• Corrosion Science and Technology
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• 제2권1호
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• pp.36-40
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• 2003

An attractive combination of corrosion resistance and mechanical properties in the temperature range -50 to $250^{\circ}C$ is offered by duplex stainless steel. However, undesirable secondary precipitation phase such as $\sigma$, $\gamma_2$ and $Cr_2N$ may taken place at the cooling stage from the welding processes. Therefore, this paper describes the influence of different welding procedures such as manual metal arc welding (MMA), tungsten inert gas welding (TIG) and vacuum brazing on corrosion resistance of the welded joint for UNS S31803 duplex stainless steel. Microstructure and chemical compositions of the welded joint were examined. The weight loss of specimens immersed in 6% $FeCl_3$ solution at $47.5^{\circ}C$ for 24-hours was determined and used to evaluate the pitting resistance of duplex stainless steel and their welds. The region of heat-affected zone of specimen obtained by the MMA is much wider than that resulted from TIG, therefore, the weight loss of welds by MMA was larger than that of weld by TIG. The weight loss of brazed specimens cooled from slow cooling rate was larger than those of specimens cooled from high cooling rate, because the precipitation of $\sigma$ phase. Beside that, the weight loss of brazed specimen is greater than those of the welded specimens. The galvanic corrosion was observed in brazed duplex stainless steel joints in the chloride solution.

• 한국초전도ㆍ저온공학회논문지
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• 제20권3호
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• pp.11-14
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• 2018

$MgB_2$ superconducting properties have been investigated with the surface-treated boron powders using the chemical solvents. Various solvents were used such as acetone, ethanol, methanol, and water to possibly modify the surface condition of raw boron powders as received. This treatment was done at an argon gas environment inside the glove box to reduce the further contamination during and after chemical treatments. It was found that $T_c$ values were increased to 37.58-37.73 K from the pure sample of 37.50 K when they were treated in inert environment. High- fields $J_c$ at both 5 & 20 K was all increased regardless of any kinds of chemical treatments mentioned above. It is also noted that the $J_c$ at low-fields were increased in the order of solvents: ethanol > acetone > pure $MgB_2$ = methanol > water.

• 한국기계가공학회지
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• 제16권1호
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• pp.112-117
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• 2017

The arc, generated by Tungsten Inert Gas(TIG) welding, is stable and provides excellent quality of the weld. Since automation is difficult, a lot of work is performed by hand. In addition, to obtain the uniform weld quality is difficult when using a base metal having a nonuniform welding line, or when welding inside a pipe. Generally, TIG welding power has the characteristic of constant-current. The welding voltage is changed in proportion to the arc length. Hence, the automatic voltage control equipment should be applied at the TIG welding system. The automatic voltage control equipment has been designed using LabVIEW software. It consists of a manufactured voltage divider circuit, and jig for moving the torch. The voltage measurements and driving of the motor were performed through the algorithm implementation in LabVIEW. Welding was conducted while increasing the arc length. In this process, it was confirmed that the automatic voltage control equipment kept the arc length constant.

• 한국음향학회지
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• 제14권6호
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• pp.5-12
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• 1995

본 논문에서는 열음향 냉장시스템을 음향적으로 해석하고 주어진 조건을 만족시키는 열음향냉장시스템의 설계방법을 제시하였다. 열음향 냉장시스템은 음파의 에너지를 단열팽창, 수축의 원리를 이용하여 열에너지로 변환시키는 열음향변환기이다. 열음향 냉장시스템은 일반 가정용 스피커 유닛을 사용하는 구동부, 실제의 온도 구배가 생기게 되는 스택 부분, 그리고 정상파를 생성시키는 본체 부분인 공명기 등으로 구성된다. 음향학적인 해석을 통해 주어진 조건을 만족시키도록 전체 공명기의 크기를 결정하고 스택의 크기와 위치를 설정하여 이에 따라 실제의 시스템을 설계하였다. 끝으로 설계된 공명기의 기계적 임피던스를 모의실험을 통해 구하였다.

• 소성∙가공
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• 제26권6호
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• pp.365-371
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• 2017

During sling wear of a ferrous metal, a surface layer is formed. Its microstructure, constituting phases, and mechanical property are different from those of the original wearing material. Since wear occurs at the layer, it is important to characterize the layer and understand how wear rate changes with different layers. Various layers are formed depending on external wear conditions such as load, sliding speed, counterpart material, and environmental conditions. In this research, sliding wear tests of pure iron were carried out against two different counterparts (AISI 52100 bearing steel and $Al_2O_3$) in the air and in an inert Ar gas atmosphere. Pure iron was employed to exclude other effects from secondary phases in steel on the wear. Wear tests were performed at room temperature. Worn surfaces, wear debris, and cross-sections were analyzed after the test. It was found that these two different counterparts and environments produced diverse layers, resulting in significant changes in wear rate. Against the bearing steel, pure iron showed higher wear rate in an Ar atmosphere due to severe adhesion than that in the air. On the contrary, the iron showed much higher wear rate in the air against $Al_2O_3$. Different layers and wear rates were analyzed and discussed by oxidation, severe plastic deformation, and adhesion at wearing surfaces.

• Journal of Welding and Joining
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• 제25권3호
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• pp.28-36
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• 2007

A bulk amorphous NiTiZrSiSn powder produced using an inert gas atomization was sprayed by kinetic spraying process that is basically a solid-state deposition process onto a mild steel substrate. They were successfully overlaid onto the mild steel substrate. In order to evaluate the tribological behavior of the kinetic sprayed NiTiZrSiSn BMG (Bulk Metallic Glass) coatings, a partially crystallized coating and a fully crystallized coating were prepared by the isothermal heat treatments. Tribological behaviors were investigated in view of friction coefficient, hardness and amorphous phase fraction of coating layer. Surface morphologies and depth in the wear tracks were observed and measured by scanning electron microscope and alpha-step. From the examination of the scratch wear track microstructure, transition from the ductile like deformation (micro cutting) to the brittle deformation (micro fracturing) in the scratch groove was observed with the increase of the crystallinity.

• 비파괴검사학회지
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• 제13권3호
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• pp.31-38
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• 1993

포항가속기 저장링 진공챔버는 진공도가 $10^{-10}Torr$로 유지될 수 있도록 설계되었고, 초고진공에 적합하도록 TIG용접을 하여 헬륨에 대한 누설률이 $1{\times}10^{-10}Torr{\cdot}{\ell}/sec$ 이하의 기밀성이 요구되고 있다. 저장링 진공챔버에 적용된 TIG용접방법과 결함에 대해 논하고 누설검사에 사용된 헬륨누설검사기의 원리 및 검사방법에 대해서 보고하고자 한다.

• 한국분말재료학회지
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• 제24권2호
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• pp.122-127
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• 2017

Fe-6.5 wt.% Si alloys are widely known to have excellent soft magnetic properties such as high magnetic flux density, low coercivity, and low core loss at high frequency. In this work, disc-shaped preforms are prepared by spark plasma sintering at 1223 K after inert gas atomization of Fe-6.5 wt.% Si powders. Fe-6.5 wt.% Si sheets are rolled by a powder hot-rolling process without cracking, and their microstructure and soft magnetic properties are investigated. The microstructure and magnetic properties (saturation magnetization and core loss) of the hot-rolled Fe-6.5 wt.% Si sheets are examined by scanning electron microscopy, electron backscatter diffraction, vibration sample magnetometry, and AC B-H analysis. The Fe-6.5 wt.% Si sheet rolled at a total reduction ratio of 80% exhibits good soft magnetic properties such as a saturation magnetization of 1.74 T and core loss ($W_{5/1000}$) of 30.7 W/kg. This result is caused by an increase in the electrical resistivity resulting from an increased particle boundary density and the oxide layers between the primary particle boundaries.

• 한국대기환경학회지
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• 제18권6호
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• pp.437-452
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• 2002

The Metropolitan Tracer Experiment (METREX) was performed over the Washington, D.C. area using two inert, non-deposition perfluorocarbon gases for over 1 year period (November 1983∼December 1984). Two perfluorocarbon gas tracers (PDCH, PMCH) were released simultaneously at intervals of every 36 hours for 6 hours, regardless of the meteorological conditions in metropolitan area. Samples were collected continuously for 8 hours at a central downtown and two adjacent suburban locations. Monthly air samples were collected at 93 sites across the whole region (at urban, suburban, and rural locations). The purpose of this study is to simulate INPUFF and ISCST model using METREX data, and to compare calculated and observed concentrations. In the case of INPUFF simulation, two meteorological input data were used. One is result data from wind field model which was calculated by diagnostic wind model (DWM), the other is meteorological data observed at single station. Here, three kinds of model calculation were performed during April and July 1984; they include (1) INPUFF model using DWM data (2) INPUFF model using single meteorological data (3) ISCST model. The monthly average concentration data were used for statistic analysis and to draw their horizontal distribution patterns. Eight-hour-averaged concentration was used to describe movement of puff during the episode period. The results showed that the concentrations calculated by puff model (INPUFF) were better than plume model (ISCST). In the case of puff model (INPUFF), a model run using wind field data produced better results than that derived by single meteorological data.

• Nuclear Engineering and Technology
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• 제33권2호
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• pp.175-183
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• 2001

Various welding processes are now available for end cap closure of nuclear fuel element such as TG(Tungsten Inert Gas) welding, magnetic resistance welding and laser welding. Even though the resistance and TIG welding processes are widely used for manufacturing commercial fuel elements, they can not be recommended for the remote seal welding of a fuel element at a hot cell facility due to the complexity of electrode alignment, difficulity in the replacement of parts in the remote manner and a large heat input for a thin sheath. Therefore, the Nd:YAG laser system using optical fiber transmission was selected for Zircaloy-4 end cap welding inside hot cell. The laser welding apparatus was developed using a pulsed Nd:YAG laser of 500 watt average power with optical fiber transmission. The weldability of laser welding was satisfactory with respect to the microstructures and mechanical properties comparing with TIG and resistance welding. The optimum operation processes of laser welding and the optical fiber transmission system for hot cell operation in a remote manner have been developed The effects of irradiation on the properties of the laser apparatus were also being studied.