• 대한기계학회논문집
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• 제12권5호
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• pp.1083-1091
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• 1988

본 연구에서는 위의 두번째 연구동향과 맥락을 같이하는 것으로서 스테인리스 강(SUS304)에 대한 진공브레이징 연구 및 탄소강의 진공 브레이징에 대한 연구결과들 을 토대로 하여 SUS304와 탄소강과의 진공브레이징 현상을 연구하였는데 특히 모재의 탄소함유량, 브레이징시간 및 접합부 틈새(joint clearance)등에 따라 접합부에 나타 나는 여러 금속학적 현상의 규명 및 접합강도(joint strength)에 대해 변수들이 미치 는 영향을 연구 하였다.

• 한국표면공학회지
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• 제39권1호
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• pp.35-42
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• 2006

In this study, the fatigue properties on the cavitation damage of the flame quenched 8.8Al-bronze (8.8Al-4.5Ni-4.5Fe-Cu) as well as the current nuclear pump impeller materials (8.8Al-bronze, STS316 and SR50A) has been investigated using an ultrasonic vibratory cavitation test. For this the impact loads of cavitation bubbles generated by ultrasonic vibratory device quantitatively evaluated and simultaneously the cavitation erosion experiments have been carried out. The fatigue analysis on the cavitation damage of the materials has been made from the determined impact load distribution (e.g. impact load, bubble count) and erosion parameters (e.g. incubation period, MDPR). According to Miner's law, the determined exponents b of the F-N relation ($F^b$ N = Constant) at the incubation stage (N: the number of fracture cycle) were 5.62, 4.16, 6.25 and 8.1 for the 8.8Al-bronze, flame quenched one, STS316 and SR50A alloys. respectively. At the steady state period, the exponents b of the F-N' curve (N': the number of cycle required for $1{\mu}m$ increment of MDP) were determined as 6.32, 5, 7.14 and 7.76 for the 8.8Al-bronze, flame quenched one, STS316, and SR50A alloys, respectively.

• 한국표면공학회지
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• 제40권4호
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• pp.175-179
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• 2007

An Fe-Ni-Co based superalloy Incoloy 909 (Incoloy 909) has been used for gas turbine engine component material. This alloy is susceptible to high temperature oxidation and corrosion because of the absence of corrosion resistant Cr. For the improvement of durability of the component of Incoloy 909 aluminizing-chromate coating by pack cementation process has been investigated at relatively low temperature of about $550^{\circ}C$ to protect the surface microstructure and properties of Incoloy 909 substrate. As a previous study to aluminizing-chromate coating by pack cementation of Incoloy 909, the optimal aluminizing process has been investigated. The size effects of source Al powder and inert filler $Al_O_3$ powder and activator selection have been studied. And the dependence of coating growth rate on aluminizing temperature and time has also been studied. The optimal aluminizing process for the coating growth rate is that the mixing ratio of source Al powder, activator $NH_4Cl$ and filler $Al_O_3$ are 80%, 1% and 19% respectively at aluminizing temperature $552^{\circ}C$ and time 20 hours.

• 한국자기학회지
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• 제8권6호
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• pp.357-361
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• 1998

직류 및 고주파 마그네트론 스파터링 방법으로 제조한 CoZr/Ag/CoCr 삼층박막에 대해, 강자성 공명 실험을 수행하므로서 비자성층인 Ag 층의 두께변화가 CoZr층과 CoCr층 사이의 교환결합(Exchabge coupling)에 미치는 영향을 고찰했다. CoZr/Ag/CoCr 삼층박막에서 층간 결합세기(Coupling strength) K'은 Ag층의 두께가 증가함에 따라 급격히 증가하여 Ag 층의 두게가 10$\AA$일 때, 최대값 748 Oe을 보였다. Ag 층의 두께가 20~100$\AA$인 영역에서 K'은 진동하는 모습을 보이는데, 이와 같은 특성은 80Ni-Fe/Cu/Co 다층박막에 대해 H.Koizumi 등이 관측한 결과와 유사한 모습으로서, 스원인규명을 위해 지속적인 연구가 요망된다고 생각한다. 그리고, Ag층의 두께가 100$\AA$ 이상 증가하면 층간 상호작용은 0으로 수렴하는 모습이 보인다. 모든 시료에 대해 K'은 0보다 큰 특성을 보이므로, CoZr층과 CoCr층 사이의 상호작용은 강자성 결합으로 해석된다.

• Corrosion Science and Technology
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• 제20권4호
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• pp.210-229
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• 2021

To safely operate domestic nuclear power plants approaching the end of their design life, the material degradation management strategy of the components is important. Among studies conducted to improve the soundness of nuclear reactor components, research methods for understanding the degradation of reactor internals and preparing management strategies were surveyed. Since the IGSCC (Intergranular Stress Corrosion Cracking) initiation and propagation process is associated with metal dissolution at the crack tip, crack initiation sensitivity was decreased in the hydrogenated water with decreased crack sensitivity but occurrence of small surface cracks increased. A stress of 50 to 55% of the yield strength of the irradiated materials was required to cause IASCC (Irradiation Assisted Stress Corrosion Cracking) failure at the end of the reactor operating life. In the threshold-stress analysis, IASCC cracks were not expected to occur until the end of life at a stress of less than 62% of the investigated yield strength, and the IASCC critical dose was determined to be 4 dpa (Displacement Per Atom). The stainless steel surface oxide was composed of an internal Cr-rich spinel oxide and an external Fe and Ni-rich oxide, regardless of the dose and applied strain level.

• Nuclear Engineering and Technology
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• 제51권4호
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• pp.1109-1116
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• 2019

It is essential to predict the radioactivity distribution around the reactor cooling system (RCS) during obligatory cyclic operation of AP-1000. A home-developed program CPA-AP1000 is upgraded to predict the response of activated corrosion products (ACPs) in the RCS. The program is written in MATLAB and it uses state of the art MCNP as a subroutine for flux calculations. A pair of cyclic power profiles were superimposed after initial full power operation. The effect of cyclic operation is noticed to be more prominent for in-core surfaces, followed by the primary coolant and out-of-core structures. The results have shown that specific activity trends of $^{56}Mn$ and $^{24}Na$ promptly follow the power variations, whereas, $^{59}Fe$, $^{58}Co$, $^{99}Mo$ and $^{60}Co$ exhibit a sluggish power-following response. The investigations pointed out that promptly power-following response of ACPs in the coolant is vital as an instant radioactivity source during leakage incidents. However, the ACPs with delayed power-following response in the out-of-core components are perceived to cause a long-term activity. The present results are found in good agreement with those for a reference PWR. The results are useful for source term monitoring and optimization of work procedures for an innovative reactor design.

• 한국분말재료학회지
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• 제26권3호
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• pp.201-207
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• 2019

Tungsten heavy alloys (W-Ni-Fe) play an important role in various industries because of their excellent mechanical properties, such as the excellent hardness of tungsten, low thermal expansion, corrosion resistance of nickel, and ductility of iron. In tungsten heavy alloys, tungsten nanoparticles allow the relatively low-temperature molding of high-melting-point tungsten and can improve densification. In this study, to improve the densification of tungsten heavy alloy, nanoparticles are manufactured by ultrasonic milling of metal oxide. The physical properties of the metal oxide and the solvent viscosity are selected as the main parameters. When the density is low and the Mohs hardness is high, the particle size distribution is relatively high. When the density is high and the Mohs hardness is low, the particle size distribution is relatively low. Additionally, the average particle size tends to decrease with increasing viscosity. Metal oxides prepared by ultrasonic milling in high-viscosity solvent show an average particle size of less than 300 nm based on the dynamic light scattering and scanning electron microscopy analysis. The effects of the physical properties of the metal oxide and the solvent viscosity on the pulverization are analyzed experimentally.

• 천문학회지
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• 제52권3호
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• pp.57-69
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• 2019

We present an analysis of the chemical abundances and kinematics of six low-mass dwarf stars, previously claimed to be candidate hypervelocity stars (HVSs). We obtained moderate-resolution (R ~ 6000) spectra of these stars to estimate the abundances of several chemical elements (Mg, Si, Ca, Ti, Cr, Fe, and Ni), and derived their space velocities and orbital parameters using proper motions from the Gaia Data Release 2. All six stars are shown to be bound to the Milky Way, and in fact are not even considered high-velocity stars with respect to the Galactic rest frame. Nevertheless, we attempt to characterize their parent Galactic stellar components by simultaneously comparing their element abundance patterns and orbital parameters with those expected from various Galactic stellar components. We find that two of our program stars are typical disk stars. For four stars, even though their kinematic probabilistic membership assignment suggests membership in the Galactic disk, based on their distinct orbital properties and chemical characteristics, we cannot rule out exotic origins as follows. Two stars may be runaway stars from the Galactic disk. One star has possibly been accreted from a disrupted dwarf galaxy or dynamically heated from a birthplace in the Galactic bulge. The last object may be either a runaway disk star or has been dynamically heated. Spectroscopic follow-up observations with higher resolution for these curious objects will provide a better understanding of their origin.

• Nuclear Engineering and Technology
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• 제53권4호
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• pp.1210-1217
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• 2021

The analysis of ⁴¹Ca in concrete generated from the nuclear facilities decommissioning is critical for ensuring the safe management of radioactive waste. An analytical method for the determination of ⁴¹Ca in concrete is described. ⁴¹Ca is a neutron-activated long radionuclide, and hence, for accurate analysis, it is necessary to completely extract Ca from the concrete sample where it exists as the predominant element. The decomposition methods employed were the acid leaching, microwave digestion, and alkali fusion. A comparison of the results indicated that the alkali fusion is the most suitable way for the separation of Ca from the concrete sample. Several processes of hydroxide and carbonate precipitation were employed to separate ⁴¹Ca from interferences. The method relies on the differences in the solubility of the generated products. The behavior of Ca and the interfering elements such as Fe, Ni, Co, Eu, Ba, and Sr is examined at each separation step. The purified ⁴¹Ca was measured by a liquid scintillation counter, and the quench curve and counting efficiency were determined by using a certified reference material of known ⁴¹Ca activity. The recoveries in this study ranged from 56 to 68%, and the minimum detectable activity was 50 mBq g^-1 with 0.5 g of concrete sample.

• 한국표면공학회지
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• 제55권6호
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• pp.448-459
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• 2022

Generally, steel is the most commonly used in the industry because of good strength, processability and cost-effectiveness. Steel can be surface-treated such as coating or used as an alloy by adding elements such as Cr, Ni, Zr, and Al to increase corrosion resistance. However, even if steel is used in same environment corrosion resistance is sharply lowered when it is exposed to a high temperature for a fixed or extended period of time due to an overload or other factors. In particular, the use of hot-dip aluminized plated steel, which is used in high-temperature atmospheres, is increasing due to the surface Al₂O₃ oxide film. This steel necessitates an urgent solution as issues of corrosion resistance limitations often appear. It is an important issue that not only cause analysis but also the research for the surface treatment method that can be solved. Thus, in this study, Cr in which it is expected to be effective in corrosion resistance and heat resistance attempted to deposit on hot dip aluminized plated steel with PVD sputtering. And it was possible to present the surface treatment application of various types of industrial equipment exposed to high temperature and basic design guidelines for use by confirming the corrosion resistance of hot dip Al-Si plated steel with Cr film deposited at high temperature.