• 한국주조공학회지
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• 제10권5호
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• pp.435-443
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• 1990

By using the centrifugal atomization, which is one of the rapid solidification processes, Al-5,10wt%Pb alloys which are monotectic alloys were melted at 150K over two liquid phase line in the phase diagram. The melted alloy was poured on the rotating disk, being made into atomized powders, and then the solidified microstructure and morphology of the powder were investigated. This study converted the produced powders into strips by strained powder rolling. According to sintering temperature, the microstructure and hardness were investigated. The solidified structure of the powders were almost cellular dendritic structure. Pb particles ($2.0-3.0{\mu}m$) were fairl distributed in the Al matrix. Powder shapes were irregular. Rolling property and the compacting was good, respectively, because of increasing mechanical interlocking and surface area in the small size powders. With increasing temperature, the boundarys of powders were in porous form due to the diffusion. Pb particles which were surrounding the pores were inverse-segregated at the surface of the powders. With increasing of sintering temperature, the hardness of the powders and the strips decreased. In particular rolling-strip, the hardness abruptly decreased due to the release of work-hardening.

• 한국주조공학회지
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• 제27권4호
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• pp.167-172
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• 2007

In the present study, the microstructural evolution and mechanical properties of $Al_{71.6}Ge_{28.4}$ eutectic alloy have been investigated. Stable (fcc ${\alpha}$-Al and diamond cubic ${\beta}$-Ge) and various metastable crystalline (monoclinic, rhombohedral) phases were produced by competitive phase selection during non-equilibrium processing methods i.e. melt spinning and injection casting. The as-injection casted samples containing metastable-equilibrium eutectic (${\alpha}$-Al + monoclinic) structure showed much higher strength than samples with equilibrium eutectic (${\alpha}-Al+{\beta}-Ge$) structure but plasticity disappointingly diminished. In order to endow the enhanced ductility without significant strength drop, the alloys was heat-treated at transition temperature from metastable phase to stable phase. The annealed specimen displayed the phase transformed microstructural evolution and enhanced macroscopic plasticity.

• 열처리공학회지
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• 제10권2호
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• pp.81-92
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• 1997

The effect of alloying elements, precipitate size, its distribution, and dislocation substructure resulted from warm rolling or cold rolling in the superplastic Al-Mg alloy system was investigated. One of the major requirements for fine structure superplasticity is that the grain size should be very small. Fine grain structure is controlled by the dislocation substructure and the dynamic recrystallization during hot or warm working. The recovery of Al-Mg base alloys was constrained resulting in relatively high dislocation density when the alloys were warm rolled. In particular, Al-Mg-Zr alloy exhibited the smallest sub-grain size among Al-Mg alloys containing Mn, Cu, Zr as a third element. The Al-Mg-Mn alloy cold rolled 80% after hot rolling showed the maximun strain rate sensitivity exponent, m, of 0.75 under strain rate of $7.1{\times}10^{-4}/s$ at $500^{\circ}C$. The elongation of the alloys was limited in spite of high m values due to large dispersoids containing appreciable amount of Fe impurities.

• 열처리공학회지
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• 제9권1호
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• pp.19-26
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• 1996

Melt-quenching of steels leads to various metallographic effects such as refinement of grain size, extension of the solid solubility of carbon and alloying elements, and is expected to improve the mechanical properties of conventional steels. Furthermore, this technique is a useful method for producing sheet directly from liquid state. And it will lend itself to development as a continuous cast process which offers significant savings in energy and product costs. The purpose of this study is to present the microstructures of melt-quenched austenitic stainless steels. As the results of this study, the morphology of melt-quenched microstructure show that the roll contact area is columnar structure, and the free surface area is dendrite structure. As the line speed increases, the ratio of $d_{colunnar}/d_{total}$ increases from 0.12 to 0.60, but the ribbon thickness decreases from $150{\mu}m$ to $30{\mu}m$.

• 한국표면공학회지
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• 제52권6호
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• pp.364-370
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• 2019

Fe-Mn-Si-Ni-Cr-TiC alloys have a shape memory property, recovering initial shape by heating. With an aim to improve a durability and stability of building and infrastructure, this Fe-based shape memory alloy (FSMA) can be employed to reinforce concrete structure with creation of compressive residual stress. In this work, corrosion resistance of FSMA was compared with general rebar and S400 carbon steel to evaluate the stability in concrete environment. Potentiodynamic polarization test in de-ionized water, tap-water and 3.5 wt.% NaCl solution with variations of pH was used to compare the corrosion resistance. FSMA shows better corrosion resistance than rebar and S400 in tested solutions. However, Cl-containing solution is critical to significantly reduce the corrosion resistance of FSMA. Therefore, though FSMA can be a promising candidate to replace the rebar and S400 for the reinforcement of concrete structure, serious cautions are required in marine environments.

• Nuclear Engineering and Technology
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• 제53권5호
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• pp.1619-1625
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• 2021

This paper demonstrates the possible nondestructive analysis of iron artifacts' metallurgical characteristics using neutron imaging. Ancient kingdoms of the Korean Peninsula used a direct smelting process for ore smelting and iron bloom production; however, the use of iron blooms was difficult because of their low strength and purity. For reinforcement, iron ingots were produced through refining and forge welding, which then underwent various processes to create different iron goods. To demonstrate the potential analysis using neutron imaging, while ensuring artifacts' safety, a sand iron ingot (SI-I) produced using ancient traditional iron making techniques and a sand iron knife (SI-K) made of SI-I were selected. SI-I was cut into 9 cm², whereas the entirety of SI-K was preserved for analysis. SI-I was found to have an average grain size of 3 ㎛, with observed α-Fe (ferrite) and pearlite with a body-centered cubic (BCC) lattice structure. SI-K had a grain size of 1-3 ㎛, α-Ferrite on its backside, and martensite with a body-centered tetragonal (BCT) structure on its blade. Results show that the sample's metallurgical characteristics can be identified through neutron imaging only, without losing any part of the valuable artifacts, indicating applicability to cultural artifacts requiring complete preservation.

• Applied Microscopy
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• 제32권1호
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• pp.31-37
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• 2002

[ $Mg_{68}Zn_{28}Y_4$ ] 합금의 응고 조직은 primary solidification phase, primary solidification phase로부터 성장된 ${\alpha}-Mg$ dendrite, 그리고 응고 말기에 형성된 eutectic structure의 세 가지형태 조직으로 구성되어져 있다. Primary solidification phase에는 매우 큰 정도의 phason strain이 존재하고 있으며, $a=27.2{\AA}\;and\;{\alpha}=63.43^{\circ}$의 격자상수를 갖는 1/1 rhombohedral approximant가 존재한다. 이와 같은 rhombohedral approximant의 구조는 six dimensional face centered hyper-cubic lattice에 phason strain을 도입함에 의해 얻어질 수 있다. Decagonal phase는 icosahedral phase로부터 방위 관계를 가지며 형성되며, $Mg_4Zn_7$는 decagonal phase로부터 방위관계를 가지며 성장한다. 이는 세 상간에 구조적 유사성이 존재하고 있음을 의미하며, 응고시 용질원자의 분배에 의해 이들 세 상이 순서대로 형성되어진다.

• 한국주조공학회지
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• 제15권4호
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• pp.351-359
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• 1995

The effects of In and Be additions on the aging behaviors and mechanical properties in the Al-Cu-Li alloy were investigated using the transmission electron microscope, the scanning electron microscope, hardness and tensile strength measurement. The aging is promoted and the double hardness peak is appeared by the addition of In and Be in the Al-Cu-Li alloy. The strength is increased, but the elongation and toughness are decreased by the addition of In in the Al-Cu-Li alloy. And the Al-Cu-Li-In-Be alloy has good combination with the strength, the elogation and toughness than Al-Cu-Li-In alloy.

• 한국주조공학회지
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• 제9권3호
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• pp.228-236
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• 1989

The relationships between nodularity, tensile property and ultrasonic velocity were studied in ductile iron castings having similar matrix structure. Also, the effects of heat treatment and the number of graphite nodules on the ultrasonic velocity were investigated. The results were as follows 1. The ultrasonic velocity increased proportionally with increassing nodularity and tensile strength. 2. The ultrasonic velocity in annealed and normalized state decreased average 1.7% and 3.4% respectively than that in as cast state. 3. The ultrasonic velocity increased with increasing the number of graphite nodules. Therefore, ductile iron castings can be evaluated in the only case of castings having the same manufacturing history by ultrasonic velocity.

• 한국주조공학회지
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• 제12권2호
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• pp.155-161
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• 1992

This study has been performed in increase the wear resistance characteristic and the mechanical properties of high Mn steel castings with an addition of Ni to $1{\sim}4%$ range. The initial structure of plastic cememtite has been possible to transform perfect austenite with watertoughening treatment. Increasing Ni content, the most wear loss has shown that ore has crushed until 100kg and decreased with increasing ore amount at ascast, the similar tendency has shown at heat treatment. Chang of hardness has shown high values that ore has been crushed until 300kg, both as cast and treatment added 2%Ni.