• Nuclear Engineering and Technology
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• 제51권2호
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• pp.495-500
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• 2019

When a new fuel is developed, various mechanical properties are absolutely necessary for a safety analysis of the fuel for the licensing and prediction of its mechanical behavior during operation and accident conditions. In this paper, a mechanically equivalent surrogate plate of U-Mo dispersion fuel is presented using tungsten, substitute material of U-Mo particle. A surrogate plate, composed of tungsten/aluminum dispersion meat and aluminum alloy cladding, is manufactured with the same fabrication process with that of fuel plate except that a tungsten powder is used instead of U-Mo powder. A modal test showed that the surrogate plate and fuel plate have similar dynamic characteristics, and a tensile test demonstrated the similarity of the material property up to the yield strength range. The conducted tests proved that the surrogate tungsten plate has equivalent mechanical behaviors with that of a fuel plate, which leads to the acceptable use of a surrogate fuel assembly using tungsten/aluminum dispersion meat in various mechanical tests. The surrogate fuel assembly can be utilized for various out-of-pile characteristic tests, which are necessary for the licensing achievement of a research reactor that uses U-Mo dispersion fuel as a driver.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.200.1-200.1
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• 2016

Tungsten coatings on the graphite (CX-2320) were successfully deposited using the vacuum plasma spraying (VPS) method. An optimum coating procedure was developed and coating thicknesses of $409{\mu}m$ (without an interlayer) and $378{\mu}m$ (with an interlayer) were obtained with no cracks and no signs of delamination. The mechanical characteristics and microstructure of the tungsten coating layers were investigated using a Vickers hardness tester, FE-SEM, EDS, and XRD. The effect of a titanium interlayer on the properties of the tungsten coating was investigated. It was shown that the titanium interlayer prevented the diffusion of carbon to the tungsten layer, thereby suppressing the formation of tungsten carbide. Vickers hardness data yielded values that were 62.5 ~ 80.46% of those for bulk tungsten, indicating that tungsten coatings on graphite can be utilized as a plasma-facing material. High heat flux tests were performed by using thermal plasma with a maximum flux of $10MW/^2$. Vickers hardness after the heat flux test is performed to see a change in the mechanical properties. The formationof a tungsten carbide and the effect of the titanium interlayer for the diffusion barrier are investigated by using energy dispersion spectroscopy (EDS).

• 대한기계학회논문집A
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• 제38권12호
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• pp.1325-1333
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• 2014

Near miss 방식 대응체의 충격자 분산 패턴은 위협체의 무력화에 큰 영향을 미친다. 본 연구에서는 near miss 방식 대응체의 원통형 텅스텐 충격자가 폭발에 의하여 분산될 경우 그 패턴을 수치해석적으로 분석하였다. 폭약의 질량과 형상을 충격자의 분산 패턴에 영향을 미치는 인자로 고려하였으며 두 가지 형상 모델 즉, 상부와 하부가 동일한 두께를 갖는 평행 형상과 상부 및 하부 두께가 각기 다른 테이퍼 형상으로 설정하였다. 해석 결과, 분산된 충격자는 임의 공간의 2 차원 평면상에서 고리 모양을 형성하였으며 폭약 형태가 동일한 경우 폭약 질량이 증가함에 따라 화망 면적은 증가하고, 아울러 테이퍼 형상 폭약의 경우, 평행 형상의 폭약에 비해 큰 화망 면적이 형성됨을 확인하였다. 화망 면적과 충격자 분산 밀도 평가를 바탕으로 near miss 방식 대응체의 충격자 분산 패턴 제어를 위해서는 물리적 특성, 즉 폭약의 질량뿐 만 아니라 형상 또한 주요 설계 요소가 됨을 알 수 있었다.

• 마이크로전자및패키징학회지
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• 제18권4호
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• pp.55-61
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• 2011

n형 $Bi_2(Te_{0.9}Se_{0.1})_3$ 분말을 기계적 합금화 공정으로 제조하고 텅스텐 분말을 분산시켜 $550^{\circ}C$에서 30분간 가압소결 후, 텅스텐 함량에 따른 열전특성을 분석하였다. 텅스텐 분말을 분산시키지 않은 $Bi_2(Te_{0.9}Se_{0.1})_3$ 가압소결체의 상온 출력인자는 $21.9{\times}10^{-4}$ $W/m-K^2$ 이었으며, 1 vol% 텅스텐 분말의 분산에 의해 상온 출력인자가 $30.5{\times}10^{-4}$ $W/m-K^2$로 증가하였다. 텅스텐 분말을 분산시키지 않은 $Bi_2(Te_{0.9}Se_{0.1})_3$ 가압소결체는 상온에서 0.52의 무차원 성능지수를 나타내었으며, 1 vol% 텅스텐 분말의 분산에 의해 무차원 성능지수가 0.95로 크게 향상되었다.

• 분석과학
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• 제19권5호
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• pp.394-399
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• 2006

본 연구에서는 반도체 웨이퍼 연마 공정에 사용한 산화제와 첨가제의 연마 속도에 미치는 영향과 전기 화학적 특성에 대해 조사하였다. 산화제로는 과산화수소, 질산화 철과 요오드산 칼륨을 사용하였으며, 이들은 연마액의 pH와 종류에 따라 텅스텐 막질에서 상이한 산화반응을 나타내었다. 이러한 차이점은 연마성능에 영향을 끼치며, 과산화수소는 식각반응이 질산화 철과 요오드산 칼륨에서는 부동태 반응이 우세하였다. 그리고 염기성 화합물인 TMAH와 KOH를 연마액에 첨가하였을 때 텅스텐에 대한 전위 에너지 변화 증가 및 연마 제거속도 증가를 확인할 수 있었으며, 제타 전위 값의 절대 값 증가를 통해 분산성 향상에도 도움이 되는 것을 알 수 있었다. 마지막으로 음이온 계면 활성제중 평균 분자량이 25만인 폴리아크릴산을 100 ppm 첨가시 연마 입자의 뭉침 현상이 줄어들면서 분산성 향상에 효과적인 것을 알 수 있었다.

• Advances in materials Research
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• 제6권1호
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• pp.79-91
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• 2017

In the present work, a design of experiment (DOE) technique using Taguchi method, has been applied to optimize the properties of ODS tungsten heavy alloys(WHAs). In this work Taguchi method involves nine experiments groups for four processing parameters (compaction pressure, sintering temperature, binding material type, and oxide type) with three levels was implemented. The signal-to-noise (S/N) ratio and analysis of variance (ANOVA) were employed to obtain the optimal process parameter levels and to analyze the effect of these parameters on density, electrical conductivity, hardness and compressive strength values. The results showed that all the chosen factors have significant effects on all properties of ODS tungsten heavy alloys samples. The density, electrical conductivity and hardness increases with the increase in sintering temperature. The analysis of the verification experiments for the physical properties (density and Electrical conductivity) has shown that Taguchi parameter design can successfully verify the optimal parameters, where the difference between the predicted and the verified values of relative density and electrical conductivity is about 1.01% and 1.15% respectively.

• Nuclear Engineering and Technology
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• 제53권5호
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• pp.1593-1601
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• 2021

Oxide dispersion strengthening (ODS) tungsten alloys are highly desirable in irradiation applications. However, how to improve the properties of ODS-tungsten alloys efficiently has been worth studying for a long time. Here we report a nanostructuring approach that achieves W-La₂O₃ alloy with a high level of flexural strength and Vickers hardness at room temperature, which have the maximum value of 581 MPa and 703 Hv, respectively. This method named solution combustion synthesis (SCS) can generate 30 nm coating structures W-La₂O₃ composite powders by using Keggin-type structural polyoxometalates as raw materials in a fast and low-cost process. The composite powder can be fabricated to W-La₂O₃ alloy with an optimal microstructure of submicrometric W grains coexisting with nanometric oxide particles in the grain interior, and a stability interface structure of grain boundaries (GBs) by forming transition zones. The method can be used to prepare new ODS alloys with excellent properties in the future.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.109-110
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• 2006

We have studied the effect of C/Ti atomic ratio of TiCx (x=0.5, 0.75 and 1.0) raw powder on the properties of the Ti-Mo-WTiC sintered hard alloy. The decrease of C/Ti atomic ratio accelerated the densification in the sintering process. The hardness was remarkably improved up to 1350HV with decreasing the C/Ti atomic ratio because of increase of TiCx phase volume content and its fine dispersion. From the results of electro-chemical tests in acid and 3% NaCl solutions, it was obvious that every alloy had excellent corrosion resistance, which meant about 200 times better than that of WC-Co cemented carbide.

• 대한치과보철학회지
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• 제37권5호
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• pp.545-566
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• 1999

The use of pure titanium and titanium alloys have been increased recently in fixed, removable prosthodontics and implant fields as a framework. But when they were used for superstructures of implant or metal framework of removable prosthesis, welding is necessary to reconnect the fracture site to control the casting distortions. To overcome the difficulties in soldering the titanium due to high oxidation property, much effort have been devoted. In this study, some of mechanical properties were compared between pure titanium and Ti-6Al-4V alloy by using after welding, electron beam welding technique and tungsten arc welding. Mechanical properties such as tensile strength, yield strength, elongation and microhardness were measured. And, in order to compare the effect of welding site and surrounding metal tissue according to the welding condition, SEM photographs were taken and element distribution was observed by Wave Dispersion Spectroscopy. Through analyses of the data, following results were obtained; 1. In items such as tensile strength, yield strength and elongation according to the welding techniques of pure titanium, only tungsten arc welded group showed significant lower value than other groups(P<0.05). 2. In items such as tensile strength and yield strength according to the welding techniques of Ti-6Al-4V alloy, control group and tungsten arc welded group showed significant difference among all the groups(P<0.05). 3. Ti-6Al-4V alloy exhibited significantly greater elongation than control group when the laser welding method and electron beam welding method were used, and elongation showed increasing tendency. 4. Pure titanium specimens exhibited increasing tendency of microhardness regardless of the weld-ing technique applied, and especially tungsten arc welded group demonstrated a great increase of microhardness than parent metal. 5. There was no hardness change in laser welded group and electron beam welded group of Ti-6Al-4V alloy, but in tungsten arc welded group, hardness changed greatly from parent metal to weld seam. 6. Through the metallographic examination and scanning electron microscopy, laser welding caused central fusion and recristallizations were formed and tungsten arc welding caused localized fusion to 0.3-0.7mm from the surface.

• 대한기계학회논문집A
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• 제25권10호
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• pp.1535-1540
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• 2001

This study presents the possibility of scratch reduction on wafer in CMP by applying the ultrasonic and megasonic energy into the slurry which might contain large abrasive particles. Experiments were conducted to verify the dispersion ability of agglomerated particles by applying ultrasonic, megasonic waves and analyze the particle distribution of used slurry in case, of sonic energy assisted or none. And the dispersion stability of megasonic waves was investigated through the experiment of stability of the dispersed slurry, Finally, to confirm that the distribution of particles in slurry by ultrasonic waves was actually related to scratches on wafer when CMP was done, tungsten blanket wafer was processed, by CMP to compare and investigate scratches on wafer.