• Journal of Powder Materials
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• v.26 no.4
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• pp.311-318
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• 2019

The objective of this study is to investigate the influence of powder shape and densification mechanism on the microstructure and mechanical properties of Ti-6Al-4V components. BE powders are uniaxially and isostatically pressed, and PA ones are injection molded because of their high strengths. The isostatically compacted samples exhibit a density of 80%, which is higher than those of other samples, because hydrostatic compression can lead to higher strain hardening. Owing to the higher green density, the density of BE-CS (97%) is found to be as high as that of other samples (BE-DS (95%) and P-S (94%)). Furthermore, we have found that BE powders can be consolidated by sintering densification and chemical homogenization, whereas PA ones can be consolidated only by simple densification. After sintering, BE-CS and P-S are hot isostatically pressed and BE-DS is hot forged to remove residual pores in the sintered samples. Apparent microstructural evolution is not observed in BE-CSH and P-SH. Moreover, BE-DSF exhibits significantly fine grains and high density of low-angle grain boundaries. Thus, these microstructures provide Ti-6Al-4V components with enhanced mechanical properties (tensile strength of 1179 MPa).

• Advances in concrete construction
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• v.11 no.5
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• pp.367-374
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• 2021

The present study investigated the effect of the combined carbonation and steam curing on the physicochemical properties and CO₂ uptake of the Portland cement concrete. Four different curing regimes were adopted during the initial 10 h of curing to evaluate the potential of carbonation curing as an alternative to conventional steam curing in the precast concrete industry from environmental and practical viewpoints. Four combinations of carbonation and steam curing conditions were applied as curing regimes to the samples at an early age. The test results indicated that the samples treated with the combined carbonation and steam curing exhibited higher early strength development compared to the other samples, signifying that carbonation curing can reduce the production time of precast concrete. Furthermore, the CO₂ uptake capacity of the samples was calculated and found to be as high as 18% with respect to the mass of the paste samples. Hence, the simultaneous utilization of steam and CO₂ for the fabrication of precast concrete members has the potential to make precast concrete greener and more cost-effective.

• Korean Journal of Metals and Materials
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• v.47 no.11
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• pp.699-706
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• 2009

Deformation behavior of pure aluminum during equal channel angular pressing (ECAP) was simulated using a three-dimensional version of the finite element method in conjunction with a constitutive model based on the dislocation density and cell evolution. The three-dimensional finite element analyses for the prediction of microstructural features, such as the variation of the dislocation density and the cell size with the number of ECAP, are reported. The calculated stress and strain and their distributions are also investigated for the route Bc ECAP processed pure aluminum. The results of finite element analyses are found to be in good agreement with experimental results for the dislocation cell size. Due to the accumulation of strain throughout the workpiece and an overall trend to saturation in cell size, a decrease of the difference in cell size with the number of passes (1~4) was predicted.

• Journal of Ceramic Processing Research
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• v.19 no.6
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• pp.483-491
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• 2018

Effects of additives on phase development and physico-mechanical properties of mullite-carbon was investigated. Powdered clay, kaolinite and graphite of predetermined compositions were blended with additives using ball mill for 3 hrs at 60 rev/min. Samples were produced by uniaxial compression and sintered between $1400^{\circ}C$ and $1600^{\circ}C$ for one hr. They were characterized for various properties, developed phases and microstructural features. It was observed that the properties and phase developments in the samples were influenced by the additives. 10 wt % SiC served as nucleating point for SiC around $1400^{\circ}C$. 10wt % $TiO_2$ lead to development of 2.5 wt % TiC at $1500^{\circ}C$ which increased to 6.8 wt % at $1600^{\circ}C$. Ifon clay in the sample leads to development of anorthite and microcline in the samples. 10wt % $TiO_2$ is effective as anti-oxidant for graphite up to $1500^{\circ}C$. Base on strength and absorbed energy, sample C (with 10wt % $TiO_2$) sintered at $1500^{\circ}C$ is considered to be optimum.

• Transactions of Materials Processing
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• v.30 no.4
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• pp.195-200
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• 2021

In this study, we investigated the dominant processing variables that would influence the microstructural development of AA6061 deformed by differential speed rolling (DSR) at ambient temperature. For this purpose, we carried out a series of DSR on the samples to investigate the effects of roll speed ratio, sample rotation, and number of operation under specific rotation. Among these, the condition with a height reduction of 75% at a speed ratio of 1:4 through rotation along rolling direction (RR) displayed the pronounced results of more homogenous matrix-structure and superior mechanical properties than the others tested in this study. This was mainly due to the cross shearing of macro-shear pattern in segment where dynamic recrystallization took place with ease throughout the sample. Thus, an average microhardness value of 101 Hv was obtained in the present sample deformed by 4-pass DSR with RR where macro cross-shearing was effectively applied.

• Journal of Powder Materials
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• v.28 no.4
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• pp.287-292
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• 2021

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.

• Journal of Electrochemical Science and Technology
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• v.13 no.3
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• pp.377-389
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• 2022

The current global energy supply depends heavily on fossil fuels. This makes technology such as direct water splitting from harvesting solar energy in photoelectrochemical (PEC) systems potentially attractive due to its a promising route for environmentally benign hydrogen production. In this study, undoped and nickel-doped molybdenum oxide photoanodes (called photoanodes S₁ and S₂ respectively) were synthesized through electrodeposition by applying -1.377 V vs Ag/AgCl (3 M KCl) for 3 hours on an FTO-coated glass substrate immersed in molibdatecitrate aqueous solutions at pH 9. Scanning electron microscopy (SEM), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) were used for microstructural and compositional characterizations of the photoanodes. In addition, the optical and photoelectrochemical characterizations of these photoanodes were performed by UV-Visible spectroscopy, and linear scanning voltammetry (LSV) respectively. The results showed that all the photoanodes produced exhibit conductivity and catalytic properties that make them attractive for water splitting application in a photoelectrochemical cell. In this context, the photoanode S₂ exhibited better photocatalytic activity than the photoanode S₁. In addition, photoanode S₂ had the lowest optical band-gap energy value (2.58 eV), which would allow better utilization of the solar spectrum.

• Journal of the Korean Society for Heat Treatment
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• v.37 no.2
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• pp.58-65
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• 2024

In the present study, the effect of annealing condition on the microstructures and mechanical properties of the cold-rolled CoCrFeMnNi high entropy alloys were studied. Annealing treatment was performed under six different temperatures. Microstructural analyses confirmed that annealing below 800℃ resulted in the formation of intermetallic sigma (σ) phase within face-centered cubic (FCC) matrix, and this σ phase has beneficial effects on the formation of fine-grained structures through retardation of grain growth and recrystallization due to Zener pinning effect. This led to the enhanced yield strength and tensile strength of ~646 and ~855 MPa, respectively. The microstructures annealed above 800℃ demonstrated single FCC phase, and fully-recrystallized single FCC microstructure resulted in a slight increase in ductility with a considerable decrease in strength. The evolution of mechanical properties, such as strength, ductility, and strain hardening exponent, will be discussed.

• Nuclear Engineering and Technology
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• v.52 no.12
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• pp.2860-2866
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• 2020

Oxide dispersion-strengthened materials W-1wt%Pr₂O₃ and W-1wt%La₂O₃ were synthesized by wet chemical method and spark plasma sintering. The field emission scanning electron microscopy (FE-SEM) analysis, XRD and Vickers microhardness measurements were conducted to characterize the samples. The irradiations were carried out with a 5 keV helium ion beam to fluences up to 5.0 × 10²¹ ions/m² under 600 ℃ using the low-energy ion irradiation system. Transmission electron microscopy (TEM) study was performed to investigate the microstructural evolution in W-1wt%Pr₂O₃ and W-1wt%La₂O₃. At 1.0 × 10²⁰ He⁺/m², the average loops size of the W-1wt%Pr₂O₃ was 4.3 nm, much lower than W-1wt% La₂O₃ of 8.5 nm. However, helium bubbles were not observed throughout in both doped W materials. The effects of pre-irradiation with 1.0 × 10²¹ He⁺/m² on trapping of injected deuterium in doped W was studied by thermal desorption spectrometry (TDS) technique using quadrupole mass spectrometer. Compared with the samples without He⁺ pre-irradiation, deuterium (D) retention of doped W materials increased after He⁺ irradiation, whose retention was unsaturated at the damage level of 1.0 × 10²²D₂⁺/m². The present results implied that irradiation effect of He⁺ ions must be taken into account to evaluate the deuterium retention in fusion material applications.

• Korean Journal of Materials Research
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• v.11 no.1
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• pp.8-14
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• 2001

Microstructural evolution and creep failure behavior of GTD 111 have been studied. Solidification and precipitation behaviors of the alloy during casting have been analyzed by microstructural observations. It has been found that MC carbides solidify just before the $\gamma$/$\gamma$' eutectic solidification. The ηphase was found to be formed by transformation of Ti-rich $\gamma$'phase. PFZ has formed in the vicinity of the transformed $\eta$ phase. A few MC particles, which have been identified as TaC, precipitated within the PFZ. Creep failure along grainboundary was dominant at and above $871^{\circ}C$. Creep failure above$ 871^{\circ}C$ was caused by the propagation of surface cracks and internal cracks. Creep crack has initiated at the microporosities embedded on the grainboundary. The $\eta$phase and PFZ have been found to be little or no effect on creep crack initiation.