• Title/Summary/Keyword: Microstructural evolution

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Microstructure and Properties of $Cr_{2}O_{3}$additive ternary PZT Ceramics ($Cr_{2}O_{3}$이 첨가된 PNN-PZT 압전세라믹스에서의 미세구조 및 특성)

  • 박정호;김철수;김성곤;이상렬
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2001.07a
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    • pp.972-975
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    • 2001
  • The effect of Cr$_2$O$_3$(0 to 0.5 wt%) doping on the microstructure and electrical properties of ternary Pb(Zr,Ti)O$_3$-Pb(Ni,Nb)O$_3$piezoelectric ceramic has been investigated. Abnormal grain growth (grain size 3.3 to 11.2 $\mu$m) and densification are found. Minor additives of $\leq$0.1 wt% improve the mechanical coupling factor, but with more additives of $\geq$0.2 wt% electrical properties deteriorate. Thus, these phenomna can be ascribed mainly to anomalous developed microstructure. The large grains were composed of a core region that is free of Cr and a surrounding shell region rich in Cr. The interfaces between the core and the shell were composed of misfit dislocations. The mechanical properties of the specimens were strongly influenced by this microstructural change. The microstrutural and compositonal evolution of the specimens containing different amounts of Cr$_2$O$_3$were monitored. Electrical properties were measured and related to the variations in the microstructure.

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Development of {110}<110> Textured Ag Substrate for YBCO Coated Conductors ({110}<110> 집합조직을 가지는 YBCO 박막 선재용 Ag Substrate 개발)

  • 임준형;김정호;지봉기;장석헌;김규태;주진호;김찬중;홍계원
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.17 no.1
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    • pp.94-100
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    • 2004
  • We fabricated textured Ag substrates for YBCO coated conductor and evaluated the effects of annealing temperature on microstructural evolution, texture formation, and surface morphology. Ag ingot, as an initial specimen, was prepared by plasma arc melting(PAM). Subsequently, the ingot was cold rolled to 100 ${\mu}{\textrm}{m}$ thick tape and annealed at temperatures of 600-80$0^{\circ}C$. The texture and surface morphology of the substrate were characterized by pole-figure and atomic force microscopy(AFM) profile, respectively. It was observed that a strong {110}<110> texture was formed after annealing and its symmetry improved as annealing temperature increased. The full-width at half-maximum(FWHM) of {110}<110> pole was as sharp as 10$^{\circ}$ for the substrate annealed at 80$0^{\circ}C$. On the other hand, it was found that the thermal grooving and faceting became remarkable as annealing temperature increased : root-mean-square(RMS) roughness of the substrate annealed at 80$0^{\circ}C$ was 39.2 nm. The substrate of strong texture and smooth surface, fabricated in our study, is considered to be suitable for use as a substrate for the epitaxial deposition of superconductor film.

Microstructure and Mechanical Properties of High-Strength Low-Carbon Bainitic Steels with Enhanced Deformability (높은 변형능을 갖는 저탄소 베이나이트계 고강도강의 미세조직과 기계적 특성)

  • Hwang, Byoungchul
    • Korean Journal of Materials Research
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    • v.23 no.8
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    • pp.423-429
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    • 2013
  • Recently, steel structures have increasingly been required to have sufficient deformability because they are subjected to progressive or abrupt displacement arising from structure loading itself, earthquake, and ground movement in their service environment. In this study, high-strength low-carbon bainitic steel specimens with enhanced deformability were fabricated by varying thermo-mechanical control process conditions consisting of controlled rolling and accelerated cooling, and then tensile and Charpy V-notch impact tests were conducted to investigate the correlation between microstructure and mechanical properties such as strength, deformability, and low-temperature toughness. Low-temperature transformation phases, i.e. granular bainite (GB), degenerate upper bainite(DUB), lower bainite(LB) and lath martensite(LM), together with fine polygonal ferrite(PF) were well developed, and the microstructural evolution was more critically affected by start and finish cooling temperatures than by finish rolling temperature. The steel specimens start-cooled at higher temperature had the best combination of strength and deformability because of the appropriate mixture of fine PF and low-temperature transformation phases such as GB, DUB, and LB/LM. On the other hand, the steel specimens start-cooled at lower temperature and finish-cooled at higher temperature exhibited a good low-temperature toughness because the interphase boundaries between the low-temperature transformation phases and/or PF act as beneficial barriers to cleavage crack propagation.

Effect of Scancium Content on The Hot Extrusion of Al-Zn-Mg-(Sc) Alloy (Al-Zn-Mg-(Sc) 합금의 고온가공성에 미치는 Sc 함량의 영향)

  • Kim, Jin-Ho;Kim, Jeoung-Han;Yeom, Jong-Taek;Lee, Dong-Geun;Park, Nho-Kwang
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2006.05a
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    • pp.184-187
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    • 2006
  • The effects of scandium content and extrusion parameters on Al-Zn-Mg-(Sc) alloys were examined. Three kinds of Al-Zn-Mg-(Sc) alloys with up to 0.30 wt.% Sc were prepared. The compression test was conducted to investigate the microstructure evolution during hot deformation. Despite of microstructural differences in the alloys, deformation behaviors were very similar. After extrusion at $350^{\circ}C$ with the ram speed of 15mm/sec, AA7075 showed a moderate surface quality compared with other Sc containing alloys, which was attributed to low flow stresses. AA7075 showed coarse-grained bands in surface region. With the ram speed of 1.5mm/sec at $350^{\circ}C$, the surface quality of the alloys was sound due to low friction stresses and deformation heating. As the Sc content increased, tensile strengths and elongations at room temperature improved.

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A Study of Joining Method of BSCCO(2223) Tape (BSCCO(2223) 초전도 선재의 접합공정 연구)

  • 김정호;김중석;김태우;지붕기;주진호;나완수
    • Progress in Superconductivity and Cryogenics
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    • v.1 no.2
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    • pp.1-7
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    • 1999
  • we evaluated the effects of joining process such as contact method. shape of joined area and pressure on the electrical and mechanical properties of Bi-2223 superconducting tape, Specifically. the current capacity of the jointed tape was measured as a function of uniaxial pressure. and the thermal shock, bonding strength and the thermal of the tape were evaluated and correlated to the microstructural evolution. It was observed that the current capacity was significanrly dependent on the uniaxial pressure The jointed tape, fabricated with a pressure of 1,000-1,600 Mpa. showed the highest value of current capacity results from improvements in core density, contacting area and grain alignment, ect. In addition, the strength of jointed tape was measured to be 86 Mpa, which is about 88% of the unjoined ape's strength. The irreversible strain($\varepsilon$irrev) for the jointed tape was measured to be 0.1%, smaller than that of unjoined tape ($\varepsilon$irrev= 0.3%). The decrease in the strength and irreversible strain for jointed tape is believed to be due to the irregular geometry/morphology of the transition area of the tape.

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Effect of Starting Crystallographic Phase on the Mechanical Properties of Hot-Pressed SiC Ceramics (초기분말의 결정상이 $Al_2O_3$를 소결 조제로한 고온가압 SiC 세라믹스의 기계적 특성에 미치는 영향)

  • 정동익;강을손;최원봉;백용기
    • Journal of the Korean Ceramic Society
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    • v.29 no.3
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    • pp.232-240
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    • 1992
  • Densification behavior, microstructural evolution, and mechanical properties of hot-pressed specimens using $\beta$-SiC and $\alpha$-SiC powder with Al2O3 additive were studied. Beta-SiC powder was fully densified as 205$0^{\circ}C$, but $\alpha$-SiC powder was at 210$0^{\circ}C$. The maximum flexural strength and the fracture toughness of the specimen hot-pressed using $\beta$-SiC powder were 681 MPa and 6.7 MPa{{{{ SQRT {m } }}, and thosevalues of specimen hot-pressed using $\alpha$-SiC powder were 452 MPa and 4.7 MPa{{{{ SQRT {m } }}, respectively. The strength superiority of specimen hot-pressed using $\beta$-SiC powder was due to the finer grain size, and higher density. The higher toughness of specimen hot-pressed using $\beta$-SiC powder than $\alpha$-SiC powder than $\alpha$-SiC powder was due to the crack deflection mechanism arised from the difference of thermal expansion coefficient between $\alpha$ and $\beta$-SiC phases which were co-existed in the sintered body.

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전도성 기판에 도입된 산화아연 나노월의 능동적 성장법과 전자소자

  • Kim, Dong-Chan;Lee, Ju-Ho;Bae, Yeong-Suk;Choe, Won-Cheol;Jo, Hyeong-Gyun;Lee, Jeong-Yong
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2010.06a
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    • pp.54-54
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    • 2010
  • This article reports a spontaneous method for controlling the growth mode from vertically arrayed ultra-slim MgZnO nanowires to nanowalls through the Zn random motion of seeds formed by surface phase separation by Mg injection near an evaporation temperature of Zn. The random motion of single crystal MgZnO seeds with relative Zn rich phase played a vital role in the growth of the MgZnO nanowalls. The seeds were networked with increasing Zn flux compared with Mg flux and closing to the evaporation temperature of Zn on phase separation layers. We achieved fabrication of MgZnO nanowalls on various non- and conducting substrates by this advanced growth method. The MgZnO nanowalls hydrogen sensor showed an improved sensing performance compared to the MgZnO nanowires grown under the similar conditions. Based on the microstructural characterizations, the growth procedure and models for the evolution of the structure transition from MgZnO nanowires to nanowalls on the Si substrates are proposed for phased growth times.

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Characteristic Investigation on Super-Hydrophobicity of PTFE Thin Films Deposited on Al Substrates Using RF-Magnetron Sputtering Method (고주파 마그네트론 스퍼터링 방법을 사용하여 Al 기판위에 증착된 PTFE 박막의 초-발수에 관한 특성 연구)

  • Bae, Kang;Kim, Hwa-Min
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.24 no.1
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    • pp.64-69
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    • 2011
  • Super-hydrophobic properties have been achieved on the rf-sputtered polytetrafluoroethylene(PTFE) films deposited on etched aluminum surfaces. The microstructural evolution created after etching has been investigated by FESEM. The water contact angle over $160^{\circ}$ can be achieved on the rf-sputtered ultra-tihn PTFE film less than 10 nm coated on aluminum surface etched with 7 wt.%, 12.5 wt.%, and 15 wt.% HCl concentration for 12 min. XPS analysis have revealed the presence of a large quantity of $-CF_3$ and $-CF_2$ groups in the rf-sputtered PTFE films that effectively can reduce the surface energy of etched aluminum. The presence of patterned morphology along with the low surface energy at the rf-sputtered PTFE coating makes the aluminum surface with high super-hydrophobic property.

The Effect of Heat Treatment on the Microstructural Evolution and Mechanical Properties of Co-base Materials (CO-기 합금의 열처리에 의한 미세조직 및 기계적 특성변화에 관한 연구)

  • Kim, Gi-Yeob;Jung, Byong-Ho;Ahn, Yong-Sik
    • Journal of Power System Engineering
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    • v.5 no.2
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    • pp.63-70
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    • 2001
  • To obtain the optimal condition of heat treatment of wear-resistant alloy, hardness and Charpy V-notch test have been performed with Co-based Stellite No.4, No.6 and Tribaloy 800 alloys, following by heat treatment at the various conditions. Heat treatment at $1250^{\circ}C$ for 1 hours caused the as-casted Tribaloy 800 with FCC crystal structure to transform to HCP structure and lamellar eutectic structure was disappeared, which did not influence on the hardness. Aging at $800^{\circ}C$ for 20 hours, following by $1250^{\circ}C$ for 2 hours heat treatment has enhanced hardness significantly, which is due to the precipitation of large amounts of Laves-phase. The hardness of Stellite alloys was increased by the aging at $800^{\circ}C$ to 5 hours, and was nearly constant by the aging over 5 hours. The toughness of Stellite alloys was a few influenced by the aging treatment.

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AGS Distribution in Low-Speed Round-Oval Rolling of S20C Steel (S20C강 저속 라운드-모발 압연의 AGS 분포)

  • Kwon H. C.;Lee H. W.;Lee Y.;Im Y. T.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2004.08a
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    • pp.297-306
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    • 2004
  • This study investigated Austenite Grain Size (AGS) distribution in Low-Speed Round-Oval Rolling. Rolling experiments were done along with the AGS numerical modeling to characterize the final AGS distribution and its kinetics behavior. For bar rolling experiment, we utilized the pilot rolling mill, operating at 34 fixed rpm, at POSCO Technical Research Laboratories. To investigate the microstructural observation, the rigid-viscoplastic finite element analysis was combined with Hodgson's AGS evolution model. To consider the transient thermal history in the integrative AGS modeling, additivity rule was introduced. The integrated analysis revealed that static or meta-dynamic recrystallization is responsible for the AGS difference in the inner or outer region of rolled bar. Comparative study showed that the current AGS modeling approach can be used to model the overall AGS distribution in bar rolling processes. For more accurate AGS prediction, the AGS modeling method should be verified under the various rolling conditions such as different rolling speeds and different deformations.

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