• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2002.05a
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• pp.17-18
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• 2002

• Proceedings of the Korean Magnestics Society Conference
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• 1993.03a
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• pp.52-53
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• 1993

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05b
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• pp.84-89
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• 1998

Alloy 600 및 alloy 690과 Ni-8Cr-lOFe 합금 등의 응력부식(stress corrosion cracking, SCC) 거동을 고온의 염기성 분위기에서 C-ring 시편을 사용하여 연구하였다. Alloy 600과 alloy 690을 여러 조건에서 열처리하여 etching한 후 탄화물의 분포와 입계 주변의 Cr고갈 정도 등의 미세조직을 광학현미경과 주사 전자현미경(SEM)으로 관찰하였다. 이들 재료에 대한 SCC 시험을 315$^{\circ}C$의 40% NaOH 수용액에서 일정한 부하전위(부식전위 + 200㎷)를 가하면서 수행하였으며, 동일 조건에서의 분극거동도 측정하였다. Alloy 600 MA(mill anneal) 및 TT(thermal treatment)의 SCC 저항성은 alloy 690 TT와 Ni-8Cr-10Fe SA(solution anneal)보다 낮았다. Alloy 600 TT 재료는 alloy 600 MA 및 SA 재료에 비해 SCC 저항성이 더 컸다. 고용 탄소농도는 alloy 600의 SCC 저항성에 큰 영향을 주지 못했다. 대부분의 Alloy 600은 균열전파 입계균열을 보였으나, 일부에서는 입계 및 입내 혼합양상(mixed mode cracking)을 보였다. 염기성 분위기에서 Ni기 합금의 SCC 거동을 미세조직, 분극거동의 관점에서 고찰하였다.

• Journal of Powder Materials
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• v.27 no.5
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• pp.414-419
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• 2020

In the present study, we investigated the austenite stability of a sintered Fe-based nanocrystalline alloy. The volume fraction of austenite was measured based on the X-ray diffraction data of sintered Fe-based nanocrystalline alloys, which were prepared by high-energy ball milling and spark plasma sintering. The sintered alloy samples showed a higher volume fraction of austenite at room temperature as compared to the equilibrium volume fraction of austenite obtained using thermodynamic calculations, which resulted from the nanosized crystalline structure of the sintered alloy. It was proved that the austenite stability of the sintered Fe-based alloy increased with a rise in the amount of austenite stabilizing elements such as Mn, Ni, and C; however, it increased more effectively with a decrease in the actual grain size. Furthermore, we proposed a new equation to predict the martensite starting temperature for sintered Fe-based alloys.

• Nuclear Engineering and Technology
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• v.52 no.3
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• pp.589-596
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• 2020

Many components in the assembly section of Sodium-cooled Fast Reactor are made of good corrosionresistant 316 LN Stainless Steel material. To avoid self-welding of the components with the coolant sodium at elevated temperature, hardfacing is inevitable. Ni-based colmonoy-5 is used for hardfacing due to its lower dose rate by Plasma Transferred Arc process due to its low dilution. Since Ni-Cr-B-Si alloy becomes very fluidic while depositing, the major height of the weld overlay rests inside the groove. Hardfacing is also done over the plain surface where grooving is not possible. Therefore, grooved and ungrooved hardfaced specimens were prepared at different travel speeds. Fe content at every 100 ㎛ of the weld overlay was studied by Energy Dispersive Spectroscopy and also the micro hardness was determined at those locations. A correlation between iron dilution from the base metal and the micro hardness was established. Therefore, if the Fe content of the weld overlay is known, the hardness at that location can be obtained using the correlation and vice-versa. A new correlation between micro hardness and dilution coefficient is obtained at different locations. A comparative study between those specimens is carried out to recommend the optimum travel speed for lower dilution.

• 연구논문집
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• s.27
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• pp.201-208
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• 1997

To improve the joining characteristics of metallic converter substrate for exhaust gas cleaning, high temperature brazing process has been studied. In this study, the effect of chemical composition of brazing filler metal on the oxidation behavior of brazed joints was investigated closely. Brazing was carried out at $1200^\circC$ in vacuum furnace using nickel-based filler metals : BNi-5 powder(Ni-Cr-Si base alloy) and MBF-50 foil(Ni-Cr-Si-B). The MBF-50 containing 1-1.5 wt%B showed relatively poor oxidation resistance of the brazed joints compared to BNi-5, because of the faster invasion of oxygen through the Kirkendal voids along the interface of mother alloy/filler metal.

• Nuclear Engineering and Technology
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• v.41 no.1
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• pp.107-112
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• 2009

Corrosion of nickel-base alloys (Hastelloy C-276, Inconel 625, and Inconel X-750) in $500^{\circ}C$, 25MPa supercritical water (with 10 wppb oxygen) was investigated to evaluate the suitability of these alloys for use in supercritical water reactors. Oxide scales formed on the samples were characterized by gravimetry, scanning electron microscopy/energy dispersive spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The results indicate that, during the 1000h exposure, a dense spinel oxide layer, mainly consisting of a fine Cr-rich inner layer ($NiCr_{2}O_{4}$) underneath a coarse Fe-rich outer layer ($NiFe_{2}O_{4}$), developed on each alloy. Besides general corrosion, nodular corrosion occurred on alloy 625 possibly resulting from local attack of ${\gamma}$" clusters in the matrix. The mass gains for all alloys were small, while alloy X -750 exhibited the highest oxidation rate, probably due to the absence of Mo.

• Journal of the Korean Magnetics Society
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• v.16 no.5
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• pp.249-254
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• 2006

CoFeNi alloys are some of the most studied soft magnetic materials because of their superial properties over FeNi alloys as write head core materials in HDD and MEMS. We studied the effect of magnetic property according to size and orientation of crystal for electroplated Co-Fe-Ni alleys. In case of heat treated ternary alloy, it affect the change of crystal size and structure. In this study, it intends to improve the magnetic properties of CoFeNi thin film by heat treatment. Minimized coercivity and increased magnetization are due to heat treatment from $300^{\circ}C\;to\;400^{\circ}C$. As a bcc phase formation, it grow to amount of magnetization.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1316-1317
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• 2006

The paper investigates the possibility to avoid extrinsic embrittlement of $Ni_3Al$, also increasing the high temperature strength, by alloying with both Fe - of a high strengthening effect and Cr - able to remove a part of diffused oxygen along the grain boundaries. As Cr homogenization in $Ni_3Al$ is difficult because of its low diffusion coefficient, for its improving a mechanical alloying (MA) step before the compound synthesis by Self-propagating High-temperature Synthesis (SHS) was adopted. The obtained better homogenization resulted in higher mechanical resistance and deformability than of the unalloyed $Ni_3A/Ni_3Al$ alloys of the same composition obtained without MA step.

• Korean Journal of Metals and Materials
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• v.50 no.6
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• pp.463-468
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• 2012

A 71.5 wt%Mg-23.5 wt%Ni-5 wt%$Fe_2O_3$ (Mg-23.5Ni-$5Fe_2O_3$) sample was prepared by a quite simple process, reactive mechanical grinding, and its hydriding and dehydriding properties were then investigated. The reactive mechanical grinding of Mg with Ni and $Fe_2O_3$ is considered to facilitate nucleation and shorten the diffusion distances of the hydrogen atoms. After the hydriding-dehydriding cycling, the Mg-23.5Ni-$5Fe_2O_3$ sample contained $Mg_2Ni$ phase. Expansion and contraction of the hydride-forming materials (Mg and $Mg_2Ni$) with the hydriding and dehydriding reactions are also considered to increase the hydriding and dehydriding rates of the mixture by forming defects and cracks leading to the fragmentation of the particles. The temperature dependence of the hydriding rate of the sample is discussed.