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대한금속재료학회(구 대한금속학회)> 대한금속재료학회지> 텅스텐 나노박막의 상변태를 이용한 반투명 면상발열체 형성 연구

KCI등재SCISCOUPUS

텅스텐 나노박막의 상변태를 이용한 반투명 면상발열체 형성 연구

Fabrication of Semi-transparent W film Heaters via Phase Transformation

최지윤 ( Jiyun Choi ) , 최두호 ( Dooho Choi )
  • : 대한금속재료학회
  • : 대한금속재료학회지 59권9호
  • : 연속간행물
  • : 2021년 09월
  • : 664-669(6pages)
대한금속재료학회지

DOI


목차

1. 서 론
2. 실험 방법
3. 결과 및 고찰
4. 결 론
REFERENCES

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In this study, we prepared highly thermostable semi-transparent heaters composed of W layers with thicknesses of 1-20 nm, on which a 30 nm-thick ZnO layer was deposited to serve as an anti-oxidation barrier. The optical transmittance and sheet resistance of the heaters could be greatly modulated by varying the W layer thickness. For layer thicknesses up to 10 nm, the initial Joule heating above 100 ℃ significantly reduced the sheet resistance, by 300% for a 6 nm-thick W layer at a fixed voltage for a duration of 400 s. During the test period, heater current and heating capability continuously increased. In subsequent heater operations, the heaters exhibited highly reproducible heating capability. In contrast, for films thicker than 10 nm, the Joule heating process resulted in only a marginal reduction in sheet resistance, i.e., by 4% for a 20 nm-thick W layer. In order to investigate the sharp dependence of heater characteristics on thickness, we performed x-ray diffraction analyses, which revealed that the films thinner than 10 nm were composed of both the equilibrium low-resistivity α-phase and metastable high-resistivity β-phase, and films thicker than 10 nm contained mostly α-phase. The Joule heating process for the thinner films was found to transform the β-phase into α-phase at temperatures above 100 ℃, which resulted in significant improvement in the heating capability of the 6 nm-thick W layer. For films thicker than 10 nm, the W layers contained mostly α-phase and no such transformation-induced effects were observed. Finally, W heaters composed of α-phase exhibited highly thermostable and reproducible heater properties, which make the heaters suitable for applications with semi-transparent heaters.
(Received April 29, 2021; Accepted June 1, 2021)

UCI(KEPA)

간행물정보

  • : 공학분야  > 금속공학
  • : KCI등재
  • : SCI,SCOPUS
  • : 월간
  • : 1738-8228
  • : 2288-8241
  • : 학술지
  • : 연속간행물
  • : 1963-2021
  • : 6952


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59권10호(2021년 10월) 수록논문
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KCI등재 SCI SCOPUS

1저온 템퍼링을 이용한 1.2 GPa급 페라이트계 경량철강 개발

저자 : 배효주 ( Hyo Ju Bae ) , 고광규 ( Kwang Kyu Ko ) , 박형석 ( Hyoung Seok Park ) , 정재석 ( Jae Seok Jeong ) , 김정기 ( Jung Gi Kim ) , 성효경 ( Hyokyung Sung ) , 설재복 ( Jae Bok Seol )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 10호 발행 연도 : 2021 페이지 : pp. 683-691 (9 pages)

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Previously reported low-Mn ferritic-based lightweight steels are potential candidates for industrial applications, however, they typically exhibit lower strength, with < 1 GPa and lower strength-ductility balance, than medium- and high-Mn austenitic lightweight steels. Herein, we introduce a low-temperature tempering-induced partitioning (LTP) treatment that avoids the strength-ductility dilemma of low-Mn ferritic-based steels. When the LTP process was performed at 330 ℃ for 665 s, the strength of typical ferritic base Fe-2.8Mn5.7Al0.3C (wt%) steel with heterogeneously sized metastable austenite grains embedded in a ferrite matrix, exceeded 1.1 GPa. Notably, the increased strength-ductility balance of the LTP-processed ferritic steel was comparable to that of the high-Mn based austenitic lightweight steel series. Using microscale to nearatomic scale characterization we found that the simultaneous improvement in strength and total elongation could be attributed to size-dependent dislocation movement, and controlled deformation-induced martensitic transformation.
(Received May 14 2021; Accepted July 5, 2021)

KCI등재 SCI SCOPUS

2나노구조의 ZrB2-Al2O3 복합재료 합성과 소결

저자 : 손인진 ( In-jin Shon )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 10호 발행 연도 : 2021 페이지 : pp. 692-697 (6 pages)

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ZrB2 is considered a candidate material for ultra-high temperature ceramics because of its high thermal conductivity, high melting point, and low coefficient of thermal expansion. Despite these attractive properties, ZrB2 applications are limited by its low fracture toughness below the brittle-ductile transition temperature. To improve its ductile properties, the approach universally utilized has been to add a second material to form composites, and to fabricate nanostructured materials. In this study a dense nanostructured ZrB2-Al2O3 composite was rapidly sintered using the pulsed current activated heating (PCAH) method within 3 min in one step, from mechanically synthesized powders of ZrB2 and Al2O3. Consolidation was accomplished using an effective combination of current and mechanical pressure. A highly dense ZrB2- Al2O3 composite with a relative density of up to 97.4% was fabricated using the simultaneous application of 70 MPa pressure and a pulsed current. The fracture toughness and hardness of the ZrB2-Al2O3 composite were 3.9 MPa.m1/2 and 1917 kg/㎟, respectively. The fracture toughness of the composite was higher than that of monolithic ZrB2.
(Received May 7 2021; Accepted July 20, 2021)

KCI등재 SCI SCOPUS

3ERNiFeCr-2 용가재 적용에 따른 CM247LC 초내열합금 용접부 응고균열 민감도 변화 거동

저자 : 김경민 ( Kyeong-min Kim ) , 정혜은 ( Hye-eun Jeong ) , 정예선 ( Ye-seon Jeong ) , 이의종 ( Uijong Lee ) , 이형수 ( Hyungsoo Lee ) , 서성문 ( Seong-moon Seo ) , 천은준 ( Eun-joon Chun )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 10호 발행 연도 : 2021 페이지 : pp. 698-708 (11 pages)

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The metallurgical aspects of weld solidification cracking in Ni-based superalloys (with Ti+Al > 5 mass%) have not been widely investigated thus far. Herein, the solidification cracking susceptibility of the CM247LC superalloy and its welds with ERNiFeCr-2 filler wire was quantitatively evaluated using a novel modified Varestraint testing method, for the successful manufacturing of CM247LC superalloy gas turbine blades. It was found that the solidification brittle temperature range (BTR) of the CM247LC superalloy was 400 K. This measurement was obtained with a high-speed thermo-vision camera. The BTR increased to 486 K for the CM247LC/ERNiFeCr-2 welds (dilution ratio: 74%). Theoretical calculations (i.e., the Scheil equation, performed using Thermo-Calc software) were conducted to determine the temperature range in which both solid and liquid phases coexist, together with the microstructural characterization of the solidification cracking surfaces. The greater increase in BTR for the CM247LC/ERNiFeCr-2 welds than that for CM247LC was attributed to the enlargement of the solid-liquid coexistence temperature range. This correlated with the formation of a low-temperature Laves phase during the terminal stage of solidification, and was affected by the diluted Nb and Fe components in the ERNiFeCr-2 filler metal. Based on the experimental and theoretical results, the proposed modified Varestraint testing method for dissimilar welds is expected to be an effective testing process for solidification cracking behavior in the manufacturing of high-soundness CM247LC superalloy welds.
(Received June 24 2021; Accepted July 16, 2021)

KCI등재 SCI SCOPUS

4수소 분위기에서 Mg와 VCl3의 밀링에 의한 Mg의 수소 흡수 방출 특성의 향상

저자 : 송명엽 ( Myoung Youp Song ) , 이성호 ( Seong Ho Lee ) , 곽영준 ( Young Jun Kwak )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 10호 발행 연도 : 2021 페이지 : pp. 709-717 (9 pages)

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VCl3 (vanadium (III) chloride) was selected as an additive to Mg to increase the hydrogenation and dehydrogenation rates and the hydrogen storage capacity of Mg. Instead of MgH2, Mg was used as a starting material since Mg is cheaper than MgH2. Samples with a composition of 95 wt% Mg + 5 wt% VCl3 (named Mg-5VCl3) were prepared by milling in hydrogen atmosphere (reactive milling). In the first cycle (n=1), Mg-5VCl3 absorbed 5.38 wt% H for 5 min and 5.95 wt% H for 60 min at 573 K in 12 bar hydrogen. The activation of Mg-5VCl3 was completed after three hydrogenation-dehydrogenation cycles. During milling in hydrogen, β-MgH2 and γ-MgH2 were produced. The formed β-MgH2 and γ-MgH2 are considered to have made the effects of reactive milling stronger as β-MgH2 and γ-MgH2 themselves were being pulverized. The introduced defects and the interfaces between the Mg and the phases formed during the reactive milling and during hydrogenation-dehydrogenation cycling are believed to serve as heterogeneous active nucleation sites for MgH2 and Mg-H solid solution. The phases generated during hydrogenation-dehydrognation cycling are also believed to prevent the particles from coalescing during hydrogenation-dehydrognation cycling.
(Received June 13 2021; Accepted July 28, 2021)

KCI등재 SCI SCOPUS

5RF sputtering으로 증착된 ZnO 박막을 전자 수송층으로 사용한 양자점 발광 다이오드에 관한 연구

저자 : 강명석 ( Myoungsuk Kang ) , 김지완 ( Jiwan Kim )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 10호 발행 연도 : 2021 페이지 : pp. 718-723 (6 pages)

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We report a highly efficient quantum dot light emitting diode (QLEDs) with a radio frequency (RF) sputtered ZnO thin film as an electron transport layer (ETL) instead of the conventional ZnO nanoparticles (NPs) by solution process. ZnO NPs have been used as a key material to improve the performance of QLEDs, but the charge imbalance in ZnO NPs resulting from fast electron injection, and their limited uniformity are significant disadvantages. In this study, ZnO layers were deposited by RF sputtering with various O2 partial pressures. All of the ZnO films showed preferential growth along the (002) direction, smooth morphology, and good optical transmittance. To test their feasibility for QLEDs, we fabricated devices with RF sputtered ZnO layers as an ETL, which has the inverted structure of ITO/RF sputtered ZnO/QDs/CBP/MoO3/Al. The optical/electrical characteristics of two devices, comprised of RF sputtered ZnO and ZnO NPs, were compared with each other. QLEDs with the sputtered ZnO ETL achieved a current efficiency of 11.32 cd/A, which was higher than the 8.23 cd/A of the QLEDs with ZnO NPs ETL. Next, to find the optimum ZnO thin film for highly efficient QLEDs, deposition conditions with various O2 partial pressures were tested, and device performance was investigated. The maximum current efficiency was 13.33 cd/A when the ratio of Ar/O2 was 4:3. Additional oxygen gas reduced the O vacancies in the ZnO thin film, which resulted in a decrease in electrical conductivity, thereby improving charge balance in the emission layer of the QLEDs. As a result, we provide a way to control the ZnO ETL properties and to improve device performance by controlling O2 partial pressure.
(Received June 14 2021; Accepted July 9, 2021)

KCI등재 SCI SCOPUS

6Charge Transport and Thermoelectric Properties of Sn-Doped Tetrahedrites Cu12Sb4-ySnyS13

저자 : Hee-jae Ahn , Il-ho Kim

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 10호 발행 연도 : 2021 페이지 : pp. 724-731 (8 pages)

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In this study, tetrahedrite compounds doped with Sn were prepared by mechanical alloying and hot pressing, and their charge transport and thermoelectric properties were analyzed. X-ray diffraction analysis revealed that both the synthetic powders and sintered bodies were synthesized as a single tetrahedrite phase without secondary phases. Densely sintered specimens were obtained with relatively high densities of 99.5%-100.0% of the theoretical density, and the component elements were distributed uniformly. Sn was successfully substituted at the Sb site, and the lattice constant increased from 1.0348 to 1.0364 nm. Positive signs of the Hall and Seebeck coefficients confirmed that the Sn-doped tetrahedrites were p-type semiconductors. The carrier concentration decreased from 1.28 × 1019 to 1.57 × 1018 cm-3 as the Sn content decreased because excess electrons were supplied by doping with Sn4+ at the Sb3+ site of the tetrahedrite. The Seebeck coefficient increased with increasing Sn content, and Cu12Sb3.6Sn0.4S13 exhibited maximum values of 238-270 μVK-1 at temperatures of 323-723 K. However, the electrical conductivity decreased as the amount of Sn doping increased. Thus, Cu12Sb3.9Sn0.1S13 exhibited the highest electrical conductivity of (2.24-2.40) × 104 Sm-1 at temperatures of 323-723 K. A maximum power factor of 0.73 mWm-1K-2 was achieved at 723 K for Cu12Sb3.9Sn0.1S13. Sn substitution reduced both the electronic and lattice thermal conductivities. The lowest thermal conductivity of 0.49-0.60Wm-1K-1 was obtained at temperatures of 323-723 K for Cu12Sb3.6Sn0.4S13, where the lattice thermal conductivity was dominant at 0.49-0.57 Wm-1K-1. As a result, a maximum dimensionless figure of merit of 0.66 was achieved at 723 K for Cu12Sb3.9Sn0.1S13.
(Received July 12, 2021; Accepted July 28, 2021)

KCI등재 SCI SCOPUS

7Glycothermally Synthesized Self-aggregated ZnS Spherical Particles for Methyl Orange Photodecomposition

저자 : Sang-jun Park , Jeong-hwan Song

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 10호 발행 연도 : 2021 페이지 : pp. 732-740 (9 pages)

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Using ethylene glycol (C2H6O2) as the solvent, ZnS particles were synthesized in high yield at a relatively low temperature of 125 ℃ via the glycothermal method. We report a facile method for preparing spherical self-aggregated ZnS particles from ZnS nanocrystals, using zinc acetate as the Zn2+ source and thiourea as a sulfur source, without mineralization or other agents. The crystal phase structure, morphology, size, surface chemical composition, and optical properties of the self-aggregated ZnS particles were characterized using XRD, FE-SEM, TEM, XPS, BET, and UV-Vis absorption. The ZnS particles had a cubic phase zinc blende structure without any other impurities. The average crystallite size of the synthesized primary nanocrystal, estimated from XRD peak width and TEM images, was nearly 4 nm. FE-SEM images showed that all of the ZnS consisted of self-aggregated particles with a spherical morphology and a size of approximately 0.2 μm~0.5 μm, and contained many tiny primary nanocrystals. The prepared ZnS exhibited strong photoabsorption in the UV region. The optical band gap decreased from 3.85 eV to 3.62 eV as the glycothermal reaction temperature was increased, due to improvement in particle size and crystallization. The effects of the glycothermal reaction temperature on the photocatalytic activity of the synthesized self-aggregated ZnS particles were investigated by the photodecomposition of methyl orange (MO) dye under UV illumination (λ = 365 nm). The prepared ZnS exhibited excellent photocatalytic degradation with increasing reaction temperature, of 125 ℃ (5%), 150 ℃ (10%), 175 ℃ (60%), and 200 ℃ (90%) after irradiation for 60 min. It was found that the ZnS particle prepared at 200 ℃ achieved the highest photocatalytic degradation, with nearly 100% MO decomposition after 90 min, by various photogenerated radical scavengers.
(Received June 9 2021; Accepted July 6, 2021)

KCI등재 SCI SCOPUS

8고분자 전해질 연료전지의 산소환원반응에 대한 Pt-M 합금 촉매의 최근 연구 동향

저자 : 심유진 ( Yu-jin Shim ) , 정원석 ( Won Suk Jung )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 10호 발행 연도 : 2021 페이지 : pp. 741-752 (12 pages)

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Due to environmental pollution and global warming, research on new energy sources that can replace fossil fuels is important. A fuel cell is an eco-friendly energy conversion system that discharges water, and uses hydrogen as fuel. Although platinum is a widely used catalyst in PEMFCs, it has commercial limitations because of its low stability and high cost. Pt-based bimetal catalysts are being studied to improve performance and reduce the cost of fuel cell catalysts. Pt-M is excellent in terms of performance, stability, and cost, avoiding the disadvantages of the Pt catalyst. Studies on various bimetallic catalysts have been conducted, and among them, studies on Pt-Ni, Pt-Co, and Pt-Fe have been the most active. This review summarizes reports of fuel cell catalysts using Pt-M from 2014 to 2020. In recent studies, in order to improve the Pt-M performance, there have been attempts to change the pretreatment, the type of support, and the composition of Pt and M. There have also been studies that have applied new synthetic methods, which are different from traditional synthetic methods. Many Pt-M catalysts have shown better performance than commercial Pt/C, and exhibited stable performance in durability tests.
(Received May 29 2021; Accepted July 7, 2021)

KCI등재 SCI SCOPUS

9질소 5N 가스 분위기에서 다공질 ZrFe 합금의 산화 안정화

저자 : 김광배 ( Kwangbae Kim ) , 진새라 ( Saera Jin ) , 임예솔 ( Yesol Lim ) , 이현준 ( Hyunjun Lee ) , 김성훈 ( Seonghoon Kim ) , 노윤영 ( Yunyoung Noh ) , 송오성 ( Ohsung Song )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 10호 발행 연도 : 2021 페이지 : pp. 753-759 (7 pages)

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A porous ZrFe alloy specimen was prepared as a 6 × 3 mm (diameter × thickness) disk. The reaction of the ZrFe alloy was confirmed while the whole system was maintained at a target temperature, which was increased from 150 ℃ to 950 ℃ in a 99.999% low purity nitrogen atmosphere, consisting of 10 ppm of impurity gas. Surface color, pore size, stabilized layer, and phase change were confirmed with optical microscopy, scanning electron microscopy-energy dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Micro-Raman, according to temperature. The surface color of the ZrFe alloy changed from metallic silver to dark gray as the temperature increased. In the EDS and XPS results, nitrogen component was not observed, and oxygen content increased on each surface at the elevated temperatures. In this way, the ZrFe alloy was stabilized in a low purity nitrogen atmosphere, preventing rapid nitride reactions.
(Received June 1 2021; Accepted July 16, 2021)

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KCI등재SCISCOUPUS

1압력 용기 재료 SA508에서 열적 처리에 따른 입계 파괴의 원인

저자 : 김성수 ( Sung Soo Kim ) , 정종엽 ( Jung Jong Yeob ) , 김영석 ( Young Suk Kim )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 9호 발행 연도 : 2021 페이지 : pp. 589-601 (13 pages)

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Intergranular(IG) fracture due to thermal treatment has been reported in a reactor pressure vessel(RPV) steel of Russian light water reactor in last decade. This is attributed to grain boundary segregation of phosphorus (P) or precipitation of carbide, etc.. This is a finding a difference in microstructure before and after IG cracking; this cannot explain the cause of the IG embrittlement. This old paradigm follows only correlation. Recently, a mechanism in which IG embrittlement occurs due to a decrease in entropy of a material has been reported at a temperature where atomic diffusion is possible. It is anticipated that new paradigm can explain the IG embrittlement of RPV based on a causal relationship. Thus, the thermal treatment at 350-420 ℃ was applied to RPV steel of SA508 and IG cracking was confirmed. DSC analysis was applied to confirm whether a decrease in entropy due to a short range ordering reaction occurs in SA508. It was possible to quantify the entropy change(ΔS= Q/T) through DSC measurement. A lattice changes due to thermal treatment were confirmed using XRD analysis in aged specimens. The results showed that lattice contraction by aging causes a reduction of fracture toughness. The internal stress formed inside the material due to entropy reduction can be calculated by multiplying the exothermic energy per unit mass by the density. This relationship is expressed by a equation of stress(σ) = exothermic heat(ΔQ) x density(ρ).
(Received May 21, 2021; Accepted June 28, 2021)

KCI등재SCISCOUPUS

2Si 및 Al 함량과 항온열처리조건이 초고강도 마르텐사이트-베이나이트 Fe-0.2C-2.0Mn 복합조직강의 미세조직과 인장특성에 미치는 영향

저자 : 이응혁 ( Eung Hyuk Lee ) , 유창재 ( Chang Jae Yu ) , 이홍범 ( Hong-bum Lee ) , 김지훈 ( Ji-hoon Kim ) , 서동우 ( Dong-woo Suh )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 9호 발행 연도 : 2021 페이지 : pp. 602-612 (11 pages)

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This study investigated the influence of partial replacement of Si by Al on the microstructure and tensile properties of ultra-high strength steels with martensite-bainite complex microstructure produced by austenitization and subsequent isothermal heat treatment around Ms temperature. When the isothermal heat treatment was done below the Ms temperature, the fraction of martensite increased with the lower isothermal temperature, but the fractions of constituent phases in the final microstructure were not significantly affected by the partial replacement of Si by Al. Nevertheless, the increase in Al content in the complex phase steel accelerated the bainite transformation, which is thought to be associated with the increase of the free energy difference between FCC and BCC. The enhancement of the bainite transformation not only effectively suppressed the martensite formation upon final cooling when the isothermal temperature was above the Ms temperature but also helped refine the final microstructure when subjected to isothermal heat treatment below the Ms temperature. The yield strengths of the investigated complex phase steels were little influenced by the partial replacement of Si with Al, as long as the fractions of the constituent phases were comparable. This possibly originates with the solid solution hardening and the microstructure refinement with Al addition.
(Received June 8, 2021; Accepted June 30, 2021)

KCI등재SCISCOUPUS

3고내식 합금도금 PosMAC® 강판의 개발과 응용 특성

저자 : 손일령 ( Il-ryoung Sohn ) , 김태철 ( Tae-chul Kim ) , 주광일 ( Gwang-il Ju ) , 김명수 ( Myung-soo Kim ) , 김종상 ( Jong-sang Kim )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 9호 발행 연도 : 2021 페이지 : pp. 613-623 (11 pages)

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PosMAC® is a hot dipping Zn-Mg-Al coated steel sheet developed by POSCO. PosMAC®3.0 shows excellent anti-corrosion performance and is suitable for construction and solar energy systems in severe corrosive environments. PosMAC®1.5 has a superior surface quality and is preferred for automotive and home appliances. The advanced anti-corrosion properties of PosMAC® comes from a dense corroded layer which forms on coated surfaces, compared with traditional Zn coatings such as GI, GA and EG. PosMAC® steels show superior corrosion protection compared to GI coatings in cyclic corrosion tests, despite an approximate 30% reduction in coating weight. The PosMAC® has excellent application properties for the arc welding of automotive chassis. It has a heat resistance that is more robust than the GI coating, and maintains excellent corrosion protection near the welds of the chassis. Zn-Mg-Al coatings, whose chemical compositions are similar to PosMAC® coatings, have very low surface friction properties compared to the GI coating. The friction coefficient of PosMAC® is stabilized to 0.09~0.11. In contrast, the GI coating showed higher friction coefficients of 0.2~0.3 in the repeated friction test. PosMAC® would be appropriate for complex forming parts with less galling, given these low friction resistance properties. It is expected that the industrial demand for PosMAC® steel will increase in the near future, thanks to its Zn saving and high anti-corrosion performance.
(Received October 9, 2020; Accepted May 24, 2021)

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4유한요소해석을 이용한 AA1100의 변형 불균일성에 미치는 다축 단조 유형의 영향 연구

저자 : 김민성 ( Min-seong Kim ) , 김정균 ( Jeong Gyun Kim ) , 유태현 ( Tae Hyun Yoo ) , 조유연 ( You Yeon Jo ) , 이성 ( Seong Lee ) , 정효태 ( Hyo-tae Jeong ) , 최시훈 ( Shi-hoon Choi )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 9호 발행 연도 : 2021 페이지 : pp. 624-639 (16 pages)

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The effect of 3 forging routes (Route A - 1~12 passes by plane forging (PF) and reverse-plane forging (R-PF), Route B - 1~6 passes by PF and R-PF, 7~12 passes by diagonal forging (DF) and reverse-diagonal forging (R-DF), Route C - 1~12 passes by DF and R-DF) on maximum load to produce the workpiece, deformation heterogeneity and hydrostatic pressure distribution in AA1100 was theoretically investigated using finite element analysis (FEA). The maximum load per pass required to complete 1 cycle of the SPD process was different depending on the forging routes. Route A was relatively higher than Route B and C. From the results of effective strain, the deformation heterogeneity was predicted at the center, edge, and corner regions of the AA1100 workpiece produced by Route A and B. However, the distribution of effective strain in Route C was relatively more homogeneous than Route A and B. The average hydrostatic pressure, which is closely related to the suppression of crack formation in the workpiece under multi-axial forging, was predicted to be relatively bigger in Route C than Route A and B.
(Received December 1, 2020; Accepted March 2, 2021)

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5Effect of Interfacial Intermetallic Compounds Morphology on Mechanical Properties of Laser Brazing of Aluminum to Steel

저자 : Kwang-hyeon Lee , Su-jin Lee , In-duck Park , Kwang-deok Choi , Chung-yun Kang , Jeong Suh , Tae-jin Yoon

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 9호 발행 연도 : 2021 페이지 : pp. 640-651 (12 pages)

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The paper provides experimental details of the welding and specific examples of welding aluminum welding battery cans and conductive tabs for battery pack manufacture. In this study, we provide experimental details of a process for joining dissimilar materials used in sealing battery parts. A laser brazing technique was used for the lap joining of aluminum alloy and a deep drawing quality stainless steel, with an Al-Si filler metal. These materials are commonly used in battery applications, as materials for the cap plate, tab plate and can. The relationships among the width of the brazed zone, formation of intermetallic compounds (IMCs), shape of the joint interface, and joint strength were systematically investigated with respect to the laser power and filler wire feeding rate. When a low and medium laser power (1.2-2.0 kW) was applied, the joint strength was very low, and fracture occurred across the band-shaped IMC layer. With a further increase in the applied laser power (2.2-2.8 kW), a new needle-like IMC composed of Al13Fe5 with a monoclinic crystal structure was formed, and it penetrated the brazed zone. In addition, the width of the brazed zone increased due to the partial melting of the aluminum. The joint efficiency under a high laser power condition was 70% compared to that of the base material. Fractures occurred alternately along the needle-shaped IMC and filler metal zone. Since the fracture propagated along the needle-like IMCs inside the brazed zone, the peak load was higher than that of the band-shaped IMCs.
(Received April 21 2021; Accepted June 17, 2021)

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6적층제조 공정으로 구현된 형상 적응형 냉각채널 적용 다이캐스팅 금형의 냉각성능 평가

저자 : 박유진 ( Yu Jin Park ) , 김억수 ( Eok Soo Kim ) , 이정훈 ( Jeong Hun Lee ) , 최지환 ( Ji Hwan Choi ) , 윤필환 ( Pil Hwan Yoon ) , 강호정 ( Ho Jeong Kang ) , 김동현 ( Dong Hyun Kim ) , 박용호 ( Yong Ho Park ) , 고종완 ( Jong Wan Ko )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 9호 발행 연도 : 2021 페이지 : pp. 652-663 (12 pages)

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A cooling channel with an optimized design provides not only high throughput with gravity die casting, but also guarantees product quality. A conformal cooling channel (CC) whose structure follows the shapes or surfaces of the mold cavity has attracted great attention in the die casting industry, because it allows rapid and uniform cooling. However, implementing conformal cooling remains highly challenging, because the complicated geometries of CC are difficult to form using conventional fabrication methods such as drilling and milling. In recent years, advances in additive manufacturing (AM) technology have made it possible to fabricate products with complex and elaborate structures. In this paper, a gravity die casting mold with CC was designed and built using AM technology. The cooling channel performance was estimated and evaluated using an Al-Si-Cu alloy casting simulation and die casting experiments, respectively. The casting simulation results showed that the cooling performance of the CC was enhanced by ca. 10% compared with that of a conventional cooling channel. The experimental cooling performance of the CC improved by ca. 8% compared to that of a conventional cooling channel, and the increment in performance was consistent with the simulation results. In addition, microstructural evidence clarified that the effective cooling performance of CC could be attributed to the decrement (ca. 17%) of the secondary dendrite arm spacing (SDAS) of the Al-Si-Cu alloy. In this research, AM technology provides a novel way to fabricate functionally superior CC molds that are hardly producible with traditional methods.
(Received May 14, 2021; Accepted June 4, 2021)

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7텅스텐 나노박막의 상변태를 이용한 반투명 면상발열체 형성 연구

저자 : 최지윤 ( Jiyun Choi ) , 최두호 ( Dooho Choi )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 9호 발행 연도 : 2021 페이지 : pp. 664-669 (6 pages)

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In this study, we prepared highly thermostable semi-transparent heaters composed of W layers with thicknesses of 1-20 nm, on which a 30 nm-thick ZnO layer was deposited to serve as an anti-oxidation barrier. The optical transmittance and sheet resistance of the heaters could be greatly modulated by varying the W layer thickness. For layer thicknesses up to 10 nm, the initial Joule heating above 100 ℃ significantly reduced the sheet resistance, by 300% for a 6 nm-thick W layer at a fixed voltage for a duration of 400 s. During the test period, heater current and heating capability continuously increased. In subsequent heater operations, the heaters exhibited highly reproducible heating capability. In contrast, for films thicker than 10 nm, the Joule heating process resulted in only a marginal reduction in sheet resistance, i.e., by 4% for a 20 nm-thick W layer. In order to investigate the sharp dependence of heater characteristics on thickness, we performed x-ray diffraction analyses, which revealed that the films thinner than 10 nm were composed of both the equilibrium low-resistivity α-phase and metastable high-resistivity β-phase, and films thicker than 10 nm contained mostly α-phase. The Joule heating process for the thinner films was found to transform the β-phase into α-phase at temperatures above 100 ℃, which resulted in significant improvement in the heating capability of the 6 nm-thick W layer. For films thicker than 10 nm, the W layers contained mostly α-phase and no such transformation-induced effects were observed. Finally, W heaters composed of α-phase exhibited highly thermostable and reproducible heater properties, which make the heaters suitable for applications with semi-transparent heaters.
(Received April 29, 2021; Accepted June 1, 2021)

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8Porous MnO2/ carbon Hybrid Material with Improved Electrochemical Performance

저자 : Venugopal Nulu

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 9호 발행 연도 : 2021 페이지 : pp. 670-676 (7 pages)

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In this work, MnO2 nanoparticles were embedded in a carbon matrix as a porous composite, fabricated using a simple chemical route followed by low-temperature annealing, with activated carbon (AC) as the carbon source in the composite preparation. The porous MnO2/carbon structures contained some selective nanoparticles coated with carbon. The structural feature was identified by transmission electron microscopy (TEM). The surface area and pore size distribution of the materials were investigated by N2 adsorption/desorption isotherms, and demonstrated a high surface area of about 80 ㎡ g-1. AC is a readily available carbon source that can easily form a composite with MnO2 nanoparticles, forming a distinctive porous morphology. When employed as an anode material for lithium-ion batteries (LIB), the composite electrode demonstrated high specific capacities with an initial discharge capacity of 2500 mAh g-1 and maintained about 1391 mAh g-1 after fifty cycles. It also demonstrated excellent high rate performance, delivering more than 500 mAh g-1 of specific capacity at 3000 mA g-1, which is a higher capacity than a conventional graphite anode. Overall, the MnO2/ carbon composite electrode delivered superior anode performance, which was attributed to the improved surface area of the carbon hybridized MnO2 nanoparticles. The porous composite has benefits for lithium storage performance.
(Received April 29 2021; Accepted June 21, 2021)

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9Al과 SnO2 혼합 분말을 사용한 일차원 Al과 Al2O3 나노/마이크로구조의 저온 성장

저자 : 이근형 ( Geun-hyoung Lee )

발행기관 : 대한금속재료학회 간행물 : 대한금속재료학회지 59권 9호 발행 연도 : 2021 페이지 : pp. 677-681 (5 pages)

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One-dimensional Al and Al2O3 nano/microstructures were fabricated via thermal oxidation of Al and SnO2 powder mixtures at temperatures below the melting point of Al (660 ℃). Furthermore, the synthesis process was carried out in air at atmospheric pressure, which made the process very simple and easy. Sn metal particles with spherical shape were observed on the tips of the Al and Al2O3 nano/microstructures, suggesting that the nano/microstructures were grown via a catalyst-assisted growth mechanism. The Sn acted as a catalyst for growing the Al and Al2O3 nano/microstructures. The Sn with low melting point (232 ℃) was produced via the reduction of SnO2 by Al, and formed catalyst droplets at the growth temperatures. Al atoms diffused and dissolved into the Sn liquid droplets, leading to the nucleation and then the growth of the Al and Al2O3 nano/microstructures. At 400 ℃, the diffusion of Al atoms into the Sn liquid droplets was associated with high stress generated at the Al2O3/Al interface. At 600 ℃ close to the melting point of Al, Al atoms were diffused from the thin Al liquid layer, which was formed on the surface of the Al powder, to the Sn liquid droplets. Simultaneously, the Al atoms reacted with oxygen in air and formed solid Al2O3 nuclei. A relatively strong ultraviolet emission band centered at 330 nm was observed in the sample prepared at 600 ℃.
(Received May 5, 2021; Accepted June 2, 2021)

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