Journal of Powder Materials

Coercivity Enhancement of Nd₂₃Dy₁₀Fe₆₄TM₂B₁ Sintered Magnet by Convergent Heat Treatment: Hoon-Sup Kim, Se-Hoon Kim, Jin-Woo Kim, Young-Do Kim; J Korean Powder Metall Inst. 2010;17(1):1-6.; DOI: https://doi.org/10.4150/KPMI.2010.17.1.001

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In this study, a convergent heat treatment was performed in certain temperature regions in order to control the microstructures of Nd-rich phases and to reduce thermal stress on grain boundaries which could be caused during expansion and shrinkage of Nd-rich and Nd_2Fe_14B phases. The difference of thermal expansion coefficient between Nd_2Fe_14B and Nd-rich phases is the mechanism for convergent heat treatment. The Nd-rich phases which were located in junctions could penetrate into the grain boundaries between Nd_2Fe_14B phases due to the difference of thermal expansion coefficient. Through the convergent heat treatment, the microcracks that were observed in cyclic heat treatment were not observed and coercivity was increased to 34.05 kOe at 8 cycles.

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Sintering Behavior and Phase Analysis of (Nd, Dy)-Fe-B Powder
Se-Hoon Kim, Jin-Woo Kim, Young-Do Kim
Journal of Korean Powder Metallurgy Institute.2010; 17(2): 154. CrossRef

Effect of Process-Control Agents on Characteristics of Amorphous Al-Y-Ni-Co Alloy Powder Produced by Mechanical Alloying: H.V. Nguyen, J.C. Kim, J.S. Kim, Y.J. Kwon, Y.S. Kwon; J Korean Powder Metall Inst. 2010;17(1):7-12.; DOI: https://doi.org/10.4150/KPMI.2010.17.1.007

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Abstract PDF: In this work, effect of various process-control agents (PCAs) on the mechanical alloying of amorphous alloy of Al_85Y_8Ni_5Co_2 has been investigated. The dependence of the particle shape, size and crystallization behavior of the amorphous alloy powders on the type of PCAs and their concentrations was investigated by using X-ray diffraction, field-emission scanning electron microscopy and differential scanning calorimetry. It was found that the additive of toluene could affect positively the amorphization and thermally induced crystallization processes, as well as the size refinement, morphology and particle-size distribution of as-milled powders in comparison with alloy obtained without PCA.

Influence of α-SiC Seed Addition on Spark Plasma Sintering of β-SiC with Al-B-C: Microstructural Development: Kyeong-Sik Cho, Hyun-Kwuon Lee, Sang-Woo Lee; J Korean Powder Metall Inst. 2010;17(1):13-22.; DOI: https://doi.org/10.4150/KPMI.2010.17.1.013

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The unique features of spark plasma sintering process are the possibilities of a very fast heating rate and a short holding time to obtain fully dense materials. beta-SiC powder with 0, 2, 6, 10 wt% of alpha-SiC particles (seeds) and 4 wt% of Al-B-C (sintering aids) were spark plasma sintered at 1700-1850°C for 10 min. The heating rate, applied pressure and sintering atmosphere were kept at 100°C/min, 40 MPa and a flowing Ar gas (500 CC/min). Microstructural development of SiC as function of seed content and temperature during spark plasma sintering was investigated quantitatively and statistically using image analysis. Quantitative image analyses on the sintered SiC ceramics were conducted on the grain size, aspect ratio and grain size distribution of SiC. The microstructure of SiC sintered up to 1700°C consisted of equiaxed grains. In contrast, the growth of large elongated SiC grains in small matrix grains was shown in sintered bodies at 1750°C and the plate-like grains interlocking microstructure had been developed by increasing sintering temperature. The introduction of alpha-SiC seeds into beta-SiC accelerated the grain growth of elongated grains during sintering, resulting in the plate-like grains interlocking microstructure. In the alpha-SiC seeds added in beta-SiC, the rate of grain growth decreased with alpha-SiC seed content, however, bulk density and aspect ratio of grains in sintered body increased.

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Effect of Sintering Temperature on Microstructure and Mechanical Properties for the Spark Plasma Sintered Titanium from CP-Ti Powders
Kyeong-Sik Cho, In-Beom Song, Min-Hyeok Jang, Ji-Hye Yoon, Myung-Hoon Oh, Jae-Keun Hong, Nho-Kwang Park
Journal of Korean Powder Metallurgy Institute.2010; 17(5): 365. CrossRef

Improvement of Microstructural Anisotropy of Nd-Fe-B-Ga-Nb Alloy by the Control of Hydrogen Reaction: S.H. Lee, D.H. Kim, J.H. Yu, D.W. Lee, B.K. Kim; J Korean Powder Metall Inst. 2010;17(1):23-28.; DOI: https://doi.org/10.4150/KPMI.2010.17.1.023

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Abstract PDF: HDDR treated anisotropic Nd-Fe-B powders have been widely used for the sheet motors and the sunroof motors of hybrid or electric vehicles, due to their excellent magnetic properties. Microstructural alignment of HDDR treated powders are mostly depending on the hydrogen reaction in disproportionation step, so the specific method to control hydrogenation reaction is required for improving magnetic properties. In disproportionation step, hydrogenation pressure and reaction time were controlled in the range of 0.15~1.0 atm for 15~180 min in order to control the micorstructural alignment of Nd_2Fe_14B phase and, at the same time, to improve remanence of HDDR treated magnet powders. In this study, we could obtain a well aligned anisotropic Nd-Fe-B-Ga-Nb alloy powder having high remanence of 12 kG by reducing hydrogen pressure down to 0.3 atm in disproportionation step.

A Study on the Behavior of Combustion Wave Propagation and the Structure of Porous TiNi Body during Self-propagating High-temperature Synthesis Process: Ji-Soon Kim, Victor E. Gjuntera, Jin-Chun Kim, Young-Soon Kwon; J Korean Powder Metall Inst. 2010;17(1):29-35.; DOI: https://doi.org/10.4150/KPMI.2010.17.1.029

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We produced cylindrical porous TiNi bodies by Self-propagating High-temperature Synthesis (SHS) process, varying the heating schedule prior to ignition of a loose preform compact made from (Ti+Ni) powder mixture. To investigate the effect of the heating schedule on the behaviour of combustion wave propagation and the structure of porous TiNi shape-memory alloy (SMA) body, change of temperature in the compact during SHS process was measured as a function of time and used for determining combustion temperature and combustion wave velocity. Microstructure of produced porous TiNi SMA body was observed and the results were discussed with the combustion characteristics. From the results it was concluded that the final average pore size could be controlled either by the combustion wave velocity or by the average temperature of the preform compact prior to ignition.

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Microwave-induced substitutional-combustion reaction of Fe3O4/Al ceramic matrix porous composite
C. C. Lee, N. Yoshikawa, S. Taniguchi
Journal of Materials Science.2011; 46(21): 7004. CrossRef

Production and Properties of Amorphous TiCuNi Powders by Mechanical Alloying and Spark Plasma Sintering: J.C. Kim, E.H. Kang, Y.S. Kwon, J.S. Kim, Si-Young Chang; J Korean Powder Metall Inst. 2010;17(1):36-43.; DOI: https://doi.org/10.4150/KPMI.2010.17.1.036

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In present work, amorphous TiCuNi powders were fabricated by mechanical alloying process. Amorphization and crystallization behaviors of the TiCuNi powders during high-energy ball milling and subsequent microstructure changes were studied by X-ray diffraction and transmission electron microscope. TEM samples were prepared by the focused ion beam technique. The morphology of powders prepared with different milling times was observed by field-emission scanning electron microscope and optical microscope. The powders developed a fine, layered, homogeneous structure with milling times. The crystallization behavior showed that glass transition, T_g, onset crystallization, T_x, and super cooled liquid range DeltaT=T_x-T_g were 628, 755 and 127K, respectively. The as-prepared amorphous TiCuNi powders were consolidated by spark plasma sintering process. Full densified TiCuNi samples were successfully produced by the spark plasma sintering process. Crystallization of the MA powders happened during sintering at 733K.

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Fabrication of Ultra Fine Grained Molybdenum and Mechanical Properties
Se-Hoon Kim, Young-Ik Seo, Dae-Gun Kim, Myung-Jin Suk, Young-Do Kim
Journal of Korean Powder Metallurgy Institute.2010; 17(3): 235. CrossRef

A Study on Rheological Behavior of Cordierite Honeycomb Extrusion Paste: Yong-Ik Song, Hyung-Tae Kim, Jin-Gu Lee, Won-Jung Yoon, Sung-Soo Ryu; J Korean Powder Metall Inst. 2010;17(1):44-51.; DOI: https://doi.org/10.4150/KPMI.2010.17.1.044

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Abstract PDF: The rheological behavior of a cordierite honeycomb extrusion paste was investigated by measuring torque values in a Brabender plastograph. The extrusion pastes were formulated using binder (methy cellulose, MC), solvent (water), plasticizer (ploy ethylene glycol, PEG) and lubricants (oleic acid, OA). The mixing sequence and optimum organic binder, at least for homogeneous mixed state, can be determined from the rheological point of view. 3%MC-30%H_2O-1.5%PEG-1.0%OA with respect to the cordierite powder was chosen as a binder composition for the extrusion process of cordierite powder.

Microstructure and Mechanical Behavior of Ultrafine Grained Bulk Al Processed by High Pressure Torsion of the Al Powders: Soo-Hyun Joo, Seung-Chae Yoon, Chong-Soo Lee, Hyong-Seop Kim; J Korean Powder Metall Inst. 2010;17(1):52-58.; DOI: https://doi.org/10.4150/KPMI.2010.17.1.052

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Bulk nanostructured metallic materials are generally synthesized by bottom-up processing which starts from powders for assembling bulk materials. In this study, the bottom-up powder metallurgy and High Pressure Torsion (HPT) approaches were combined to achieve both full density and grain refinement at the same time. After the HPT process at 473K, the disk samples reached a steady state condition when the microstructure and properties no longer evolve, and equilibrium boundaries with high angle grain boundaries (HAGBs) were dominant. The well dispersed alumina particles played important role of obstacles to dislocation glide and to grain growth, and thus, reduced the grain size at elevated temperature. The small grain size with HAGBs resulted in high strength and good ductility.

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Ultrafine Grained Cu-diamond Composites using High Pressure Torsion
Eun-Yoo Yoon, Dong-Jun Lee, Taek-Soo Kim, Hyoung-Seop Kim
Journal of Korean Powder Metallurgy Institute.2012; 19(3): 204. CrossRef
Densification of Copper Powders using High-pressure Torsion Process
Dong-Jun Lee, Eun-Yoo Yoon, Soo-Young Kang, Jung-Hwan Lee, Hyoung-Seop Kim
Journal of Korean Powder Metallurgy Institute.2012; 19(5): 333. CrossRef
Densification and Nanocrystallization of Water-Atomized Pure Iron Powder Using High Pressure Torsion
Eun-Yoo Yoon, Dong-Jun Lee, Ha-Neul Kim, Hee-Soo Kang, Eon-Sik Lee, Hyoung-Seop Kim
Journal of Korean Powder Metallurgy Institute.2011; 18(5): 411. CrossRef

Synthesis and Characterization of Y-doped SrTiO₃ Powder by Pechini Method: Mi-Young Yoon, R.H. Song, D.R. Shin, Hae-Jin Hwang; J Korean Powder Metall Inst. 2010;17(1):59-64.; DOI: https://doi.org/10.4150/KPMI.2010.17.1.059

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8 mol% Y-doped SrTiO_3 powder was synthesized by Pechini method from titanium isopropoxide, strontium nitrate, yttrium nitrate, citric acid and ethylene glycol. A Y_2Ti_2O_7 pyrochlore phase-free perovskite powder was obtained by calcining a polymeric resin, which was prepared from a precursor solution, at 500°C in an air atmosphere. Low temperature calcination could lead to a fine-grained microstructure. In the case of a solid-state reaction, an extended heat-treatment at high temperature in a reduced atmosphere needed to obtain a single phase perovskite SrTiO_3.

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Characteristics of Sr0.92Y0.08TiO3-δ Anode in Humidified MethaneFuel for Intermediate Temperature Solid Oxide Fuel Cells
Eun Kyung Park, Jeong Woo Yun
Journal of Electrochemical Science and Technology.2016; 7(1): 33. CrossRef
Characteristics of Sr0.92Y0.08TiO3-δAnode in Humidified MethaneFuel for Intermediate Temperature Solid Oxide Fuel Cells
Eun Kyung Park, Jeong Woo Yun
Journal of Electrochemical Science and Technology.2016; 7(1): 33. CrossRef
Synthesis of NiTi Alloy Powder by the Reaction of NiO-TiH2 Mixing Powders
Ki Cheol Jeon, Han-Eol Lee, Da-Mi Yim, Sung-Tag Oh
journal of Korean Powder Metallurgy Institute.1970; 22(4): 266. CrossRef

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