• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2003.10a
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• pp.65-66
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• 2003

1. The oxidation resistance of $Y_{2}O_{3}$ containing Ni-base alloy is superior to that of the alloy without $Y_{2}O_{3}$. 2. The appearance of oxides of Ni-20Cr-20Fe-5Nb-$1Y_{2}O_{3}$ alloy is similar to that of oxides in commercial PM1000 and MA754 alloy. 3. The oxides in ODS alloy are grown mainly at particle boundaries.

• Korean Journal of Metals and Materials
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• v.48 no.6
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• pp.523-532
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• 2010

Co-application of organic coating and cathodic protection has not provided enough durability to low-alloyed steels inseawater ballast tank (SBT) environments. An attempt has made to study the effect of alloy elements (Al, Cr, Cu, Mo, Ni, Si, W) on general and localized corrosion resistance of steels as basic research to develop new low-allowed steels resistive to corrosion in SBT environments. For this study, we measured the corrosion rate by the weigh loss method after periodic immersion in synthetic seawater at $60^{\circ}C$, evaluated the localized corrosion resistance by an immersion test in concentrated chloride solution with the critical pH depending on the alloy element (Fe, Cr, Al, Ni), determined the permeability of chloride ion across the rust layer by measuring the membrane potential, and finally, we analyzed the rust layer by EPMA mapping and compared the result with the E-pH diagram calculated in the study. The immersion test of up to 55 days in the synthetic seawater showed that chromium, aluminium, and nickel are beneficial but the other elements are detrimental to corrosion resistance. Among the beneficial elements, chromium and aluminium effectively decreased the corrosion rate of the steels during the initial immersion, while nickel effectively decreased the corrosion rate in a longer than 30-day immersion. The low corrosion rate of Cr- or Al-alloyed steel in the initial period was due to the formation of $Cr_2FeO_4$ or $Al_2FeO_4$, respectively -the predicted oxide in the E-pH diagram- which is known as a more protective oxide than $Fe_3O_4$. The increased corrosion rate of Cr-alloyed steels with alonger than 30-day exposure was due to low localized corrosion resistance, which is explained bythe effect of the alloying element on a critical pH. In the meantime, the low corrosion rate of Ni-alloyed steel with a longer than 30-day exposure wasdue to an Ni enriched layer containing $Fe_2NiO_4$, the predicted oxide in the E-pH diagram. Finally, the measurement of the membrane potential depending on the alloying element showed that a lower permeability of chloride ion does not always result in higher corrosion resistance in seawater.

• Korean Journal of Metals and Materials
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• v.48 no.8
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• pp.741-748
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• 2010

We studied the corrosion and oxidation properties of Fe-18Cr-0.4Nb-(0.1~0.6)Ti-(1~3)Si-(0.5~2)Mo stainless steel. The resistance to general and pitting corrosion was evaluated and the results were analyzed by Response Surface Methodology (RSM) as a function of alloy composition. The effects of alloy composition and heat treatment on the oxidation resistance were also examined. Mo increased both general corrosion resistance and pitting corrosion resistance. Si improved the resistance of the alloys to pitting corrosion. Si was also beneficial for general corrosion resistance of the alloys containing Mo at more than 1 wt.%. However, Mo was detrimental when its content was lower. Effects of Ti on general corrosion properties appeared to be weak and a high concentration of Ti appeared to deteriorate pitting resistance. The thickness of the oxidation scale increased and adhesion of the scale worsened as the temperature increased from $800^{\circ}C$ to $900^{\circ}C$. Weight gain of the alloys due to oxidation at $900^{\circ}C$ clearly showed that the resistance to oxidation is improved by annealing at $860^{\circ}C$ and an increase of Si content.

• Journal of Powder Materials
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• v.29 no.1
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• pp.22-27
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• 2022

Conventionally, metal materials are produced by subtractive manufacturing followed by melting. However, there has been an increasing interest in additive manufacturing, especially metal 3D printing technology, which is relatively inexpensive because of the absence of complicated processing steps. In this study, we focus on the effect of varying powder size on the synthesis quality, and suggest optimum process conditions for the preparation of AlCrFeNi high-entropy alloy powder. The SEM image of the as-fabricated specimens show countless, fine, as-synthesized powders. Furthermore, we have examined the phase and microstructure before and after 3D printing, and found that there are no noticeable changes in the phase or microstructure. However, it was determined that the larger the powder size, the better the Vickers hardness of the material. This study sheds light on the optimization of process conditions in the metal 3D printing field.

• Journal of Power System Engineering
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• v.16 no.5
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• pp.76-82
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• 2012

Duplex stainless steels have the dual microstructure of austenite and ferrite phases. This steel exhibits generally a high corrosion resistance and higher mechanical strength compared with austenitic stainless steels. The steels used in the investigation have the chemical composition of Fe-22Cr-xNi-yMn-0.2N in which the contents of Ni and Mn were varied with maintaining the equal [Ni/Cr] equivalent. The fraction of ferrite phase was increased with the increase of annealing temperature. The impact factor of Mn element on the [Ni] equivalent was amended on the basis of the results of the investigation. 4Mn-2Ni alloy showed the highest pitting corrosion resistance. The fraction ratio, grain size and misorientation angle between grains were measured, and the correlation with pitting potential was investigated.

• Nuclear Engineering and Technology
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• v.41 no.2
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• pp.149-154
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• 2009

The microstructure, the corrosion behavior and the oxide properties were examined for Zr-1.5Nb-0.4Sn-0.2Fe-0.1Cr (HANA-4) alloys which were subjected to two different final annealing temperatures: $470^{\circ}C$ and $570^{\circ}C$. HANA-4 was shown to have $\ss$-enriched phase with a bcc crystal structure and Zr(Nb,Fe,Cr)$_2$ with a hcp crystal structure with $\ss$-enriched phase being more frequently observed compared with Zr(Nb,Fe,Cr)$_2$. The corrosion rate of HANA-4 was increased with an increase of the final annealing temperature in the PWR-simulating loop, $360^{\circ}C$ pure water and $400^{\circ}C$ steam conditions, which was correlated well with a reduction in the size of the columnar grains in the oxide/metal interface region. The oxide growth rate of HANA-4 was considerably affected by the alloy microstructure determined by the final annealing temperature.

• Journal of Powder Materials
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• v.9 no.3
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• pp.189-198
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• 2002

In this work, transient liquid phase (TLP) bonding of Ni-Cr heat resisted cast alloy (HP) was investigated. And also the behaviors of the solid particles distributed in the interlayer during TLP bonding were investigated. The MBF-60 and solid particles (Ni, Fe, and $Al_2O_3$ powders respectively) added MBF-60 which will be a liquid phase coexisting with solid particles at the bonding temperature were used as insert metal. The effective and sound bonding was possible by spark plasma sinter-bonding due to the differences of electric resistance between base metal and liquid insert layer which creates high temperature region. During the isothermal solidification, $Al_2O_3$ particles and solid particles of liquid phase sintered insert metal have shown no growth, while Ni and Fe particles grow rapidly. In this TLP bonding using the MBF-60 and distributed Fe, Ni particles as insert materials, the whole isothermal solidification process was dominated by the growth rate of the solid particles distributed in the interlayer.

• Korean Journal of Materials Research
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• v.10 no.8
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• pp.532-539
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• 2000

Co-0.5C-(15~20)Cr-20Ni-8W-(2~7)Fe alloy bond in diamond-impregnated abrasive tool was synthesized by ball-milling and mechanical alloying process. When the powders were mechanical alloyed for 6h, micro-welding in most metal powders was observed irrespective of addition of stearic acid. Without stearic acid in metal powders, partial-ly coarse powders were obtained, which could be unfaverable to the densification of composite of composite powders. The hot-pressed compacts showed rupture strength of 1100MPa and hardness of about $46H_{RC}$, respectively.

• Corrosion Science and Technology
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• v.11 no.4
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• pp.141-150
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• 2012

Stress corrosion cracks in Alloy 600 compact tension specimens tested at $325^{\circ}C$ in a simulated primary water environment of pressurized water reactor were analyzed by analytical transmission electron microscopy and secondary ion mass spectroscopy (SIMS). From a fine-probe chemical analysis, oxygen was found on the grain boundary just ahead of the crack tip, and chromium oxides were precipitated on the crack tip and the grain boundary attacked by the oxygen diffusion, leaving a Cr/Fe depletion (or Ni enrichment) zone. The oxide layer inside the crack was revealed to consist of a double (inner and outer) layer. Chromium oxides existed in the inner layer, with NiO and (Ni,Cr) spinels in the outer layer. From the nano-SIMS analysis, oxygen was detected at the locations of intergranular chromium carbides ahead of the crack tip, which means that oxygen diffused into the grain boundary and oxidized the surfaces of the chromium carbides. The intergranular chromium carbide blunted the crack tip, thereby suppressing the crack propagation.

• Journal of Welding and Joining
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• v.13 no.3
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• pp.147-156
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• 1995

The change of microstructure in the bonded interlayer and tensile properties of joints were studied for liquid phase diffusion bonding using STS-310 and Incoloy-825 as base metal and base metal+B alloy as insert inetal. Main experimental results obtained in this study are as follows. 1) The optimum amount of B addition into the insert metal was found to be about 4mass%. 2) When isothermal solidification was completed, the microstructure in the bonded interlayer was the same with that of the base metal because of the grain boundary migration in the bonded interlayer. 3) All of the tensile specimen fractured at base metal and joints bonded at optimum condition exhibited tensile properties in excess of base metal requirements. 4) It was determined that fine car-borides and bordes such as M$_{23}$(C,B)$_{6}$, Cr$_{2}$B, and CrB in STS-310S and TiB in Incoloy-825 exist at the grain boundary around bonded interlayer. These precipitates almost disappeared after homogenizing treatment at 1373K for 86.4ks.s.