• 제목/요약/키워드: Nanocrystallization

검색결과 19건 처리시간 0.022초

금속분말의 고압비틀림 성형시 나노결정화 (Nanocrystallization of Metallic Powders during High Pressure Torsion Processing)

  • 윤승채;김형섭
    • 한국소성가공학회:학술대회논문집
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    • 한국소성가공학회 2007년도 춘계학술대회 논문집
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    • pp.105-106
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    • 2007
  • Microstructure and hardness of metallic powder of Cu was studied after high pressure torsion (HPT) with 10 torsions and high pressure of 6 GPa. The size Cu grain decreases drastically after HPT and reaches the nano size range. During HPT, Cu powder increases hardness and Hall-Petch hardening, due to the decreasing grain size. In this study, effect of HPT on the hardness of Cu powders and consolidation with Nanocrystalline of the work reported here. The results indicated that Cu powder has a beneficial effect on homogeneous deformation, reducing grain size.

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금속분말의 고압비틀림 성형시 나노결정화 (Nanocrystallization of Metallic Powders during High Pressure Torsion Processing)

  • 윤승채;곽은정;김택수;홍순익;김형섭
    • 소성∙가공
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    • 제16권5호통권95호
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    • pp.360-363
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    • 2007
  • Microstructure and microhardness of metallic powders of pure copper were studied after high pressure torsion(HPT) processing with 10 turns of die rotation and high pressure of 6 GPa. The grain size of copper decreases drastically after HPT and reaches nanometer size ranges. During HPT, the hardness of consolidates of copper powders increases with increasing the temperature of HPT processing. Examinations of the fracture surfaces indicated evidence of ductile fracture. The results proved that HPT of copper powders has a beneficial effect for homogeneous deformation with reducing grain size.

Influence of Stress-strain on the Microstructural Change in the Metallic Glass and Metallic Glass Matrix Composite

  • Kim, Song-Yi;Lee, A-Young;Oh, Hye-Ryung;Lee, Min-Ha
    • Applied Microscopy
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    • 제45권2호
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    • pp.44-51
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    • 2015
  • At room temperature, metallic glasses deform inhomogeneously by strain localization into narrow bands as a result of yielding due to an external force. When shear bands are generated during deformation, often nanocrystals form at the shear bands. Experimental results on the deformation of bulk metallic glass in the current study suggest that the occurrence of nanocrystallization at a shear band implies the loading condition that induces deformation is more triaxial in nature than uniaxial. Under a compressive stress state, the geometrical constraint strain imposed by the stress triaxiality plays a crucial role in the deformation-induced nanocrystallization at the shear bands.

저온 분사 코팅 공정에서 충돌속도에 따른 CuNiTiZr 벌크 비정질 소재의 활성화 에너지와 결정화 거동 분석 (Effects of Impact Velocity on Crystallization and Activation Energy of Cu-based Bulk Metallic Glasses in Kinetic Spray Coating)

  • 윤상훈;배규열;김정환;이창희
    • 한국표면공학회지
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    • 제41권6호
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    • pp.301-307
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    • 2008
  • In this paper, nanocrystallization of CuNiTiZr bulk metallic glass (BMG) subjecting to a kinetic spraying, dependent on impact velocity, was investigated by numerical and experimental approaches. The crystallization fraction and nucleation activation energy of initial feedstock and as-deposited coating were estimated by DSC and Kissinger method, respectively. The results of numerical modeling and experiment showed that the crystalline fraction and nucleation activation energy in BMG coatings were depended on kinetic energy of incident particle. Upon impact, the conversion of particle kinetic energy leads to not only decreasing free energy barrier but also increasing the driving force for an amorphous to crystalline phase transformation. The nanocrystallization of BMGs is associated with the strain energy delivered by a plastic deformation with a high strain rate.

Cu 첨가에 따른 Al-Y-Ni의 나노결정화 거동 (Nanocrystallization Behavior of Al-Y-Ni with Cu Additions)

  • 홍순직;천병선;강세선;이임렬
    • 한국분말재료학회지
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    • 제9권1호
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    • pp.19-24
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    • 2002
  • This paper reports the results of an investigation into the effect of Cu additions upon the nano-crystallization behaviour of an Al-Y-Ni alloy. 1 at.% Cu was added to a base alloy of Al/sub 88/Y₄Ni/sub 8/ either by substitution for Al to form Al/sub 87/Y₄Ni/sub 8/Cu₁, or by substitution for Ni to form Al/sub 88/Y₄Ni/sub 7/Cu₁. Consistent with previous findings in the literature, the substitution of Cu for Al was found to increase the thermal stability of the amorphous phase whereas the substitution of Cu for Ni was found to decrease its thermal stability. Comparing the microstructures of these alloys after heat treatment to produce equivalent volume fractions of Al nanocrystals showed average grain sizes of 14 nm, 12 nm and 9 nm for the alloys Al/sub 88/Y₄Ni/sub 8/, Al/sub 87/Y₄Ni/sub 8/Cu₁respectively. The effect of Cu in refining the size of the nanocrystals was attributed to enhanced nucleation increasing the number density of the nanocrystals, rather than diffusion limited or interface limited growth.

와이어 브러싱한 알루미늄 판재 표면 및 압연접합 계면의 미세조직 및 기계적 성질 (Microstructure Evolution and Mechanical Properties of Wire-Brushed Surface and Roll-Bonded Interface of Aluminum Sheets)

  • 김수현;김형욱;강주희;어광준
    • 대한금속재료학회지
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    • 제49권5호
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    • pp.380-387
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    • 2011
  • Wire brushing, which is a typical surface preparation method for roll bonding, has recently been highlighted as a potentially effective method for surface nanocrystallization. In the present study, the microstructure evolution and hardness of the wire-brushed surface and roll-bonded interface of a 1050 aluminum sheet were investigated. Wire brushing formed protruded layers with a nanocrystalline structure and extremely high surface hardness. After roll bonding, the protruded layers remained as hard layers at the interface. Due to their hardness and brittleness the interface hard layers, can affect the interface bonding properties and also play an important role determining the mechanical properties of multi-layered clad sheets.

Nanocrystallization of Cu-Based Bulk Glassy Alloys upon Annealing

  • Pengjun, Cao;Dong, Jiling;Haidong, Wu;Peigeng, Fan;Anruo, Zhou
    • Applied Microscopy
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    • 제46권1호
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    • pp.32-36
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    • 2016
  • The Cu-based bulk glassy alloys in Cu-Zr-Ti-Ni systems were prepared by means of copper mold casting. The Cu-based bulk glassy alloys samples were tested by X-ray diffractomer (XRD), differential scanning calorimeter, scanning electron microscopy (SEM), Instron testing machine and Vickers hardness instruments. The result indicated that the prepared Cu-Zr-Ti-Ni alloys were bulk glassy alloys. The temperature interval of supercooled liquid region (${\Delta}T_x$) was about 45.48 to 70.98 K for the Cu-Zr-Ti-Ni alloy. The Vickers hardness was up to 565 HV for the $Cu_{50}Zr_{25}Ti_{15}Ni_{10}$ bulk glassy alloy. The $Cu_{50}Zr_{25}Ti_{15}Ni_{10}$ bulk glassy alloys were annealed in order to obtain nanocrystals. The results showed that the Vickers hardness was raise up to 630 HV from 565 HV. As shown in XRD results, the amorphous alloys changed to nanocrystals, which were $Cu_8Zr_3$, $Cu_3Ti_2$ and CuZr, improved the hardness. The SEM analysis showed that the compression fractured morphology of amorphous alloys was brittle fracture, and the fracture morphology after annealing was ductile fracture. This proved that annealing of amorphous to nanocrystals can improve the plasticity and toughness of amorphous alloys.

극저온 볼 밀링을 통한 Ibuprofen 분말의 나노화II (Nanocrystallization of Ibuprofen by Cryogenic Ball Milling II)

  • 조현갑;이경엽;백영남;박훈재;이상목
    • 한국정밀공학회:학술대회논문집
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    • 한국정밀공학회 2004년도 추계학술대회 논문집
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    • pp.442-446
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    • 2004
  • Reducing the particle size of drug materials down to submicron is an important matter in pharmaceutical industry. Cryogenic milling technology is one of the mechanical milling processes, which is mostly utilized in refining grain size of metal and ceramics at extremely low temperature environment. This technique has not been readily studied in application to medical and biotechnology. This paper, therefore, describes the application of cryogenic milling process to reduce particle size of Ibuprofen. The shape and size of the Ibuprofen particle before and after the cryogenic ball milling process were analyzed. XRD analysis was performed to examine a change in crystallinity of Ibuprofen by the cryogenic ball milling process. The results showed that the size of Ibuprofen particles was reduced to 1/10 or less of its initial size. The results also showed that the degree of crystallinity of Ibuprofen was slightly reduced after cryogenic ball milling with nitrogen

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