Journal of Powder Materials

Volume 9(6); December 2002

Nanocomposite Magnetic Materials: Schultz Ludwig, Bollero Alberto, Handstein Axel, Hinz Dietrich, Muller Karl-Hartmut, Kumar Golden, Eckert Juergen, Gutfleisch Oliver, Kirehner Anke; J Korean Powder Metall Inst. 2002;9(6):381-393.; DOI: https://doi.org/10.4150/KPMI.2002.9.6.381

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Abstract PDF: Recent developments in nanocrystalline and nanocomposite rare earth-transition metal magnets are reviewed and emphasis is placed on research work at IFW Dresden. Principal synthesis methods include high energy ball milling, melt spinning, mold casting and hydrogen assisted methods such as reactive milling and hydrogenation-disproportionation-desorption-recombination. These techniques are applied to NdFeB-, PrFeB- and SmCo-type systems with the aim to produce high remanence magnets with high coercivity. Concepts of maximizing the energy density in nanostructured magnets by either inducing a texture via anisotropic HDDR or hot deformation or enhancing the remanence via magnetic exchange coupling are evaluated. With respect to high temperature applications melt spun Sm(Co_0.74Fe_0.1Cu_0.12Zr_0.04)_7.5 ribbons were prepared, which showed coercivities of up to 0.53 T at 500°C. Partially amorphous Nd_60Fe_xCo_30-xAl_10(0leqxleq30) alloys were prepared by copper mold casting. The effect of transition metal content on the glass-forming ability and the magnetic properties was investigated. The Nd_60Co_30Al_10 alloy exhibits an amorphous structure shown by the corresponding diffraction pattern. A small substitution of Co by 2.5 at.% Fe results In the formation of Fe-rich crystallites embedded in the Nd-rich amorphous matrix. The Fe-rich crystallites show hard magnetic behaviour at room temperature with a coercivity value of about 0.4 T, relatively low saturation magnetization and a Curie temperature of 500 K.

High Strength Nanostructured Metastable Alloys: Jurgen Eckert, Birgit Bartusch, Frank Schurack, Guo He, Ludwig Schultz; J Korean Powder Metall Inst. 2002;9(6):394-408.; DOI: https://doi.org/10.4150/KPMI.2002.9.6.394

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Abstract PDF: Nanostructured high strength metastable Al-, Mg- and Ti-based alloys containing different amorphous, quasicrystalline and nanocrystalline phases are synthesized by non-equilibrium processing techniques. Such alloys can be prepared by quenching from the melt or by powder metallurgy techniques. This paper focuses on one hand on mechanically alloyed and ball milled powders containing different volume fractions of amorphous or nano-(quasi)crystalline phases, consolidated bulk specimens and, on the other hand. on cast specimens containing different constituent phases with different length-scale. As one example. Mg_55Y_15Cu_30- based metallic glass matrix composites are produced by mechanical alloying of elemental powder mixtures containing up to 30 vol.% Y_2O_3 particles. The comparison with the particle-free metallic glass reveals that the nanosized second phase oxide particles do not significantly affect the glass-forming ability upon mechanical alloying despite some limited particle dissolution. A supercooled liquid region with an extension of about 50 K can be maintained in the presence of the oxides. The distinct viscosity decrease in the supercooled liquid regime allows to consolidate the powders into bulk samples by uniaxial hot pressing. The Y_2O_3 additions increase the mechanical strength of the composites compared to the Mg_55Y_15Cu_30 metallic glass. The second example deals with Al-Mn-Ce and Al-Cu-Fe composites with quasicrystalline particles as reinforcements, which are prepared by quenching from the melt and by powder metallurgy. Al_98-xMn_xCe_2 (x =5,6,7) melt-spun ribbons containing a major quasicrystalline phase coexisting with an Al-matrix on a nanometer scale are pulverized by ball milling. The powders are consolidated by hot extrusion. Grain growth during consolidation causes the formation of a micrometer-scale microstructure. Mechanical alloying of Al_63Cu_25Fe_12 leads to single-phase quasicrystalline powders. which are blended with different volume fractions of pure Al-powder and hot extruded forming Al_100-x(Al_0.63Cu_0.25Fe_0.12)_x (x = 40,50,60,80) micrometer-scale composites. Compression test data reveal a high yield strength of sigma_ygeq700 MPa and a ductility of varepsilon_plgeq5% for than the Al-Mn-Ce bulk samples. The strength level of the Al-Cu-Fe alloys is sigma_yleq550 MPa significantly lower. By the addition of different amounts of aluminum, the mechanical properties can be tuned to a wide range. Finally, a bulk metallic glass-forming Ti-Cu-Ni-Sn alloy with in situ formed composite microstructure prepared by both centrifugal and injection casting presents more than 6% plastic strain under compressive stress at room temperature. The in situ formed composite contains dendritic hcp Ti solid solution precipitates and a few Ti_3Sn,;beta-(Cu, Sn) grains dispersed in a glassy matrix. The composite micro- structure can avoid the development of the highly localized shear bands typical for the room temperature defor-mation of monolithic glasses. Instead, widely developed shear bands with evident protuberance are observed. resulting in significant yielding and homogeneous plastic deformation over the entire sample.

Nanoscale Metal Powders Production and Applications: Bernd-H Gunther; J Korean Powder Metall Inst. 2002;9(6):409-415.; DOI: https://doi.org/10.4150/KPMI.2002.9.6.409

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Abstract PDF: In this review the methods for production and processing of isolated or agglomerated nanoscale metal particles embedded in organic liquids (nanosuspensions) and polymer matrix composites are elucidated. Emphasis is laid on the techniques of inert gas condensation (IGC) and high pressure sputtering for obtaining highly porous metal powders ("nanopowder") as well as on vacuum evaporation on running liquids for obtaining nanosuspensions. Functional properties and post-processing are outlined in view of applications in the fields of electrically conductive adhesives and anti-microbially active materials for medical articles and consumer goods.mer goods.

Synthesis of Intermetallics and Nanocomposites by High-Energy Milling: F. Bernd, Kubsch H., Bohm Alexander, Zumdick M., Weissgaerber Thomas; J Korean Powder Metall Inst. 2002;9(6):416-421.; DOI: https://doi.org/10.4150/KPMI.2002.9.6.416

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Abstract PDF: Elemental powders are used in high energy milling processes for the synthesis of new compounds. The low temperature solid state reactions during milling in inert gas atmosphere may result in intermetallic phases, carbides, nitrides or silicides with a nanocrystalline structure. To obtain dense materials from the powders a pressure assisted densification is necessary. On the other side the defect-rich microstructure can be used for activated sintering of elemental powder mixtures to obtain dense bodies by pressureless sintering. Results are discussed for nanocrystalline cermet systems and for the sintering of aluminides and silicides.

Mechanically Driven Decomposition of Intermetallics: Young-Soon Kwon, Hyun-Sik Kim, Konstantin B. Gerasimov; J Korean Powder Metall Inst. 2002;9(6):422-432.; DOI: https://doi.org/10.4150/KPMI.2002.9.6.422

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Abstract PDF: Mechanically driven decomposition of intermetallics during mechanical milling(MM 1 was investigated. This process for Fe-Ce and Fe-Sn system was studied using conventional XRD, DSC, magnetization and alternative current susceptibility measurements. Mechanical alloying and milling form products of the following composition (in sequence of increasing Gecontent): alpha(alpha_1) bcc solid solution, alpha+beta-phase (Fe_2-xGe), beta-phase, beta+FeGe(B20), FeGE(B20), FeGe(B20)+FeGe_2,FeGe_2,FeGe_2+Ge, Ge. Incongruently melting intermetallics Fe_6Ge_5 and Fe_2Ge_3 decompose under milling. Fe_6Ge_5 produces mixture of hata-phase and FeGe(B20), Fe_2Ge_3 produces mixture of FeGe(B20) and FeGe_2 phases. These facts are in good agreement with the model that implies local melting as a mechanism of new phase for-mation during medchanical alloying. Stability of FeGe(B20) phase, which is also incongruently melting compound, is explained as a result of highest density of this phase in Fe-Ge system. Under mechanical milling (MM) in planetary ball mill, FeSn intermetallic decomposes with formation Fe_5Sn_3 and FeSn_2 phases, which have the biggest density among the phases of Fe-Sn system. If decomposition degree of FeSn is relatively small(<60%), milled powder shows superparamagnetic behavior at room temperature. For this case, magnetization curves can be fitted by superposition of two Langevin functions. particle sizes for ferromagnetic Fe_5Sn_3 phase determined from fitting parameters are in good agreement with crystalline sizes determined from XRD data and remiain approximately chageless during MM. The decomposition of FeSn is attributed to the effects of local temperature and local pressure produced by ball collisions.

Synthesis and Compaction of Al-based Nanopowders by Pulsed Discharge Method: Chang-Kyu Rhee, Geun-Hee Lee, Whung-Whoe Kim; J Korean Powder Metall Inst. 2002;9(6):433-440.; DOI: https://doi.org/10.4150/KPMI.2002.9.6.433

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Synthesis and compaction of Al-base nano powders by pulsed discharge method were investigated. The aluminum based powders with 50 to 200 nm of diameter were produced by pulsed wire evaporation method. The powders were covered with very thin oxide layer. The perspective process for the compaction and sintering of nanostructured metal-based materials stable in a wide temperature range can be seen in the densification of nano-sized metal powders with uniformly distributed hard ceramic particles. The promising approach lies in utilization of natural uniform mixtures of metal and ceramic phases, e.g. partially oxidized metal powders as fabricated in our synthesis method. Their particles consist of metal grains coated with oxide films. To construct a metal-matrix material from such powder, it is necessary to destroy the hard oxide coatings of particles during the compaction process. This goal was realized in our experiments with intensive magnetic pulsed compaction of aluminum nanopowders passivated in air.

Citations

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Thermodynamic modeling and characterizations of Al nanoparticles produced by electrical wire explosion process
L. Santhosh Kumar, S.R. Chakravarthi, R. Sarathi, R. Jayaganthan
Journal of Materials Research.2017; 32(4): 897. CrossRef
Electrochemical properties of Sn/C nanoparticles fabricated by redox treatment and pulsed wire evaporation method
Ju-Seok Song, Gyu-Bong Cho, Jou-Hyeon Ahn, Kwon-Koo Cho
Applied Surface Science.2017; 415: 14. CrossRef
Investigation of Nano-Molybdenum Carbide Particle Produced by Wire-Explosion Process
Ramanujam Sarathi, Ravula Sugunakar Reddy, Rashmi S. Tavarmani, Akira Okamoto, Hisayuki Suematsu, Parasuraman Selvam, Uthandi Kamachi Mudali, Muthusamy Kamaraj
IEEE Transactions on Plasma Science.2015; 43(10): 3470. CrossRef
Synthesis and characterization of hexagonal nano tungsten carbide powder using multi walled carbon nanotubes
S. Aravinth, Binu Sankar, M. Kamaraj, S.R. Chakravarthy, R. Sarathi
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Nanodispersion-Strengthened Metallic Materials: Thomas Weissgaerber, Christa Sauer, Bernd Kieback; J Korean Powder Metall Inst. 2002;9(6):441-448.; DOI: https://doi.org/10.4150/KPMI.2002.9.6.441

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Abstract PDF: Dispersions of non-soluble ceramic particles in a metallic matrix can enhance the strength and heat resistance of materials. With the advent of mechanical alloying it became possible to put the theoretical concept into practice by incorporating very fine particles in a flirty uniform distribution into often oxidation- and corrosion- resistant metal matrices. e.g. superalloys. The present paper will give an overview about the mechanical alloying technique as a dry, high energy ball milling process for producing composite metal powders with a fine controlled microstructure. The common way is milling of a mixture of metallic and nonmetallic powders (e.g. oxides. carbides, nitrides, borides) in a high energy ball mill. The heavy mechanical deformation during milling causes also fracture of the ceramic particles to be distributed homogeneously by further milling. The mechanisms of the process are described. To obtain a homogeneous distribution of nano-sized dispersoids in a more ductile matrix (e.g. aluminium-or copper based alloys) a reaction milling is suitable. Dispersoid can be formed in a solid state reaction by introducing materials that react with the matrix either during milling or during a subsequent heat treatment. The pre-conditions for obtaining high quality materials, which require a homogeneous distribution of small dis-persoids, are: milling behaviour of the ductile phase (Al, Cu) will be improved by the additives (e.g. graphite), homogeneous introduction of the additives into the granules is possible and the additive reacts with the matrix or an alloying element to form hard particles that are inert with respect to the matrix also at elevated temperatures. The mechanism of the in-situ formation of dispersoids is described using copper-based alloys as an example. A comparison between the in-situ formation of dispersoids (TiC) in the copper matrix and the milling of Cu-TiC mixtures is given with respect to the microstructure and properties, obtained.

Synthesis of Ultra Eine Mn_xZn_1-xFe₂O₄(x = 0.69~0.74) Powder and Its Magnetic Properties: Jae-Eun Kwak, Wan-Jae Lee; J Korean Powder Metall Inst. 2002;9(6):449-454.; DOI: https://doi.org/10.4150/KPMI.2002.9.6.449

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Abstract PDF: MnxZn_1-xFe_2O_4 (x=0.69~0.74) powders synthesized by the thermal decomposition of organic acid salts. The obtained powders were uniform in composition and ultra-fine particle with about 400 nm. The amount of spinel phase of these powders was about 50% in X-ray diffraction patterns. The calcination of powder was carried out at 900°C for 2 hours in air. After the powders were calcined. the mean size of powder was about 500 nm and the amount of spinel phase was increased over about 65%. The maximum amount of spinel phase was about 75% in the specimen of X=0.72. The magnetic properties of calcined Mn_0.72Zn_0.28Fe_2O_4 powders were the best among the different among the different compositions.

Effect of Heat Treatment on the Microstuctures and Mechanical Properties of TiC Dispersed Ni-base Alloy: Seong-Hyeon Hong, Keum-Chul Hwang, Won-Hyuk Rhee, Eog-Yong Chin; J Korean Powder Metall Inst. 2002;9(6):455-462.; DOI: https://doi.org/10.4150/KPMI.2002.9.6.455

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Abstract PDF: The microstructures and properties of TiC dispersed nickel-base alloy were studied in this work. The alloy prepared by powder metallurgical processing was solution treated, 1st-aged at 880°C for 16 hours, and then 2nd-aged at 760°C for 4 hours. Microstucture of sintered specimen showed that TiC particles are uniformly dispersed in Ni base alloy. In the specimen aged at 880°C for 8 hours, the fine gammaNi_3(Al,Ti) precipitates with round shape are observed and the very fine gammaNi_3(Al,Ti) particles with round shape are precipitated in the specimen aged at 760°C for 4 hours. The presence of gammaprecipitates in TiC/Ni base alloy increased the hardness and wear resistance of the specimen. The hardness and wear resistance of the Ni-base with TiC are higher than those of conventional Ni-base superalloy X-750 because of dispersion strengthening of TiC particles. The hardness, transverse rupture strength and resistance of the specimen 2nd-aged at 760°C for 4 hours are higher than those of 1st-aged specimen due to ultrafine gammaNi_3(Al,Ti) precipitates.

탄소나노소재의 제조와 응용전망: J Korean Powder Metall Inst. 2002;9(6):463-470.; DOI: https://doi.org/10.4150/KPMI.2002.9.6.463

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