• Korean Journal of Metals and Materials
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• v.56 no.11
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• pp.796-804
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• 2018

The Charpy impact toughness of the heat affected zone (HAZ) of electro gas welded 390 MPa yield strength grade steel, manufactured by a thermo mechanically controlled process, was investigated. The effects of added Nb on the toughness of the steel and the factors influencing scatter in toughness are discussed in the present work. It was observed that adding Nb to the steel led to the deterioration of HAZ toughness. The presence of soluble Nb in the HAZ increased its hardenability and resulted in a larger amount of low toughness bainitic microstructure. Microstructural observations in the notch root area revealed the significant role of different microstructures in the area. In the presence of a larger amount of bainitic microstructures, the HAZ exhibited a lower Charpy toughness with a larger scatter in toughness. A softened zone with a lower hardness than the base metal was formed in the HAZ. However, theoretical analysis revealed that the presence of the zone might not be a problem in a real welded joint because of the plastic restraint effect enforced by surrounding materials.

• Korean Journal of Metals and Materials
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• v.49 no.11
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• pp.874-881
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• 2011

The present study describes a new technique to extract the primary silicon from an Al-Si alloy melt using centrifugal force during its solidification. The primary silicon was separated from an Al-50 wt.%Si alloy by centrifugal force in the form of a foam, which facilitated subsequent acid leaching to extract the pure silicon due to its wide surface area. The foam recovery after centrifugal separation was decreased as centrifugal acceleration was increased. The final recovery after acid leaching became closer to the solid fraction of the alloy, which was calculated from the Al-Si binary phase diagram, with increasing centrifugal acceleration due to the effective removal of the attached Al on the foam. The purity of the primary silicon obtained by the centrifugal separation method was over 99.99%, with only aluminum being also present.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.122-122
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• 2012

The exterior structures of natural organisms have continuously evolved by controlling wettability, such as the Namib Desert beetle, whose back has hydrophilic/hydrophobic contrast for water harvesting by mist condensation in dry desert environments, and some plant leaves that have hierarchical micro/nanostructures to collect or repel liquid water. In this work, we have provided a method for wettability contrast on metals by both nano-flake or needle patterns and tuning of the surface energy. Metals including steel alloys and aluminum were provided with hierarchical micro/nanostructures of metaloxides induced by fluorination and a subsequent catalytic reaction of fluorine ions on metal surfaces in water with various ranges from room to boiling temperature of water. Then, a hydrophobic material was deposited on the structured surfaces, rendering superhydrophobicity. Plasma oxidization induces the formation of superhydrophilic surfaces on selective regions surrounded by superhydrophobic surfaces. We show that wettability contrast surfaces align liquid water within patterned hydrophilic regions during the condensation process. Furthermore, this method could have a greater potential to align other liquids or living cells.

• Transactions of Materials Processing
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• v.23 no.8
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• pp.469-474
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• 2014

With the increased concerns of environmental issues, industries are paying more attention to lightweight metals. Because the high degree of springback is an obstacle to the widespread use of lightweight metals, many investigations have been conducted to reduce springback by increasing temperature. However, increasing the temperature of the whole die or the material is energy inefficient, since generally only a limited area of the material is deformed during sheet metal forming. As a solution to this problem, focused heating that only heats the area where plastic deformation occurs may be an alternative approach. In the current study, V-bending tests were conducted at various temperatures after the AZ31, Ti-GR2 sheets were locally heated using near-infrared (NIR) radiation in order to evaluate the effect of temperature on springback. The results of the experiment confirm that the NIR focused heating reduces the springback of AZ31, Ti-GR2 alloys with increasing temperature.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.15 no.2
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• pp.125-133
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• 2017

KAERI is conducting research on spent cladding hulls and additive metals to generate a solidification host matrix for the noble metal fission product waste in anode sludge from the electro-refining process to minimize the volume of waste that needs to be disposed of. In this study, alloy compositions Zr-17Cr, Zr-22Cr, and Zr-27Cr were prepared with or without eight noble metals representing fuel waste using induction melting. The microstructures of the resulting alloys were characterized and electrochemical corrosion tests were conducted to evaluate their corrosion characteristics. All the compositions had better corrosion characteristics than other Zr-based alloys that were evaluated for comparison. Analysis of the leach solution after the corrosion test of the Zr-22Cr-8NM specimen indicated that the noble metals were not leached during corrosion under 500 mV imposed voltage, which simulates a highly oxidizing disposal environment. The results of this study confirm that Zr-Cr based compositions will likely serve as chemically stable waste forms.

• Corrosion Science and Technology
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• v.14 no.4
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• pp.166-171
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• 2015

Knowledge of how metal releases from the stainless steels used in food processing applications and cooking utensils is essential within the framework of human health risk assessment. A new European standard test protocol for testing metal release in food contact materials made from metals and alloys has recently been published by the Council of Europe. The major difference from earlier test protocols is the use of citric acid as the worst-case food simulant. The objectives of this study were to assess the effect of citric acid at acidic, neutral, and alkaline solution pH on the extent of metal release for stainless steel grades AISI 304 and 316, commonly used as food contact materials. Both grades released lower amounts of metals than the specific release limits when they were tested according to test guidelines. The released amounts of metals were assessed by means of graphite furnace atomic absorption spectroscopy, and changes in the outermost surface composition were determined using X-ray photoelectron spectroscopy. The results demonstrate that both the pH and the complexation capacity of the solutions affected the extent of metal release from stainless steel and are discussed from a mechanistic perspective. The outermost surface oxide was significantly enriched in chromium upon exposure to citric acid, indicating rapid passivation by the acid. This study elucidates the effect of several possible mechanisms, including complex ion- and ligand-induced metal release, that govern the process of metal release from stainless steel under passive conditions in solutions that contain citric acid.

• Korean Journal of Metals and Materials
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• v.50 no.1
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• pp.52-58
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• 2012

Hydrogen-delayed fracture (HDF) was analyzed from the deposited weld metals of 600-MPa and 800-MPa flux-cored arc (FCA) welding wires, and then from the diffusible hydrogen behavior of the weld zone. Two types of deposited weld metal, that is, rutile weld metal and alkali weld metal, were used for each strength level. Constant loading test (CLT) and thermal desorption spectrometry (TDS) analysis were conducted on the hydrogen pre-charged specimens electrochemically for 72 h. The effects of microstructures such as acicular ferrite, grain-boundary ferrite, and low-temperature-transformation phase on the time-to-failure and amount of diffusible hydrogen were analyzed. The fracture time for hydrogen-purged specimens in the constant loading tests decreased as the grain size of acicular ferrite decreased. The major trapping site for diffusible hydrogen was the grain boundary, as determined by calculating the activation energies for hydrogen detrapping. As the strength was increased and alkali weld metal was used, the resistance to HDF decreased.

• Journal of Powder Materials
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• v.22 no.2
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• pp.100-104
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• 2015

The porous metals are known as relatively excellent characteristic such as large surface area, light, lower heat capacity, high toughness and permeability. The Fe-Cr-Al alloys have high corrosion resistance, heat resistance and chemical stability for high temperature applications. And then many researches are developed the Fe-Cr-Al porous metals for exhaust gas filter, hydrogen reformer catalyst support and chemical filter. In this study, the Fe-Cr-Al porous metals are developed with Fe-22Cr-6Al(wt) powder using powder compaction method. The mean size of Fe-22Cr-6Al(wt) powders is about $42.69{\mu}m$. In order to control pore size and porosity, Fe-Cr-Al powders are sintered at $1200{\sim}1450^{\circ}C$ and different sintering maintenance as 1~4 hours. The powders are pressed on disk shapes of 3 mm thickness using uniaxial press machine and sintered in high vacuum condition. The pore properties are evaluated using capillary flow porometer. As sintering temperature increased, relative density is increased from 73% to 96% and porosity, pore size are decreased from 27 to 3.3%, from 3.1 to $1.8{\mu}m$ respectively. When the sintering time is increased, the relative density is also increased from 76.5% to 84.7% and porosity, pore size are decreased from 23.5% to 15.3%, from 2.7 to $2.08{\mu}m$ respectively.

• The korean journal of orthodontics
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• v.33 no.5 s.100
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• pp.351-358
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• 2003

Nickel and chromium are two major metals used in the alloys of most orthodontic appliances. But these metals are known to cause hypersensitivity, dermatitis, and asthma. In addition, a significant carcinogenic and mutagenic potential has been demonstrated for compounds containing these metals. The purpose of this study was to find out how much nickel and chromium was released from orthodontic appliances, and which factors would influence the release. The simulated orthodontic appliances were constructed for a half of a mandibular arch and incubated in $0.05\%$ NaCl solution at $37^{\circ}C$. Nickel and chromium release was quantified with an Inductively Coupled Plasma (ICP) spectroanalyzer. The results were as follows : 1. From simulated orthodontic appliances, nickel was released $9.83-70.0{\mu}g/day$ but the release of chromium was not detectable in Limit of 10ppb. 2. The amount of nickel release was significantly different between the types of appliances. 3. The galvanic condition increased the amount of nickel release, which was not statistically significant. 4. The sand blasting increased the amount of nickel release, which was also not statistically significant.

• Journal of Biomedical Engineering Research
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• v.6 no.1
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• pp.37-46
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• 1985

Development of a dental Ni-Cr alloy system for porcelain veneering crown and bridge was studied in this research. The principles of alloy design were a) It should not contain toxic beryllium. b) It should have low melting Point. c) It should be easily ground and polished. d) It should possess an adequate strength to resist the deformational force In the mouth. e) It should be bondable Ivith porcelain by chemically. After investigating the effect of minor elements such as boron and rare earth metals on the mechanical properties of the Ni-Cr alloy system, the compromised ideal composition for dental use was determined. The composition was l9.6%, Cr, 5.6% Mo, 3.4% Si, 1, 0% Fe, 0.01% Ti, 0.5-1.0% B, 0.2-0.6% misch metal, balance Ni. To compare the performance of experimental alloy with commercially available alloys, the properties such as strength, melting point, and bond strength were measured. The results Ivere as follows: a) Boron increases the strength of the alloy but reduces the elongation. b) Misch metal increases the strength when the boron content is low, but does not increase the strength when boron content is high. And it reduces the elongation drastically, c) Mechanical strength of the experimental alloy was not superior to commercially available Be containing alloy, but handling performance such as castability, ease of granting and polishing, and cuttability were superior to the Be containing alloy.