• 제목/요약/키워드: Liquid Segregation

검색결과 79건 처리시간 0.028초

WC기 초경합금중 WC/WC界面의 구조와 입계편석 (Stucture and Intergranular Segregation of WC/WC Grain Boundaries in WC-Based Cemented Carbides)

  • 신순기
    • 한국재료학회지
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    • 제10권9호
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    • pp.612-618
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    • 2000
  • WC-Co와 WC-Co 초경합금중 WC/WC 입계의 구조와 입계 편석상태를 알아볼 목적으로 HRTEM과 EDS를 이용하여 연구하였다. 일부의 입계들은 액상에 의하여 분리된 상태로 관찰되었으나, 상당수는 원자적 상태의 연소계면이었다. 또 연속계면 중 WC-Co 합금에서는 Co 상이 편석되어 있었으며, WC-VC-Co 합금에서는 Co와 V이 동시에 편석되어 있음을 알 수 있었다. 그 편석의 폭은 약6nm이었다. 연속 계면 중 V의 편석은 소결 또는 열처리 시에 일어나는 입계 이동을 억제하는 데 효과적인 역할을 할 것으로 여겨졌다. 동시에 이것은 WC-Co 초경합금에서 VC 첨가에 의한 입성상 억제기구를 설명할 수 있는 것으로 사료되었다.

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High-Efficiency Inhibition of Gravity Segregation in Al-Bi Immiscible Alloys by Adding Lanthanum

  • Jia, Peng;Zhang, Jinyang;Geng, Haoran;Teng, Xinying;Zhao, Degang;Yang, Zhongxi;Wang, Yi;Hu, Song;Xiang, Jun;Hu, Xun
    • Metals and materials international
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    • 제24권6호
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    • pp.1262-1274
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    • 2018
  • The inhibition of gravity segregation has been a long-standing challenge in fabrication and applications of homogeneous immiscible alloys. Therefore, the effect of rare-earth La on the gravity segregation of Al-Bi immiscible alloys was investigated to understand the homogenization mechanism. The results showed that the addition of La can completely suppress the gravity segregation. This is attributed to the nucleation of Bi-rich liquid phase on the in-situ produced $LaBi_2$ phase and the change of the shape of $LaBi_2@Bi$ droplets. In addition, a novel strategy is developed to prepare the homogeneous immiscible alloys through the addition of rare-earth elements. This strategy not only is applicable to other immiscible alloys, but also is conducive to finding more elements to suppress the gravity segregation. This study provided a useful reference for the fabrication of the homogeneous immiscible alloys.

반용융 다이캐스팅 공정에 있어서 속도제어방법이 제품의 특성에 미치는 영향 (The Effect of Velocity Control Method on the Part Characteristic in Semi-Solid Die Casting)

  • 서판기;강충길;손영익
    • 대한기계학회논문집A
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    • 제26권10호
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    • pp.2034-2043
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    • 2002
  • The process design to produce a near net shape home-appliance compressor component using semi-solid die casting process is performed. In order to obtain a good component without defects such as liquid segregation and porosity, the relationship between pressure and time, and plunger tip displacement and injection velocity are proposed with repeated trial and error. The effect of the velocity variation in the process parameters on liquid segregation and extraction is investigated to produce the aluminum frame part(a kind of compressor part) with good mechanical properties. The mechanical characteristic of semi-solid die casting formed parts for AlSi7Mg0.65r(A357) and AlSi17Cu4Mg(A390) are investigated with a view to minimizing the occurrence of defects. To investigate of application possibility at industry field, A380 aluminum alloy with 8∼9% silicon contents used for the squeeze casting process. The obtained mechanical properties is compared with semi-solid die casting.

Fractional Melting에 의한 Si 정련에 관한 연구 (Refining of Silicon by Fractional Melting Process)

  • 김귀욱;윤우영
    • 한국주조공학회지
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    • 제17권6호
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    • pp.598-607
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    • 1997
  • Fractional melting process involves heating an alloy within its liquid-solid region simultaneously ejecting liquid from the solid-liquid mixture. The extent of the purification obtained is comparable to that obtained in multi-pass zone refining. The new fractional melting process in which centrifugal force was used for separating the liquid from the mixture has been developed and applied to the purification of the metallic grade. Refining ratio depends on partition ratio, cake wetness and diffusion in the solid, and it was controlled by various processing parameters such as rotating speed and heating rate. The new parameter called "refining partition coefficient" has been suggested to estimate the effects of processing variables on the refining ratio. Because major impurities in MG-silicon such as Fe, Al, Ni have a low segregation coefficient, good purification effect is expected. The results of refining MG-silicon(98%) showed that 3N-Si was obtained in refined solid of 50% of the original sample.

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알루미늄재료의 Rheo-forming을 위한 성형공정해석 (Process Analysis for Rheo-Forming of Aluminum Materials)

  • 서판기;정영진;정경원;강충길
    • 한국소성가공학회:학술대회논문집
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    • 한국소성가공학회 2001년도 춘계학술대회 논문집
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    • pp.124-128
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    • 2001
  • Two-dimensional solidification analysis during rheology forming process of semi-solid aluminum ahoy has been studied Two-phase fluid flow model to investigate the velocity field and temperature distribution is proposed. The unposed mathematical model is applied to the die shape of the two type. To calculate the velocities and temperature fields during rheology forming process, the each governing equation correspondent to the liquid and solid region are adapted. Theoretical model on the basis of the two-phase flow model is the mixture rule of solid and liquid phases. This approach is based on the liquid and solid viscosity.

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액상과 고상의 유동현상을 고려한 레오로지 성형공정의 표면결함예측을 위한 응고해석 (Solidification Analysis for Surface Defect Prediction of Rheology Forming Process Considering Flow Phenomena of Liquid and Solid Region)

  • 서판기;정영진;강충길
    • 대한기계학회논문집A
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    • 제26권10호
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    • pp.1971-1981
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    • 2002
  • Two-dimensional solidification analysis during rheology forming process of semi-solid aluminum alloy has been studied. Two-phase flow model to investigate the velocity field and temperature distribution is proposed. The proposed mathematical model is applied to the die shape of the two types. To calculate the velocities and temperature fields during rheology forming process, the each governing equations correspondent to the liquid and solid region are adapted. Therefore, each numerical model considering the solid and liquid coexisting region within the semi-solid material have been developed to predict the defects of rheology forming parts. The Arbitrary Boundary Maker And Cell(ABMAC) method is employed to solve the two-Phase flow model of the Navier-Stokes equation. Theoretical model basis of the two-phase flow model is the mixture rule of solid and liquid phases. This approach is based on using the liquid and solid viscosity. The Liquid viscosity is pure liquid state value, however solid viscosity is considered as a function of the shear rate, solid fraction and power law curves.

저고상율 소재의 유동 및 응고현상을 고려한 레올로지 성형공정해석 (Process Analysis for Rheology Forming Considering Flow and Solidification Phenomena in Lower Solid Fraction)

  • 정영진;조호상;강충길
    • 한국정밀공학회지
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    • 제18권9호
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    • pp.156-164
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    • 2001
  • Two-dimensional solidification analysis during rheology forming process of semi-solid aluminum alloy has been studied. Two-phase fluid flow model to investigate the velocity field and temperature distribution is proposed. The proposed mathematical model is applied to the die shape of the two types. To calculate the velocity and temperature fields during rheology forming process, the earth governing equation correspondent to the liquid and solid region are adapted. Therefore, each numerical models considering the solid and liquid region existing within the semi-solid material have been developed to predict the deflect of rheology forming gnarls. The Arbitrary Boundary Maker And Cell (ABMAC) method is employed to solve the two-phase flow model of the Navier-Stokes equation. Theoretical model on the basis of the two-phase flow model is the mixture rule of solid and liquid phases. This approach is based on the liquid and solid viscosity. The liquid viscosity is pure liquid state value, however solid viscosity is considered as a function of the shear rate, solid fraction and power law curves.

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Fe-Cu계 소결합금의 이상팽창에 관한 연구 (I) (A Study on Abnormal Expansion of Fe-Cu Sintered Alloy)

  • 송영준;김윤채
    • 한국분말재료학회지
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    • 제11권5호
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    • pp.383-390
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    • 2004
  • In order to investigate behavior of abnormal expansion of the iron-copper compacts, we compared the dilatometric curves of the compacts which mixed the copper powder to the iron powder with those of compacts which mixed the copper powder to the iron-copper alloy powder. The dilatometric curves were obtained below the sintering conditions, which heated up to 115$0^{\circ}C$ by a heating rate of 1$0^{\circ}C$/min, held for 60min at 115$0^{\circ}C$ and cooled down at a rate of 2$0^{\circ}C$/min to room temperature. The dilatometric curves of the compacts showed the different expansion behavior at temperatures above the copper melting point in spite of same chemical composition. All of the compacts of former case showed large expansion, but all of the compacts in latter case showed large contraction. The microstructures of sintered compacts also showed the different progress in alloying of the copper into the iron powder. Namely we could observe the segregation at alloy part of copper into iron powder in case of the sintered compacts, which mixed the copper powder to the iron powder, but could not observe the segregation in compacts which mixed the copper powder to the iron-copper alloy powder. But the penetration of liquid copper into the interstices between solid particles was occurred at both cases. Therefore, the showing of the different dimensional changes in the compacts in spite of same chemical composition is due to more the alloying of copper into iron powder than the penetration of liquid copper into the interstices between solid particles.

유동화제 첨가시기에 따른 콘크리트의 특성에 관한 실험적 연구 (A Study of the Characteristics of the High-flowable Concrete according to the change of charge-time of superplasticize)

  • 권춘안;전현규
    • 한국건축시공학회지
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    • 제3권1호
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    • pp.115-122
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    • 2003
  • In order to analyze liquidity change according to increasing the charge of superplasticizer, we inputted charges by dividing into six steps, 0% through 1.25%; at the same time, to observe liquidity change according to the change of charge-time, we carried out the experiment applying 30-minute intervals, i.e. at beginning of mixing, 30, 60 and 90 minutes. The results are below. 1) According to increasing the charge of superplasticizer, the liquidity of concrete was enhanced, however, when inputted 1.25%, a little segregation was occurred, which allowed us to make a conclusion that concrete performance would be deteriorated due to this segregation. 2) When we inputted 1.25% of superplsticizer, steady liquidity features were shown regardless of the charge-time of concrete, which allowed us to make a conclusion that this input would be the best for liquidity performance considering only liquidity features. 3) After analyzing the dynamical features of liquid concrete, the result showed that there was not significant effect on revelation of compressive strength. We concluded form this result that there was no influence on the stripping-time of a mold form. 4) When we charge superplasticizer in concrete more than 1%, we, in advance, should clearly judge the concrete performance required during constructing in site, as it were, the compressive strength or liquidity etc.; furthermore, we had better decide a charge and input-time of superplasticizer to meet the required performance.

Influence of Metallic Sodium on Repair Weldability for Type 316FR Stainless Steel

  • Chun, Eun-Joon;Lee, Su-Jin;Suh, Jeong;Lee, Ju-Seung;Kang, Namhyun;Saida, Kazuyoshi
    • Journal of Welding and Joining
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    • 제35권1호
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    • pp.79-88
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    • 2017
  • The effect of residual metallic sodium on the solidification cracking susceptibility of type 316FR stainless steel was investigated via transverse-Varestraint tests. And a solidification brittle temperature range (BTR) of type 316FR stainless steel was 37 K. However, the BTR expanded from 37 to 67 K, as the amount of metallic sodium at the specimen surface increased from 0 to $7.99mg/cm^2$. Microstructural observation of the weld metal suggested that metallic sodium existed in the weld metal, including in the cell boundaries, during welding solidification. Thermodynamic calculations suggested that sodium expanded the temperature range of solidliquid coexistence during welding solidification of the steel weld metal. Therefore, the increased solidification cracking susceptibility (i.e., expansion of the BTR) in the residual sodium environment was attributed to enhanced segregation of sodium during the welding solidification; this segregation, in turn, resulted in an expanded temperature range of solid-liquid coexistence.