• Title/Summary/Keyword: ultra-fine grain

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Magnetic Properties of FeCuNbSiB Nanocrystalline Alloy Powder Cores Using Ball-milled Powder

  • Kim, G. H.;T. H. Noh;Park, G. B.;Kim, K. Y.
    • Proceedings of the Korean Magnestics Society Conference
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    • 2002.12a
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    • pp.202-203
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    • 2002
  • Ribbon type nanocrystalline alloy cores have shown excellent soft magnetic properties in the high frequency range because of small crystalline anisotropy and nearly zero magnetostriction[1]. In present, however ribbon alloys gives some limit in applications such as a large inductor and reactors of PFC circuit, which are required good DC bias property and low loss in the high frequency. Powder alloys with ultra fine grain structure can be an important way to overcome this kind of disadvantage, and to improve the high frequency soft magnetic properties in conventional metallic powder cores[2]. (omitted)

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Micro Metal Injection Molding Using Hybrid Micro/Nano Powders

  • Nishiyabu, Kazuaki;Kakishita, Kenichi;Osada, Toshiko;Tanaka, Shigeo
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • 2006.09a
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    • pp.36-37
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    • 2006
  • This study aims to investigate the usage of nano-scale particles in a micro metal injection molding ($\mu$-MIM) process. Nanoscale particle is effective to improve transcription and surface roughness in small structure. Moreover, the effects of hybrid micro/nano particles, Cu/Cu and SUS/Cu were investigated. Small dumbbell specimens were produced using various feedstocks prepared by changing binder content and fraction of nano-scale Cu particle (0.3 and $0.13{\mu}m$ in particle size). The effects of adding the fraction of nano-scale Cu powder on the melt viscosity of the feedstock, microstructure, density and tensile strength of sintered parts were discussed.

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The Fabrication of Poly-Si Solar Cells for Low Cost Power Utillity (저가 지상전력을 위한 다결정 실리콘 태양전지 제작)

  • Kim, S.S.;Lim, D.G.;Shim, K.S.;Lee, J.H.;Kim, H.W.;Yi, J.
    • Solar Energy
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    • v.17 no.4
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    • pp.3-11
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    • 1997
  • Because grain boundaries in polycrystalline silicon act as potential barriers and recombination centers for the photo-generated charge carriers, these defects degrade conversion effiency of solar cell. To reduce these effects of grain boundaries, we investigated various influencing factors such as thermal treatment, various grid pattern, selective wet etching for grain boundaries, buried contact metallization along grain boundaries, grid on metallic thin film. Pretreatment above $900^{\circ}C$ in $N_2$ atmosphere, gettering by $POCl_3$ and Al treatment for back surface field contributed to obtain a high quality poly-Si. To prevent carrier losses at the grain boundaries, we carried out surface treatment using Schimmel etchant. This etchant delineated grain boundaries of $10{\mu}m$ depth as well as surface texturing effect. A metal AI diffusion into grain boundaries on rear side reduced back surface recombination effects at grain boundaries. A combination of fine grid with finger spacing of 0.4mm and buried electrode along grain boundaries improved short circuit current density of solar cell. A ultra-thin Chromium layer of 20nm with transmittance of 80% reduced series resistance. This paper focused on the grain boundary effect for terrestrial applications of solar cells with low cost, large area, and high efficiency.

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Frictional Effects on the Deformation Behavior of materials and Die during Equal Channel Angular Pressing(ECAP) with Pure-Zr (Pure-Zr의 ECAP공정에서 마찰이 재료의 변형거동과 금형에 미치는 영향)

  • Kwon, G. H.;Chae, S. W.;Kwon, S. I.;Kim, M. H.;Hwang, S. K.
    • Journal of the Korean Society for Precision Engineering
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    • v.18 no.6
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    • pp.182-187
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    • 2001
  • Much research efforts have been made on the equal-channel angular pressing(ECAP)that produces ultra-fine grain size materials. Recently many materials have been tested for ECAP process, and in this paper pure-Zirconium is considered due to its applicability to nuclear reactors. Among many process parameters of ECAP, frictional effects on the deformation behavior of materials and on the stress distribution of die have been investigated. The finite element method has been employed in order to investigate this issue, and experiments have also been made to verify the numerical results.

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Relationship Between Mechanical Properties and Damping Capacity in Stainless Steel with Two Phases of Reversed Austenite and Deformation Induced Martensite (역변태 오스테나이트와 가공유기 마르텐사이트의 2상 혼합조직을 갖는 스테인리스강의 기계적 성질과 감쇠능)

  • Namgung, Won;Jung, Mok-Hwan;Lee, Hyang-Beak;Kim, Jae-Nam;Kang, Chang-Young
    • Journal of Power System Engineering
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    • v.17 no.2
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    • pp.114-120
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    • 2013
  • This study was carried out to investigate the relationship between mechanical properties and damping capacity in high manganese austenitic stainless steel with two phase mixed structure of reversed austenite and deformation induced martensite. Reversed austenite of ultra-fine grain size less than $0.3{\mu}m$ was obtained by reversion treatment. Two phase structure of deformation induced martensite and reversed austenite was obtained by annealing treatment at range of $500^{\circ}C{\sim}700^{\circ}C$ for various time in cold rolled high manganese austenite stainless steel. In stainless steel with two phase mixed structure of martensite and austenite, damping capacity decreased rapidly with the increasing hardness and strength. With the increasing elongation, damping capacity was increased rapidly and then, slowly increased.

Tensile Properties of High Mn Austenitic Stainless Steel with Two Phases of Martensite and Austenite (마르텐사이트와 오스테나이트의 2상 조직을 갖는 고 Mn 오스테나이트계 스테인리스강의 인장성질)

  • Kim, Young-Hwa;Kang, Chang-Yong
    • Journal of Ocean Engineering and Technology
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    • v.27 no.4
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    • pp.9-13
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    • 2013
  • The tensile properties of high manganese austenitic stainless steel with the two phase structures of deformation-induced martensite and reversed austenite were studied. Reversed austenite with an ultra-fine grain size of less than $0.3{\mu}m$ was obtained by reversion treatment. The two phases structures of deformation-induced martensite and reversed austenite were obtained by an annealing treatment in the range of $500^{\circ}C-700^{\circ}C$ for various times in 70% cold- rolled high-manganese austenitic stainless steel. The volume fraction of the reversed austenite increased rapidly with increases in the annealing temperature and time. In the stainless steel with the two phases of austenite and martensite, the strength decreased rapidly, while the elongation increased slowly and then rapidly increased with an increase in the volume fraction of the reversed austenite. Therefore, the strength and elongation were strongly controlled by the volume fraction of reversed austenite. A good combination of high strength and elongation could be obtained by the mixed structure of reversed austenite and deformation-induced martensite.

Effect of Reverse Transformation on the Mechanical Properties of High Manganease Austenitic Stainless Steel (고 Mn 오스테나이트계 스테인리스강의 기계적 성질에 미치는 역변태의 영향)

  • Kang, C.Y.;Hur, T.Y.
    • Korean Journal of Metals and Materials
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    • v.50 no.6
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    • pp.413-418
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    • 2012
  • This study was carried out to investigate the effect of reverse transformation on the mechanical properties in high manganese austenitic stainless steel. Over 95% of the austenite was transformed to deformation-induced martensite by 70% cold rolling. Reverse transformation became rapid above an annealing temperature of $550^{\circ}C$, but there was no significant transformation above $700^{\circ}C$. In addition, with an increasing annealing time at $700^{\circ}C$, reverse transformation was induced rapidly, but the transformation was almost completed at 10 min. There was a rapid decrese in strength and hardness with annealing at temperature above $550^{\circ}C$, while elongation increased rapidly above $600^{\circ}C$. At $700^{\circ}C$, hardness and strength decreased rapidly, and elongation increased steeply with an increasing reverse treatment time up to 10 min, whereas there were no significant change with a treatment time after 10 min. The reverse-transformed austenite showed an ultra-fine grain size less than $0.2{\mu}m$, which made it possible to strengthen the high manganese austenitic stainless steel.

Fabrication and Characteristics of Ti-Nb-Mo-CPP Composite Fabricated by High Energy Mechanical Milling and Spark Plasma Sintering (고에너지밀링과 스파크플라즈마소결을 이용한 Ti-Nb-Mo-CPP 생체복합재료의 제조 및 특성)

  • Park, Sang-Hoon;Woo, Kee-Do;Kim, Ji-Young;Kim, Sang-Mi
    • Korean Journal of Metals and Materials
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    • v.50 no.6
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    • pp.469-475
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    • 2012
  • A high-energy mechanical milling (HEMM) process was introduced to improve sinter-ability, and rapid sintering of spark plasma sintering (SPS) under pressure was used to make ultra fine grain (UFG) of Ti-Nb-Mo-CPP composites, which have bio-attractive elements, for increasing mechanical properties. Ti-Nb-Mo-CPP composites were successfully fabricated by SPS at $1000^{\circ}C$ within 5 minutes under 70 MPa using HEMMed powders. The Vickers hardness of the composites increased with increased milling time and addition of CPP contents. Biocompatibility and corrosion resistance of the Ti-Nb-Mo alloys were improved by addition of CPP, and the Ti-35%Nb-10%Mo-10%CPP alloy had better biocompatibility and corrosion resistance than the Ti-6Al-4V ELI alloy.

Magnetic Properties of Ultrafine grained Fe-Al-Nb-B-(Cu) Alloys. (Fe-Al-Nb-B-(Cu)계 초미세결정합금의 자기적 특성)

  • 박진영;서수정;김규진;김광윤;노태환
    • Journal of the Korean Magnetics Society
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    • v.6 no.4
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    • pp.218-224
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    • 1996
  • The magnetic properties and crystallization behaviors of $Fe_{83-x}Al_{x}Nb_{5}B_{12}(X=1~5at%)$ alloys were investigated. The $Fe_{80}Al_{3}Nb_{5}B_{12}$ alloy was developed a very good soft magnetic material with ultra-fine grain structure in Fe-Al-Nb-B system alloys. When 1 at% of Cu was added in Fe-Al-Nb-B alloy, the soft magnetic properties were found to improve significantly through the reduction of the grain size upto about 6~7 nm at $450^{\circ}C$. The magnetic properties of the $Fe_{79}Al_{3}Nb_{5}B_{12}Cu_{1}$ alloy were as follows : ${\mu}_{eff}(1\;kHz)=26,000,\;B_{10}=1.45\;T,\;H_{c}=25\;mOe,\;P_{c}(100\;kHz,\;0.2\;T)=55\;W/kg$, respectively.

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Densification Study of K+-beta-aluminas Prepared from Their Ultra-fine Milled Powder (초미세 분쇄 분말로 제조된 K+-beta-aluminas의 치밀화 연구)

  • Shin, Jae-Ho;Kim, Woo-Sung;Lim, Sung-Ki
    • Applied Chemistry for Engineering
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    • v.16 no.5
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    • pp.648-652
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    • 2005
  • A super ionic conductor, $K^+$-beta-aluminas, which is known to be difficult to obtain in the form of dense sintered density under atmospheric pressure, was pulverized to 350 nm mean particle size using attrition mill. The sample were pressed into tablet form by uniaxial pressing. The specimen was sintered under atmospheric pressure in powder form. Sintering temperature range was $1400^{\circ}C$ to $1650^{\circ}C$ at $50^{\circ}C$ intervals. Additionally, zone sintering was carried out to control the growth grain at high temperature ($1600^{\circ}C$). The density of specimens that were sintered at $1600^{\circ}C$ and $1650^{\circ}C$, and sintered at $1600^{\circ}C$ by zone sintering were about 93% and 95%, respectively. In the case of the lengthened sintering time to 2 h, the density of specimen was reduced to lower than 90%, since the particles were grown to the duplex microstructure.