Processing math: 100%
  • Title/Summary/Keyword: Grain refinement

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Development of Electrical Steel by Laser Magnetic Domain Refinement for Applying to Transformers of High Energy Efficiency (고효율 변압기용 레이저자구 전기강판 개발)

  • Kwon, Oh-Yeoul;Cha, Sang-Yun;Ha, Kyung-Ho;Kim, Ji-Hyun;Kim, Jae-Kwan
    • Proceedings of the KIEE Conference
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    • 2008.07a
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    • pp.625-626
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    • 2008
  • The magnetic domain-refining techniques such as ball scratching, laser irradiation and plasma have been developed to reduce the domain wall spacing and thus iron losses in Fe-3%Si grain-oriented silicon steels. In view point of magnetic properties, it was supposed that the locally residual stresses change the magnetoelastic energy of the material and thus the spacing between 180 domain walls decreases in order to reduce the magnetostatic energy. The effect of laser irradiation on iron loss and magnetostriction reduction for Fe-3%Si grain-oriented steel were investigated. Since the local tensile stresses were induced at the surface of Fe-3%Si steel by the laser irradiation, the minimum iron loss caused by reducing eddy current loss was obtained in spiete of the decrease of permeability by hindering eddy current loss was obtained in spite of the decrease of permeability by hindering the domain wall movement around the induced stress field. Furthermore, the laser treated 3%Si steel has lower magnetostriction as compared to non laser-treated steel and is less sensitive to applying pre-stresses due to the volume reduction of 90 domain in materials.

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Structure and Mechanical Characteristics of ZrCrAIN Nanocomposite Thin Films by CFUBMS (CFUBMS을 이용한 ZrCrAIN 나노복합 박막의 구조와 기계적 특성)

  • Kim Youn J.;Lee Ho Y.;Shin Kyung S.;Jung Woo S.;Han Jeon G.
    • Journal of Surface Science and Engineering
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    • v.38 no.5
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    • pp.183-187
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    • 2005
  • The quaternary ZrCrAIN nanocomposite thin films are synthesized by Closed-Field Unbalanced Magnetron Sputtering (CFUBMS). Microstructure and mechanical properties of ZrCrAIN nanocomposite thin films are studied. Grain refinement of ZrCrAIN nanocomposite thin film is occurred by controlling N2 partial pressure. Maximum hardness value according to the various N2 partial pressures is obtained at 45 GPa. It is also conformed that critical value of the grain size (d) needs to achieve the maximum hardness.

Microstructural and Mechanical Characteristics of TiZrAlN Nanocomposite Thin Films by CFUBMS (CFUBMS을 이용한 TiZrAlN 나노복합 박막의 미세 구조와 기계적 특성)

  • Kim, Youn-J.;Lee, Ho-Y.;Kim, Yong-M.;Kim, Kab-S.;Han, Jeon-G.
    • Journal of Surface Science and Engineering
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    • v.40 no.1
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    • pp.1-5
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    • 2007
  • Quaternary TiZrAlN nanocomposite thin films were synthesized by Closed-Field Unbalanced Magnetron Sputtering (CFUBMS), and their microstructure and mechanical characteristics were examined. The grain refinement of the TiZrAlN nanocomposite thin films was controlled by adjusting the N2 partial pressure. The hardness of the film varied with the N2 partial pressure and the maximum value was obtained approximately 47 GPa. It was also confirmed that there is a critical value of the grain size(dc) to need maximum hardness.

Finite Element Analysis of Densification Behavior during Equal Channel Angular Pressing Process of Powders (분말 ECAP 공정 시 치밀화의 유한요소해석)

  • Yoon, Seung-Chae;Quang, Pham;Chun, Byong-Sun;Lee, Hong-Ro;Kim, Hyoung-Seop
    • Journal of Powder Materials
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    • v.13 no.6 s.59
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    • pp.415-420
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    • 2006
  • Nanostructured metallic materials are synthesized by bottom-up processing which starts with powders for assembling bulk materials or top-down processing starting with a bulk solid. A representative bottom-up and top-down paths for bulk nanostructured/ultrafine grained metallic materials are powder consolidation and severe plastic deformation (SPD) methods, respectively. In this study, the bottom-up powder and top-down SPD approaches were combined in order to achieve both full density and grain refinement without grain growth, which were considered as a bottle neck of the bottom-up method using conventional powder metallurgy of compaction and sintering. For the powder consolidation, equal channel angular pressing (ECAP), one of the most promising method in SPD, was used. The ECAP processing associated with stress developments was investigated. ECAP for powder consolidation were numerically analyzed using the finite element method (FEM) in conjunction with pressure and shear stress.

Effects of Rare Earth Metals Addition and Aging Treatment on the Corrosion Resistance and Mechanical Properties of Super Duplex Stainless Steels

  • 박용수;김순태;이인성;송치복
    • Transactions of Materials Processing
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    • v.8 no.3
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    • pp.309-309
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    • 1999
  • Effects of rare earth metals addition and aging treatment on corrosion resistance and mechanical properties of super duplex stainless steels were investigated using optical/SEM/TEM metallographic examination, an X-ray diffraction test, a potentiodynamic anodic polarization test and a tensile test. The performance of the experimental alloy with 0.32% REM addition was compared with commercial super duplex stainless steel such as SAF 2507 when they were exposed to solution annealing heat treatment and aging treatment. The corrosion resistance in CF environments and mechanical properties of the experimental alloy were found superior to those of the commercial duplex stainless steel. The REM with larger atomic radii than those of Cr, Mo and W may fill vacancies inside the matrix and around the grain boundaries, retarding formation of harmful intermetallic σ and χ phases. In addition, fine REM oxides/oxy-sulfides (1-3㎛) seemed to enhance the retardation effects. With REM additions, strength and ductility increased due to the phase and grain refinement caused by fine REM oxides and oxy-sulfides.

Powder Densification Using Equal Channel Angular Pressing (ECAP 공정을 이용한 분말의 치밀화)

  • Yoon Seung-Chae;Seo Min-Hong;Hong Sun-Ig;Kim Hyoung-Seop
    • Journal of Powder Materials
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    • v.13 no.2 s.55
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    • pp.124-128
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    • 2006
  • In recent years, equal channel angular pressing (ECAP) has been the subject of intensive study due to its capability of producing fully dense samples having a ultrafine grain size. In this paper, the ECAP process was applied to metallic powders in order to achieve both powder consolidation and grain refinement. In the ECAP process for solid and powder metals, knowledge of the internal stress, strain and strain rate distribution is fundamental to the determination of the optimum process conditions for a given material. The properties of the ECAP processed solid and powder materials are strongly dependent on the shear plastic deformation behavior during ECAP, which is controlled mainly by die geometry, material properties, and process conditions. In this study, we investigated the consolidation, plastic deformation and microstructure evolution behaviour of the powder compact during ECAP.

The Effect of Intermediate Thermo-Mechanical Treatment on the Microstructure and Mechanical Property of 7175 Al Alloy (7175 합금 단조재의 미세조직과 기계적 성질에 미치는 중간가공열처리 영향)

  • Lee, Y.Y.;Song, Y.B.;Im, S.T.;Son, Y.I.;Lee, K.H.;Eun, I.S.
    • Journal of the Korean Society for Heat Treatment
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    • v.10 no.3
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    • pp.172-180
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    • 1997
  • The microstructure, tensile and impact properties of forgings of 7175 aluminium alloy have been studied as a function of intermediate thermo-mechanical treatment(ITMT) process. The ITMT process is consisted of warm working and recrystallization. In the case that the billet was warm-worked above 60% below 250C and recrystallized at 475C, the grain size revealed about 17μm which corresponds to one third of that of conventional process. The refinement of grain size leaded to the improved ductility and impact energy without sacrifice of tensile strength. It was found that the ITMT processed specimen behaved isotropically due to the near equiaxed grains. It was observed that the ITMT processed specimen showed the mixed fracture mode of transgranular and intergranular, instead of intergranular mode. This change of fracture mode contributed to the improved ductility and impact property.

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Fabrication of Ultra Fine Grained Molybdenum and Mechanical Properties (초미세 결정립을 가지는 몰리브덴의 제조 및 기계적 특성)

  • Kim, Se-Hoon;Seo, Young-Ik;Kim, Dae-Gun;Suk, Myung-Jin;Kim, Young-Do
    • Journal of Powder Materials
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    • v.17 no.3
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    • pp.235-241
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    • 2010
  • Mo nanopowder was synthesized by ball-milling and subsequent hydrogen-reduction of MoO3 powder. To fabricate ultra fine grained molybdenum, two-step sintering and spark plasma sintering process were employed. The grain size of specimen by two-step sintering and spark plasma sintering was around 0.6μm and 0.4μm, respectively. Mechanical properties of ultra fine grained Mo with relative density of above 90% were significantly improved at room and high temperatures comparing to commercial bulk Mo of 99% relative density. This result was mainly explained by the grain size refinement due to diffusion-controlled sintering.

Equal Channel Angular Pressing of Rapidly Solidified Al-20 wt % Si Alloy Powder Extrudates (급속응고 Al-20 wt% Si 합금분말 압출재의 ECAP)

  • Yoon, Seung-Chae;Hong, Soon-Jik;Seo, Min-Hong;Quang, Pham;Kim, Hyoung-Seop
    • Journal of Powder Materials
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    • v.11 no.2
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    • pp.97-104
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    • 2004
  • In this paper processing and mechanical properties of Al-20 wt% Si alloy was studied. A bulk form of Al-20Si alloy was prepared by gas atomizing powders having the powder size of 106-145 μm and powder extrusion. The powder extrudate was subsequently equal channel angular pressed up to 8 passes in order to refine grain and Si particle. The microstructure of the gas atomized powders, powder extrudates and equal channel angular pressed samples were investigated using a scanning electron microscope and X-ray diffraction. The mechanical properties of the bulk sample were measured by compressive tests and a micro Victors hardness test. Equal channel angular pressing was found to be effective in matrix grain and Si particle refinement, which enhanced the strength and hardness of the Al-2OSi alloy without deteriorating ductility in the range of experimental strain of 30%.

The Effect of Pd addition on Mechanical Properties at High Temperature of Mg-4Al-2Sn Alloy (Mg-4Al-2Sn 합금의 고온 기계적 특성에 미치는 Pd첨가의 영향)

  • Yim, Si-On;Kang, Byoung-Soo;Cho, Dae-Hyun;Park, Ik-Min
    • Journal of Korea Foundry Society
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    • v.37 no.4
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    • pp.101-107
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    • 2017
  • This study investigated the effect of Pd on the microstructure, tensile and creep properties of Mg-4Al-2Sn (AT42) alloy at a high temperature for transportation-related industrial applications. AT42-xPd (x = 0, 1 and 2 wt. %) alloys were prepared using a permanent mould casting method. The microstructures of the as-cast alloys were characterized by the presence of the intermetallic phases Mg17Al12, Mg2Sn and Al4Pd. The addition of Pd was found to improve the tensile properties of AT42 at room and at elevated temperatures, and to increase the creep resistance at elevated temperatures. A small amount of Pd could markedly improve the tensile properties of AT42 by means of grain-refinement and the dispersion of secondary phase strengthening. Moreover, the thermally stable phase Al4Pd effectively improves the creep resistance of AT42 due to the strengthened grain boundaries and the suppressed formation of Mg17Al12.