Journal of Powder Materials

Thermoelectric Properties of Half-Heusler ZrNiSn_1-xSb_x Synthesized by Mechanical Alloying Process and Vacuum Hot Pressing: Soon-Chul Ur; J Korean Powder Metall Inst. 2011;18(5):401-405.; DOI: https://doi.org/10.4150/KPMI.2011.18.5.401

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Abstract PDF: Half-heusler phase ZrNiSn is one of the potential thermoelectric materials for high temperature application. In an attempt to investigate the effect of Sb doping on thermoelectric properties, half-heusler phase ZrNiSn_1-xSb_x (0leqxleq0.08) was synthesized by mechanical alloying of stoichiometric elemental powder compositions, and consolidated by vacuum hot pressing. Phase transformations during mechanical alloying and hot consolidation were investigated using XRD. Sb doped ZrNiSn was successfully produced in all doping ranges by vacuum hot pressing using as-milled powders without subsequent annealing. Thermoelectric properties as functions of temperature and Sb contents were evaluated for the hot pressed specimens. Sb doping up to x=0.04 in ZrNiSn_1-xSb_x was shown to be effective on thermoelectric properties and the figure of merit (ZT) was shown to reach to the maximum at x=0.02 in this study.

Quantitative Analysis of Roughness of Powder Surface Using Three-Dimensional Laser Profiler and its Effect on Green Strength of Powder Compacts: Dong-Jun Lee, Eun-Yoo Yoon, Ha-Neul Kim, Hee-Soo Kang, Eon-Sik Lee, Hyoung-Seop Kim; J Korean Powder Metall Inst. 2011;18(5):406-410.; DOI: https://doi.org/10.4150/KPMI.2011.18.5.406

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Green strength is an important property of powders since high green strength guarantees easy and safe handling before sintering. The green strength of a powder compact is related to mainly mechanical and surface characters, governed by interlocking of the particles. In this study, the effect of powder surface roughness on the green strength of iron powders was investigated using a transverse rupture test. Three-dimensional laser profiler was employed for quantitative analyses of the surface roughness. Two different surface conditions, i.e. surface roughness, of powders were compared. The powders having rough surfaces show higher green strength than the round surface powders since higher roughness leads increasing interlocked area between the contacting powders.

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A Study on the Carbon Composite Briquette Iron Manufacturing Using Fe-containing Process Wastes
Jong Yeong Yu, Dae Young Yang, Hee Dong Shin, Il Sohn
Journal of the Korean Institute of Resources Recycling.2015; 24(3): 34. CrossRef
Obtaining Mechanical Properties of Fe Powder Using a Combined Nanoindentation and the Finite Element Method
Hyeok Jae Jeong, Dong Jun Lee, Eun Yoo Yoon, Eon Sik Lee, Nack Joon Kim, Hyeong Seop Kim
Journal of Korean Powder Metallurgy Institute.2013; 20(4): 280. 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; J Korean Powder Metall Inst. 2011;18(5):411-416.; DOI: https://doi.org/10.4150/KPMI.2011.18.5.411

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In this study, powder metallurgy and severe plastic deformation by high-pressure torsion (HPT) approaches were combined to achieve both full density and grain refinement at the same time. Water-atomized pure iron powders were consolidated to disc-shaped samples at room temperature using HPT of 10 GPa up to 3 turns. The resulting microstructural size decreases with increasing strain and reaches a steady-state with nanocrystalline (down to ~250 nm in average grain size) structure. The water-atomized iron powders were deformed plastically as well as fully densified, as high as 99% of relative density by high pressure, resulting in effective grain size refinements and enhanced microhardness values.

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Analyses of Densification and Consolidation of Copper Powders during High-Pressure Torsion Process Using Finite Element Method
Dong Jun Lee, Eun Yoo Yoon
Journal of Korean Powder Metallurgy Institute.2015; 22(1): 6. CrossRef
Microstructure Evolution and Mechanical Properties of Al-1080 Processed by a Combination of Equal Channel Angular Pressing and High Pressure Torsion
Mohamed Ibrahim Abd El Aal, Eun Yoo Yoon, Hyoung Seop Kim
Metallurgical and Materials Transactions A.2013; 44(6): 2581. CrossRef
Trend in Research of Powder Consolidation Using Severe Plastic Deformation
Eun Yoo Yoon, Dong Jun Lee, Dong-Hyun Ahn, Hyuk Jae Jeong, Hyoung Seop Kim
Journal of Korean Powder Metallurgy Institute.2013; 20(2): 148. CrossRef
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

Tribology Properties of Nanodiamond Dispersed Engine Oil: S.H. Jun, Y.R Uhm, C.K. Rhee; J Korean Powder Metall Inst. 2011;18(5):417-422.; DOI: https://doi.org/10.4150/KPMI.2011.18.5.417

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Hydrophobic nanodiamond (ND) were dispersed in engine oil (Helix Oil, Shell co.) as an additives to improve tribology properties. In this study, nanodiamond prepared by an explosive method was used. Tribology properties of both pure Helix oil and engine oil containing ND additive were evaluated. The rotating disks were made of Gray Cast Iron (240 Hv) and SKD11 (710 Hv). Surface topographies of the disks' wear tracks and friction coefficient were compared. The results show that nanodiamond-dispersed lubricants are capable of reducing these metals' wear loss. The friction coefficient is strongly affected to the hardness of wear track.

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Wear Characteristics of Lubricant with Nano-diamond Particles on Al-6061 Aluminum Alloy
Sung-Wan Hwang
Journal of the Korean Society of Manufacturing Process Engineers.2021; 20(12): 16. CrossRef
Tribological properties of nanodiamonds in aqueous suspensions: effect of the surface charge
Zijian Liu, Dustin Leininger, Amir Koolivand, Alex I. Smirnov, Olga Shenderova, Donald W. Brenner, Jacqueline Krim
RSC Advances.2015; 5(96): 78933. CrossRef

Influence of Metal-Coating Layer on an Electrical Resistivity of Thick-Film-Type Thermoelectric Modules Fabricated by a Screen Printing Process: Kyung-Tae Kim, Hye-Young Koo, Gook-Hyun Ha; J Korean Powder Metall Inst. 2011;18(5):423-429.; DOI: https://doi.org/10.4150/KPMI.2011.18.5.423

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Thermoelectric-thick films were fabricated by using a screen printing process of n and p-type bismuth-telluride-based pastes. The screen-printed thick films have approximately 30 µm in thickness and show rough surfaces yielding an empty gap between an electrode and the thick film. The gap might result in an increase of an electrical resistivity of the fabricated thick-film-type thermoelectric module. In this study, we suggest a conductive metal coating onto the surfaces of the screen-printed paste in order to reduce the contact resistance in the module. As a result, the electrical resistivity of the thermoelectric module having a gold coating layer was significantly reduced up to 30% compared to that of a module without any metal coating. This result indicates that an introduction of conductive metal layers is effective to decrease the contact resistivity of a thick-film-typed thermoelectric module processed by screen printing.

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Flexible Thermoelectric Device Using Thick Films for Energy Harvesting from the Human Body
Han Ki Cho, Da Hye Kim, Hye Sun Sin, Churl-Hee Cho, Seungwoo Han
Journal of the Korean Ceramic Society.2017; 54(6): 518. CrossRef

Morphologies of Brazed NiO-YSZ/316 Stainless Steel Using B-Ni2 Brazing Filler Alloy in a Solid Oxide Fuel Cell System: Sung-Kyu Lee, Kyoung-Hoon Kang, Hyun-Seon Hong, Sang-Kook Woo; J Korean Powder Metall Inst. 2011;18(5):430-436.; DOI: https://doi.org/10.4150/KPMI.2011.18.5.430

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Abstract PDF: Joining of NiO-YSZ to 316 stainless steel was carried out with B-Ni2 brazing alloy (3 wt% Fe, 4.5 wt% Si, 3.2 wt% B, 7 wt% Cr, Ni-balance, m.p. 971-999°C) to seal the NiO-YSZ anode/316 stainless steel interconnect structure in a SOFC. In the present research, interfacial (chemical) reactions during brazing at the NiO-YSZ/316 stainless steel interconnect were enhanced by the two processing methods, a) addition of an electroless nickel plate to NiO-YSZ as a coating or b) deposition of titanium layer onto NiO-YSZ by magnetron plasma sputtering method, with process variables and procedures optimized during the pre-processing. Brazing was performed in a cold-wall vacuum furnace at 1080°C. Post-brazing interfacial morphologies between NiO-YSZ and 316 stainless steel were examined by SEM and EDS methods. The results indicate that B-Ni2 brazing filler alloy was fused fully during brazing and continuous interfacial layer formation depended on the method of pre-coating NiO-YSZ. The inter-diffusion of elements was promoted by titanium-deposition: the diffusion reaction thickness of the interfacial area was reduced to less than 5 µm compared to 100 µm for electroless nickel-deposited NiO-YSZ cermet.

Thermoelectric Properties of Bi₂Te_2.7Se_0.3 Powder Synthesized by an Oxide-Reduction Process: Bae-Gun Park, Gil-Geun Lee, Woo-Yeol Kim, Gook-Hyun Ha; J Korean Powder Metall Inst. 2011;18(5):437-442.; DOI: https://doi.org/10.4150/KPMI.2011.18.5.437

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Abstract PDF: The present study focused on the synthesis of Bi-Te-Se-based powder by an oxide-reduction process, and analysis of the thermoelectric properties of the synthesized powder. The phase structure, chemical composition, and morphology of the synthesized powder were analyzed by XRD, EPMA and SEM. The synthesized powder was sintered by spark plasma sintering. The thermoelectric properties of the sintered body were evaluated by measuring its Seebeck coefficient, electrical resistivity, and thermal conductivity. Bi_2Te_2.7Se_0.3 powder was synthesized from a mixture of Bi_2O_3, TeO_2, and SeO_2 powders by mechanical milling, calcination, and reduction. The sintered body of the synthesized powder exhibited n-type thermoelectric characteristics. The thermoelectric properties of the sintered bodies depend on the reduction temperature. The Seebeck coefficient and electrical resistivity of the sintered body were increased with increasing reduction temperature. The sintered body of the Bi_2Te_2.7Se_0.3 powder synthesized at 360°C showed about 0.5 of the figure of merit (ZT) at room temperature.

Effect of Magnetic properties and Microstructure of Hydrogenation stage in HDDR process: S.H. Lee, J.H. Yu, Y.D. Kim; J Korean Powder Metall Inst. 2011;18(5):443-448.; DOI: https://doi.org/10.4150/KPMI.2011.18.5.443

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The HDDR(hydrogenation-disproportionation-desorption-recombination) process can be used as an effective way of converting no coercivity Nd-Fe-B material, with a coarse Nd_2Fe_14B grain structure to a highly coercive one with a fine grain. Careful control of the HDDR process can lead to an anisotropic Nd_2Fe_14B without any post aligning process. In this study, the effect of hydrogen gas input at various temperature in range of 200sim500°C of hydrogenation stage (named Modified-solid HDDR, MS-HDDR) on the magnetic properties has been investigated. The powder from the modified-solid HDDR process exhibits Br of 11.7 kG and iHc of 10.7 kOe, which are superior to those of the powder prepared using the normal HDDR process.

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The Influence of Dehydrogenation Speed on the Microstructure and Magnetic Properties of Nd-Fe-B Magnets Prepared by HDDR Process
Hee-Ryoung Cha, Ji-Hun Yu, Youn-Kyoung Baek, Hae-Woong Kwon, Yang-Do Kim, Jung-Goo Lee
Journal of Magnetics.2014; 19(1): 49. CrossRef

Synthesis and Characterization of (AgSbTe₂)₁₅(GeTe)₈₅ Thermoelectric Powder by Gas Atomization Process: Hyo-Seob Kim, Jin-Kyu Lee, Jar-Myung Koo, Byong-Sun Chun, Soon-Jik Hong; J Korean Powder Metall Inst. 2011;18(5):449-455.; DOI: https://doi.org/10.4150/KPMI.2011.18.5.449

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In this study, p-type (AgSbTe_2)_15(GeTe)_85: TAGS-85 compound powders were prepared by gas atomization process, and then their microstructures and mechanical properties were investigated. The fabricated powders were of spherical shape, had clean surface, and illustrated fine microstructure and homogeneous AgSbTe_2 + GeTe solid solution. Powder X-ray diffraction results revealed that the crystal structure of the TAGS-85 sample was single rhombohedral GeTe phase, which with a space group R_3m. The grain size of the powder particles increased while the micro Vickers hardness decreased with increasing annealing temperature within the range of 573 K and 723 K due to grain growth and loss of Te. In addition, the crystal structure of the powder went through a phase transformation from rhombohedral (R_3m) at low-temperature to cubic (F_m-3m) at high-temperature with increasing annealing temperature. The micro Vickers hardness of the as-atomized powder was around 165 Hv, while it decreased gradually to 130 Hv after annealing at 673K, which is still higher than most other fabrication processes.

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Thermoelectric properties of n-type Bi2Te3 alloys produced by a combined process of magnetic pulsed compaction (MPC) and spark plasma sintering (SPS)
Chul-Hee Lee, M. Fatih Kilicaslan, Babu Madavali, Soon-Jik Hong
Research on Chemical Intermediates.2014; 40(7): 2543. CrossRef

Microstructural Evaluation and High Temperature Mechanical Properties of Ni-22Cr-18Fe-9Mo ODS Alloy: Seok-Hoan Jeong, Suk-Hoon Kang, Chang-Hee Han, Tae-Kyu Kim, Do-Hyang Kim, Jin-Sung Jang; J Korean Powder Metall Inst. 2011;18(5):456-462.; DOI: https://doi.org/10.4150/KPMI.2011.18.5.456

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Yttrium oxide is one of the most thermo-dynamically stable materials, so that it is generally used as a dispersoid in many kinds of dispersion strengthed alloys. In this study, a nickel-base superalloy is strengthened by dispersion of yttrium oxide particles. Elemental powders with the composition of Ni-22Cr-18Fe-9Mo were mechanically alloyed(M.A.) with 0.6 wt% Y_2O_3. The MA powders were then HIP(hot isotactic press)ed and hot rolled. Most oxide particles in Ni-22Cr-18Fe-9Mo base ODS alloy were found to be Y-Ti-O type. The oxide particles were uniformly dispersed in the matrix and also on the grain boundaries. Tensile test results show that the yield strength and ultimate tensile strength of ODS alloy specimens were 1.2~1.7 times higher than those of the conventional HastelloyTM X(R), which has the same chemical compositions with ODS alloy specimens except the oxide particles.

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Effect of Y2O3 dispersoids on microstructure and creep properties of Hastelloy X processed by laser powder-bed fusion
Jovid U. Rakhmonov, Christoph Kenel, Anthony De Luca, Christian Leinenbach, David C. Dunand
Additive Manufacturing Letters.2022; 3: 100069. CrossRef
Evaluation of Creep Reliability of Powder Metallurgy and Cast-type Ni-based Superalloy by Using Ultrasonic Wave
Chan-Yang Choi, Jin-Hun Song, Se-Ung Oh, Chung-Seok Kim, Sook-In Kwun, Sung-Tag Oh, Chang-Yong Hyun, Jai-Won Byeon
Journal of Korean Powder Metallurgy Institute.2012; 19(3): 215. CrossRef

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