• Laser Solutions
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• v.16 no.3
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• pp.1-10
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• 2013

In this study, Al-Si coated boron steel(1.2 mm) were laser welded by $CO_2$ laser and hot-stamping was applied to the laser joints. Tensile properties and microstructures of the joints were investigated before and after hot-stamping. Tensile and yield strengths of the as welded specimen similar with base metal and fracture occurred base metal of boron steel. Although, in case of heat treated specimen, fracture occurred fusion zone that Al segregated zone near the bond line. These could be explained by the existence of ferrite, in the Al segregated zone near the bond line and base metal of boron steel. Before hot-stamping, hardness of base metal is lower than fusion zone and heat affected zone in spite of exist Al segregation zone($Fe_3$(Al,Si)). So fracture occurred base metal. Although, after hot-stamping, microstructure of base metal and welds zone transformed to martensite and bainite except in Al segregation zone near the bond line that $Fe_3$(Al,Si) transformed to a-ferrite. So fracture occurred Al segregation zone near the bond line.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.9
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• pp.754-760
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• 2008

A two-photon induced photoreduction process suggests a possibility for fabricating complicated metallic microstructures which can be applied to 3-D micro-circuits and optical devices, etc. The process employs the photoreduction of silver ions in a metallic solution which is composed of metallic salt ($AgNO_3$) and watersoluble polymer ((poly(4-styrenesulfonique acid) 18wt. % in $H_2O$, $(C_8H_8O_3S)_n$)). In this process, the improvement of the resolution and the uniformity of fabricated metallic structures are important issues. To address these problems, continuous forming window (CFW) is obtained from a parametric study on the conditions of laser power and scanning velocity and the direct seed generation (DSG) method is proposed. Silver nano particles are uniformly generated in a metallic solution through the DSG method, which enables the decrease of a laser power to trigger the photoreduction of silver ions as well as the increase of metal contents in a metallic solution. So the two-photon induced photoreduction property of a metallic solution is improved. Through this work, precise silver patterns are fabricated with a minimum line width of 400 nm.

• Journal of the Korean Society for Heat Treatment
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• v.23 no.6
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• pp.309-314
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• 2010

Microstructures and grain growth behaviors at elevated temperatures have been investigated for extruded Mg-2%Zn and Mg-2%Zn-0.3%Zr alloys, in order to clarify the role of Zr in grain stability of Mg-Zn alloy. The grain size of Zr-free alloy increased continuously with an increase in annealing temperature, when isochronally annealed for 60 min from 573 to 723K, while the grains of the Zr-containing alloy were relatively stable up to 723 K. The activation energies for grain growth ($E_g$) between 573 and 723 K were calculated as 77.8 and 118.6 kJ/mole for the Mg-2%Zn and Mg-2%Zn-0.3%Zr alloys, respectively, which indicates that grains in the Zr-added alloy possess higher thermal stabilities at elevated temperatures. TEM observations on the annealed Mg-2%Zn and Mg-2%Zn-0.3%Zr alloys revealed that enhanced grain stability resulting from Zr addition into Mg-Zn alloy would be ascribed to the restriction of grain growth by stable Zn-Zr nano-precipitates distributed in the microstructure.

• Economic and Environmental Geology
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• v.24 no.3
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• pp.287-299
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• 1991

The study area is mainly composed of metasedimentary rocks which are included in Ogchon, Choson and Pyongan Groups. Because of thrust faults which are developed in this area, a coal bearing formation is repeatedly distributed two times, and Choson Group is thrusted over Pyongan Group. Deformation in this area was taken place in a series of three phases ($D_1$, $D_2$ and $D_3$) ; $D_1$ was most intense whereas $D_3$ was weakest. Thrust faults developed in the upper curst duringD2 produced cataclastic rocks and fault breccia,truncating regional slaty cleavage and earlier folds which were formed during $D_1$ stage. The quartz microstructures of metapsammitic rocks in Choson and Pyongan Groups suggest that dislocation creep mechanism predominated early in fabric development, afterwards deformation mechanism was transfered to pressure solution which intensified the earlier fabrics. According to strain analysis using quartz grains and quartz aggregate grains, the strain magnitude(Es) of Pyongan Group represents larger values than that of Choson Group due to the contrast of constituent minerals, the size of original quartz grains and matrix content. Apparent flattening type in strain pattern appears in the whole area. It is suggested that the relationship between Ogchon Group and Choson Group may be thrust contact.

• Transactions of Materials Processing
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• v.18 no.6
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• pp.476-481
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• 2009

The present work demonstrates the mechanical and electrical responses of submicrocrystalline Cu-3%Ag alloy as a function of strain imposed by equal channel angular pressing(ECAP). From transmission electron microscope observation, the resulting microstructures of Cu-3%Ag alloy deformed by ECAP for 8-pass or more consist of reasonably fine, equiaxed grains without having a strong preferred orientation, suggesting that microstructure evolution is slower than that of pure-Al and its alloys owing to low stacking fault energy. The results of room temperature tension tests reveal that, as the amount of applied strain increases, the tensile strength of submicrocrystalline Cu-3%Ag alloy increases whereas losing both the ductility and the electrical conductivity. Such phenomenon can be explained based on microstructure featured by the non-equilibrium grain boundaries.

• Carbon letters
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• v.13 no.3
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• pp.178-181
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• 2012

In this work, we synthesized superhydrophobic coatings by chemical surface functionalization of multi-walled carbon nanotubes (MWCNTs). This was accomplished through the radical polymerization of 3-(trimethoxysilyl) propyl methacrylate modified MWCNTs and fluoro acrylate/methyl methacrylate. The chemical compositions and microstructures of the prepared MWCNT surface were investigated using X-ray photoelectron spectroscopy, Fourier transform infrared spectrometry, and scanning electron microscopy, respectively. The wettability of the MWCNTs surface was determined through contact angle assessments in different liquids. The resulting surface exhibited a water contact angle of $157.7^{\circ}$, which is clear evidence of its superhydrophobicity. The 3D MWCNT networks and the low surface energy of the -C-C- and -C-F- groups play important roles in creating the superhydrophobic surface of the MWCNTs.

• Journal of Powder Materials
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• v.29 no.3
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• pp.233-239
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• 2022

Aluminum alloys are extensively employed in several industries, such as automobile, aerospace, and architecture, owing to their high specific strength and electrical and thermal conductivities. However, to meet the rising industrial demands, aluminum alloys must be designed with both excellent mechanical and thermal properties. Computer-aided alloy design is emerging as a technique for developing novel alloys to overcome these trade-off properties. Thus, the development of a new experimental method for designing alloys with high-throughput confirmation is gaining focus. A new approach that rapidly manufactures aluminum alloys with different compositions is required in the alloy design process. This study proposes a combined approach to rapidly investigate the relationship between the microstructure and properties of aluminum alloys using a direct energy deposition system with a dual-nozzle metal 3D printing process. Two types of aluminum alloy powders (Al-4.99Si-1.05Cu-0.47Mg and Al-7Mg) are employed for the 3D printing-based combined method. Nine types of Al-Si-Cu-Mg alloys are manufactured using the combined method, and the relationship between their microstructures and properties is examined.

• Journal of the Korean institute of surface engineering
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• v.26 no.3
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• pp.143-148
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• 1993

Composition and microstructures of Silver-Tin alloy deposits from a pyrophosphate bath were studied under the D.C. electrolysis conditions. Cathode current efficiency and throwing power of alloy deposits de-creased with increasing current density. Tin content of Ag-Sn alloy deposits decreased noticeably with the cur-rent density and with decreasing pH. The preferred orientation of the deposits tended to change in sequence of (110)longrightarrow(111)longrightarrow(100) texture with increasing the cathode overpotential. The surface structure of alloy deposits showed the smooth surface structure with fine crystallites.

• Korean Journal of Materials Research
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• v.28 no.11
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• pp.663-670
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• 2018

H13 tool steels are widely used as metallic mold materials due to their high hardness and thermal stability. Recently, many studies are undertaken to satisfy the demands for manufacturing the complex shape of the mold using a 3D printing technique. It is reported that the mechanical properties of 3D printed materials are lower than those of commercial forged alloys owing to micropores. In this study, we investigate the effect of microstructures and defects on mechanical properties in the 3D printed H13 tool steels. H13 tool steel is fabricated using a selective laser melting(SLM) process with a scan speed of 200 mm/s and a layer thickness of $25{\mu}m$. Microstructures are observed and porosities are measured by optical and scanning electron microscopy in the X-, Y-, and Z-directions with various the build heights. Tiny keyhole type pores are observed with a porosity of 0.4 %, which shows the lowest porosity in the center region. The measured Vickers hardness is around 550 HV and the yield and tensile strength are 1400 and 1700 MPa, respectively. The tensile properties are predicted using two empirical equations through the measured values of the Vickers hardness. The prediction of tensile strength has high accuracy with the experimental data of the 3D printed H13 tool steel. The effects of porosities and unmelted powders on mechanical properties are also elucidated by the metallic fractography analysis to understand tensile and fracture behavior.

• Journal of Korea Multimedia Society
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• v.22 no.9
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• pp.992-999
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• 2019

In this paper, I lay the foundation for creating a multiscale atlas that characterizes cerebrovasculature structural changes across the entire brain of a mouse in the Knife-Edge Scanning Microscopy dataset. The geometric reconstruction of the vascular filaments embedded in the volume imaging dataset provides the ability to distinguish cerebral vessels by diameter and other morphological properties across the whole mouse brain. This paper presents a means for studying local variations in the small vascular morphology that have a significant impact on the peripheral nervous system in other cerebral areas, as well as the robust and vulnerable side of the cerebrovasculature system across the large blood vessels. I expect that this foundation will prove invaluable towards data-driven, quantitative investigations into the system-level architectural layout of the cerebrovasculature and surrounding cerebral microstructures.