• Title/Summary/Keyword: microstructural factor

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Microstructural Characterization of $CaTiO_3-NdAlO_3$-Based Ceramics

  • Suvorov, Danilo;Drazic, Goran;Valant, Matjaz;Jancar, Bostjan
    • Korean Journal of Crystallography
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    • v.11 no.4
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    • pp.195-199
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    • 2000
  • Ceramics based on CaTiO₃-NdAlO₃ solid solutions were synthesized in order to study their dielectric microwave properties. Microstructural analysis was performed with scanning electron microscopy (SEM) and transmission electron microscopy (TEM) using different analytical methods such as energy-dispersive X-ray spectroscopy (EDXS). It was observed that the heating conditions during sintering and cooling strongly affect the microstructural development of CaTiO₃-NdAlO₃-based ceramics. Various types and concentrations of structural defects were identified, for example, dislocations, twins and/or antiphase boundaries. all such defects resulted in a degradation of the dielectric microwave properties, in particular the quality factor Q. Dielectric properties of CaTiO₃-NdAlO₃-based ceramics can be improved by an appropriate thermal treatment of ceramics which results in a decrease in the concentrations of the identified microstructural defects.

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Microstructural and Piezoelectric Properties of Low Temperature Sintering PMN-PZT Ceramics with the Variations of Sintering Times (저온소결 PMN-PZT 압전세라믹의 소성시간에 따른 미세구조 및 압전특성)

  • Yoo, Ju-Hyun;Lee, Chang-Bae;Lee, Sang-Ho;Paik, Dong-Soo;Jeong, Yeong-Ho;Im, In-Ho
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.18 no.3
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    • pp.237-242
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    • 2005
  • In this paper, in order to develop the low temperature sintering ceramics for multilayer piezoelectric transformer, PMN-PZT ceramics were manufactured with the variations of sintering times, and their microstructural, piezoelectric and dielectric properties were investigated. Li$_2$CO$_3$ and Bi$_2$O$_3$ were used as sintering aids and the specimens were sintered during 30, 60, 90, 120, 150, and 180 minutes, respectively. At the specimen sintered during 90 minute, mechanical quality factor(Qm), electro-mechanical coupling factor(kp) and dielectric constant were showed the optimum values of 2,356, 0.504 and 1,266, respectively.

Microstructural Evolution of Electromagnetically Stirred Al alloy Billet During Isothermal Reheating at the Solid-liquid State (전자기 교반한 알루미늄합금 빌렛의 재가열시 고액공존구역에서의 조직변화)

  • Lee, Dock-Young
    • Journal of Korea Foundry Society
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    • v.28 no.3
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    • pp.129-135
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    • 2008
  • The reheating stage of electromagnetically stirred Al billet is a critical factor in the thixoforming process. When reheated to the solid-liquid state, the microstructure evolves to a more globular and more homogeneous structure by a coarsening mechanism, the kinetics depending on the initial microstructure. Microstructural evolution has been characterized by conventional parameters (mean size of particle and shape factor) as a function of holding time in the solid-liquid state. The aim of this study is to report experimental results concerning microstructural evolution in the solid-liquid state of electromagnetically stirred Al billet. The material was elaborated in the form of continuously cast bars solidified with electromagnetic stirring to degenerate the dendritic structure. The choice of the reheating conditions is determined by a dendritic ripening and coalescence mechanism, involving variations of both the shape and size of the particles. The reheating time has to be long enough to allow a minimum degree of spheroidizing, but has to be limited as much as possible in order to avoid excessive ripening. The optimum microstructure was obtained at the reheating temperature of near $584^{\circ}C$ and the holding time of 5 min. The only means of combining high productivity with good casting quality was to use feedstock billets whose microstructure showed rapid transformation characteristics.

Analysis of Bridging Stress Effect of Polycrystalline aluminas Using Double Cantilever Beam Method (Double Cantilever Beam 방법을 이용한 다결정 알루미나의 Bridging 응력효과 해석)

  • 손기선;이선학;백성기
    • Journal of the Korean Ceramic Society
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    • v.33 no.5
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    • pp.583-589
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    • 1996
  • In this study a new analytical model which can describe the relationship between the bridging stress and microstructure has beenproposed in order to investigate the microstructural effect on the R-curve behavior in polycrystalline aluminas since the R-curve can be derived via the bridging stress function. In the currently developed model function the distribution of grain size is considered as a microstructural factor in modeling of bridging stress function and thus the bridging stress function including three constants PM, n, and Cx, can be established analytically and quantitatively. The results indicate that the n value is closely related to the grain size distribution thereby providing a reliability of the current model for the bridging stress analysis. Thus this model which explains the correlation of the bridging stress distribution and microstructual parame-ters is useful for the systematic interpretation of microfracture mechanism including the R-curve behavior in polycrystalline aluminas.

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Microstructural and Piezoelectric Characteristics of PSN-PMN-PZT Ceramics Produced by Attrition Milling

  • Juhyun Yoo;Sukkyu Min;Jaeil Hong;Sungjae Suh;R, Soonchul-U
    • Transactions on Electrical and Electronic Materials
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    • v.2 no.3
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    • pp.18-23
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    • 2001
  • For the piezoelectric transformer application, Pb(Sb$\_$1/2/ Nb$\_$1/2/)O$_3$-Pb(Zr,Ti)O$_3$ ceramics were produced by attrition milling. Microstructural, dielectric and piezoelectric characteristics of the ceramics were investigated as a function of milling time. The particle size and grain size decreased while dielectric constant, density and mechanical quality factor (Q$\_$m/) increased with milling time. Temperature coefficient of resonant frequency (TCf$\_$r/) was shifted to positive side with increasing milling time. The attrition milling process proved to be one of the effective routes to produce transformers for high power application.

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Effect of Carbon Addition and Sintering Temperature on Densification and Microstructural Evolution of Sinter-Hardening Alloys Steels

  • Verma, N.;Anand, S.;Upadhyaya, A.
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • 2006.09a
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    • pp.557-558
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    • 2006
  • In all conventional sintered PM products, the pores present are of two types, primary and secondary. Primary pores forming during compaction and latter during sintering, due to penetration of formed liquid through the matrix grain boundary. Effect of carbon addition on diffusion of Cu in SH737-2Cu system was investigated. After compaction and transient liquid phase sintering at $1120^{\circ}C$ and $1180^{\circ}C$, samples were characterized for densification, showing rise in sintering density and reduction in swelling on carbon addition. Quantitative microstructural characterization (shape factor and pore size) revealed bimodal distribution for 0% carbon, more rounded pores for 0.9% carbon and higher sintering temperature, and pore coarsening at higher sintering temperature.

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Microstructural and piezoelectric properties of low temperature sintering PMN-PZT ceramics for multilayer piezoelectric transformer with the variations of sintering times (적층 압전변압기용 저온소결 PMN-PZT 압전세라믹의 소성시간에 따른 미세구조 및 압전특성)

  • Lee, Chang-Bae;Yoo, Ju-Hyun;Lee, Sang-Ho;Paik, Dong-Soo;Jeong, Yeong-Ho;Yoon, Hyun-Sang;Im, In-Ho
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2004.11a
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    • pp.425-430
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    • 2004
  • In this paper, in order to develop the low temperature sintering ceramics for multilayer piezoelectric transformer, PMN-PZT ceramics were manufactured with the variations of sintering times, and their microstructural, piezoelectric and dielectric properties were investigated. To manufacture multilayer piezoelectric transformer, the low temperature sintering composition is need, hence, $Li_2CO_3$ and $Bi_2O_3$ were used as sintering aids and the specimens were sintered during 30, 60, 90, 120, 150 and 180 minutes, respectively. At the specimen sintered during 90 minute, mechanical quality factor(Qm), electromechanical coupling factor(kp) and dielectric constant were showed the optimum values of 2356, 0.504 and 1266, respectively. All the specimens showed tetragonality phase, and pyrochlore phase was not shown.

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Effect of Microstructural Factors on Strength and Ductility in Hypoeutectoid Steels with Ferrite-Pearlite Structure (페라이트-펄라이트 조직 아공석강의 강도와 연성에 미치는 미세조직적 인자의 영향)

  • Lee, Sang-In;Kang, Jun-Young;Lee, Sang-Yoon;Hwang, Byoungchul
    • Journal of the Korean Society for Heat Treatment
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    • v.29 no.1
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    • pp.8-14
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    • 2016
  • This article presents a study on the tensile properties of hypoeutectoid steels with different ferrite-pearlite microstructures. Nine kinds of hypoeutectoid steel specimens were fabricated by varying carbon content and isothermal transformation temperature. The microstructural factors such as ferrite & pearlite fraction, interlamellar spacing, and cementite thickness were quantitatively measured and then tensile tests were carried out on the specimens in order to investigate the correlation of the microstructural factors with strength and ductility. The pearlite volume fraction usually increased with decreasing transformation temperature, while the pearlite interlamellar spacing and cementite thickness decreased mostly with decreasing transformation temperature, irrespective of carbon content. The tensile test results showed that the yield and tensile strengths of all the steel specimens increased and their ductility was also improved as the transformation temperature decreased. For the steel specimens investigated, the difference in the transformation temperature dependence of strength and ductility could be explained by the fact that the variation in pearlite fraction with transformation temperature noticeably affected various microstructural factors such as pearlite interlamellar spacing and cementite thickness associated with pearlite fracture mechanism such as void initiation, cementite necking, and cracking.

Microstructure and Mechanical Properties of High Strength and Stretch-Flangeability Hot-Rolled Steels (고강도-신장플랜지성 열연강의 미세조직 및 기계적 성질)

  • Chun, Eun-Joon;Lee, Ju-Seung;Do, Hyeong-Hyeop;Kim, Seong-Ju;Park, Yong-Ho;Kang, Nam-Hyun
    • Korean Journal of Materials Research
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    • v.22 no.1
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    • pp.16-23
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    • 2012
  • Research into the development of high strength (1 GPa) and superior formability, such as total elongation (10%), and stretch-flangeability (50%) in hot-rolled steel was conducted with a thermomechanically controlled hot-rolling process. To improve the overall mechanical properties simultaneously, low-carbon steel using precipitation hardening of Ti-Nb-V multimicroalloying elements was employed. And, ideal microstructural characteristics for the realization of balanced mechanical properties were determined using SEM, EBSD, and TEM analyses. The developed steel, 0.06C-2.0Mn-0.5Cr-0.2(Ti + Nb + V), consisted of ferrite as the matrix phase and second phase of granular bainite with fine carbides (20-50 nm) in both phases. The significant factor of the microstructural characteristics that affect stretch-flangeability was found to be the microstructural homogeneity. The microstructural homogeneity, manifest in such characteristics as low localization of plastic strain and internally stored energy, was identified by grain average misorientation method, analyzed by electron backscattered diffraction (EBSD) and hardness deviation between the phases. In summar, a hot-rolled steel having a composition 0.06C-2.0Mn-0.5Cr-0.2(Ti + Nb + V) demonstrated a tensile strength of 998 MPa, a total elongation of 19%, and a hole expansion ratio of 65%. The most important factors to satisfy the mechanical property were the presence of fine carbides and the microstructural homogeneity, which provided low hardness deviation between the phases.