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258 results on '"Lee, Jae Heung"'

16. Regulation of cryogenic mechanical behaviors of C-added non-equiatomic CoCrFeNiMo ferrous medium-entropy alloy via control of initial microstructure.

Author

Lee, Ji Yeong, Kwon, Hyeonseok, Lee, Jae Heung, Kwon, Jihye, Wang, Jaemin, Bae, Jae Wung, Moon, Jongun, Lee, Byeong-Joo, Heo, Yoon-Uk, and Kim, Hyoung Seop

Subjects
IRON alloys, MARTENSITIC transformations, FACE centered cubic structure, TENSILE strength, CRYSTAL grain boundaries
Abstract

• Microstructures of an MEA were manipulated by annealing at different temperatures. • The roles of microstructural features in determining DIMT kinetics were investigated. • DIMT kinetics vary depending on the presence and fraction of precipitates. • DIMT kinetics changes according to grain size and nucleation sites were quantified. This study demonstrated the potential for customizing the desired properties of the Co 18.5 Cr 12 Fe 55 Ni 9 Mo 3.5 C 2 (at.%) ferrous medium-entropy alloy by manipulating the deformation-induced martensite transformation (DIMT) behavior at liquid nitrogen temperature. This was achieved by modifying various initial microstructures through annealing at temperatures ranging from 900 to 1200 °C. The variations in DIMT kinetics were analyzed based on two main factors. (1) Inducing carbide precipitation by annealing at 900 and 1000 °C results in changes in the composition within the matrix, which may affect the stability of the face-centered cubic phase. Samples with a higher volume fraction of the carbide precipitates exhibit lower Δ G FCC→BCC and faster DIMT kinetics. (2) The onset and kinetics of DIMT are also affected by the use of martensite nucleation sites, which may vary depending on the presence of non-recrystallized regions or the grain size. In fine-grained structures, martensite primarily nucleated in the non-recrystallized regions and grain boundaries. However, in coarse-grained microstructures, martensite mainly nucleated along the in-grain shear bands and their intersections. This precise control of the microstructure results in superior properties. The samples annealed at 900 and 1000 °C with carbide precipitates and fine grains exhibit ultrahigh ultimate tensile strength, which may reach elevated values up to ∼1.8 GPa, while those annealed at 1100 and 1200 °C with larger grains and no precipitates exhibit a uniform elongation that exceeds 100 %. [Display omitted] [ABSTRACT FROM AUTHOR]

Published
2025
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27. Synergic Combination of Strength and Ductility through Both Grain Refinement and Precipitation in Al0.3CoCrNi Medium‐Entropy Alloy.

Author

Lee, Jae Heung, Kwon, Hyeonseok, Sathiyamoorthi, Praveen, Son, Sujung, and Kim, Hyoung Seop

Subjects
GRAIN refinement, DUCTILITY, TORSION, CRYSTAL grain boundaries
Abstract

To improve the tensile properties of Al0.3CoCrNi (at%), herein, medium‐entropy alloys at room temperature, high‐pressure torsion (HPT), and appropriate annealing are presented. Severe deformation due to HPT causes fine grains and evenly distributed B2 and σ precipitates with a nanometer scale through an annealing procedure. A synergic combination of yield strength over 1.0 GPa and uniform elongation over 25% is obtained due to the simultaneous utilization of both grain refinement and precipitation strengthening. [ABSTRACT FROM AUTHOR]

Published
2023
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47. Morphology and dynamic mechanical properties of nylon 66/poly(ether imide) blends

Author

Choi, Kil-Yeong, Lee, Sung-Goo, Lee, Jae Heung, and Liu, Jingjiang

Subjects
Polyamides -- Production processes -- Analysis -- Measurement, Morphology -- Analysis -- Measurement, Polyetherimide -- Production processes -- Measurement -- Analysis, Torque -- Measurement -- Analysis, Plastics -- Mixing, Engineering and manufacturing industries, Science and technology, Production processes, Analysis, Measurement
Abstract

The morphology and dynamic mechanical properties of blends of poly(ether imide) (PEI) and nylon 66 over the full composition range have been investigated. Torque changes during mixing were also measured. Lower torque values than those calculated by the log-additivity rule were obtained, resulting from the slip at the interface due to low interaction between the components. The particle size of the dispersed phase and morphology of the blends were examined by scanning electron microscopy. The composition of each phase was calculated. The blends of PEI and nylon 66 showed phase-separated structures with small spherical domains of 0.3 [similar to] 0.7 [µmeter]. The glass transition temperatures ([T.sub.g]s) of the blends were shifted inward, compared with those of the homopolymers, which implied that the blends were partially miscible over a range of compositions. [T.sub.g1], corresponding to PEI-rich phase, was less affected by composition than [T.sub.g2], corresponding to nylon 66-rich phase. This indicated that the fraction of PEI mixed into nylon 66-rich phase increased with decreasing PEI content and that nylon 66 was rarely mixed into the PEI-rich phase. The effect of composition on the secondary relaxations was examined. Both [T.sub.Β], corresponding to the motion of amide groups in nylon 66, and [T.sub.[Gamma]′], corresponding to that of ether groups in PEI, were shifted to higher temperature, probably because of the formation of intermolecular interactions between the components., INTRODUCTION Nylon plastics are extensively used in the manufacture of automobile parts, engineering products, and textile fibers, because they have many advantages in properties such as high mechanical and impact [...]

Published
1995

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