Journal of Powder Materials

Fully Porous and Porous Surfaced Ti-6Al-4V Implants Fabricated by Electro-Discharge-Sintering: (1) Fabrication Method and Fundamental Characteristics: C. Y. Hyun, J. K. Huh, W. H. Lee; J Korean Powder Metall Inst. 2005;12(5):325-331.; DOI: https://doi.org/10.4150/KPMI.2005.12.5.325

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Abstract PDF: Implant prototypes with various porosities were fabricated by electro-discharge-sintering of atomized spherical Ti-6Al-4V powders. Single pulse of 0.75 to 2.0 kJ/0.7 g-powder, using 150, 300, and 450µF capacitors was applied to produce a fully porous and porous surfaced implant compact. The solid core formed in the center of the compact after discharge was composed of acicular alpha+beta grains and porous layer consisted of particles connected in three dimensions by necks. The solid core and neck sizes increased with an increase in input energy and capacitance. On the other hand, pore volume decreased with increased capacitance and input energy due to the formation of solid core. Capacitance and input energy are the only controllable discharge parameters even though the heat generated during a discharge is the unique parameter that determines the porosity of compact. It is known that electro-discharge-sintering of spherical Ti-6Al-4V powders can efficiently produce fully-porous and porous surfaced Ti-6Al-4V implants with various porosities in a short time less then 400 isec by manipulating the discharging condition such as input energy and capacitance including powder size.

Porous and Porous Surfaced Ti-6Al-4V Implants Fabricated by Electro-Discharge-Sintering : (2) Hardness and Compressive Strength: C. Y. Hyun, J. K. Huh, W. H. Lee; J Korean Powder Metall Inst. 2005;12(5):332-335.; DOI: https://doi.org/10.4150/KPMI.2005.12.5.332

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Abstract PDF: Porous and porous surfaced Ti-6Al-4V implant compacts were fabricated by electro-discharge-sintering (EDS) of atomized spherical Ti-6Al-4V powders with a diameter of 100-150;µm, The solid core formed in the center of the compact after discharge was composed of acicular alpha+beta Widmanstatten grains, The hardness value at the solid core was much higher than that at the particle interface or particles in the porous layer, which can be attributed to both heat treatment and work hardening effects induced from EDS, The compressive yield strength was in a range of 19 to 436 MPa which significantly depends on both input energy and capacitance, Selected porous-surfaced Ti-6Al-4V implant compacts with a solid core have much higher compressive strengths compared to the human teeth and sintered Ti dental implants.

Effect of Cobalt Oxide on Carbothermal Reduction of Spray Dried Titanium-Cobalt-Oxygen Based Oxide Powder: Gil-Geun Lee, Chan-Young Kim; J Korean Powder Metall Inst. 2005;12(5):336-344.; DOI: https://doi.org/10.4150/KPMI.2005.12.5.336

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Abstract PDF: In the present study, the focus is on the effect of cobalt oxide powder in the carbothermal reduction of the titanium-cobalt-oxygen based oxide powder by solid carbon for the optimizing synthesis process of ultra fine TiC/Co composite powder. The titanium-cobalt-oxygen based oxide powder was prepared by the combination of the spray drying and desalting processes using the titanium dioxide powder and cobalt nitrate as the raw materials. The titanium-cobalt-oxygen based oxide powder was mixed with carbon black, and then this mixture was carbothermally reduced under flowing argon atmosphere. Changes in the phase structure and thermal gravity of the mixture during carbothermal reduction were analysed using XRD and TGA. Titanium-cobalt-oxygen based oxide powder desalted at 600°C had a mixture of TiO_2;and;Co_3O_4. And the one desalted at 800°C had a mixture of TiO_2;and;CoTiO_3. In the case of the former powder, the reduction of cobalt oxide powder in the titanium-cobalt-oxygen based oxide powder occurred at lower temperature than the latter one. However, the carbothermal reduction of titanium dioxide powder in the titanium-cobalt-oxygen based oxide powder with a mixture of TiO_2;and;Co_3O_4 occurred at higher temperature than the one with a mixture of TiO_2;and;CoTiO_3. And also, the former powder showed a lower TiC formation ability than the latter one.

Fabrication of Nanostructured Alumina by the Combined Processes of Magnetic Pulsed Compaction (MPC) and Spark Plasma Sintering (SPS): J. K. Lee, S. J. Hong, M. K. Lee, C. K. Rhee; J Korean Powder Metall Inst. 2005;12(5):345-350.; DOI: https://doi.org/10.4150/KPMI.2005.12.5.345

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In this study the nanostructured alpha-Al_2O_3 ceramics have been fabricated by the combined application of magnetic pulsed compaction (MPC) and subsequent spark plasma sintering (SPS), and their density and hardness properties were investigated. The alpha-Al_2O_3 prepared by the combined processes showed an increase by 8.4% in density, approaching the value close to the true density, and an enhancement by 210~400;Hv in hardness, compared to those fabricated by MPC or static compaction method followed by sintering treatment.

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Milling Behaviors of Al-B4C Composite Powders Fabricated by Mechanical Milling Process
Sung-Mo Hong, Jin-Ju Park, Eun-Kwang Park, Min-Ku Lee, Chang-Kyu Rhee, Ju-Myoung Kim, Jin-Kyu Lee
Journal of Korean Powder Metallurgy Institute.2012; 19(4): 291. CrossRef

Synthesis and Spark-plasma Sinetring of Nanoscale Al/alumina Powder by Wire Electric Explosion Process: Ji-Soon Kim, H. T. Kim, A. P. Illyin, Young-Soon Kwon; J Korean Powder Metall Inst. 2005;12(5):351-356.; DOI: https://doi.org/10.4150/KPMI.2005.12.5.351

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Abstract PDF: Nanoscale Al powder with thin layer of alumina was produced by Wire Electric Explosion (WEE) process. Spark-Plasma Sintering (SPS) was performed for the produced powder to confirm the effectiveness of SPS like so-called 'surface-cleaning effect' and so on. Crystallite size and alumina content of produced powder varied with the ratio of input energy to sublimation energy of Al wire (e/e_s): Increase in (e/e_s) resulted in the decrease of crystallite size and the increase of alumina content. Shrinkage curve during SPS process showed that the oxide surface layer could not be destroyed near the melting point of Al. It implied that there was not enough or no spark-plasma effect during SPS for Al/Alumina powder.

Thermoelectric Properties of Skutterudite Fe_xCo_4-xSb₁₂ Synthesized by Mechanical Alloying Process: Joon-Chul Kwon, Il-Ho Kim, Soon-Chul Ur; J Korean Powder Metall Inst. 2005;12(5):357-361.; DOI: https://doi.org/10.4150/KPMI.2005.12.5.357

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Abstract PDF: Fe-doped skutterudite CoSb_3 with a nominal composition of Fe_xCo_4-xSb_12(0;le;x;le;2.5) has been synthesized by mechanical alloying (MA) of elemental powders, followed by hot pressing. Phase transformations during mechanical alloying and hot pressing were systematically investigated using XRD. Single phase skutterudite was successfully produced by vacuum hot pressing using as-milled powders without subsequent annealing. However, second phase in the form of marcasite structure FeSb_2 was found to exist in case of x;ge;2, suggesting the solubility limit of Fe with Co in this system. Thermoelectric properties as functions of temperature and Fe contents were evaluated for the hot pressed specimens. Fe substitution up to x=1.5 with Co in Fe_xCo_4-xSb_12 appeared to increase thermoelectric figure of merit (ZT) and the maximum ZT was found to be 0.78 at 525K in this study.

Effect of Grain Size on Nanostructured Fe-20 wt.%Si Alloy Powders Produced by High-energy ball milling: Se-Hoon Kim, Young Jung Lee, Baek-Hee Lee, Kyu Hwan Lee, Young Do Kim; J Korean Powder Metall Inst. 2005;12(5):362-368.; DOI: https://doi.org/10.4150/KPMI.2005.12.5.362

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Abstract PDF: The structural and magnetic properties of nanostructued Fe-20 ;wt.%Si alloy powders were investigated. Commercial Fe-20 wt.%Si alloy powders (Hoeganaes Co., USA) with 99.9% purities were used to fabricate the nanostructure Fe-Si alloy powders through a high-energy ball milling process. The alloy powders were fabricated at 400 rpm for 50 h, resulting in an average grain size of 16 nm. The nanostructured powder was characterized by fcc Fe_3Si and hcp Fe_5Si_3 phases and exhibited a minimum coercivity of approximately 50 Oe.

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