induced lattice strain upon MDF. A substantial increase in microhardness and strength was observed with a minor trade-off with ductility after 12th MDF pass. Further, enhancement in strengths and microhardness were observed in post-MDF aged samples. Experimental results show the combined effect of strain hardening, grain size reduction, and precipitate hardening which influence the material strength. A combination of MDF and artificial aging has shown great potential to enhance the strength and ductility of AA2050. © 2023, ASM International.Item Enhancing surface characteristics of Mg-Zn-Sr alloy through cryo-ball burnishing; modeling and experimentation(Korean Society of Mechanical Engineers, 2024) Kudva, S.A.; Anne, G.; Ramesh, S.; Sharma, P.; Jagadeesh, C.; Ritti, L.; Naik, G.M.; Divya Deepak, G.D.In this investigation, the impact of the cryo-ball burnishing process on both the mechanical and corrosion properties of the Mg-4Zn-1Sr alloy was systematically explored. To better understand the plastic deformation occurring in Mg-4Zn-1Sr during cryo-burnishing, a finite element analysis (FEA) model was developed. The microstructure of cryo-ball burnished samples underwent characterization through scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometry (XRD), and surface properties were assessed using atomic force microscopy (AFM). Additionally, electrochemical impedance spectroscopy and potentiodynamic polarization tests were conducted in a simulated body fluid using an electrochemical workstation. Experimental findings revealed significant grain refinement and the presence of residual dislocations during the cryo-burnishing process, as evident in TEM analysis. XRD analysis indicated the presence of Mg, Mg17Sr2 and SrZn2 phases, with observable peak broadening in the cryo-burnished samples, attributed to structural refinement and lattice strain incorporation. Microhardness values increased with greater depth of press, with the DFN 1071 sample displaying a hardness of 80 ± 4 Hv (Ra = 1.853 µm), marking a 54 % improvement compared to the homogenized sample. The enhanced corrosion resistance of the Mg-4Zn-1Sr alloy due to cryo-burnishing is attributed to the combined effects of grain refinement, residual dislocations, and intermetallic phases. © The Korean Society of Mechanical Engineers and Springer-Verlag GmbH Germany, part of Springer Nature 2024.Item Combined effect of multidirectional forging and heat treatment on erosion and corrosion behaviour of the Mg-Zn-Mn alloys(Korean Society of Mechanical Engineers, 2024) Anne, G.; Hegde, A.; Kudva, S.A.; Sharma, P.; Kumar, P.; Matapati, M.; Ramesh, S.; Sharma, S.S.Multidirectional forging (MDF) was successfully applied to the Mg-4Zn-1Mn alloy for five passes at 300 °C. The grain size of 5 pass MDF processed samples reached 18 ± 3 µm from 256 ± 6 µm, and ?-Mg, MgZn2 and MnZn13 peaks were observed. Further MDF processed samples were solution treated (ST) at 300 °C for 2 h and quenched in SAE 20W40 oil and followed by artificial ageing (A) at 170 °C for four different timings including 1.5 h, 2 h, 2.5 h and 3.5 h respectively. The peak hardness of 219 Hv (5 pass MDF + H sample) was found in 2h artificial ageing which is 3.1 times higher compared to counterpart homogenised samples. Improvement of mechanical properties was attributed to smaller grain size and precipitation strengthening as well as distribution of the secondary phases. The combined effect of MDF and heat treatment was analysed using solid particle erosion tests at 30° and 90° impact angles using alumina. It was observed that higher impact angle (90°) had more erosion rate in all conditions and 5 pass MDF + H samples exhibited better erosion (0.0001 mg/g) due to higher hardness. On the other hand, polarisation and electrochemical impedance spectroscopy measurements were used to assess the alloys’ corrosion behaviour. The 3 pass MDF + H sample was found to have a corrosion rate of 0.0235 mm/y, which is two times lower than the counterpart 3 pass MDF processed samples and sixteen times lower than the homogenised sample (0.3838 mm/y). This was primarily due to the secondary phases’ better distribution and smaller grain size. © The Korean Society of Mechanical Engineers and Springer-Verlag GmbH Germany, part of Springer Nature 2024.