• Title/Summary/Keyword: boundary resistance

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Effect of Heat Treatment on the Microstructures and Properties of HVOF Sprayed Ni-Cr-W-Mo-B Alloy Coatings (초고속화염용사법으로 제조된 Ni-Cr-W-Mo-B 합금 코팅의 미세조직과 특성에 미치는 열처리 효과)

  • 민경오;이창희
    • Journal of Welding and Joining
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    • v.18 no.6
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    • pp.48-54
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    • 2000
  • The corrosion properties of Ni-Cr-W-Mo-B alloy sprayed by the high velocity oxy-fuel spraying (HVOF) was studied as a function of heat treatment by using both potentiodynamic polarization and immersion tests in the H₂SO₄ solution. The mechanical property was also evaluated by a microhardness tester. Microstructural characteristics of te as-sprayed and annealed coatings at 550, 750 and 950℃ have been analyzed by means of OM, XRD, SEM and TEM. The results showed that the corrosion resistance was improved by increasing the annealing temperature. As-sprayed coating had metastable and heterogeneous phases such as amorphous, nanocrystalline and very refined grain and precipitates, which induced a localized corrosion. The localized corrosion occurred preferentially at the unmelted particles which were composed of Ni matrix and Cr, W and Mo riched phase segregated in the boundaries. As annealing temperature was increased, the microstructure had shown some changes - reduction of porosity and s[plat boundary decomposition and crystallization of amorphous/nanocrystalline phases, grain coarsening,, formation and growth of precipitates such as {TEX}$M_{23}C_{6}${/TEX} and {TEX}$M_{7}C_{3}${/TEX}. In addition, the compositional difference between matrix and boundary phases gradually disappeared, which changed the corrosion type from localized corrosion to general corrosion and thus enhanced corrosion resistance.

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Effects of Trim Conditions on Ship Resistance of KCS in Short Waves (단파장 영역에서 운항 자세가 KCS의 선체 저항에 미치는 영향)

  • Kim, Yeoun Joo;Lee, Sang Bong
    • Journal of the Society of Naval Architects of Korea
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    • v.54 no.3
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    • pp.258-266
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    • 2017
  • Numerical simulations of turbulent two phase flows around KCS have been performed to investigate effects of trim conditions on ship resistance of KCS in short waves by utilizing waves2foam. The wave lengths of LPP/2 and LPP/4 with 1m and 2m wave heights were imposed at inlet boundary. The resistance reduction at 2m trim by head and the increase of resistance at trims by stern were observed regardless of wave lengths and wave heights. The hull pressure on fore-and-aft rather than wave patterns around bulbous bows was mainly responsible for the total resistance coefficients of KCS in short waves. A phase diagram of contribution of hull pressure to the total resistance coefficients disclosed that the phase of representing the maximum resistance in time history played an important role in the effect of trim conditions on ship resistance of KCS in short waves.

Impedance Analysis of Resistance Anomaly of $BaTiO_3$ based PTC thermistor

  • Chun, Myoung-Pyo;Myoung, Seong-Jae;Nam, Joong-Hee;Cho, Jeong-Ho
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2009.06a
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    • pp.182-182
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    • 2009
  • The effect of Re-oxidation on the PTCR properties of Sm-doped barium titanate ceramics was investigated by means of impedance spectroscopy. Electrical properties such as resistance vs. temperature, I-V curve were measured and microstructure was observed with SEM photography. Sample was fabricated with thick film process such as tape casting of green sheet, screen printing of electrode pattern, stacking, firing in reduced atmosphere and re-oxidation, etc. As the temperature of re-oxidation increases, resistance jump as a function of temperature enhances but resistance at room temperature increases. These behavior of resistance as a function of temperature, dependent on the re-oxidation condition, is analyzed with Cole-Cole impedance plot and is shown to be related with the degree of oxidation of grain boundary regardless of grain core during re-oxidation process of sample.

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Hydrodynamic Hull Form Design Using an Optimization Technique

  • Park, Dong-Woo;Choi, Hee-Jong
    • International Journal of Ocean System Engineering
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    • v.3 no.1
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    • pp.1-9
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    • 2013
  • A design procedure for a ship with minimum resistance had been developed using a numerical optimization method called SQP (Sequential Quadratic Programming) combined with computational fluid dynamics (CFD) technique. The frictional resistance coefficient was estimated by the ITTC 1957 model-ship correlation line formula and the wave-making resistance coefficient was evaluated by the potential-flow panel method with the nonlinear free surface boundary conditions. The geometry of the hull surface was represented and modified by B-spline surface modeling technique during the optimization process. The Series 60 ($C_B$=0.60) hull was selected as a parent hull to obtain an optimized hull that produces minimum resistance. The models of the parent and optimized hull forms were tested at calm water condition in order to demonstrate the validity of the proposed methodolgy.

Alternative Cone Tip Resistance Analysis Method using Rescaled Range Analysis

  • Yu, Chan;Yoon, Chun-Gyeong
    • Journal of The Korean Society of Agricultural Engineers
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    • v.47 no.7
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    • pp.37-45
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    • 2005
  • In this study, R/S analysis which was proposed by Mandelbrot & Wallis (1969) was applied to evaluate the presence of the fractal property in the cone tip resistance of in-situ CPT data. Hurst exponents (H) were evaluated in the range of 0.660$\sim$0.990 and the average was 0.875. It was confirmed that a cone tip resistance data had the characteristic of fractals and it was expected that cone tip resistance data sets are well approximated by a fBm process with an Hurst exponent near 0.875. It was also observed that the boundary between layers were obviously identified as a result of R/S analysis and it will be usage in practices.

Pullout resistance of concrete anchor block embedded in cohesionless soil

  • Khan, Abdul J.;Mostofa, Golam;Jadid, Rowshon
    • Geomechanics and Engineering
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    • v.12 no.4
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    • pp.675-688
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    • 2017
  • The anchor block is a specially designed concrete member intended to withstand pullout or thrust forces from backfill material of an internally stabilized anchored earth retaining wall by passive resistance of soil in front of the block. This study presents small-scale laboratory experimental works to investigate the pullout capacity of a concrete anchor block embedded in air dry sand and located at different distances from yielding boundary wall. The experimental setup consists of a large tank made of fiberglass sheets and steel framing system. A series of tests was carried out in the tank to investigate the load-displacement behavior of anchor block. Experimental results are then compared with the theoretical approaches suggested by different researchers and codes. The appropriate placement of an anchor block and the passive resistance coefficient, which is multiplied by the passive resistance in front of the anchor block to obtain the pullout capacity of the anchor, were also studied.

Laser Surface Alloying of Alloy 600 to Improve Its Corrosion Resistance (Allow 600 합금의 내부식성 향상을 위한 레이저 표면 합금화)

  • 신진국;강석중;서정훈;국일현;김정수
    • Laser Solutions
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    • v.2 no.1
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    • pp.16-21
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    • 1999
  • The surface of Alloy 600 was alloyed using a continuous wave $CO_2$ laser beam in order to improve its corrosion resistance. Laser surface alloying (LSA) was done by melting the surface electroplated with Cr of the alloy. The Cr concentration of the alloyed surface was 28-30 at.%, which is similar to that of Alloy 690. Alloying elements in the alloyed layer was observed to be distributed very homogeneously all over the alloyed region. According to the electrochemical and modified Huey tests, the corrosion resistance, in particular the grain boundary corrosion resistance, of the LSA specimens was significantly improved, compared with that of the as-received(AR) specimen. This improved corrosion resistance of the alloyed specimen might be attributed to the high Cr content which could make possible formation of more stable and dense passive film onto its surface.

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Physical correlation between annealing process and crystal structure and magneto-resistance of Bismuth thin films (열처리 공정과 비스무스 박막의 결정구조 및 자기저항 특성변화와의 물리적 관계)

  • Jang, Seok Woo;Seo, Young-Ho;An, Ho-Myoung
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.18 no.3
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    • pp.638-642
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    • 2014
  • In this study, we investigate on the crystal microstructure and magneto-resistance (MR) change of Bismuth(Bi) thin films for annealing process, in order to apply Bi thin films to the spin electronic devices. As-prepared Bi thin films show the randomly oriented find grains whose size was measured to about 100 nm and the very low MR (4.7 % at room temperature) while careful annealing results in not only grain growth up to ${\sim}2{\mu}m$ but also drastic MR improvement (404 % at room temperature). The drastic change in the MR after applying the annealing process is attributed to the grain growth decreasing grain boundary scattering of electron. Therefore, in this study, we confirm the annealing effect for the grain boundary formation and MR improvement of Bi thin films, and demonstrate the feasibility of spin electronic devices.

Grain Boundary Chemistry and Electrical Characteristics of Semiconducting $SrTiO_3$ Ceramics Synthesized from Surface-Coated Powders (표면 코팅된 분말을 이용하여 제조된 반도성 $SrTiO_3$ 소결체의 입계화학과 전기적 특성)

  • Park, Myung-Beom;Kim, Chong-Don;Heo, Hyun;Cho, Nam-Hee
    • Journal of the Korean Ceramic Society
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    • v.36 no.11
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    • pp.1252-1260
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    • 1999
  • The defect chemistry and electrical characteristics of the grain boundaries of semiconducting SrTiO3 ceramics synthesized with wet-chemically surface-coated powders were investigated. The starting powders were separated into groups of 1-10${\mu}{\textrm}{m}$ 10-20${\mu}{\textrm}{m}$ etc by sedimentation and sieving methods. Na+ ions were absorbed on the powder surfaces by wet chemical-treatment method. The width of the grain boundary ranged up to several nm and the intergranular materials was amorphous. The additives coated on the surface of the powders were observed to be present at the grain boundaries of the ceramics. The diffusion depth of the additives into grains was about 30nm for the SrTiO3 ceramics synthesized with 5w/o coated materials, The threshold voltage grain boundary resistance and boundary potential barrier of the ceramics increased from 0.67V/cm 2.27k$\Omega$ and 0.05eV to 80.9V/cm 13.0k$\Omega$ 1.44eV with increasing the amount of the additives from 0 to 5 w/o respectively .

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