• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.6
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• pp.609-615
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• 2012

In LSP (laser shock peening) treatment, the laser source geometries when the laser beam strikes the metal target area are diverse. The laser spot geometry affects the residual stress field beneath the treated surface of the metallic materials, which determines the characteristics of the pressure pulse. In this paper, detailed finite-element (FE) simulations on laser shock peening have been conducted in order to predict the magnitude and of the residual stresses and the depth affected in Inconel alloy 600 steel. The residual stress results are compared for circular, rectangular, and elliptical laser spot geometries. It is found that a circular spot can produce the maximum compressive residual stresses near the surface but generates tensile residual stresses at the center of the laser spot. In the depth direction, an elliptical laser spot produces the maximum compressive residual stresses. Circular and elliptical spots plastically affect the alloy to higher depths than a rectangular spot.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.33-55
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• 2016

PVD(Physical Vapour Deposition)코팅은 70년대 미국의 Multi-arc이란 기업에 의해 질화물계나 탄화물계 피막 증착이 가능한 아크이온플레팅(Arc Ion Plating) 기술이 산업에 소개되어, 주로 내마모나 내구성을 요구하는 금형, 절삭공구, 산업용 부품 분야 등에 적용되면서 꾸준한 성장세를 거듭해 왔다. 최근 들어 PVD기술은 그 수요의 급증과 더불어 보다 진화된 형태의 코팅장치 및 코팅피막들이 산업에 소개 되고 있다. 먼저 절삭가공분야에는 new composition, nano composite, multi-element composition, multi-layer, SML(Self Modification Layer)등의 코팅피막들이 단독 또는 조합된 형태로 개발되어 철계 소재를 대상으로 고경도 소재의 고속가공, 저경도~중경도 소재의 중속~고속 광범위영역에서 동시 절삭을 가능케 하였고, 비철.비금속 소재 절삭용으로 종전의 가스방식의 DLC(a-C:H)코팅을 훨씬 능가하는 ta-C Plus(Ultra super DLC) 코팅이 개발되어 고 Si함량의 Al-Si계 합금, Cu-W계, 고 섬유 CFRP, CFRM 및 반소결 상태의 세라믹 소재들을 황삭에서 정삭까지 단일 공정으로 절삭이 가능한 고성능 공구들이 개발보급되고 있다. 금속 성형분야에는 고장력 강판을 냉간에서 성형 가능한 Lubricative multi-layer coating, 열간 또는 고온에서 성형이 가능한 functional multi layer과 이형성이 더한층 개선된 dimpled(or embossed) functional multi layer 코팅들이 개발되어 산업현장에 빠르게 확산되고 있다. PVD 코팅의 또 다른 주요 적용분야로 의료분야를 들 수 있는데, 이는 코팅의 대다수가 고경도의 생체친화적인 특성을 가진데 착안되었으며, 흔히 현대성 질환이라 일컫는 과민성 체질, 과체중 및 허약체질 환자의 증가와 각종 재해 및 사고의 증가 및 인간 수명 증가에 따른 인공적인 시술의 요구증가에 편승하여 이 분야의 시장 또한 가파르게 성장하고 있다. 또한 대량으로 양산 적용단계에 접어든 자동차 핵심부품들을 비롯해서 각종 산업용, 방산용 기계 부품에도 성능 향상, 내구성 향상, 환경친화성 등 다양한 목적으로 확대 적용되고 있는 사례들을 본 발표를 통해 간략하게나마 소개하고자 한다.

• Korean Journal of Materials Research
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• v.28 no.6
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• pp.324-329
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• 2018

Needle-like NiO protecting layers on NiCrAl alloy foam, used as support for hydrogen production, are introduced through electroplated Ni and subsequent microwave annealing. To improve the stability of the NiCrAl alloy foam, oxygen concentration of microwave annealing to form a needle-like NiO layer with good chemical stability and corrosion resistance is controlled in a range of 20 and 50 %. As the oxygen concentration increases to 50 %, needle-like NiO forms a dense coating layer on the NiCrAl alloy foam; this layer formation can be attributed to accelerated growth of the (200) plane. In addition, the increased oxygen concentration causes increased NiO/Ni ratio of the resultant coating layer on NiCrAl alloy foam due to improved rate of the oxidation reaction. As a result, the introduction of dense needle-like NiO layers formed at 50 % oxygen concentration improves the chemical stability of the NiCrAl alloy foam by protecting the direct electrochemical reaction between the electrolyte and the foam. Thus, needle-like NiO can be proposed as a superb protecting layer to improve the chemical stability of NiCrAl alloy form.

• Journal of Korea Foundry Society
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• v.31 no.2
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• pp.66-70
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• 2011

Hot dip aluminizing (HDA) is widely used in industry for improving corrosion resistance of material. The formation of intermetallic compound layers during the contact between dissimilar materials at high temperature is common phenomenon. Generally, intermetallic compound layers of $Fe_2Al_5$ and $FeAl_3$ are formed at the Al alloy and Fe substrate interface. In case of cast iron, high contact angle of graphite existed in the matrix inhibits the formation of intermetallic compound layer, which carry with it the disadvantage of a reduced reaction area and mechanical properties. In present work, the process for the removal of graphite existed on the surface of specimen has been investigated. And also HDA was proceeded at $800^{\circ}C$ for 3 minutes in aluminum alloy melt. The efficiency of graphite removal was increased with the reduction of particle size in sanding process. Graphite appears to be present both in the region of melting followed by re-solidification and in the intermetallic compound layer, which could be attributed to the fact that the surface of cast iron is melted down by the formation of low melting point phase with the diffusion of Al and Si to the cast iron. Intermetallic compound layer consisted of $Fe(Al,Si)_3$ and $Fe_2Al_5Si$, the layer formed at cast iron side contained lower amount of Si.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.97.1-97.1
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• 2011

저온에서 양이온 고분자막을 사용하는 고분자 연료전지의 경우 뛰어난 성능과 다양한 응용분야로 인해 많은 연구와 실증이 이루어지고 있지만 공기극에서의 느린 산소 환원반응으로 인해 백금과 같은 귀금속의 사용이 불가피하고 백금의 제한된 매장량과 높은 가격으로 인해 상용화가 늦어지고 있다. 그래서 많은 연구자들이 합금 촉매 또는 비귀금속 촉매를 이용한 전극 개발에 집중하고 있다. 알칼리 분위기에서 저가의 전이 금속들이 백금과 비슷한 활성을 보이고 고체 음이온 교환막이 개발됨에 따라 최근 알칼리 연료전지가 다시금 큰 주목을 받고 있다. 그러나 고분자 연료전지와는 달리 아직 촉매나 전해질막, 이오노머의 특성 및 메커니즘에 관해 별로 알려진 것이 없다. 본 연구에서는 직접 개발한 세공충진막 형태의 탄화수소계의 음이온 교환막과 비귀금속 공기극 촉매를 이용하여 막전극접합체(MEA)를 개발하였고 촉매 및 이오노머 함량과 같은 전극 조성, 막전극접합체의 제조 및 체결, 가습이나 가스조성 등의 단위전지 운전조건과 같은 다양한 변수에 대해에 최적 조건을 도출하고자 하였다. 공기극 촉매는 Cu-Fe/C를 이용한 상용 촉매를 이용하였고 이오노머의 경우는 탄화수소계의 상용 제품을 사용하였으며 음이온 교환막에 전극층을 형성하기 위해서는 스프레이 공정을 이용하였다. 단위전지를 통해 성능을 확인하였고 임피던스 및 CV를 통해 전기화학적인 특성을 규명하였다. 조건의 최적화를 통해 상당한 성능 향상을 이루었으나 추가적인 성능 향상 및 내구성 확보 등에 대해 계속적인 실험을 진행할 예정이다.

• Journal of Conservation Science
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• v.35 no.5
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• pp.403-415
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• 2019

According to oral tradition, the King Sejo's palanquin is indeed the palanquin of King Sejo, the 7^th monarch of the Joseon dynasty who reigned from 1455 to 1468, which was left behind after visiting the Magoksa temple. The palanquin is painted in five colors, mainly black, white, yellow, red and green. The chromaticity measurement of the yellow pigment showed that orpiment and gold are a noticeable distinction between the lightness and b^⁎ values. In the case of the red pigment, a^⁎ values of areas painted with cinnabar tend to measure at high values. As a result of the optical microscopy, scanning electron microscopy and energy dispersive spectroscopy analyses, it was determined that Chinese ink was used for the black pigment, lead white and white clay were used for the white, and orpiment and gold for the yellow. The red pigment was found to be the result of minium, cinnabar and red ocher, atacamite was used as green pigment. Though the analysis results of the cross sections on very small exfoliation fragments of pigments, it was confirmed that white clay and lead white were used for the preparation layer. In addition, several coloration techniques were considered based on these analyses.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.5
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• pp.243-248
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• 2017

In this study copper glaze samples were prepared with varying amount of tin oxide, and the chromatic characteristics of glazes were explained on the results of spectrophotometric, crystalline phase, and microstructural analyses. The red color of copper glaze was dissipated with the addition of tin oxide and turned into achromatic color due to the decrease of CIEab values. Tin oxide homogeneously distributed in the glaze layer interfered with the red color generation coming from the growth of Cu nuclei, and formed an alloy with metal copper around bubbles. This resulted in the decrease of metal copper peak intensity with minor $Cu_2O$ peak. With the 3.79 % tin oxide addition the glaze was appeared as gray due to the black color CuO and Cassiterite $SnO_2$ phases.

• The Journal of Korean Academy of Prosthodontics
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• v.28 no.2
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• pp.165-174
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• 1990

The purpose of the study was to correlate margin design(chamfer, shoulder, shoulder with a $45^{\circ}$ bevel. with the seating and sealing of cemented full cast crowns under standardized simulated clinical conditions. Wax patterns were made with milled stainless-steel dies and rings, and were invested, burnt out, and cast. The full cast crowns were comented on individual resin dies, and a gradually diminishing load(45kg to 25kg. was applied over a 10-minute period. The specimens were sectioned centrally with a low speed diamond saw and examined with light microscope. The results were as follows : 1. Chamfer preparations demonstrated it was the best marginal seal, followed in order by the shoulder with a $45^{\circ}$ bevel, and by the shoulder(p<.05). 2. Chamfer preparations demonstrated it was the best occlusal seating, followed in order by the shoulder, and by the shoulder with a $45^{\circ}$ bevel(p<.05).

• Journal of the Korean Electrochemical Society
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• v.10 no.2
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• pp.94-103
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• 2007

The transition of interconnection metal from aluminum alloy to copper has been introduced to meet the requirements of high speed, ultra-large scale integration, and high reliability of the semiconductor device. Since copper, which has low electrical resistivity and high resistance to degradation, has different electrical and material characteristics compared to aluminum alloy, new related materials and processes are needed to successfully fabricate the copper interconnection. In this review, some important factors of multilevel copper damascene process have been surveyed such as diffusion barrier, seed layer, organic additives for bottom-up electro/electroless deposition, chemical mechanical polishing, and capping layer to introduce the related issues and recent research trends on them.

• Journal of Welding and Joining
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• v.13 no.3
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• pp.134-146
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• 1995

Aluminium nitride(AlN) is currently under investigation as potential candidate for replacing alumium oxide(Al$_{2}$ $O_{3}$) as a substrate material for for electronic circuit packaging. Brazing of aluminium nitride(AlN) to Cu with Ag base active alloy containing Ti has been investigated in vacuum. Binary Ag$_{98}$ $Ti_{2}$(AT) and ternary At-1wt.%Al(ATA), AT-1wt.%Ni(ATN), AT-1wt.% Mn(ATM) alloys showed good wettability to AlN and led to the development of strong bond between brate alloy and AlN ceramic. The reaction between AlN and the melted brazing alloys resulted in the formation of continuous TiN layers at the AlN side iterface. This reaction layer was found to increase by increase by increasing brazing time and temperature for all filler metals. The bond strength, measured by 4-point bend test, was increased with bonding temperature and showed maximum value and then decreased with temperature. It might be concluded that optimum thickness of the reaction layer was existed for maximum bond strength. The joint brazed at 900.deg.C for 1800sec using binary AT alloy fractured at the maximum load of 35kgf which is the highest value measured in this work. The failure of this joint was initiated at the interface between AlN and TiN layer and then proceeded alternately through the interior of the reaction layer and AlN ceramic itself.