• Title/Summary/Keyword: Equiaxed grain

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Microstructural Evolution during the Equal Channel Angular Pressing of Ti-6Al-4V Alloy (Ti-6AI-4V 합금의 ECAP 가공에 따른 미세조직의 변화)

  • 고영건;정원식;신동혁;이종수
    • Transactions of Materials Processing
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    • v.11 no.6
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    • pp.519-528
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    • 2002
  • The microstructural evolution during the equal channel angular pressing of Ti-6Al-4V alloy was investigated using the transmission electron microscopy (TEM). ECA pressing was carried out isothermally with route C at $600^{\circ}C$ for two types of initial microstructure, i.e., equiaxed and Widmanstatten microstructures. At an initial stage of ECA pressing, the equiaxed microstructure showed more uniform flow than the Widmanstatten microstructure. However, both microstructures were significantly refined revealing nearly equiaxed grains of 0.3$mu extrm{m}$ in diameter with high angle grain boundaries after 4 passes of ECA pressing. These ultrafine gains were found to be stable with little grain growth, when annealed up to $600^{\circ}C$ for 1hr.

Effects of Grain Morphology on Plastic Flow of Ultrafine Grained OFHC Cu (초미세립 Cu의 소성변형거동에 미치는 결정립 형상의 영향)

  • Park, L.J.;Kim, H.W.;Lee, C.S.;Park, K.T.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2009.05a
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    • pp.263-265
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    • 2009
  • In this study, ultrafine grained (UFG) oxygen free high conductivity copper (OFHC Cu) having two different grain morphologies, one the severely elongated and the other the equiaxed, was prepared by equal channel angular pressing (ECAP) with routes A and $B_c$, respectively. The results of quasi-static tensile tests at $10^{-1}\;s^{-1}$ and $1\;s^{-1}$ and dynamic compression tests at $10^3\;s^{-1}$ order revealed that the equiaxed UFG Cu exhibited higher strength and less ductility compared to the elongated one. The difference of the plastic flow characteristics between the two were rationalized by considering their dislocation mean free length based on the orientation relationship between the possible slip planes and the loading direction.

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Analysis of Toughening Mechanism of Ceramic Composites by Acoustic Emission (AE(Acoustic Emission)에 의한 세라믹 복합재료의 고인성화 기구 분석)

  • 장병국
    • Journal of the Korean Ceramic Society
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    • v.34 no.11
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    • pp.1129-1138
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    • 1997
  • Al2O3/20 vol%YAG composite containing equiaxed grains and Al2O3/20 vol%LaAl11O18 composite containing elongated grains were fabricated using Al2O3-Y2O3 composition and Al2O3-La2O3 composition, respectively, by hot-pressing. In order to investigate the influence of microstructural control of second phase on toughening effect of toughened ceramic composites, AE (acoustic emission) measurements have been coupled with fracture toughness experiments(SENB and SEPB method). A separation of the fracture toughness and analysis of toughening mechanism was possible using the AE technique. The fracture toughness of hot-pressed materials was estimated to be 3.2 MPam0.5 for monolithic alumina, 4.7 MPam0.5 for Al2O3/20 vol%YAG composite and 6.2 MPam0.5 for Al2O3/20 vol%LaAl11O18 composite. In monolithic Al2O3, toughening does not occur as a result of either microcracking or grain bridging, whereas, composites exhibit toughening effects by both microcracking in the frontal zone and gain bridging in the wake zone, resulting in an improvement of fracture toughness as compared with monolithic Al2O3. The fracture toughness of Al2O3/20 vol%LaAl11O18 composite is higher than that of Al2O3/20 vol%YAG composite. It may be attributed to the elongated microstructure of Al2O3/20 vol%LaAl11O18 composite, resulting relatively greater bridging effect.

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Microstructural Evolution of Thick Tungsten Deposit Manufactured by Atmospheric Plasma Spray Forming Route (Plasma Spray Forming 공정에 의해 제조된 텅스텐 성형체의 미세조직 형성 거동)

  • Lim, Joo-Hyun;Baik, Kyeong-Ho
    • Journal of Powder Materials
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    • v.16 no.6
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    • pp.403-409
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    • 2009
  • Plasma spray forming is recently explored as a near-net-shape fabrication route for ultra-high temperature metals and ceramics. In this study, monolithic tungsten has been produced using an atmospheric plasma spray forming and subsequent high temperature sintering. The spray-formed tungsten preform from different processing parameters has been evaluated in terms of metallurgical aspects, such as density, oxygen content and hardness. A well-defined lamellae structure was formed in the as-sprayed deposit by spreading of completely molten droplets, with incorporating small amounts of unmelted/partially-melted particles. Plasma sprayed tungsten deposit had 84-87% theoretical density and 0.2-0.3 wt.% oxygen content. Subsequent sintering at 2500$^{\circ}C$ promoted the formation of equiaxed grain structure and the production of dense preform up to 98% theoretical density.

The analysis of columnar to equiaxed dendritic transition during alloy solidification (합금응고시 주상정으로부터 등축정 수지상으로의 천이에 관한 해석)

  • 김신우
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.8 no.1
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    • pp.187-192
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    • 1998
  • Generally the solidified microstructures of materials consist of the columnar and equiaxed dendritic regions, and many theoretical studies about columnar-to-equiaxed transition have been done because that is closely related to the mechanical and physical properties of products. In this study, the modified equation based on the Hunt's analytical columnar-to-equiaxed transition condition which was derived from heterogeneous nucleation and grain growth in front of the columnar dendrite tip under directional solidification, was obtained applying the growth-velocity-dependent distribution coefficient and liquidus slope to Hunt's. The effects of the number of nucleation sites, nucleation temperature, alloy composition, growth velocity and liquid temperature gradient on the transition for Al-Cu alloys have been investigated.

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Effect of Heat Treatment Conditions on the Microstructure and Mechanical Properties of Asymmetrically Cold Rolled OFC Sheet (비대칭 냉간압연된 무산소동 판재의 열처리 조건이 미세조직과 기계적 성질에 미치는 영향)

  • Kim, S.T.;Kwon, S.C.;Kim, D.V.;Lee, J.K.;Seo, S.J.;Yoon, T.S.;Jeong, H.T.
    • Transactions of Materials Processing
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    • v.29 no.1
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    • pp.5-10
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    • 2020
  • Heat treatment conditions of 88.5% asymmetrically cold rolled oxygen free copper (OFC) sheets have been studied to obtain an equiaxed fine microstructure with a grain size of less than 10 ㎛. The commercial OFC sheets with the thickness of 10 mm were asymmetrically cold rolled by using equal speed asymmetric rolling (ESAR) processes and total rolling reduction. The thickness of the rolled sheets were 88.5% and 1.15 mm, respectively. An equiaxed fine microstructure of OFC sheets with a grain size of 6.0 ㎛ were obtained when the asymmetrically cold rolled OFC sheets were heat treated at 180℃ for 40 minutes. The tensile strength of the asymmetrically cold rolled specimen increased from 217.6 MPa to 396.1 MPa, while the elongation of the specimen asymmetrically cold rolled and heat treated increased from 29.0% to 66.9% along with an 8% increase of the tensile strength.

Effect of Large $\alpha$-Silicon Carbide Seed Grains on Microstructure and Fracture Toughness of Pressureless-Sintered $\alpha$-Silicon Carbide

  • Young-Wook Kim;Kyeong Sik Cho;June-Gunn Lee
    • The Korean Journal of Ceramics
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    • v.2 no.1
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    • pp.39-42
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    • 1996
  • ${\alpha}-SiC$ powder with or without the addition of 0.1 wt% of large ${\alpha}-SiC$ partices(seeds) was pressureless-sintered at $1950^{\circ}C$ for 0.5, 2, and 4 h using $Y_3Al_5 O_{12}$ (yttrium aluminum garnet, YAG) as a sintering aid. The materials without seeds had an equiaxed grain struture. In contrast, the materials with seeds sintered for 2 and 4 h had a duplex microstructure with large elongated grains and amall equiaxed grains. Addition of large ${\alpha}-SiC$ seeds into ${\alpha}-SiC$ accelerated the grain growth of some ${\alpha}-SiC$ grains during sintering and resulted in the increased fracture toughness of the sintered materials. The fracture toughnesses of materials with or without seeds sintered for 4 h were 6.6 and $5.2 MPa \;m^{12}$, respectively.

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A Study of the Development of a High-Strength Al-Zn Based Alloy for Die Casting I (고강도 Al-Zn기 다이캐스팅 합금개발에 관한 연구 I)

  • Shin, Sang-Soo;Yeom, Gil-Yong;Kim, Eok-Soo;Lim, Kyung-Mook
    • Korean Journal of Metals and Materials
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    • v.48 no.10
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    • pp.936-941
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    • 2010
  • Al-Zn based alloys are the most common types of wrought Al alloys. Although Al-Zn alloys have high strength, they cannot be applied to a conventional casting process. In this study, Al-Zn-based alloys applicable to a die casting process were developed successfully. The developed Al-45 wt% Zn-based alloys showed a fine equiaxed grain structure and high strength. A fine equiaxed grain having an average size of $25{\mu}m$ was obtained by the die casting process. The UTS and elongation of the new alloy are 475 MPa and ~3.5%, respectively. In addition, we elucidate the effect of a Zn addition on variations in different mechanical properties and the microstructure characteristics of (Al96.3-xZnxCu3Si0.4Fe0.3) x=20, 30, 40, and 45 wt% alloys fabricated by a die casting process.

High Temperature Deformation Behavior of Nano Grain W Produced by SPD-PM Process

  • Oda, Eiji;Ohtaki, Takao;Kuroda, Akio;Fujiwara, Hiroshi;Ameyama, Kei;Yoshida, Kayo
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • 2006.09a
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    • pp.126-127
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    • 2006
  • In this study, nano grain W is fabricated by Severe Plastic Deformation-Powder Metallurgy (SPD-PM) process. W powder and W-Re powder mixtures are processed by SPD-PM process, a Mechanical Milling (MM) process. As results, a nano grain structure, whose grain size is approximately 20nm, is obtained in W powder after MM for 360ks. A nano grain W compact, whose grain size 630nm, has excellent deformability above 1273K. A nano grain W-10Re compact is composed of equiaxed grain, a grain growth is restrained and has low dislocation density after the large deformation; therefore it is considered that W-Re compact shows superplasticity.

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Study on Grain Refinement of Al-7Si Based Alloys with TiC (Al-7Si 합급의 결정립 미세화에 미치는 TiC 첨가의 영향)

  • Han, Yun-Sung;Choi, Chang-Ock
    • Journal of Korea Foundry Society
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    • v.23 no.2
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    • pp.63-68
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    • 2003
  • Al-Ti-C grain refiner form a relatively new alternative to the existing class of Al-Ti-B type grain refiners for achieving fine equiaxed structures in aluminum alloys during casting and solidification. The present study was carried out to investigate the influence of Al-Ti-C master alloys on the grain structure of Al-7Si alloys. The present study also investigates the relationship between grain refining efficiency and concentrations of Fe and Si in hypo-eutectic Al-Si alloys using Al-3Ti-0.13C master alloys. It is found that several parameters affect significantly the grain refining performance in silumin alloys. The present study reports the influence of various parameters such as alloy content, master alloy addition level, melt holding time and superheat on the grain refining efficiency in Al-7Si alloys.