• 비파괴검사학회지
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• 제34권3호
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• pp.233-240
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• 2014

나노/마이크로 소자의 개발이 활발해짐에 따라 나노/마이크로 박막의 기계적 물성의 정밀 측정에 대한 필요성이 점차 커지고 있다. 기존의 파괴적인 방법의 한계를 극복하기 위한 방법으로, 유도초음파를 이용한 비파괴적인 박막 물성 방법에 대한 관심이 늘어나고 있다. 유도초음파를 이용하여 박막의 물성을 측정하는 실험을 설계하거나, 물성 측정에 대한 실험 결과를 이해하는데 있어 박막의 분산선도를 이해하는 것은 필수적이라 할 수 있다. 본 연구에서는, 전달 행렬법을 이용하여 박막의 분산선도를 계산하는 방법을 제시하고, 이를 금속 박막에 적용하여 그 특성을 관찰하였다. 전달 행렬법을 이용하여 다층판에서의 주파수에 따라 유도초음파가 전파하는 속도를 계산하여 상용 프로그램과 비교하여 그 타당성을 확인하였다. 이러한 방법을 Si 기판 위에 증착된 Al 금속 박막에 적용하여 얻은 분산곡선의 분석을 통해, 박막의 두께 조건에 따른 모드와 분산 및 비분산 특성이 나타나는 구간을 관찰할 수 있었다.

• 한국지반공학회논문집
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• 제18권6호
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• pp.129-139
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• 2002

최근 지반 특성과 지반 오염도의 조사를 위해 유전상수 측정기법을 적용하기 위한 연구가 활발히 진행되고 있다. 본 연구에서는 다양한 함수비와 건조단위중량을 갖는 화강풍화토와 주문진표준사의 유전상수를 75kHz～12MHz의 주파수 범위에서 측정하였다. 사질토의 유전상수는 주파수가 증가함에 따라 감소하는 분산거동을 보였다. 또한 함수 비나 건조단위중량이 증가함에 따라 배향분극에 기여하는 물분자의 양이 증가하고 유전상수가 1인 공기의 양이 감소하여 유전상수가 증가하였다. 흙의 유전특성은 함수비와 건조단위중량을 모두 고려한 수분밀도에 선형적으로 비례하는 경향을 나타내었다. Maxwell식, Topp식, CRIM식에 의한 계산값과 측정된 값을 비교한 결과 기존의 식은 유전상수의 분산거동을 고려하지 못하고 있기 때문에 저주파에서는 측정값과 차이를 나타내었다.

• Tribology and Lubricants
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• 제29권5호
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• pp.298-303
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• 2013

In this work, the effect of applied load on the wear behavior of Al/SiC composites was studied. Al/SiC composites were fabricated following the thermal spray process. Dry sliding wear tests were performed on these composites under four different applied loads, i.e., 5, 10, 15, and 20 N. The wear behaviors of the composites under these applied loads were investigated using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Under applied loads of up to 15 N, the wear rates of Al/SiC composites decreased with an increase in the applied load because of the formation of an adhesion layer on the worn surface. However in the case of an applied load of 20 N, the wear rate was significantly high because the formation and fracture of the adhesion layer were repeated continuously. These results show that the wear behaviors of the tested composites are significantly influenced owing to the applied loads.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1999년도 제29회 춘계학술대회
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• pp.220-224
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• 1999

Sliding wear test was employed to determine the effect of whisker content and orientation on the firiction and wear behavior of SiC whisker reinforced alumina. Composites containing unidirectionally oriented whiskers were prepared by a modified tape casting followed by lamination, binder removal and hot pressing in order to align the whiskers in the tape casting direction. Wear coefficients on three directions were measured; parallel and normal to the tape casting direction on the tape casting surface and normal to lamination direction on surfnce normal to the tape casting direction. In the effect of whisker orientation, the highest wear rate was obtained in the direction parallel tape casting direction and the lowest in the direction normal to lamination direction at all temperatures. Silicon oxide layer amoothing the surface was detected by energy dispersive X-ray analysis on the worn surface.

• 대한의용생체공학회:의공학회지
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• 제15권4호
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• pp.389-394
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• 1994

The age-hardening behavior and the structural changes in a commercial dental Au-Ag-Cu-Pd alloy were investigated by means of hardness test, optical and scanning electron microscopic observation, energy dispersive spectroscopy and X-ray diffraction study. The drastic reduction in hardness by prolonged aging occurred after a rapid increase in hardness at the initial stage by the isothermal aging at $350^{\circ}C$. This softening was due to the broad precipitates formation of the lamellar structure which was composed of the f.c.t. AuCu I ordered f.c.t. phase containing Pd and the f.c.c. Ag-rich $\alpha$1 solid solution f.c.c.phase containing Au.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2015년도 추계학술대회 논문집
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• pp.268-268
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• 2015

The corrosion protection behavior of AZ31 magnesium alloy (Mg alloy) with cathodic electrophoretic coating (E-coating) pretreated by cerium-based conversion coatings at various pH was investigated in this study. Cerium-based conversion coatings (CeCCs) were deposited on AZ31 Mg alloy by immersion treatment in the nitrate-based cerium salt solution. The morphology and composition of the CeCCs were analyzed using scanning electron microscopy and energy dispersive X-ray spectroscopy. The corrosion properties of the AZ31 Mg alloy pretreated with cerium coating and subsequently E-coated were studied during salt-spray testing. The surface morphologies of the E-coated Mg alloy were examined in detail after different testing times using digital photography. It was found that the protective properties of the E-coating on AZ31 Mg alloy generated are heavily dependent upon the CeCC factors such as treatment time, coating thickness and pH of the solution.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2015년도 춘계학술대회 논문집
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• pp.107-107
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• 2015

In order to investigate electrochemical behavior and biocompatibility of Co-Cr dental alloy by electrochemical corrosion test and MTT assay, the xCo-25Cr-yW-zNi alloys were used in this study. Samples of Co-Cr-W-Ni alloys were manufactured using arc melting furnace. The microstructure of the alloys was examined by optical microscopy (OM), Field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), MTT assay, and corrosion test. Corrosion resistance increased slightly as cobalt (Co) content increased. And bioactivity was concerned with nickel (Ni) and tungsten (W). Biocompatibility of Co-Cr alloy depended on Ni and W contents.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2002년도 학술발표회 논문집(II)
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• pp.1027-1033
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• 2002

The solute transport in a two-dimensional heterogeneous porous medium is numerically studied by using a random walk particle tracking (RWPT) method. Lognormally isotropic hydraulic conductivity fields are generated by using the turning band methods with mean zero and four different values of standard deviation. The numerical transport experiments are carried out to investigate the large time and spatial effects of the variable pore velocity field on solute plumes. The behavior of the solute plume through numerical simulations is presented in terms of longitudinal and transverse spatial moments: displacement of center-of-mass, plume spread variance and skewness coefficient. It was observed that the dispersive behavior of the solute plume is strongly affected by the degree of heterogeneity in the flow domain.

• Tribology and Lubricants
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• 제39권6호
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• pp.228-234
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• 2023

In this study, reciprocating wear tests are performed on AISI 52100 bearing steel to investigate its tribological behavior in a hexagonal boron nitride (h-BN) water solution. The h-BN-based aqueous lubricant is prepared using an atoxic procedure called ultrasonic sonication in pure water. Ball-on-flat reciprocating sliding experiments are conducted, where the ball is slewed on a fixed flat at 50-㎛ displacement. The lubricating behavior of h-BN is compared with that of deionized (DI) water. Results show that the friction coefficient is higher in h-BN testing than that in DI tests, but the results are equalized as the friction coefficient reaches a stable level. Scanning electron microscopic images reveal significant material loss in the center and mild abrasion on the edge of the wear scar in h-BN tests. However, these effects are minor in DI water situations. The results of energy-dispersive X-ray spectroscopy show that considerable oxidation occurs in the central zone of the wear scar in h-BN cases with strong adhesion and material removal. These findings reveal the importance of determining ideal circumstances that can tolerate material friction and wear.

• Corrosion Science and Technology
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• 제20권6호
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• pp.367-372
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• 2021

The effect of carbon addition on the general corrosion behavior of high-chromium cast iron (HCCI) was studied by a scanning electron microscope with energy dispersive spectroscopy (SEM-EDS) or electron back-scattered diffraction (EBSD), or electrochemical polarization techniques in 0.1 mol dm^-3 H₂SO₄ + 0.05 mol dm^-3 HCl at room temperature. The addition of 2.1-2.8 wt% carbon to HCCI increased the fraction of eutectic austenite and eutectic carbide phases, while that of HCCI decreased the fraction of the primary austenitic phase. Potentiostatic polarization of the HCCI at -0.35 V_SSCE or 0.0 V_SSCE resulted in preferential general corrosion of the primary austenitic or eutectic austenitic phases, respectively. The decrease in corrosion current density and the shift in noble corrosion potential direction with increasing carbon content in the HCCI indicated that the fraction and the chemical composition of austenitic (primary and eutectic) and carbide phases were strongly related to the general corrosion behavior of the HCCI.