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Sathiyamoorthi, Praveen,Moon, Jongun,Bae, Jae Wung,Asghari-Rad, Peyman,Kim, Hyoung Seop Elsevier 2019 Scripta materialia Vol.163 No.-
<P><B>Abstract</B></P> <P>Ultrafine-grained materials with nanotwins are expected to produce a remarkable combination of strength and ductility. In the present study, ultrafine-grained CoCrNi medium-entropy alloy with nanotwins is fabricated by high-pressure torsion followed by annealing; and investigated for cryogenic tensile properties. The alloy exhibits superior cryogenic tensile properties with a tensile strength of ~2 GPa and tensile strain of ~27%. The cryogenic tensile strength of ultrafine-grained sample increased by 67% as compared to the cryogenic tensile strength of coarse-grained sample due to fine grain size, annealing nanotwins, residual dislocation density, and strong temperature dependence of yield strength.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Fine tuning of tensile properties in CrCoNi medium entropy alloy through cold rolling and annealing
Sathiyamoorthi, Praveen,Asghari-Rad, Peyman,Bae, Jae Wung,Kim, Hyoung Seop Elsevier 2019 Intermetallics Vol.113 No.-
<P><B>Abstract</B></P> <P>In the present study, tensile properties of CrCoNi medium entropy alloy with different microstructures (recovery, partial recrystallization, recrystallization) were investigated by subjecting cold-rolled samples to different annealing conditions. The microstructure of the cold-rolled sample showed the presence of severely deformed grains with several deformation twins. Annealing of the cold-rolled samples at 700 °C and above for 60 min led to fully recrystallized microstructure, while annealing at temperatures lower than 700 °C led to recovery and partially recrystallized microstructures. The annealed samples showed a typical strength-ductility trade-off with an increasing fraction of recrystallized grains and increasing average grain size in samples with partially recrystallized and fully recrystallized microstructure, respectively. Fine tuning of microstructure led to a remarkable combination of strength (~1 GPa) and uniform elongation (28%) in the sample with partially recrystallized microstructure, which consists of ~77% of recrystallized grains with an average recrystallized grain size of ~3 μm.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Fine tuning of microstructure through cold rolling and annealing. </LI> <LI> A reasonable ductility requires minimum of 55% of recrystallized grains. </LI> <LI> Optimal tensile properties achieved in sample with 77% recrystallized grains. </LI> <LI> Combination of strengthening from back stress and Hall-Petch effect. </LI> </UL> </P>
Yim, Dami,Sathiyamoorthi, Praveen,Hong, Soon-Jik,Kim, Hyoung Seop Elsevier 2019 Journal of alloys and compounds Vol.781 No.-
<P><B>Abstract</B></P> <P>In this study, the TiC-reinforced CoCrFeMnNi high-entropy alloy (HEA) composite was fabricated using water atomization (WA), mechanical milling (MM), and spark plasma sintering (SPS). The microstructural evolution and mechanical properties of TiC-reinforced HEA composite are investigated using electron backscatter diffraction, transmission electron microscopy, and room temperature compression tests. The addition of 5 wt% of TiC nano-particles to CoCrFeMnNi HEA resulted in fine grain size, high yield strength, and high strain hardening. The average grain size achieved for alloys with and without TiC after sintering is 5.1 μm and 10.6 μm, respectively. The addition of TiC increases the compressive yield strength from ∼507 MPa to ∼698 MPa and compressive fracture strength from ∼1527 MPa to ∼2216 MPa, without sacrificing the ductility. The strengthening behavior of TiC-reinforced CoCrFeMnNi HEA composite is quantitatively discussed based on grain boundary strengthening, dislocation strengthening, and dispersion strengthening. The role of TiC nano-particles in the strain hardening improvement is investigated with respect to the dislocation-particle interaction and consequently increased dislocation density.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Fabrication of TiC reinforced CoCrMnFeNi high entropy alloy composite by powder metallurgy route. </LI> <LI> TiC particles prevents grain boundary movement and results in fine grain size of FCC matrix after sintering. </LI> <LI> CoCrMnFeNi-TiC composite shows enhanced mechanical properties as compared to CoCrMnFeNi alloy. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Asghari-Rad, Peyman,Sathiyamoorthi, Praveen,Bae, Jae Wung,Moon, Jongun,Park, Jeong Min,Zargaran, Alireza,Kim, Hyoung Seop Elsevier 2019 Materials science & engineering. properties, micro Vol.744 No.-
<P><B>Abstract</B></P> <P>In the present study, V<SUB>10</SUB>Cr<SUB>15</SUB>Mn<SUB>5</SUB>Fe<SUB>35</SUB>Co<SUB>10</SUB>Ni<SUB>25</SUB> (at%) high-entropy alloy (HEA) of a single phase face-centered cubic structure with various grain sizes was fabricated. The influences of grain size on the work-hardening behavior and deformation mechanisms were investigated. The fine-grained and coarse-grained samples showed different work hardening behaviors during room temperature tensile deformation. Microstructural analysis revealed the presence of a high-density tangled dislocation structure without any mechanical twinning in the fine-grained sample, while mechanical twinning was observed to be the additional deformation mechanism in the coarse-grained sample.</P>
Thi-Cam Nguyen, Nhung,Moon, Jongun,Sathiyamoorthi, Praveen,Asghari-Rad, Peyman,Kim, Geon Hyeong,Lee, Chong Soo,Kim, Hyoung Seop Elsevier 2019 Materials science & engineering. properties, micro Vol.764 No.-
<P><B>Abstract</B></P> <P>In this study, the superplasticity of nanostructured V<SUB>10</SUB>Cr<SUB>15</SUB>Mn<SUB>5</SUB>Fe<SUB>35</SUB>Co<SUB>10</SUB>Ni<SUB>25</SUB> (at%) high-entropy alloy processed by high-pressure torsion was investigated using high-temperature tensile testing in the temperature range of 873–1073 K and strain rate range of 5.0✕10<SUP>−4</SUP> to 1.0✕10<SUP>−2</SUP> s<SUP>−1</SUP>. The alloy exhibited extreme elongation at these elevated temperatures, with the greatest elongation of 770% at 973 K without any necking or a notable cavity in the fracture area. Other impressive achievements were also recorded (700% elongation at 1073 K and 3.3✕10<SUP>−3</SUP> s<SUP>−1</SUP> and 600% elongation under other conditions). The equiaxed microstructure was maintained in both the deformed and undeformed regions of the tensile specimen, demonstrating that grain-boundary sliding is the dominant mechanism of superplasticity.</P>
Asghari-Rad, Peyman,Choi, Yeon Taek,Nguyen, Nhung Thi-Cam,Sathiyamoorthi, Praveen,Kim, Hyoung Seop The Korean Powder MetallurgyMaterials Institute 2021 한국분말재료학회지 (KPMI) Vol.28 No.4
In this study, the layered structures of immiscible Fe and Cu metals were employed to investigate the interface evolution through solid-state mixing. The pure Fe and Cu powders were cold-consolidated by high-pressure torsion (HPT) to fabricate a layered Cu-Fe-Cu structure. The microstructural evolutions and flow of immiscible Fe and Cu metals were investigated following different iterations of HPT processing. The results indicate that the HPT-processed sample following four iterations showed a sharp chemical boundary between the Fe and Cu layers. In addition, the Cu powders exhibited perfect consolidation through HPT processing. However, the Fe layer contained many microcracks. After 20 iterations of HPT, the shear strain generated by HPT produced interface instability, which caused the initial layered structure to disappear.