• Transactions of the KSME C: Technology and Education
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• v.4 no.2
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• pp.93-99
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• 2016

High pressure nozzles and turbines of a gas turbine engine should be required to be operated under extreme operating conditions in order to maximize the performance. Engine manufactures have utilized nickel-base superalloys, enhanced cooling design, and thermal barrier coating techniques to overcome them and furthermore, material modeling, finite element analysis, optimization techniques, and etc. have been utilized widely for elaborate predictions. We aim to evaluate the effects on the low cycle fatigue life of the high pressure turbine blade caused by thermal barrier coatings and the cooling design of the endwall of the first stage turbine nozzle. To achieve it, the structural analysis, which utilized the results of conjugate heat transfer analysis as loading boundary conditions, was performed and then the results were the input for the assessment of low cycle fatigue life at several critical zones.

• 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.

• Clean Technology
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• v.17 no.1
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• pp.1-12
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• 2011

Scientists and engineers have altered the properties of materials such as metals, alloys, polymers, ceramics, and so on, to suit the ever changing needs of our society. Man-made engineering materials generally demonstrate excellent mechanical properties, which often tar exceed those of natural materials. However, all such engineering materials lack the ability of self-healing, i.e. the ability to remove or neutralize microcracks without intentional human interaction. The damage management paradigm observed in nature can be reproduced successfully in man-made engineering materials, provided the intrinsic character of the various types of engineering materials is taken into account. Various self-healing ptotocols that can be applied for the organic materials such as polymers, ionomers and composites can be developed by utilizing suitable chemical reactions and physical intermolecular interactions.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.137-137
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• 2013

지속 가능한 발전을 위해, 한정된 자원인 석유의 고갈을 막기 위해 석유를 수송에너지로 주로 사용하는 자동차에서 바이오 디젤이나 연료전지, 전기자동차 등 다양한 대안이 제시되고 있다. 그러나 식량 가격 상승, 낮은 안정성, 인프라 확충 등의 문제의 해결이 필요할 뿐만 아니라, 석유의 소비를 감소시키는 대신, 지구에서 소비할 수 있는 다른 형태의 에너지를 소모한다는 측면에서 근본적인 에너지 문제의 해결책의 모색이 필요하다. 19세기 후반, 백열전구의 필라멘트 용도로 사용되기 시작한 탄소 섬유는, 철에 비해 5배 가볍고 강도는 10배가 높으며 내열성이 뛰어난 소재로서, 복합소재의 형태로 제조되어 비행기, 우주선, 풍력 발전 블레이드 등 다양한 산업 분야에서 소재의 장점을 발휘하는 재료로 적용 분야가 확대되고 있다. 특히 비행기 분야에서는 최근 비행기 몸체 구조에 기존 알루미늄 합금을 탄소섬유복합재가 대체하고 있으며, 최근에는 부피 기준 50% 가량까지 탄소섬유 복합재를 사용하여 비행기를 제작하고 있다. 이에 따라 기존에 비해 20% 가량 연료 소모가 감소하여, 비행기 한 대 당 연간 2,700톤의 이산화탄소 배출을 저감하고 있다. 이와 같이 탄소섬유 복합재를 다양한 분야에 적용함으로써, 에너지 문제에 대한 보다 근본적인 접근이 가능하다. 그러나 탄소섬유 복합소재는 금속 등 기존 재료에 비해 높은 가격으로 상용 자동차 등 에너지 소비량이 많은 분야에 널리 적용되는데 한계가 존재한다. 이와 같이 높은 탄소섬유의 가격은, 원가의 50% 가량을 차지하는 PAN 원사 가격과 나머지 반절에 해당하는 안정화/탄화 공정 비용에서 기인하는 것으로, 미국의 ORNL (Oak Ridge National Laboratory), 한국의 KIST 복합소재연구소 등에서는 원사, 안정화 공정, 탄화 공정 등 다양한 측면에서 탄소섬유 복합재의 가격을 절감할 수 있는 방안을 연구 중이다. 미국 ORNL에서는 마이크로웨이브 플라즈마를 이용하여 기존에 열을 이용해 수행하던 탄화 공정 비용을 크게 절감하고 있으며, KIST에서는 대기압 플라즈마를 이용하여 기존에 열을 이용해 2시간 가량이 소요되는 안정화 공정을, 대기압 플라즈마를 이용하여 30분여로 단축된 시간에 수행하는 공정을 개발 중이다. 본 발표에서는 탄소섬유 복합재의 개요와, 탄소섬유 가격 절감 방안으로서의 플라즈마에 대해 논의하며 대기압 플라즈마의 다양한 응용에 대해 소개할 예정이다.

• Journal of Powder Materials
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• v.27 no.1
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• pp.37-43
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• 2020

The Fe-22wt.%Cr-6wt.%Al foams were fabricated via the powder alloying process in this study. The structural characteristics, microstructure, and mechanical properties of Fe-Cr-Al foams with different average pore sizes were investigated. Result of the structural analysis shows that the average pore sizes were measured as 474 ㎛ (450 foam) and 1220 ㎛ (1200 foam). Regardless of the pore size, Fe-Cr-Al foams had a Weaire-Phelan bubble structure, and α-ferrite was the major constituent phase. Tensile and compressive tests were conducted with an initial strain rate of 10^-3/s. Tensile yield strengths were 3.4 MPa (450 foam) and 1.4 MPa (1200 foam). Note that the total elongation of 1200 foam was higher than that of 450 foam. Furthermore, their compressive yield strengths were 2.5 MPa (450 foam) and 1.1 MPa (1200 foam), respectively. Different compressive deformation behaviors according to the pore sizes of the Fe-Cr-Al foams were characterized: strain hardening for the 450 foam and constant flow stress after a slight stress drop for the 1200 foam. The effect of structural characteristics on the mechanical properties was also discussed.

• Korean Journal of Crystallography
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• v.14 no.2
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• pp.51-55
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• 2003

SrTiO₃ (STO) thin fims were deposited on the biaxially textured Ni-3 wt%W alloy substrates to be used as a single buffer layer for YBa₂CU₃O/sub 7-8/(YBCO) coated conductor. Thin films of YBCO and STO were deposited using pulsed laser. The deposition condition for epitaxial growth of STO on the textured metal was identified, and YBCO coated conductor with a single STO buffer layer with critical current density of 1.2 MA㎠ at 77 K under zero magnetic field and critical temperature of 86 K, was fabricated.

• Journal of Technologic Dentistry
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• v.31 no.3
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• pp.27-34
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• 2009

This study compared and analyzed changes to the mechanical characteristics to nonprecious metal alloy for porcelain fused to metal crowns when it's repetitively used without the addition of new alloy. Metal samples were made with the Verabond V nonprecious metal alloy. Those samples to measure tensile and yield strength were made in the standardized design(ISO 22674), those to measure bond strength in the $25mm{\times}3mm{\times}0.5mm$ format, and those to measure hardness in the $10mm{\times}10mm{\times}1mm$ format. A ceramic to measure bond strength was made at the center of the metal sample in the length of $8{\ss}{\AE}$ by using Noritaker Super Porcelain EX-3. Ten samples were prepared for one, three and five repetitions of casting each. The test results were as follows: 1. The more casting was repeated, the more significantly tensile strength dropped. 2. The more casting was repeated, the more significantly yield strength dropped. 3. Repetitive casting didn't cause significant changes to bond strength. 4. The Vickers hardness significantly fell with increasing repetitions of casting. There were no changes to bond strength observed with the increasing number of repeating casting. But tensile strength, yield strength, and Vickers hardness decreased. Those results indicate that repeated casting can affect durability and that careful attention should be paid by avoiding repetitive use or excessive increase of uses when no new alloy is added.

• The Journal of Korean Academy of Prosthodontics
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• v.38 no.2
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• pp.160-168
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• 2000

This study evaluated the effects of four adhesive metal primers on the shear bond strength of a heat curing denture base resin(Lucitone 199) to cobalt-chromium alloy(Biosil-f). The adhesive metal primers were Cesead Opaque Primer, Metal Primer, MR Bond, and Super-Bond liquid. The metal surface primed or nonprimed was filled with the heat-curing methyl methacrylate resin. The specimens were stored in water at $37^{\circ}C$ for 24 hours and the alternately immersed in water bath at $5^{\circ}C\;and\;55^{\circ}C$ for up to 2,000 thermal cycles. Shear bond strengths were measured using UTM at a crosshead speed of 0.5mm/min. Failure surface were examined under magnifying glasses. All the primers examined improved the shear bond strength between denture base resin and cobalt-chromium alloy compared with nonprimed specimens before thermal cycling. The bond strength of Cesead Opaque Primer was greatest. And after 2,000 thermal cycles, the bond strengths between resin and cobalt-chromium alloy were decreased but the difference between thermal cycling 0 and 2,000 at Cesead Opaque primer and Metal Primer were not significant. This study indicated that Cesead Opaque Primer & Metal Primer is effective primers to obtain higher bond strength between heat cured denture base resin and cobalt-chromium alloy.

• 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.39 no.4
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• pp.417-432
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• 2001

The pcf metal primers on the bond strength and durability of 4-META/MMA-TBB resins adhered to an Au-Ag-Pd alloy. For this study, the specimens were divided into 8 groups as follows: Thermocyle 0 : (1) control group : sandblast, (2) Group I : sandblast + Cesead Opaque Primer; (3) Group II : sandblast + Metal Primer; (4) Group III : sandblast + V-Primer; Thermocyle 10,000 (5) control sandblast: (6) Group I : sandblast + Cesead Opaque Primer: (7) Group II : sandblast + Metal Primer; (8) Group III sandblast + V-Primer. The shear bond strength was determined using an Instron were observed with the use of scanning electron microscope. Finally, the strengths of bonded joints were evaluated with regard to their adherence energy using a wedge test. The results obtained were as follows ; (1) The shear bond strength of 4-META/MMA-TBB resin to the Au-Ag-Pd alloy was significantly improved in all the groups treated with the primers (p<0.05). (2) Regardless of the adhesive primers used, a significant difference was observed in the bond strength of the thermocycle 0 groups and 10,000 groups (p<0.05). (3) Both before and after thermocycling, the strongest bond strength between the resin an the alloy was obtained after treatment with a metal primer containing MEPS (p<0.05). (4) In the wedge test, the adherence energies of the control group and Group III decreased more rapidly than those of Group I and II during the 2nd day of storage in water.