• Title, Summary, Keyword: mechanical alloying

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Phase Transformation Properties of Cu/TiO2 Photocatalyst Powders Fabricated by Mechanical Alloying (기계적 합금화법으로 제조된 Cu/TiO2 촉매용 분말의 상변화 특성)

  • 안인섭;배승열;이영란;고봉석
    • Journal of Korean Powder Metallurgy Institute
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    • v.9 no.2
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    • pp.110-115
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    • 2002
  • In order to obtain the nano size $10wt%Cu-TiO_2$composite powders by mechanical alloying method for useful composite catalysis, the effects of mechanical alloying time on the formationof $10wt%Cu-TiO_2$ composite powders were analyzed. The phase transformation behaviors were experimented as the heat treating temperature increased. Homogeneous 10wt% Cu-rutile type $TiO_2$composite powders were synthesized in 40 hours by mechanical alloying. After 60 hours mechanical alloying 50 nm size $TiO_2$powders were obtained. Both the phase of mechanically alloyed 10 wt% $Cu-TiO_2$ and pure $TiO_2$ powders were not transformed to anatase after annealing at the temperature range between 350 to 500 $^{\circ}C$. The intermetallic compound of $Cu_2Ti_4$O was formed after 10 hours mechanical alloying, however it could be considered that this intemetallic phase dose not prevent the transformation of rutile $TiO_2$ to the anatase phase after heat treatment at the temperature between 350 and $550^{\circ}C$.

Nanocrystalline and Ultrafine Grained Materials by Mechanical Alloying

  • Wang, Erde;Hu, Lianxi
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • pp.829-830
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    • 2006
  • Recent research at Harbin Institute of Technology on the synthesis of nanocrystalline and untrafine grained materials by mechanical alloying/milling is reviewed. Examples of the materials include aluminum alloy, copper alloy, magnesium-based hydrogen storage material, and $Nd_2Fe_{14}B/{\alpha}-Fe$ magnetic nanocomposite. Details of the processes of mechanical alloying and consolidation of the mechanically alloyed nanocrystalline powder materials are presented. The microstructure characteristics and properties of the synthesized materials are addressed.

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Determination of the Degree of Alloying by Detection of Residual Ferromagnetic Elements for Intermetallic Alloys Processed by Mechanical Alloying (잔류 자성원소 검출에 의한 금속간화합물의 기계적 합금화 공정에서의 합금화 정도 해석)

  • Ur, Soon-Chul
    • Korean Journal of Materials Research
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    • v.13 no.9
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    • pp.561-566
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    • 2003
  • Mechanical alloying(MA) process using elemental powders followed by hot pressing has been applied to some intermetallic alloy system containing ferromagnetic elements, such as NiAl and $FeSi_2$. A modified thermogravimetric analysis (TGA) technique was used to investigate the degree of alloying in milled powders and hot consolidated specimens as well as heat-treated bulk specimens. It is shown that the measurement of Curie temperatures in MA intermetallic powders and consolidated specimens containing ferromagnetic components, when determined as a function of milling and heat treatment parameters, can give some insight into the progress and mechanism of alloying.

Effects of Mechanical Alloying on the Structure of Rapid Solidified Al-(1, 3, 5 )Cr Alloys (급속냉각한 Al-(1, 3, 5)Cr 합금의 조직에 미치는 기계적 합금화의 영향)

  • Jhee, T.G.;Kim, W.C.
    • Journal of the Korean Society for Heat Treatment
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    • v.6 no.4
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    • pp.194-203
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    • 1993
  • Rapid solidified splats Al-(1, 3, 5Cr) Alloys were produced by atomization-splat quenching method. Effects of mechanical alloying on the structure and mechanical properties of rapidly solidified Al-(1, 3, 5)Cr alloys were studied. Degree of mechanical alloying of Al-(1, 3, 5)Cr alloys can be determined by observing the microstructural refinement, microhardness and microstructure of Al-(l, 3, 5)Cr splats during processing. In the initial stage of mechanical alloying of the Al-(1, 3, 5)Cr splats fracturing of the grain boundaries occured first, followed after fracturing of zone A regions. Saturation hardness of Al-(1, 3, 5)Cr alloys increased proportionally with increasing concentration of the solute (Cr). Age hardening was not observed in these alloys. Decomposition temperature of Al-1Cr splats after mechanical alloying was higher than that of Al-5Cr splats. The density of $Al_7$ Cr precipitates increased proportionally with increasing chromium content, as a result, there was a transition to finely and spherically dispersed phase after mechanical alloying.

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The Effects of Mechanical Alloying Conditions on the Formation of Mn-sulfide (망간황화물형성에 미치는 기계적합금화 공정변수의 영향)

  • 안인섭;박동규;정광철
    • Journal of Korean Powder Metallurgy Institute
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    • v.8 no.4
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    • pp.253-257
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    • 2001
  • The effects of mechanical alloying conditions on the formation of Mn-sulfide powders were analyzed. Impeller rotating speed, lubricant coating and added amounts of process control agent(stearic acid) were selected as a process control factor. MnS compounds are synthesized in 3 hours by mechanical alloying at the alternative milling condition. Discontinuous rotating speed of 1200rpm for 4 minutes and 1000rpm for 1 minute shows more effects on the compound formation of MnS. After coating of lubricant on the wall, elementary Mn and sulfur were partially remained by mechanical alloying. The friction effects of the wall and grinding media on the powders are significantly important to form the compound of MnS.

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Thermoelectric Properties of Half-Heusler TiCoSb Synthesized by Mechanical Alloying Process

  • Ur, Soon-Chul
    • Korean Journal of Materials Research
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    • v.21 no.10
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    • pp.542-545
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    • 2011
  • Half-Heusler alloys are a potential thermoelectric material for use in high-temperature applications. In an attempt to produce half-Heusler thermoelectric materials with fine microstructures, TiCoSb was synthesized by the mechanical alloying of stoichiometric elemental powder compositions and then consolidated by vacuum hot pressing. The phase transformations during the mechanical alloying and hot consolidation process were investigated using XRD and SEM. A single-phase, half- Heusler allow was successfully produced by the mechanical alloying process, but a minor portion of the second phase of the CoSb formation was observed after the vacuum hot pressing. The thermoelectric properties as a function of the temperature were evaluated for the hot-pressed specimens. The Seebeck coefficients in the test range showed negative values, representing n-type conductivity, and the absolute value was found to be relatively low due to the existence of the second phase. It is shown that the electrical conductivity is relatively high and that the thermal conductivities are compatibly low in MA TiCoSb. The maximum ZT value was found to be relatively low in the test temperature range, possibly due to the lower Seebeck coefficient. The Hall mobility value appeared to be quite low, leading to the lower value of Seebeck coefficient. Thus, it is likely that the single phase produced by mechanical alloying process will show much higher ZT values after an excess Ti addition. It is also believed that further property enhancement can be obtained if appropriate dopants are selectively introduced into this MA TiCoSb System.

Fabrication of Aluminum/Aluminum Nitride Composites by Reactive Mechanical Alloying

  • Yu, Seung-Hoon;Shin, Kwang-Seon
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • pp.1294-1295
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    • 2006
  • Various reactions and the in-situ formation of new phases can occur during the mechanical alloying process. In the present study, Al powders were strengthened by AlN, using the in-situ processing technique during mechanical alloying. Differential thermal analysis and X-ray diffraction studies were carried out in order to examine the formation behavior of AlN. It was found that the precursors of AlN were formed in the Al powders and transformed to AlN at temperatures above $600^{\circ}C$. The hot extrusion process was utilized to consolidate the composite powders. The microstructure of the extrusions was examined by SEM and TEM. In order to investigate the mechanical properties of the extrusions, compression tests and hardness measurements were carried out. It was found that the mechanical properties and the thermal stability of the Al/AlN composites were significantly greater than those of conventional Al matrix composites.

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Synthesis of $\textrm{TiB}_2$ Powder by Mechanical Alloying and the Effect of Zr and Ta Substitution for Ti (기계적합금법에 의한 $\textrm{TiB}_2$ 분말의 제조 및 Zr과 Ta이 합성에 미치는 영향)

  • Hwang, Yeon;Kang, Eul-Son
    • Korean Journal of Materials Research
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    • v.9 no.8
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    • pp.787-791
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    • 1999
  • TiB$_2$powders were prepared by mechanical alloying, and the effect of Zr and Ta substitution for Ti was investigated. It was possible to produce titanium diboride phase by mechanical alloying titanium and boron elemental powders for 280 hours. The amorphization reaction, a common process which occurs during mechanical alloying, has not been found. When zirconium of which atomic radius was larger than that of titanium was substituted for Ti, the alloying time was greatly reduced. On the contrary, substitution of tantalum for titanium prolonged the alloying time because of the less negative heat of formation of tantalum diboride than that of titanium diboride.

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