Faculty Publications
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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 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.