• Journal of Powder Materials
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• v.18 no.4
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• pp.359-364
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• 2011

Zr-Ti alloy powders were successfully synthesized by magnesium thermal reduction of metal chlorides. The evaporated and mixed gasses of $ZrCl_4+TiCl_4$ were injected to liquid magnesium and the chloride components were reduced by magnesium leading to the formation of $MgCl_2$. The released Zr and Ti atoms were then condensed to particle forms inside the mixture of liquid magnesium and magnesium chloride, which could be dissolved fully in post process by 1~5% HCl solution at room temperature. By the fraction-control of individually injected $ZrCl_4$ and $TiCl_4$ gasses, the final compositions of produced alloy powders were changed in the ranges of Zr-0 wt.%~20 wt.%Ti and their purity and particle size were about 99.4% and the level of several micrometers, respectively.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.4
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• pp.324-329
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• 2010

Fuel rods using in nuclear power plants consist of uranium dioxide pellets enclosed in zirconium alloy(zircaloy) tubes. It is vitally important for the pellet surface to remain free from pits, cracks and chipping defects after it is loaded into the tubes to prevent local hot spots during reactor operation. This paper investigates the feasibility study for detecting surface flaws of pellets contained within nuclear fuel rod through X-ray tomography simulation. Reconstructed images used by parallel and fan-beam filtered back projection method were presented and confirmed the accessibility between simulation data and MPS(missing pellet surface) image data.

• Journal of Korea Foundry Society
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• v.30 no.6
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• pp.217-223
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• 2010

Foamed metal has become an attractive material, which has unique physical, thermal, acoustic, damping and mechanical properties, because large amount of pores are distributed in the metal matrix. Therefore, metal foam can be used for the light weight application in automotive, locomotive, aerospace fields. Aluminum foams have been developed successfully and will be employed in the next generation of energy absorption boxes. Magnesium alloys are most eligible candidate to substitute aluminum alloy, especially for lower density and higher damping properties in wide industrial fields. Magnesium alloy foams are expected to be particularly advantageous due to two thirds the density of aluminum. However, foaming magnesium have been weakness of high activity, difficult processing and very dangerous. In order to upgrade this problem, AM50 magnesium alloy which has better characteristic is safe to use through foaming time and alloying element in this study.

• Transactions of the Korean hydrogen and new energy society
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• v.15 no.4
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• pp.266-273
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• 2004

The objective of this study is an understanding of stress corrosion cracking of metals that is recognized to mostly limit the lifetime of the structural materials by comparing the features of delayed hydride cracking of zirconium alloys with those of stress corrosion cracking (SCC) of Ni-based alloys and hydrogen cracking of stainless steels. To this end, we investigated a dependence of delayed hydride cracking (DHC) velocity on the applied stress intensity factor and yield strength, and correlated a temperature dependence of the striation spacing and the DHC velocity. We reviewed a similarity of the features between the DHC of zirconium alloys, the SCC of Ni-based alloys and turbine rotor steels, and the hydrogen cracking of stainless steels and discussed the SCC phenomenon in metals with our DHC mode.

• Korean Journal of Materials Research
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• v.25 no.8
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• pp.376-385
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• 2015

The effects of Nb and Cr addition on the microstructure, corrosion and oxide characteristics of Zr based alloys were investigated. The corrosion tests were performed in a pressurized water reactor simulated-loop system at $360^{\circ}C$. The microstructures were examined using OM and TEM, and the oxide properties were characterized by low-angle X-ray diffraction and TEM. The corrosion test results up to 360 days revealed that the corrosion rates were considerably affected by Cr content but not Nb content. The corrosion resistance of the Zr-xNb-0.1Sn-yCr quaternary alloys was improved by an increasing Nb/Cr ratio. The crystal structure of the precipitates was affected by a variation of the Nb/Cr ratio. The Zr-Nb beta-enriched precipitates were mainly formed in the high Nb/Cr ratio alloy while $Zr(NbCr)_2$ precipitates were frequently observed in the low Nb/Cr ratio alloy. The studies of oxide characteristics revealed that the corrosion resistance was related to the crystal structure of the precipitate.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.2
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• pp.189-195
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• 2004

The pressure tubes, which contain high temperature heavy water and fuel, are within the core of a CANDU nuclear reactor, and are thus subjected to high stresses, temperature gradient, and neutron flux. Further, it is well known that pressure tubes of cold-worked Zr-2.5Nb materials result in hydrogen diffusion, which create fully-hydrided regions (frequently called Blister). Thus a proper investigation of hydrogen diffusion within zirconium-alloy nuclear components, such as CANDU pressure tube and fuel channels is essential to predict the structural integrity of these components. In this respect, this paper presents numerical investigation of hydrogen diffusion to quantify the hydrogen concentration fur blister growth of CANDU pressure tube. For this purpose, coupled temperature-hydrogen diffusion analyses are performed by means of two-dimensional finite element analysis. Comparison of predicted temperature field and blister with published test data shows good agreement.

• Resources Recycling
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• v.26 no.6
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• pp.3-9
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• 2017

In this study, plasma arc remelting behaviors according to arc current, arc voltage, and types of plasma gas were investigated using Kroll processed Ti sponges as anode. In the discharge pressure range of vacuum pump ($200{\sim}300kgf/cm^2$), the arc voltage did not vary greatly with the increase of discharge pressure at a given arc length. This means that the pressure in the vacuum chamber during operation hardly changes and the atmospheric pressure maintains. Under various conditions of arc currents (700~900A), the arc voltage slightly increased with arc current. The effects of anode materials and operational variables on the arc length-arc voltage relationship were compared with the results in previous studies. When the atmospheric gas changed from argon to helium, double effect of improvement on the output of the steady state was observed. The increase of output in the plasma arc device was accompanied by an increase in the melting rate of the Ti sponge and the quality of the ingot surface was also improved. The plasma arc remelting of the new scrap titanium and the old scrap zirconium alloy could result in the fabrication of an ingot with high surface quality.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.4
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• pp.342-348
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• 2003

Ultrasonic backscattering profiles of the Zr plates(with a thickness of 1.32mm) with/without Be-Zr alloy layer(with a thickness of $100{\mu}m$) were measured at various incidence positions to evaluate the characteristics of Be diffusion layer. Four principal subprofiles were observed in the backward ultrasound radiated from leaky Lamb waves. The angles and the intensities of the subprofile peaks decreased by the stiffening effect of Be layer. Generation and change of the subprofiles were explained by the acoustical property, collective group velocity and leaky factor difference of the plates under consideration. Backward radiation subprofiles turned out to be an useful method for evaluating thin diffusion layers on plates.

• Korean Journal of Materials Research
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• v.18 no.11
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• pp.597-603
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• 2008

Oxide effects experiments on massive hydriding reactions of Zr alloy with hydrogen gas were carried out at $400^{\circ}C$ under 1 atm in a $H_2$ environment with a thermo-gravimetric apparatus (TGA). Experimental results for oxide effects on massive hydriding kinetics show that incubation time is not proportional to oxide thickness. The results also show that the massive hydriding kinetics of pre-filmed Zr alloys follows linear kinetic law and that the hydriding rates are similar to that of oxide-free Zr alloys once massive hydriding is initiated. Unlikely microstructure of the oxide during incubation time, physical defects such as micro-cracks and pores were observed in the oxide after incubation time. Therefore, it seems that the massive hydriding of Zr alloys can be ascribed to short circuit paths and mechanical or physical defects, such as micro-cracks and pores in the oxide, rather than to hydrogen diffusion through the oxide resulting from the increase of oxygen vacancies in the hypo-stoichiometric oxide.

• Journal of the Korean Ceramic Society
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• v.47 no.2
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• pp.106-112
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• 2010

This paper presents some experimental results on incubation time for massive hydriding of Zr alloys with oxide thickness. Oxide effects experiments on massive hydriding reaction of commercial Zr alloy claddings and pre-oxidized Zr alloys with hydrogen gas were carried out in the temperature range from 300 to $400^{\circ}C$ with thermo-gravimetric apparatus. Experimental results for oxide effects on massive hydriding kinetics show that incubation time is not proportional to oxide thickness and that the massive hydriding kinetics of pre-filmed Zr alloys follows linear kinetic law and the hydriding rate are similar to that of oxide-free Zr alloys once massive hydriding is initiated. There was a difference in micro-structures between oxide during incubation time and oxide after incubation time. Physical defects such as micro-cracks and pores were observed in only oxide after incubation time. Therefore, the massive hydriding of Zr alloys seems to be ascribed to short circuit path, mechacical or physical defects, such as micro-cracks and pores in the oxide rather than hydrogen diffusion through the oxide resulting from the increase of oxygen vacancies in the hypostoichiometric oxide.