• Title, Summary, Keyword: microstructure

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Effects of Sintering Additives on the Microstructure Development in Silicon Oxynitride Ceramics

  • Kim, Joosun;Chen, I-Wei
    • The Korean Journal of Ceramics
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    • v.6 no.3
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    • pp.224-228
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    • 2000
  • Using a small amount of additives and amorphous Si₂N₂O powders, O-SiAlON ceramics have been hot-pressed and its microstructure and mechanical properties were investigated. Scandium oxide was demonstrated to be an effective densification additive for O-SiAlON. Amorphous Si₂N₂O was densified at relatively low temperatures and a microstructure with acicular grains was developed. Fine grains found in materials obtained from amorphous powders suggest that nucleation and crystallization of O-SiAlOH is relatively easy compared with the Si₃N₄-SiO₂reaction.

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Separation of Blood Cell and Blood Plasma Using Microstructure (미세구조물을 이용한 혈구/혈장 분리)

  • Kim, Duckiong;Seo, Jee-Hoon;Son, Sang Uk;Kim, Jae Yun;Yoon, Eui Soo
    • 유체기계공업학회:학술대회논문집
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    • pp.743-747
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    • 2004
  • In this study, micro blood separators capable of separating blood cell and blood plasma using microstructure are fabricated and their feasibility and separation performance are evaluated. Test results show the possibility of separating blood cell and blood plasma using microstructure. To improve separation performance and anti-clogging characteristic, technical points of tested micro blood separators are discussed and improved designs are presented.

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Interfacial Electrical/Dielectric Characterization in Low Temperature Polycrystalline Si

  • Hwang, Jin-Ha
    • Journal of the Microelectronics and Packaging Society
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    • v.12 no.1
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    • pp.77-85
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    • 2005
  • Impedance spectroscopy was applied to low temperature polycrystalline Si in order to investigate the electrical/dielectric information in polycrystalline Si. By combined microstructure and impedance spectroscopy works, it was shown that the electrical information is sensitive to the corresponding microstructure, i.e., the grain size and distribution, judged from the capacitance vs. grain size relationship. At $360 mJ/cm^2$, the maximum in capacitance and the minimum in resistance correspond to the largest grain sizes of unimodal distribution in polycrystalline Si. The electrical/dielectric characterization is compared with Raman spectroscopic characterizations in terms of microstructure.

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A Manufacturing Process analysis of Large Exhaust Valve Spindle considering Microstructure Evolution (미세조직 변화를 고려한 대형 배기밸브 스핀들 제조공정 해석)

  • Jeong Ho-Seung;Cho Jong-Rae;Park Hee-Cheon
    • Journal of the Korean Society of Marine Engineering
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    • v.29 no.8
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    • pp.938-945
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    • 2005
  • The microstructure evolution in hot forging process is composed of dynamic recrystallization during deformation as well as grain growth during dwell time. Therefore, the control of forging parameters such as strain, strain rate. temperature and holding time is important because the microstructure change in hot working affects the mechanical properties. Modeling equations are developed to represent the flow curve. grain size. recrystallized volume fraction and grain growth phenomena by various tests. The developed modeling equations were combined with thermo-viscoplastic finite element modeling to predict the microstructure change evolution during hot forging process. The large exhaust valve spindle (head diameter of 512mm) was simulated by closed die forging with hydraulic press and cooled in air after forging. The preform was heated to each 1080 and 1150$^{\circ}C$. Numerical calculation was performed by DEFORM-2D. a commercial finite element code. Heat transfer can be coupled with the deformation analysis in a non-isothermal deformation analysis. In order to obtain the fine and homogeneous microstructure and good mechanical properties in forging. the FEM would become a useful tool in the simulation of the microstructure development. In forging, appropriate temperature, strain and strain rate and rapid cooling are required to obtain the fine grain microstructure The optimal forging temperature and effective strain range of Nimonic 80A for large exhaust valve spindle are about 1080$\∼$l120$^{\circ}C$ and 150$\∼$200$\%$.

Microstructure Control of Cu base amorphous Alloys by Extrusion (압출공정을 이용한 Cu 계 비정질 합금의 미세조직제어)

  • Kim, Taek-Soo;Lee, Jin-Kyu
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • pp.236-240
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    • 2007
  • In order to control the microstructure of amorphous/crystalline composites, gas atomized $Cu_{54}Ni_{6}Zr_{22}Ti_{18}$ metallic glass powders wrapped in a crystalline brass were extruded repeatedly. The size of microstructure in the resultant composites was varied depending on the pass of extrusion as well as on the area reduction ratio. The microstructure could be estimated using an equation of $r_n=r_{n-1}/R^{1/2}$, where R is reduction ratio and $r_n$ is the resultant radius of the extruded bar after n pass. Theory of microstructural refinement as well as the relationship between the resultant microstructures and mechanical properties was discussed.

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FE Analysis of Hot Forging Process and Microstructure Prediction for Lower Arm Connector (로워암 커넥터 열간단조 공정의 유한요소해석 및 미세조직 예측)

  • Park, Jong-Jin;Hwang, Han-Sub;Lee, Sang-Joo;Hong, Seung-Chan;Lim, Sung-Hwan;Lee, Kyung-Sub;Lee, Kyung-Jong
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.27 no.7
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    • pp.1243-1250
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    • 2003
  • In the present study, hot forging process for a lower arm connector of an automobile was investigated. An FEM code, DEFORM-3D, was used to analyze the process and the process parameters, such as temperature, strain and strain rate, were obtained. The microstructure of the connector was predicted by applying the Sellars and Yada microstructure evolution models to the process parameters. The method of microstructure prediction used in the present study seems to be effective for the quality assurance of a forged automotive product.

The Effect of Globule size on the Mechanical Properties in Semi-Solid Forming of Aluminium Alloys (알루미늄소재의 만용융성형 공정에서 구상화의 크기가 기계적 성질에 미치는 영향)

  • 박상문;강충길
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • pp.21-24
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    • 2002
  • One of the factors influences on microstructure of semi-solid product is forging pressure. Generally, the more forging pressure makes the more fine microstructure in semi-solid compression test. The microstructure and mechanical properties were investigated according to the forging pressure. The applied pressure is 110MPa, 140MPa and 170MPa, respectively. Heat treatment conditions also influence to the microstructure and mechanical properties of semi-solid product. T6 heat treatment was performed and the evaluation of microstructure and mechanical properties was investigated according to the aging time in T6 heat treatment.

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Reheating Process and FEM Analysis of Inductive Heating (재가열 공정과 유도 가열의 FEM 해석)

  • 손영익
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • pp.195-198
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    • 1999
  • For the thixoforming process beside an existing solidus-liquidus interval, the reheating conditions to obtain the globular microstructure are very important. It relies on the control of globular microstructure of semi-solid alloys that contain non-dendritic particles. To obtain the globular microstructure in cross section of billet, the optimal design of the induction coil is necessary. Therefore, in this paper the optimal coil design to minimize electromagnetic end effect will be proposed. The results of coil design were also applied to the reheating process to obtain a fine globular microstructure. Finally, reheating data base of aluminum alloys for thixoforming and FEM model for induction heating based on the optimal coil design have been proposed.

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Role of Interface on the Development of Microstructure in Carbon-Carbon Composites

  • Dhakate, S.R.;Mathur, R.B.;Dhami, T.L.;Chauhan, S.K.
    • Carbon letters
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    • v.3 no.4
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    • pp.192-197
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    • 2002
  • Microstructure plays an important role in controlling the fracture behaviour of carbon-carbon composites and hence their mechanical properties. In the present study effort was made to understand how the different interfaces (fiber/matrix interactions) influence the development of microstructure of the matrix as well as that of carbon fibers as the heat treatment temperature of the carbon-carbon composites is raised. Three different grades of PAN based carbon fibres were selected to offer different surface characteristics. It is observed that in case of high-strength carbon fiber based carbon-carbon composites, not only the matrix microstructure is different but the texture of carbon fiber changes from isotropic to anisotropic after HTT to $2600^{\circ}C$. However, in case of intermediate and high modulus carbon fiber based carbon-carbon composites, the carbon fiber texture remains nearly isotropic at $2600^{\circ}C$ because of relatively weak fiber-matrix interactions.

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EHect of Carbide Addition on Riping and Wear Properties of HSS (탄화물의 첨가가 고속도강의 HIP과 마모에 미치는 영향)

  • 김득중
    • Journal of Korean Powder Metallurgy Institute
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    • v.3 no.3
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    • pp.188-195
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    • 1996
  • In recent times the potential application of the high speed steel produced by HIP process for wear resistant and cutting materials are increasing. In this work the microstructure of Anval 30 produced by HIP process was investigated and the effect of WC, TiC addition on microstructure formation and wear properties were studied. After HIP process at 1150 $^{\circ}C$, the original feature of spherical raw powders was not removed and consequently, nonuniform microstructure was formed. However the WC added by simple powder mixture incereased the sinterbility of high speed steel and uniform microstructure formed. The wear characteristics of Anval 30 with carbide addition were tested at RT and $600^{\circ}C$. The uniform microstructure played an more important role in wear resistance as compared with the hardness.

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