• 한국마이크로전자및패키징학회:학술대회논문집
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• 한국마이크로전자및패키징학회 2000년도 추계 기술심포지움 논문집
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• pp.57-57
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• 2000

본 논문에서는 MCM 및 패키지의 Lid로 사용되는 합금인 Kovar (Fe-Ni-Co alloy) 와 LTCC (Low Temperature Co-fired Ceramics) 간의 Brazing 특성을 연구하였다. 기존에 사용되고 있는 알루미나 패키지의 경우, 주로 80$0^{\circ}C$ 이상의 온도에서 Brazing을 실시하고 있으며, 조성은 Ag-Cu 계열을 사용하고 있다. 하지만, LTCC 의 경우, 소결온도가 85$0^{\circ}C$ 내외로서 기존의 방법을 그대로 적용하기는 어려움이 있다. 또한 Brazing 특성에 따른 접착 강도는 Brazing Alloy 의 영향뿐만 아니라 LTCC 와 전도체 전극사이의 Metallization 에 크게 영향을 받는다. 따라서, 본 논문에서는 Brazing Alloy의 종류 (Ag-Cu, Au-Sn) 및 Brazing 조건에 따른 Brazing 특성뿐만 아니라, 전도체 전극내 유리질 함량에 따른 Brazing 특성을 평가하여 LTCC/Kovar 간의 최적의 Brazing 조건을 구현하고자 하였다.

• 대한금속재료학회지
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• 제48권6호
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• pp.523-532
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• 2010

Co-application of organic coating and cathodic protection has not provided enough durability to low-alloyed steels inseawater ballast tank (SBT) environments. An attempt has made to study the effect of alloy elements (Al, Cr, Cu, Mo, Ni, Si, W) on general and localized corrosion resistance of steels as basic research to develop new low-allowed steels resistive to corrosion in SBT environments. For this study, we measured the corrosion rate by the weigh loss method after periodic immersion in synthetic seawater at $60^{\circ}C$, evaluated the localized corrosion resistance by an immersion test in concentrated chloride solution with the critical pH depending on the alloy element (Fe, Cr, Al, Ni), determined the permeability of chloride ion across the rust layer by measuring the membrane potential, and finally, we analyzed the rust layer by EPMA mapping and compared the result with the E-pH diagram calculated in the study. The immersion test of up to 55 days in the synthetic seawater showed that chromium, aluminium, and nickel are beneficial but the other elements are detrimental to corrosion resistance. Among the beneficial elements, chromium and aluminium effectively decreased the corrosion rate of the steels during the initial immersion, while nickel effectively decreased the corrosion rate in a longer than 30-day immersion. The low corrosion rate of Cr- or Al-alloyed steel in the initial period was due to the formation of $Cr_2FeO_4$ or $Al_2FeO_4$, respectively -the predicted oxide in the E-pH diagram- which is known as a more protective oxide than $Fe_3O_4$. The increased corrosion rate of Cr-alloyed steels with alonger than 30-day exposure was due to low localized corrosion resistance, which is explained bythe effect of the alloying element on a critical pH. In the meantime, the low corrosion rate of Ni-alloyed steel with a longer than 30-day exposure wasdue to an Ni enriched layer containing $Fe_2NiO_4$, the predicted oxide in the E-pH diagram. Finally, the measurement of the membrane potential depending on the alloying element showed that a lower permeability of chloride ion does not always result in higher corrosion resistance in seawater.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 D
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• pp.1504-1507
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• 1999

We have grown vertically aligned carbon nanotubes in a large area of Co-Ni codeposited Si substrates by the thermal CVD using $C_2H_2$ gas. Since the discovery of carbon nanotubes, Synthesis of carbon nanotubes for mass production has been achieved by several methods such as laser vaporization arc discharge, and pyrolysis. In particular, growth of vertically aligned nanotubes is of technological importance for applications to FED. Recently, vertically aligned carbon nanotubes have been grown on glass by PECVD Aligned carbon nanotubes can be also grown on mesoporous silica and Fe patterned porous silicon using CVD. Despite such breakthroughs in the growth, the growth mechanism of the alignment are still far from being clearly understood. Furthermore, FED has not been clearly demonstrated yet at a practical level. Here, we demonstrate that carbon nanotubes can be vertically aligned on catalyzed Si substrate when the domain density reaches a certain value. We suggest that steric hindrance between nanotubes at an initial stage of the growth forces nanotubes to align vertically and then nanotubes are further grown by the cap growth mechanism.

• 한국분말재료학회지
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• 제29권3호
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• pp.213-218
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• 2022

This study investigates the interfacial reaction between powder-metallurgy high-entropy alloys (HEAs) and cast aluminum. HEA pellets are produced by the spark plasma sintering of Al_0.5CoCrCu_0.5FeNi HEA powder. These sintered pellets are then placed in molten Al, and the phases formed at the interface between the HEA pellets and cast Al are analyzed. First, Kirkendall voids are observed due to the difference in the diffusion rates between the liquid Al and solid HEA phases. In addition, although Co, Fe, and Ni atoms, which have low mixing enthalpies with Al, diffuse toward Al, Cu atoms, which have a high mixing enthalpy with Al, tend to form Al-Cu intermetallic compounds. These results provide guidelines for designing Al matrix composites containing high-entropy phases.

• 소성∙가공
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• 제31권5호
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• pp.273-280
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• 2022

Although the mechanical properties of high-entropy alloys depend on the annealing conditions, limited works were established to investigate the annealing effect on the mechanical properties of Mo-added high-entropy alloys. Therefore, in the present work, the annealing effects on the microstructural evolution and mechanical properties of Mo-added high-entropy alloy were investigated. As a result, incomplete recrystallization from the limited annealing time not only suppresses deformation-induced phase transformation during cryogenic tensile test but also induces a deformation instability that results into the ductility reduction compare with the fully recrystallized sample. This result represents adjustment of annealing time is useful to control both transformation-induce plasticity and deformation instability of high-entropy alloys, and this can be applied to control the mechanical properties of metallic alloys by combining pre-straining and subsequent annealing.

• 대한금속재료학회지
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• 제46권9호
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• pp.577-584
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• 2008

The electrolytic reduction of spent oxide fuel involves the liberation of oxygen in a molten LiCl electrolyte, which results in a chemically aggressive environment that is too corrosive for typical structural materials. So, it is essential to choose the optimum material for the process equipment handling molten salt. In this study, corrosion behavior of Inconel 713LC, Inconel MA 754, Nimonic 80A and Nimonic 90 in the molten salt $LiCl-Li_2O$ under an oxidizing atmosphere was investigated at $650^{\circ}C$ for 72~216 hrs. Inconel 713LC alloy showed the highest corrosion resistance among the examined alloys. Corrosion products of Inconel 713LC were $Cr_2O_3$, $NiCr_2O_4$ and NiO, and those of Inconel MA 754 were $Cr_2O_3$ and $Li_2Ni_8O_{10}$ while $Cr_2O_3$, $LiFeO_2$, $(Cr,Ti)_2O_3$ and $Li_2Ni_8O_{10}$ were produced from Nimonic 80A. Also, corrosion products of Nimonic 90 were found to be $Cr_2O_3$, $(Cr,Ti)_2O_3$, $LiAlO_2$ and $CoCr_2O_4$. Inconel 713LC showed local corrosion behavior and Inconel MA 754, Nimonic 80A, Nimonic 90 showed uniform corrosion behavior.

• 한국재료학회지
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• 제7권3호
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• pp.218-223
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• 1997

과냉각액체구역(${\Delta}T_{x}=T_{x}-T_{g}$)을 갖는 $Fe_{80}P_{10}C_{6}B_{4}$ 조성에 천이금속(Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Co, Ni, Pd, Pt및 Cu)를 첨가하여 이들 원소가 유리화온도($T_{g}$), 결정화온도($T_{x}$) 및 과냉액체구역 (${\Delta}T_{x}$)에 미치는 영향에 \ulcorner여 조사하였다. $Fe_{80}P_{10}C_{6}B_{4}$ 합금의 ${\Delta}T_{x}$ 값은 27K였으나 이 합금에 Hf, Ta 및 Mo을 각각 4at%첨가하면 그 값이 40k 이상으로 증가하였다. 이같은 ${\Delta}T_{x}$ 값의 증가는 유리화온도($T_{g}$의 상승보다 결정화온도($T_{x}$)의 상승폭이 크기 때문이다. $T_{g}$ 및 $T_{x}$는 외각전자밀도(e/a)가 약 7.38에서 7.05로 감소할수록 상승하였다. e/a의 감소는 천이금속과 다른 구성원소(반금속)사이의 상호결합상태를 의미한다. 즉 $T_{g}$ 및 $T_{x}$의 상승은 강한 상호결합력에 기인하는 것으로 사료된다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 추계학술대회 논문집 학회본부 C
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• pp.891-893
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• 1999

Invar alloys have characteristics with very low thermal expansion coefficient and low tensile strength. The mechanical properties of invar alloy have to being improved to apply for structural materials, especially for core of transmission line in electrical field. It is necessary low thermal expansion and high strength core material to transmit increased current capacity. In this paper, we investigated effect of Mo addition affected to thermal and mechanical properties and microstructure in Fe-Ni-Co ternary system.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 C
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• pp.1599-1601
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• 2000

To study invar alloy as a core material for large ampacity over-head transmission line which have high strength and low thermal expansion coefficient simultaneously, thermal expansion coefficient, physical properties and hardness of Fe-Ni-Co-xC alloy have been studied. It is necessary that invar alloy possess low thermal expansion coefficient and high strength for increased capacity over-head transmission line. In this paper we tried to find out the effect of carbon addition related with mechanical and physical properties. It was found that the thermal expansion coefficient and hardness were increased with carbon addition for whole composition range but the saturation magnetization was decreased except for the range of 0.1$\sim$0.4%C.

• 한국표면공학회지
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• 제39권4호
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• pp.173-178
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• 2006

Incoloy alloy 909 is an Fe-Ni-Co based superalloy that is attractive for gas turbine engine applications. The absence of chromium, however, makes the alloy more susceptible to oxidation in high temperature. To improve the oxidation resistance aluminizing was performed by high activity low temperature pack cementation process. Aluminizing condition was examined with different times and temperatures. Optimum aluminizing conditions were at the temperature of $552^{\circ}C$ for 20 hrs. In the optimized condition, the thickness of the aluminized layer was about $20{\mu}m$. Also, the aluminized layer made the alloy to increase the resistance to the corrosion.