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 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 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 Investigation of Tribological Characteristics of Cu-Ti Alloys Processed by Multi-Axial Cryo-Forging(Springer, 2022) Ramesh, S.; Shivananda Nayaka, H.S.; Anne, G.; Arun, M.N.; Naik, G.M.Cu-XTi alloys (X = 1.5 and 4.5%) were subjected to multi-axial forging (MAF) under cryogenic condition up to three passes successfully. Characteristics of the MAF-processed alloys were analyzed using microstructural analysis, hardness and wear tests. Worn surface morphology and elemental analysis was performed by scanning electron microscopy. The hardness of samples increases with higher MAF passes due to strain hardening and grain refinement. Wear test was done for six various sliding distances (500, 1000, 1500, 2000, 2500 and 3000 m), two different loads (10 and 20 N), and two different velocities (1 and 2 m/s) using the pin-on-disk wear test rig. Wear loss of as-received samples is higher than MAF-pressed samples due to an increase in hardness, but wear loss increases as the load increases. Coefficient of friction is reduced with the increase in MAF pass, which is due to strain hardening effect. The worn surface exhibits the plastic deformation regions, delamination, plowing and formation of oxide layers, which was revealed by energy-dispersive X-ray spectroscopy analysis. Also, MAF-processed samples exhibited abrasive wear mechanism as a result of formation of oxygen layer as revealed in SEM micrographs. © 2022, ASM International.