• 제목/요약/키워드: Solidification structure

검색결과 177건 처리시간 0.026초

오스테나이트계 스테인리스강 용접부의 금속학적 현상에 관한 연구(2) - STS 304 용접부 조직특성 및 고온균열 감수성에 미치는 질소의 영향 - (A Study of Weld Fusion Zone Phenomena in Austenitic Stainless Steels(2) - Effects of Nitrogen on Microstructural Evolution and Hot Cracking Susceptibility GTA Welds in STS 304 -)

  • 이종섭;김숙환
    • Journal of Welding and Joining
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    • 제18권1호
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    • pp.59-69
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    • 2000
  • The purpose of the present study was to investigate weld metallurgical phenomena such as primary solidification mode, microstructural evolution and hot cracking susceptibility in nitrogen-bearing austenitic stainless steel GTA welds. Eight experimental heats varying nitrogen content from 0.007 to 0.23 wt.% were used in this study. Autogenous GTA welding was performed on weld coupons and the primary solidification mode and their microstructural characteristics were investigated from the fusion welds. Varestraint test was employed to evaluate the solidification cracking susceptibility of the heats and TCL(Total Crack Length) was used as cracking susceptibility index. The solidification mode shifted from primary ferrite to primary austenite with an increase in nitrogen content. Retained delta ferrite exhibited a variety of morphology as nitrogen content varied. The weld fusion zone exhibited duplex structure(austenite+ferrite) at nitrogen contents less than 0.10 wt.% but fully austenitic structure at nitrogen contents more than 0.20 wt.%. The weld fusion zone in alloys with about 0.15 wt.% nitrogen experienced primary austenite + primary ferrite solidification (mode AF) and contained delta ferrite less than 1% at room temperature. Regarding to solidification cracking susceptibility, the welds with fully austenitic structure exhibited high cracking susceptibility while those with duplex structure low susceptibility. The cracking susceptibility increased slowly with an increase in nitrogen content up to 0.20 wt.% but sharply as nitrogen content exceeded 0.20 wt.%, which was attributed to solidification mode shift fro primary ferrite to primary austenite single phase solidification.

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PFC법에 있어서의 Al-Cu 다결정리본의 응고특성 (Solidification Characteristics of Al-Cu Polycrystalline Ribbons in Planar Flow Casting)

  • 이경구;이상목;홍준표
    • 한국주조공학회지
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    • 제15권4호
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    • pp.408-415
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    • 1995
  • Polycrystalline Al-Cu ribbons were produced by planar flow casting(PFC). Solidification behavior and microstructual changes of the ribbons have been investigated as a function of ribbon thickness and processing parameters. The solidification front velocity, V varies within the ribbon, decreasing with increasing the distance, S from the wheel-contact surface, as $V=17.6S^{-1}$. In Al-4.5wt%Cu alloy, rapid decrease in solidification velocity toward the free surface causes a change in solidification morphology from planar to cellular, and finally, to dendritic. The length and inclination of columnar grains solidified with planar front were related to the wheel velocity. The transition from particulate degenerate eutectic structure to regular lamellar eutectic structure was observed to be caused by a difference of the relative growth velocites of ${\alpha}-Al$ and ${\theta}$ during solidification in the Al-Cu eutectic alloy.

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Mg-Zn-Y 합금에서 준결정 및 준결정 유사상 (Quasicrystals And Related Approximant Phases in Mg-Zn-Y)

  • 박은수;옥재범;김원태;김도향
    • Applied Microscopy
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    • 제32권1호
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    • pp.31-37
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    • 2002
  • [ $Mg_{68}Zn_{28}Y_4$ ] 합금의 응고 조직은 primary solidification phase, primary solidification phase로부터 성장된 ${\alpha}-Mg$ dendrite, 그리고 응고 말기에 형성된 eutectic structure의 세 가지형태 조직으로 구성되어져 있다. Primary solidification phase에는 매우 큰 정도의 phason strain이 존재하고 있으며, $a=27.2{\AA}\;and\;{\alpha}=63.43^{\circ}$의 격자상수를 갖는 1/1 rhombohedral approximant가 존재한다. 이와 같은 rhombohedral approximant의 구조는 six dimensional face centered hyper-cubic lattice에 phason strain을 도입함에 의해 얻어질 수 있다. Decagonal phase는 icosahedral phase로부터 방위 관계를 가지며 형성되며, $Mg_4Zn_7$는 decagonal phase로부터 방위관계를 가지며 성장한다. 이는 세 상간에 구조적 유사성이 존재하고 있음을 의미하며, 응고시 용질원자의 분배에 의해 이들 세 상이 순서대로 형성되어진다.

냉각속도에 따른 Al-2.7wt%Li 합금계의 응고조직 (Solidification Structure of Al-2.7wt%Li Alloys by Cooling Rate Controlled)

  • 심동섭;최정철;조형호;권해욱
    • 한국주조공학회지
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    • 제11권5호
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    • pp.398-405
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    • 1991
  • Al-Li alloy has a high strength with low density. Practically this alloy should use by the material which made from the rapid solidification. Therefore we examine the solidification structures of alloy with cooling rate. According to cooling rate increased, grain size and secondary dendrite arm spacing were smaller. Also grain size was further smaller by Zr added. To obtain more fine solidification structure, rapid solidification by single roll melt spinning was performed. According to higher wheel speed, cooling rate increased and cell size was smaller. Because of locally different cooling rate, different cell size was obtained in same specimen. More than cooling rate $10^6^{\circ}C$ /sec, zone A(insensible zone to corrosion)was obtained.

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동결건조 공정에서 동결제의 응고조건이 기공특성에 미치는 영향 (Effect of Solidification Condition of Sublimable Vehicles on the Pore Characteristics in Freeze Drying Process)

  • 석명진;김지순;오승탁
    • 한국분말재료학회지
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    • 제21권5호
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    • pp.366-370
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    • 2014
  • The present study demonstrates the effect of solidification condition on the pore structure in freeze drying process using the slurries of CuO/sublimable vehicles. Camphene and Camphor-45 wt% naphthalene based slurries with 14 vol% CuO powder were frozen into a mold at $-25^{\circ}C$, followed by sublimation at room temperature. The green bodies were hydrogen-reduced and sintered at $500^{\circ}C$ for 1 h. The porous Cu specimen, frozen the CuO/camphene slurry into the heated mold of the upper part, showed large pores with unidirectional pore channels and small pores in their internal wall. Also, it was observed that the size of large pores was decreasing near the bottom part of specimen. The change of pore structure depending on the freezing condition was explained by the nucleation behavior of camphene crystals and rearrangement of solid powders during solidification. In case of porous Cu prepared from CuO/Camphor-naphthalene system, the pore structure exhibited plate shape as a replica of the original structure of crystallized vehicles with hypereutectic composition.

Pb-20wt%Cu 합금의 일방향 응고시 Cu 수지상 결정성장에 대한 시험편의 회전효과 (The Effects of Sample Rotation on Cu-Dendritic Growth During the Directional Solidification of Pb-20wt%Cu Alloy)

  • 김신우
    • 한국주조공학회지
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    • 제14권6호
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    • pp.508-513
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    • 1994
  • For Pb-20wt%Cu alloys, severe macrosegregation due to density difference of the resulting phases in normal directional solidification has been minimized and a uniformly aligned dendritic structure has been produced by axially rotating the sample of 5mm diameter in conjunction with horizontal directional solidification. Under the constant growth velocity of $20{\mu}m/sec$, increasing the rotation rate from 0.18 to 12rpm results in a transition from an aligned columnar to an equiaxed Cu-dendritic structure. With a constant rotation rate of 0.18rpm, increasing the growth velocity from 10 to $50{\mu}m/sec$ also has promoted a transition from columnar to equiaxed structure.

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급속 응고한 Al-Pb 편정 합금의 조직과 성질;I. 급속 응고 조직 특성 (Structure and Properties of Rapidly-Solidified Al-Pb Monotectic Alloys.;I. Characteristics of Rapidly-Solidified Microstructure)

  • 김명호;배차헌;이호인
    • 한국주조공학회지
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    • 제9권1호
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    • pp.73-79
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    • 1989
  • Microstructural characteristics of Al-3.63wt.%Pb hyper-monotectic alloy rapidly-solidified by melt spinning were examined. Possibility of forming a planar liquid -solid interface during rapid solidification of this alloy was also considered with a morphological stability theory, and a mechanism of forming banded structure observed at the bottom parts of melt-spinned specimens was considered as well. Application of the absolute stability criterion predicts the liquid-solid interface of the primary aluminium phase to be able to maintain a planar interface during the early stage of rapid solidification. Formation of banded structure was supposed to be resulted from the release of latent heat during solidification, which affect the stability of a planar liquid-solid interface.

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일방향응고시킨 Al-Fe-Ni 합금의 조직과 기계적 성질 (The structures and mechanical properties of unidirectionally solidified Al-Fe-Ni alloy)

  • 김여원;신민교
    • Journal of Advanced Marine Engineering and Technology
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    • 제7권1호
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    • pp.79-90
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    • 1983
  • The examination for the changes of structures and mechanical properties in directionally solidified Al-Fe-Ni alloys containing the small amount of Fe and Ni was carried out by the varying the composition and solidification rate R of alloy, provided that the temperature gradient was 80 .deg.C/cm. The result were obtained as follows. A) In proportion to the increase of the solidification rate (R), the crystallized phase of this alloy was changed from the Ribbon-type structure to the Rod-type structure. B) The strength was rapidly increased in the changing process of composite shape from the Ribbon-type to the Rod-type with the solidification rate (R) increasing. C) The fiber stress (${\sigma}^f$) and Young's modulus ($E_f$) calculated for the Rod-type structure were 220 kg/$mm^2$ and 11, 800 kg/$mm^2$ respectively, which were in good accord with the rule of Mixtures.

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고(<24%)Mn 플럭스코어드와이어를 사용한 다층 용접 시 초층 응고조직의 결정면방위에 따른 미세조직과 경도 (Microstructure and Hardness of 1st layer with Crystallographic Orientation of Solidification Structure in Multipass Weld using High Mn-Ni Flux Cored Wire)

  • 한일욱;엄정복;윤중길;이봉근;강정윤
    • Journal of Welding and Joining
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    • 제34권5호
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    • pp.77-82
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    • 2016
  • In this study, Microstructure and hardness of 1st layer with crystallographic orientation were investigated about solidification structure in multipass weld using high Mn-Ni flux cored wire. Microstructure of solidification consisted of austenite matrix and a little ${\varepsilon}-phase$ in grain boundaries. Orientation of grains was usually (001), (101), (111). According to crystallographic orientation, morphology of primary dendrite was different. The depletion of Fe and the segregation of Mn, C, Ni, Si, Cu, Cr, O were found along the grain boundaries. The area of segregation was wide with an order of (001), (101), (111) grains. And hardness of grains with crystallographic orientation increased with an order of (001), (101), (111) grains because of the segregation along dendrite boundary.

Development of High Strength Mg-Zn-Gd Alloys by Rapid Solidification Processing

  • Kim, Min-Chul;Yamasaki, Michiaki;Kawamura, Yoshihito
    • 한국분말야금학회:학술대회논문집
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    • 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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    • pp.1048-1049
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    • 2006
  • Rapidly solidified ribbon-consolidation processing was applied for preparation of high strength bulk Mg-Zn-Gd alloys. Mg alloys have been used in automotive and aerospace industries. Rapid solidification (RS) process is suitable for the development of high strength Mg alloys, because the process realizes grain-refinement, increase in homogeneity, and so on. Recently, several nanocrystalline Mg-Zn-Y alloys with high specific tensile strength and large elongation have been developed by rapidly solidified powder metallurgy (RS P/M) process. Mg-Zn-Y RS P/M alloys are characterized by long period ordered (LPO) structure and sub-micron fine grains. The both additions of rare earth elements and zinc remarkably improved the mechanical properties of RS Mg alloys. Mg-Zn-Gd alloy also forms LPO structure in -Mg matrix coherently, therefore, it is expected that the RS Mg-Zn-Gd alloys have excellent mechanical properties. In this study, we have developed high strength RS Mg-Zn-Gd alloys with LPO structure and nanometer-scale precipitates by RS ribbon-consolidation processing. $Mg_{97}Zn_1Gd_2$ and $Mg_{95.5}Zn_{1.5}Gd_3$ and $Mg_{94}Zn_2Gd_4$ bulk alloys exhibited high tensile yield strength (470 MPa and 525 MPa and 566 MPa) and large elongation (5.5% and 2.8% and 2.4%).

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