• Title, Summary, Keyword: microstructure

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Sub-regional Slicing Method (SSM) to Fabricate 3D Microstructure Effectively in Nano-Stereolithography Process (극미세 3차원 형상제작의 효율성 향상을 위한 영역분할 단면법에 관한 연구)

  • Park S.H.;Lim T.W.;Yang D.Y.;Yi S.Y.;Kong H.J.;Lee K.S.
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.264-267
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    • 2005
  • A subregional slicing method (SSM) is proposed to increase the nanofabrication efficiency of a nano-stereolithography (NSL) process based on two-photon polymerization (TPP). The NSL process can be used to fabricate 3D microstructures via the accumulation of layers of uniform thickness; hence, the precision of the final 3D microstructure depends on the layer thickness. The use of a uniform layer thickness means that, to fabricate a precise microstructure, a large number of thin slices is inevitably required. leading to long processing times. In the SSM proposed here, however, the 3D microstructure is divided into several subregions on the basis of the geometric slope, and then each of these subregions is uniformly sliced with a layer thickness determined by the geometric slope characteristics of each subregion. Subregions with gentle slopes are sliced with thin layer thicknesses, whereas subregions with steep slopes are sliced with thick layer thicknesses. Here, we describe the procedure of the SSM based on TPP, and discuss the fabrication efficiency of the method through the fabrication of a 3D microstructure.

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Fabrication SiCN micro structures for extreme high temperature systems (초고온 시스템용 SiCN 마이크로 구조물 제작)

  • Thach, Phan Dui;Chung, Gwiy-Sang
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • pp.216-216
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    • 2009
  • This paper describes a novel processing technique for the fabrication of polymer-derived SiCN (silicone carbonitride) microstructures for extreme microelectromechanical system (MEMS) applications. A polydimethylsiloxane (PDMS) mold was formed on an SU-8 pattern using a standard UV photolithographic process. Next, the liquid precursor, polysilazane, was injected into the PDMS mold to fabricate free-standing SiCN microstructures. Finally, the solid polymer SiCN microstructure was cross-linked using hot isostatic pressure at $400^{\circ}C$ and 205 bar. The optimal pyrolysis and annealing conditions to form a ceramic microstructure capable of withstanding temperatures over $1400^{\circ}C$ were determined. Using the optimal process conditions, the fabricated SiCN ceramic microstructure possessed excellent characteristics includingshear strength (15.2 N), insulation resistance ($2.163{\times}10^{14}\;{\Omega}$, and BDV (1.2 kV, minimum). Since the fabricated ceramic SiCN microstructure has improved electrical and physical characteristics compared to bulk Si wafers, it may be applied to harsh environments and high-power MEMS applications such as heat exchangers and combustion chambers.

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Control of Nano-Scaled Surface Microstructure of Al Sample for Improving Heat Release Ability (Al 소재의 방열특성 향상을 위한 미세조직 제어 연구)

  • Yeo, In-Chul;Kang, In-Cheol
    • Journal of Korean Powder Metallurgy Institute
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    • v.22 no.1
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    • pp.21-26
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    • 2015
  • In this study, the control of microstructure for increasing surface roughness of Al with an electro-chemical reaction and a post treatment is systematically investigated. The Al specimen is electro-chemically treated in an electrolyte. In condition of the post treatment at $100^{\circ}C$ for 10 min, a change of the surface microstructure occur at 50V (5 min), and a oxidized layer is at 400V, to which lead a decreasing surface roughness. The minimum temperature of the post treatment for a change of microstructure is $80^{\circ}C$. Moreover, in the condition of 300V (5 min), the electro-chemical reaction is followed by the post treatment at $100^{\circ}C$, the critical enduring time for the change of microstructure is 3 min. The longer post treatment time leads to the rougher surface. The treated Al specimen demonstrate better heat release ability owing to the higher surface roughness than the non-treated Al.

EBSD Microstructural Characterisation of Oxide Scale on Low Carbon Steel

  • Birosca, S.;De Cooman, B.C.
    • Corrosion Science and Technology
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    • v.7 no.3
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    • pp.182-186
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    • 2008
  • The microstructures of the oxide scale developed at high temperature on steels are very complex and their development depends on many factors including time, temperature, oxidation conditions and alloying elements. The classical model of an oxide scale on steel consisting of wüstite, magnetite and haematite layers, is more complicated in reality and its properties change with the factors that affect their development. An understanding of the oxide scale formation and its properties can only be achieved by careful examination of the scale microstructure. The oxide scale microstructure may be difficult to characterise by conventional techniques such as optical or standard scanning electron microscopy. An unambiguous characterisation of the scale and the correct identification of the phases within the scale are difficult unless the crystallographic structure for each phase in the scale is considered and a simultaneous microstructure-microtexture analysis is carried out. In the current study Electron Backscatter Diffraction (EBSD) has been used to investigate the microstructure of iron oxide layers grown on low carbon steels at different times and temperatures. EBSD has proved to be a powerful technique for identifying the individual phases in the oxide scale accurately. The results show that different grain shapes and sizes develop for each phase in the scale depending on time and temperature.

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.

Morphological optimization of process parameters of randomly oriented carbon/carbon composite

  • Raunija, Thakur Sudesh Kumar;Manwatkar, Sushant Krunal;Sharma, Sharad Chandra;Verma, Anil
    • Carbon letters
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    • v.15 no.1
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    • pp.25-31
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    • 2014
  • A microstructure analysis is carried out to optimize the process parameters of a randomly oriented discrete length hybrid carbon fiber reinforced carbon matrix composite. The composite is fabricated by moulding of a slurry into a preform, followed by hot-pressing and carbonization. Heating rates of 0.1, 0.2, 0.3, 0.5, 1, and $3.3^{\circ}C/min$ and pressures of 5, 10, 15, and 20 MPa are applied during hot-pressing. Matrix precursor to reinforcement weight ratios of 70:30, 50:50, and 30:70 are also considered. A microstructure analysis of the carbon/carbon compacts is performed for each variant. Higher heating rates give bloated compacts whereas low heating rates give bloating-free, fine microstructure compacts. The compacts fabricated at higher pressure have displayed side oozing of molten pitch and discrete length carbon fibers. The microstructure of the compacts fabricated at low pressure shows a lack of densification. The compacts with low matrix precursor to reinforcement weight ratios have insufficient bonding agent to bind the reinforcement whereas the higher matrix precursor to reinforcement weight ratio results in a plaster-like structure. Based on the microstructure analysis, a heating rate of $0.2^{\circ}C/min$, pressure of 15 MPa, and a matrix precursor to reinforcement ratio of 50:50 are found to be optimum w.r.t attaining bloating-free densification and processing time.

Microstructure and Mechanical Properties of a Copper Alloy Sheet Processed by a Differential Speed Rolling (이속압연에 의해 가공된 동합금 판재의 조직 및 기계적 특성)

  • Lee, Seong-Hee
    • Korean Journal of Materials Research
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    • v.22 no.11
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    • pp.581-586
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    • 2012
  • The microstructure and mechanical properties of a copper alloy sheet processed by differential speed rolling (DSR) were investigated in detail. A copper alloy with thickness of 3 mm was rolled to a 50% reduction at ambient temperature without lubrication and with a differential speed ratio of 2.0:1. For comparison, conventional rolling (CR), in which the rolling speeds of the upper and lower rolls is 2.0 m/min, was also performed under the same rolling conditions. The shear strain of the sample processed by CR showed positive values at the positions of the upper roll side and negative values at the positions of the lower roll side. On the other hand, the sample processed by the DSR showed zero or positive shear strain values at all positions. However, the microstructure and mechanical properties of the as-rolled copper alloys did not show such significant differences between the CR and the DSR. The samples rolled by the CR and the DSR exhibited a typical deformation structure. In addition, the DSR processed samples showed a typical rolling texture in which {112}<111>, {011}<211> and {123}<634> components were developed at all positions. Therefore, it is concluded that the DSR was very effective for the introduction of a uniform microstructure throughout the thickness of the copper alloy.

Forging Process Technology as Observed in the Microstructure of a Hammer Scale Excavated from the Naju Bogam-ri Remains (나주 복암리 유적 출토 단조박편의 미세조직을 통한 단야 공정 기술체계 연구)

  • Song, Jung Il;Woo, Kee Do
    • Korean Journal of Metals and Materials
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    • v.50 no.8
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    • pp.599-603
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    • 2012
  • The microstructure of a hammer scale excavated from the Bogam-ri was examined in an effort to understand the iron technologies applied in the manufacturing of an iron forging process technology. The microstructures of oxide layer in the hammer scale were found to have crucial information about the ancient iron forging process treatment. The microstructure observed in the hammer scale can be distinguished by the forging process. First, the microstructure of the oxide layer in the hammer scale created by the forging process is Wstite (FeO) in the form of leaves. Latterly, the microstructure of the $W{\ddot{u}}stite$(FeO) in the hammer scale is observed to be in the form of a flat shape formed by a repeating forging process.

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.