• 제목/요약/키워드: Ultrafine Grains

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ECAP 가공에 의해 제조된 초미세립 OFHC Cu 봉재의 미세조직 및 기계적 특성의 균질성 (Homogeneity of Microstructure and Mechanical Properties of Ultrafine Grained OFHC Cu Bars Processed by ECAP)

  • 지정훈;박이주;김형원;황시우;이종수;박경태
    • 대한금속재료학회지
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    • 제49권6호
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    • pp.474-487
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    • 2011
  • Bars of OFHC Cu with the diameter of 45 mm were processed by equal channel angular pressing up to 16 passes via route $B_c$, and homogeneity of their microstructures and mechanical properties was examined at every four passes which develop the equiaxed ultrafine grains. In general, overall hardness, yield strength and tensile strength increased by 3, 7, and 2 times respectively compared with those of unECAPed sample. Cross-sectional hardness exhibited a concentric distribution. Hardness was the highest at the center of bar and it decreased gradually from center to surface. After 16 passes, overall hardness decreased due to recovery and partial recrystallization. Regardless of the number of passage, yield strength and tensile strength were quite uniform at all positions, but elongation showed some degree of scattering. At 4 passes, coarse and ultrafine grains coexisted at all positions. After 4 passes, uniform equiaxed ultrafine grains were obtained at the center, while uniform elongated ultrafine grains were manifested at the upper half position. At the lower half position, grains were equiaxed but its size were inhomogeneous. It was found that inhomogeneity of grain morphology and grain size distribution at different positions are to be attributed to scattering in elongation but they did not affect strength. The present results reveal the high potential of practical application of equal channel angular pressing on fabrication of large-sized ultrafine grained bars with quite homogeneous mechanical properties.

ARB법에 의한 Cu-Fe-P합금의 초미세결정립 형성 (Formation of Ultrafine Grains in Cu-Fe-P Alloy by Accumulative Roll-Bonding Process)

  • 이성희;한승전;김형욱;임차용
    • 한국재료학회지
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    • 제19권8호
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    • pp.432-436
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    • 2009
  • A Cu-Fe-P copper alloy was processed by accumulative roll-bonding (ARB) for ultra grain refinement and high strengthening. Two 1mm thick copper sheets, 30 mm wide and 300 mm long, were first degreased and wire-brushed for sound bonding. The sheets were then stacked on top of each other and roll-bonded by about 50% reduction rolling without lubrication at ambient temperature. The bonded sheet was then cut into two pieces of the same dimensions and the same procedure was repeated for the sheets up to eight cycles. Microstructural evolution of the copper alloy with the number of the ARB cycles was investigated by optical microscopy (OM), transmission electron microscopy(TEM), and electron back scatter diffraction(EBSD). The grain size decreased gradually with the number of ARB cycles, and was reduced to 290 nm after eight cycles. The boundaries above 60% of ultrafine grains formed exhibited high angle boundaries above 15 degrees. In addition, the average misorientation angle of ultrafine grains was 30 degrees.

극저온 압연에 의한 초세립 5083 A1 Alloy 제조 연구 (Formation of Ultrafine Grains in 5083 Al Alloy by Cryogenic Rolling Process)

  • 이영범;심혜정;남원종
    • 소성∙가공
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    • 제13권2호
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    • pp.137-141
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    • 2004
  • The large deformation at cryogenic temperature is expected as one of the effective methods to produce large bulk ultrafine grained materials. The effects of annealing temperature, 150∼$300^{\circ}C$, on microstructures and mechanical properties of the sheets received 85% reduction at cryogenic temperature were investigated, in comparison with those at room temperature. Annealing of 5083 Al alloy deformed 85%, at $200^{\circ}C$ for an hour,. resulted in the considerable increase of tensile elongation without the great loss of strength and the occurrence of equiaxed grains less than 300nm in diameter.

Ultrafine Grained Steels Processed by Equal Channel Angular Pressing

  • Shin, Dong Hyuk
    • Corrosion Science and Technology
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    • 제5권1호
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    • pp.23-26
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    • 2006
  • Recent development of ultrafine grained (UFG) low carbon steels by using equal channel angular pressing (ECAP) and their room temperature tensile properties are reviewed, focusing on the strategies overcoming their inherent mechanical drawbacks. In addition to ferrite grain refinement, when proper post heat treatments are imposed, carbon atom dissolution from pearlitic cementite during ECAP can be utilized for microstructural modification such as uniform distribution of nano-sized cementite particles or microalloying element carbides inside UFG ferrite grains and fabrication of UFG ferrite/martensite dual phase steel. The utilization of nano-sized particles is effective on improving thermal stability of UFG low carbon ferrite/pearlite steel but less effective on improving its tensile properties. By contrast, UFG ferrite/martensite dual phase steel exhibits an excellent combination of ultrahigh strength, large uniform elongation and extensive strain hardenability.

극저온 압연에 의한 초세립 Al 5083 Alloy 제조 (Formation of ultrafine Grains in the Al 5083 Alloy by Cryogenic Rolling Process)

  • 이영범;심혜정;남원종
    • 한국소성가공학회:학술대회논문집
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    • 한국소성가공학회 2003년도 추계학술대회논문집
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    • pp.163-167
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    • 2003
  • The large deformation at cryogenic temperature would be one of the effective methods to produce large bulk UFG materials. The effects of annealing temperature 150∼300$^{\circ}C$, on microstructure and mechanical properties of the sheets received 85% reduction at cryogenic temperature were investigated. In comparison with those at room temperature. Annealing of 5083 Al alloy deformed 85%, at 200$^{\circ}C$ for an hour, results in the considerable increase of tensile elongation without the great loss of strength and the occurrence of equiaxed grains less than 300nm in diameter.

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극저온 압연한 Al 1050의 결정립 미세화 및 재결정 거동 (Formation of Ultrafine Grain and Recrystallization in 1050 Al Alloy Rolled at Cryogenic Temperature)

  • 이영범;송형락;남원종
    • 소성∙가공
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    • 제13권5호
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    • pp.455-460
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    • 2004
  • The deformation and annealing behaviors of a 1050 Al alloy deformed at cryogenic temperature were investigated, focusing on the evolution of microstructures and mechanical properties. Especially, the effects of annealing temperature, $150~300^{\circ}C$, on microstructures and mechanical properties of the sheets received reduction of 88% at cryogenic temperature were investigated. The significant change in mechanical properties with the annealing temperatures of $200~300^{\circ}C$ would be attributed to the variations in the volume fraction of recrystallized grains and coarse equiaxed grains.

Eutectic Nanocomposites for Thermophotovoltaic Application

  • Han, Young-Hwan;Lee, Jae-Hyung;Kakegawa, Kazuyuki
    • Transactions on Electrical and Electronic Materials
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    • 제11권6호
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    • pp.249-252
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    • 2010
  • The ground amorphous powder was consolidated into a dense sintered body with a typical ultrafine $Al_2O_3-GdAlO_3$ eutectic structure by spark plasma sintering (SPS). Sintered material with ultrafine and dense eutectic structure was obtained by an appropriate combination of rapid quenching and SPS at lower temperature and more quickly than by conventional sintering. The $Al_2O_3$-based rare earth eutectic ceramics for solar cell emitters are believed to have a higher efficiency and the $Al_2O_3$ based eutectic ceramics with ultrafine grains will be one of the promising materials showing excellent selective emitter characteristics.

ECAP가공에 의한 초미세립 순수 티타늄의 피로 특성 향상 (Improvement of Fatigue Properties in Ultrafine Grained Pure Ti after ECAP(Equal Channel Angular Pressing))

  • 이영인;박진호;최덕호;최명일;김호경
    • 대한기계학회논문집A
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    • 제29권11호
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    • pp.1494-1502
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    • 2005
  • Fatigue life and notch sensitivity of the ultrafine grained pure Ti produced by ECAP was investigated. The ECAPed sample with the true strain of 460$\%$ showed near equiaxed grains with an average size of about 0.3 $\mu$m. After ECAP, the ultimate tensile strength was increased by 60$\%$, while the tensile ductility was decreased by 31$\%$. The ECAPed ultrafine grained pure Ti samples showed high notch sensitivity and significant improvement of high cycle fatigue limit by a factor of 1.67. The ECAPed samples also show high notch sensitivity (K$_{f}$/K$_{t}$ = 0.96). It can be concluded that ECAP is the effective process for achieving high fatigue strength in Ti by increasing its tensile strength through grain refinement

초미립 SiC가 첨가된 질화규소에서 미세구조에 미치는 Bedding의 영향 (Effect Of Bedding on the Microstructure of Si3N4 with Ultrafine SiC)

  • 이홍한;김득중
    • 한국분말재료학회지
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    • 제10권1호
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    • pp.57-62
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    • 2003
  • The effect of bedding on the microstructure of $Si_3N_4$ added with ultra-fine SiC was investigated. The bedding and the addition of ultra-fine SiC effectively inhibited grain growth of $Si_3N_4$ matrix grain. The microstructures of the specimens sintered with bedding powder consisted of fine-grains as compared with the specimens sintered without bedding powder. In addition, the grain size and the difference of grain size between the specimens sintered with bedding and without bedding was reduced with increasing SiC content. Some ultra-fine SiC particles were trapped in the $Si_3N_4$ grains growed. The number of SiC particles trapped in the $Si_3N_4$ grains increased with increasing the grain growth. When ultra-fine SiC particles were added in the $Si_3N_4$ ceramics, the strength was improved but the toughness was decreased, which was considered to be resulted from the decrease of the grain size.

ECAP가공에 의한 초미세립 소재의 기계적 물성 (Mechanical Properties of Ultrafine Grained Materials via Equal-Channel Angular Pressing)

  • 고영건;김우겸;안정용;박경태;이종수;신동혁
    • 소성∙가공
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    • 제15권2호
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    • pp.105-111
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    • 2006
  • A study was made to investigate the microstructure and the mechanical properties of low-carbon steel, Al-Mg alloy and Ti-6Al-4V alloy each representing bcc, fcc and hcp crystal structures, respectively fabricated by equal-channel angular(ECA) pressing. After a series of ECA pressings was performed, most grains were significantly refined below ${\mu}m$ in diameter with high mis-orientation of grain boundaries irrespective of different crystal structure used. Regarding the strain hardening capability, tensile tests of ultrafine grain (UFG) dual-phase (ferrite/martensite) steel which was different from UFG ferrite-pearlite steel were carried out at ambient temperature, and corresponding mechanical properties were discussed in relation to modified C-J analysis. Low-temperature and/or high strain-rate superplasticity of the UFG Al-Mg alloy and UFG Ti-6Al-4V alloy were also studied. Based on the analysis used in this study, it was concluded that UFG alloys exhibited the enhanced mechanical properties as compared to coarse-grained (CG) counterparts.