• Title/Summary/Keyword: Microstructure

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Effect of Heat Input on the Mechanical Properties of SA508 class 3 Steel Weldments with Submerged Arc Welding (SA508 class 3 서브머지드 아크용접부의 기계적 성질에 미치는 입열량의 영향)

  • Seo Yun-seok;Koh Jin-Hyun;Kim Nam-Hoon;Oh Se-Yong;Choo Kee-Nam
    • Journal of Welding and Joining
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    • v.22 no.5
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    • pp.38-45
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    • 2004
  • The present study is to investigate the effect of heat input on the microstructure, tensile properties and toughness of single-pass submerged arc bead-in-groove welds produced on SA508 class 3 steels. The heat input was varied in the range of 1.6, 3.2 and 5.0 kJ/mm. The toughness of weld metals was evaluated by using subsize Charpy V-notch specimens in the temperature range of -19$0^{\circ}C$ to 2$0^{\circ}C$. The weld microstructure and fractography were observed by optical and scanning electron microscopies, respectively. With increasing heat inputs, tensile strength and hardness of weld metals were decreased while elongation was increased. The poor notch toughness at 1.6 kJ/mm was attributed to the formation of ferrite with aligned second phase and banitic microstructure with high yield strength while that at 5.0 kJ/mm was due to the presence of grain boundary and polygonal ferrites. The microstructure of the intermediate energy input welds consisted of a high proportion of acicular ferrite with limited polygonal ferrites, which provide improved notch toughness.

Effect of Nitrogen Volume in Ar-N2 Shielding Gas on Microstructure and Hardness of GTA Welded Pure Ti (순 Ti GTA 용접부의 미세조직과 경도에 미치는 Ar-N2 보호가스 중 질소량의 영향)

  • An, Hyun-Jun;Jeon, Ae-Jeong;Hong, Jae-Keun;Jeong, Bo-Young;Lee, Jong-Sub;Kang, Chung-Yun
    • Journal of Welding and Joining
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    • v.30 no.2
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    • pp.70-75
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    • 2012
  • In this study, effect of nitrogen volume in the shielding gas of Ar-$N_2$ mixing gas on the bead shape, hardness and microstructure of GTA welds of 3mm thick Commercial Pure Ti was investigated. As the nitrogen volume increased, the welding current for full penetration was reduced and hardness in the fusion zone significantly increased compared with that of the base metal, but there is no difference in the hardness of HAZ. Microstructure in the fusion zone with pure Ar gas changed from equiaxed alpha of the base metal to serrated alpha. On the other hand, microstructure using Ar-$N_2$ mixing gas changed to acicular alpha. With the increasing of nitrogen content, the amount of acicular alpha increased and the size of that was fine.

Residual Stress on Concentric Laminated Fibrous Al2O3-ZrO2 Composites on Prolonged High Temperature Exposure

  • Sarkar, Swapan Kumar;Lee, Byong Taek
    • Korean Journal of Materials Research
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    • v.23 no.9
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    • pp.531-536
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    • 2013
  • This paper investigates the effect of prolonged high temperature exposure on concentric laminated $Al_2O_3-ZrO_2$ composites. An ultrafine scale microstructure with a cellular 7 layer concentric lamination with unidirectional alignment was fabricated by a multi-pass extrusion method. Each laminate in the microstructure was $2-3{\mu}m$ thick. An alternate lamina was composed of 75%$Al_2O_3$-(25%m-$ZrO_2$) and t-$ZrO_2$ ceramics. The composite was sintered at $1500^{\circ}C$ and subjected to $1450^{\circ}C$ temperature for 24 hours to 72 hours. We investigated the effect of long time high temperature exposure on the generation of residual stress and grain growth and their effect on the overall stability of the composites. The residual stress development and its subsequent effect on the microstructure with the edge cracking behavior mechanism were investigated. The residual stress in the concentric laminated microstructure causes extensive micro cracks in the t-$ZrO_2$ layer, despite the very thin laminate thickness. The material properties like Vickers hardness and fracture toughness were measured and evaluated along with the microstructure of the composites with prolonged high temperature exposure.

Microstructure and Varistor Properties of ZPCCAE Ceramics with Erbium

  • Nahm, Choon-Woo;Heo, Jae-Seok;Lee, Geun-Hyung
    • Transactions on Electrical and Electronic Materials
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    • v.15 no.4
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    • pp.213-216
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    • 2014
  • The microstructure and varistor properties of ZPCCAE ($ZnO-Pr_6O_{11}-CoO-Cr_2O_3-Al_2O_3-Er_2O_3$) ceramics were investigated with different erbium amounts. Analysis of the microstructure indicated that the ceramics consisted of ZnO grains as a bulk phase, and intergranular layers (mixture of $Pr_6O_{11}$ and $Er_2O_3$) as a minor secondary phase. With the increase of the doped erbium amount, the densities of sintered pellets increased from 5.63 to $5.82g/cm^3$, and the average grain size decreased from 9.0 to $5.7{\mu}m$. The increase of the doped erbium amount increased the breakdown field from 2,649 to 5,074 V/cm, and the nonlinear coefficient from 27.6 to 39.1. It was found that in the range of 0.25 to 0.5 mol%, the doped erbium had little effect on the microstructure and electrical properties.

Effect of Phosphorus Addition on Microstructure and Mechanical Properties of Sintered Low Alloy Steel (저합금강 소결체의 미세조직 및 기계적 특성에 미치는 인(P) 첨가의 영향)

  • Kim, Yoo-Young;Cho, Kwon-Koo
    • Journal of Powder Materials
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    • v.27 no.1
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    • pp.31-36
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    • 2020
  • Phosphorus is an element that plays many important roles in powder metallurgy as an alloy element. The purpose of this study is to investigate the influence of phosphorus addition on the microstructures and mechanical properties of sintered low-alloy steel. The sintered low-alloy steels Fe-0.6%C-3.89%Ni-1.95%Cu-1.40%Mo-xP (x=0, 0.05, 0.10, 0.15, 0.20%) were manufactured by compacting at 700 MPa, sintering in H2-N2 at 1260 ℃, rapid cooling, and low-temperature tempering in Ar at 160 ℃. The microstructure, pore, density, hardness, and transverse rupture strength (TRS) of the sintered low-alloy steels were evaluated. The hardness increased as the phosphorus content increased, whereas the density and TRS showed maximum values when the content of P was 0.05%. Based on microstructure observation, the phase of the microstructure changed from bainite to martensite as the content of phosphorus is increased. Hence, the most appropriate addition of phosphorus in this study was 0.05%.

Microstructure and Properties of $Cr_{2}O_{3}$additive ternary PZT Ceramics ($Cr_{2}O_{3}$이 첨가된 PNN-PZT 압전세라믹스에서의 미세구조 및 특성)

  • 박정호;김철수;김성곤;이상렬
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2001.07a
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    • pp.972-975
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    • 2001
  • The effect of Cr$_2$O$_3$(0 to 0.5 wt%) doping on the microstructure and electrical properties of ternary Pb(Zr,Ti)O$_3$-Pb(Ni,Nb)O$_3$piezoelectric ceramic has been investigated. Abnormal grain growth (grain size 3.3 to 11.2 $\mu$m) and densification are found. Minor additives of $\leq$0.1 wt% improve the mechanical coupling factor, but with more additives of $\geq$0.2 wt% electrical properties deteriorate. Thus, these phenomna can be ascribed mainly to anomalous developed microstructure. The large grains were composed of a core region that is free of Cr and a surrounding shell region rich in Cr. The interfaces between the core and the shell were composed of misfit dislocations. The mechanical properties of the specimens were strongly influenced by this microstructural change. The microstrutural and compositonal evolution of the specimens containing different amounts of Cr$_2$O$_3$were monitored. Electrical properties were measured and related to the variations in the microstructure.

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Evaluation of Homogeneous Ultra-fine Grain Refinements via Equal Channel Angler Pressing Process (등통로각압축공정을 통한 결정립의 균질한 초미세립화에 대한 고찰)

  • Kim, W.;Lee, H.H.;Seo, S.J.;Lee, J.K.;Yoon, T.S.;Kim, H.S.
    • Transactions of Materials Processing
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    • v.27 no.4
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    • pp.222-226
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    • 2018
  • Severe plastic deformation (SPD) is a promising method for drastically enhancing the mechanical properties of the materials by grain refinement of metallic materials. However, inhomogeneous deformation during the SPD process results in the inhomogeneous microstructure of the SPD-processed material. We manufactured cylindrical copper specimens of 42 mm in diameter with ultrafine grains (UFG) using an equal channel angular pressing (ECAP) to figure out the relationship between homogeneous microstructure and the number of the processing passes. Two specimens, which are ECAP-processed 4 times (4pass) and 6 times (6pass) each with Route Bc, are prepared for comparison of mechanical properties and microstructure. The results show that the mechanical properties of the two specimens (4pass and 6pass) are similar. Moreover, both the specimens show highly enhanced mechanical properties. The 4pass specimen, however, shows inhomogeneity in hardness distribution, while the 6pass specimen shows a homogeneous distribution. Microstructure analysis reveals that the 4pass specimen has an inhomogeneous microstructure with incompletely refined grain structure. This inhomogeneity of the 4pass specimen could be explained by the circumferential rotation during ECAP process.

Microstructure Evolution of Superalloy Nimonic 80A (초내열합금 Nimonic 80A의 미세조직 변화에 관한 연구)

  • Jeong H. S.;Cho J. R.;Park H. C.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2004.05a
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    • pp.174-177
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    • 2004
  • The nickel-based alloy Nimonic 80A possesses strength, and corrosion, creep and oxidation resistance at high temperature. These products are used for aerospace, marine engineering and power generation, etc. 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. It is necessary to understand the microstructure variation evolution. The microstructure change evolution occurs by recovery, recrystallization and grain growth phenomena. The dynamic recrystallization evolution has been studied in the temperature range $950-1250^{\circ}C$ and strain rate range $0.05-5s^{-1}$ using hot compression tests. The metadynamic recrystallization and grain growth evolution has been studied in the temperature range $950-1250^{\circ}C$ and strain rate range 0.05, $5s^{-1}$, holding time range 5, 10, 100, 600 sec using hot compression tests. Modeling equations are developed to represent the flow curve, recrystallized grain size, recrystallized fraction and grain growth phenomena by various tests. Parameters of modeling equation are expressed as a function of the Zener-Hollomon parameter. The modeling equation for grain growth is expressed as a function of initial grain size and holding time.

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A development of fabrication processes of microstructure using SU-8 PR (SU-8 PR을 이용한 마이크로 구조물 제작 공정 개발)

  • 김창교;장석원;노일호
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.13 no.2
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    • pp.68-72
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    • 2003
  • In this paper, we developed a new thick photoresist fabrication technology for 3-dimensional microstructures. In general, like as AZ photoresist was coated with thin film thickness about 1 $\mu\textrm{m}$ to 30 $\mu\textrm{m}$, but photoresist like SU-8 has thickness of several tens $\mu\textrm{m}$ or more and high aspect ratio. When we fabricate a microstructure using the thick photoresist like SU-8, cracks on the SU-8 thick photoresist are appeared by stress which was caused by sudden cooling down during bake of the thick photoresist spun on wafer. Thus, it was hard to fabricate the microstructure using the thick photoresist for electroplating. In this paper, we developed a new process to produce a 3-dimensional microstructure without the crack by stress through a suitable thick photoresist coating, time control of cool down and time control of PEB (Post Expose Bake).

Rolling of AZ31 Alloy and Microstructure of Rolled Plates (압연조건에 따른 AZ31 마그네슘합금판재의 변형거동 및 미세조직 변화)

  • Ha, T.K.;Jeong, H.T.;Sung, H.J.;Park, W.J.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2006.05a
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    • pp.63-66
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    • 2006
  • The effect of warm rolling under various conditions on the microstructure and mechanical property was investigated using an AZ31 Mg alloy sheet. Several processing parameters such as initial thickness, thickness reduction by a single pass rolling, rolling temperature, roll speed, and roll temperature were varied to elicit an optimum condition for the warm rolling process of AZ31 Mg alloy. Microstructure and mechanical properties were measured for specimens subjected to rolling experiments of various conditions. Warm rolling of 30% thickness reduction per pass was possible without any side-crack at temperatures as low as $200^{\circ}C$ under the roll speed of 30 m/min. The initial microstructure before rolling was the mixed one consisting of partially recrystallized and cast structures. Grain refinement was found to occur actively during the warm rolling, producing a very fine grain size of 7 mm after 50% reduction in single pass rolling at $200^{\circ}C$. Yield strength of 204MPa, tensile strength of 330MPa and uniform elongation of 32% have been obtained in warm rolled sheets.

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