• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.147-147
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• 2015

The multilayer structure of the organic light emitting diode has merits of improving interfacial characteristics and helping carriers inject into emission layer and transport easier. There are many reports to control hole injection from anode electrode by using transition metal oxide as an anode buffer layer, such as V2O5, MoO3, NiO, and Fe3O4. In this study, we apply thin films of LiF which is usually inserted as a thin buffer layer between electron transport layer(ETL) and cathode, as an anode buffer layer to reduce the hole injection barrier height from ITO. The thickness of LiF as an anode buffer layer is tested from 0 nm to 1.0 nm. As shown in the figure 1 and 2, the luminous efficiency versus current density is improved by LiF anode buffer layer, and the threshold voltage is reduced when LiF buffer layer is increased up to 0.6 nm then the device does not work when LiF thickness is close to 1.0 nm As a result, we can confirm that the thin layer of LiF, about 0.6 nm, as an anode buffer reduces the hole injection barrier height from ITO, and this results the improved luminous efficiency. This study shows that LiF can be used as an anode buffer layer for improved hole injection as well as cathode buffer layer.

• Journal of the Korean Society for Precision Engineering
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• v.32 no.8
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• pp.681-685
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• 2015

Hastelloy C-276 composed of Cr, Mo, and Ni is a versatile, corrosion-resistant alloy with numerous industrial applications including its use in nuclear reactors, general chemical plants, and as a superconducting base material. Of especial significance, it can be used as a thin-sheet type whereby lap-joint welding is occasionally necessary. The main welding problems for thin-sheet metals are deformation and burn-through from an excessive heat input. Laser welding can minimize these problems because it has a high energy density and low heat effect on the base material. In this study, the laser-welding characteristics of lap-joint Hastelloy C-276 sheet metal were determined. The criteria of the laser-welding variables were chosen using a heat-conduction analysis, and the optimal welding parameters were selected by experimenting with an Nd:YAG laser.

• Journal of Welding and Joining
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• v.16 no.6
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• pp.59-68
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• 1998

In this study, effects of solidification modes (primary $\delta$-ferrite, primary ${\gamma}$-austenite) on the pit initiation and propagation in the 304L and 316L austenitic stainless steel weld metals were investigated. The solidification mode of weld metal was controlled by the addition of nitrogen to Ar shielding gas. Through the electrochemical experiments (potentiodynamic anodic polarization and potentiostatic time-current transient test) and metallographic examination (microstructure and elemental distribution), the following results were obtained. The more the volume content of nitrogen in the shielding gas were, the lower critical current density for passivity was observed. In comparison with weldments solidified through the primary $\delta$-ferrite solidification mode and the primary ${\gamma}$-solidification mode, the former showed higher critical pitting potential and a longer incubation time for stable pit initiation than the latter. However, in the pit propagation stage the former exhibited a faster dissolution rate than the latter. These results were believed to ee related to the distribution of alloying elements such as Cr, Mo, Ni and S.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.9
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• pp.547-550
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• 2014

In this study, the electrical characteristics of the nickel (Ni)/carbon nanotube (CNT)/$SiO_2$ structures were investigated in order to analyze the mechanism of CNT in MOS device structures. We fabricated 4H-SiC MOS capacitors with or without CNTs. CNT was dispersed by isopropyl alcohol. The capacitance-voltage (C-V) and current-voltage (I-V) are characterized. Both devices were measured by Keithley 4200 SCS. The experimental flatband voltage ($V_{FB}$) shift was positive. Near-interface trap charge density ($N_{it}$) and negative oxide trap charge density ($N_{ox}$) value of CNT embedded MOS capacitors was less than that values of reference samples. Also, the leakage current of CNT embedded MOS capacitors is higher than reference samples. It has been found that its oxide quality is related to charge carriers and/or defect states in the interface of MOS capacitors.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.496-496
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• 2013

스마트윈도우는 디스플레이, 산업용 외장재 등 다양한 분야에 응용이 가능하며, 특히 전기변색을 이용한 디바이스는 나노코팅 기술을 통한 나노입자 및 나노가공제어 등 나노융합기술을 접목할 수 있다. 전기변색 디바이스는유리 또는 필름 기판소재를 통해 제작이 가능하며, 본 연구에서는 전기변색의 산화, 환원반응에 의해 재료의 광특성이 가역적으로 변화할 수 있는 물질을 증착하여 기존 라미네이터 및 Sol-Gel방식의 전해질보다 열화현상에의한 성능저하를 막아주는 박막전해질 코팅 연구이다. 전기변색 소자는 외부 인가 전압(external voltage)에 의해 유도된 전하의 주입(injection) 과 추출(extraction)을 통하여 그 광학적 특성(optical property)을 가역적으로(reversibly) 변 화시킬 수 있는 특징을 가지고 있다. 전기변색소재의 원리를 간략하게 설명하면 대표적인 환원착색 물질인 전기변색층(WO, MoO, Nb2O5 등)으로 Li+ 또는 H+과 전자가 주입되면 전기변색되고 방출 시는 투명하게 되며, 반대로산화착색 물질인(V2O5, NiO, IrO, MnO 등)으로 Li+ 또는 H+과 전자가 방출되면 변색되고 주입되면 투명하게 되는 것이다. 본 연구에서는 전자가 주입되는 환원착색물질인 WO와 함께 Ta2O5박막을 증착하여 광학적특성을 연구하고 박막의 두께 및 전압인가에따른 변색 및 응답속도를 연구하고자 한다.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.14 no.1
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• pp.15-23
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• 2018

A compact heat exchanger is one of critical components in a very high temperature gas-cooled reactor (VHTR). Alloy 617 (Ni-Cr-Co-Mo) is considered as one of leading candidates for this application due to its excellent thermal stability and strengths in anticipated operating conditions. On the basis of current ASME code requirements, sixty sheets of this alloy are prepared for diffusion welding, which is the key technology to have a reliable compact heat exchanger. Optical microscopic analysis show that there are no cracks, incomplete bond, and porosity at/near the interface of diffusion weldment, but Cr-rich carbides and Al-rich oxides are identified through high resolution electron microscopic analysis. In high-temperature tensile testing, superior yield strengths of the diffusion weldment compared to the code requirement are obtained up to 1223 K ($950^{\circ}C$). However, both tensile strength and ductility drop rapidly at higher temperature due to the insufficient grain boundary migration across the interface of diffusion weldment. Best fit curves for minimum yield strength and average tensile strength are drawn from the experimental tensile results of this study.

• Journal of the Korean Society for Heat Treatment
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• v.12 no.4
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• pp.327-337
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• 1999

A series of Ni-Cr-Mo alloy steels were austenitized, quenched to martensite, and tempered at various temperature and time conditions. Tensile testing was conducted at room temperature with cylindrical specimens, and hardness was measured using Rockwell hardness tester. In the tempering stage I, high strain hardening and yield strength accounted for the high ultimate strength and hardness. In the tempering stage II, strengths and hardness linearly decreased with increasing tempering temperature. Specimens tempered in the temperin stage III showed incipient discontinuous yielding and tensile strengths only slightly higher than yield strengths. Ductilities decreased slightly in specimens tempered in the tempered martensite embrittlement range, and severely decreased in specimens tempered for 10 hours at $500^{\circ}C$ in the temper embrittlement range. Specimens tempered at $600^{\circ}C$ for 10 hours showed recrystallized microstructures, a number of fine dimples, and increased strain hardening, probably due to the precipitation of alloy carbides. The simple formulae for the mechanical properties of these steels were suggested as a function of carbon content and Hollomon-Jaffe tempering parameter.

• Journal of the Korean Society for Heat Treatment
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• v.19 no.1
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• pp.3-9
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• 2006

The phase changes, nitride precipitation and hardness variations of 14%Cr-6.7Ni-0.65Mo-0.26Nb-0.05V-0.03C super martensitic stainless steel were investigated after nitrogen permeation heat treatment at a temperature range between $1050^{\circ}C$ and $1150^{\circ}C$. The nitrogen-permeated surface layer was transformed into austenite. The rectangular type NbN, NbCrN precipitates and fine round type precipitate were coexisted in the surface austenite layer, while the interior region that was free from nitrogen permeation kept the martensitic phase. The hardness of surface austenite showed 280 Hv, while the interior region of martensite phase represented 340 Hv. When tempering the nitrogen-permeated steel at $450^{\circ}C$, a maximum hardness of 433 Hv was appeared, probably this is attributed to the secondary hardening effect of the precipitates. The nitrogen concentration decreased gradually with increasing depth below the surface after showing a maximum of 0.3% at the outmost surface. The strong affinity between nitrogen and Cr enabled the substitutional element Cr to move from interiors to the surface when nitrogen diffuse form surface to the interior. Corrosion resistance of nitrogen permeated steel was superior to that of solution-anneaed steel in the solution of 1N $H_2SO_4$.

• Journal of Powder Materials
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• v.27 no.1
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• pp.31-36
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• 2020

Phosphorus is an element that plays many important roles in powder metallurgy as an alloy element. The purpose of this study is to investigate the influence of phosphorus addition on the microstructures and mechanical properties of sintered low-alloy steel. The sintered low-alloy steels Fe-0.6%C-3.89%Ni-1.95%Cu-1.40%Mo-xP (x=0, 0.05, 0.10, 0.15, 0.20%) were manufactured by compacting at 700 MPa, sintering in H₂-N₂ at 1260 ℃, rapid cooling, and low-temperature tempering in Ar at 160 ℃. The microstructure, pore, density, hardness, and transverse rupture strength (TRS) of the sintered low-alloy steels were evaluated. The hardness increased as the phosphorus content increased, whereas the density and TRS showed maximum values when the content of P was 0.05%. Based on microstructure observation, the phase of the microstructure changed from bainite to martensite as the content of phosphorus is increased. Hence, the most appropriate addition of phosphorus in this study was 0.05%.

• Journal of Welding and Joining
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• v.10 no.1
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• pp.12-19
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• 1992

용접능률의 향상을 위한 대입열용접법의 적용은 과도한 입열량으로 인하여 용접부의 인성이 저 하한다는 점에서 그 적용에 주의를 요한다. 본 보에서는 대입열용접시 열영향부의 인성 저하의 원인과 그 대책을 강재의 측면에서 검토하였다. 고장력강을 용접하면 입열량이 증가함에 따라 오스테나이트 결정립이 조대화되고 상부 베이나이트와 도상 마르텐사이트가 생성되어 인성이 저하한다. 그 대책으로서는 용접 열싸이클과정중 안정한 질화물, 산화물등을 모재에 미세분산시켜 오스테나이트 결정립 성장을 억제하고, 페라이트, 펄라이트 변태를 촉진시킨다. 이러한 석출물의 형성을 위해서는 주로 Ti, Ca, REM, B등의 합금원소가 이용된다. 소입성이 높은 주질고장력 강에서는 석출물의 분산에 의한 페라이트의 변태 촉진 보다는 Mn, Ni, Cr, Mo, V등의 합금원 소를 첨가하여 소입성을 높여 인성이 우수한 하부 베이나이트 조직을 형성하든가, 탄소량을 저 감시켜 도상 마르텐사이트의 생성을 억제하므로서 인성을 확보한다. 현재 국내에서 제조되고 있는 대입열용접용강중 인장강도 50kgf/mm$^{2}$급강은 기본적으로 용접부 인성이 우수한 TMCP법으로 제조되며, Ti등을 첨가하여 석출물의 효과를 이용하고 N을 억제하여 기지의 인 성을 향상시키는 등의 방법을 병용하고 있다. 인장강도 60kgf/mm$^{2}$ 급강은 조질처리에 의하여 제조되며, 50kgf/mm$^{2}$급강과 같이 Ti, B등의 첨가에 의한 석출물의 효과를 이용 하고 있다.