• 한국분말재료학회지
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• 제5권2호
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• pp.89-97
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• 1998

Sintering behavior of nanostructured(NS) W-Cu powders prepared by mechanical alloying (MA) was investigated as a function of sintering temperature. MA NS W-2owt%Cu and W-3owt%Cu composite powders with the crystal size of 20-30 nm were annealed at 90$0^{\circ}C$, and thermal characteristics of those powders were investigated by DSC. Sintering behavior of MA NS W-Cu composite powders was investigated during the solid-state sintering and the Cu-liquid phase sintering. The new nanosintering phenonenon of MA W-Cu powders at solid-state sintering temperature was suggested to explain the W-grain growth in the inside of MA powders. The sintering densification of MA NS W-Cu powders was enhanced at Cu melting temperature by arrangement of MA powders, i.e., the first rearrangement of MA powders was occurred, and then the rearrangement of W-grains in the sintered parts was also took place during liquid-phase sintering, i.e., the second rearrangement was happened. Due to the double rearrangement process of MA NS W-Cu powders, the high sintered density with more than 96%o was obtained and the fine and high homogeneous state of W and Cu phases was achieved by sintering at 1200 $^{\circ}C$.

• 한국분말재료학회지
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• 제17권1호
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• pp.36-43
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• 2010

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 ${\Delta}T=T_x-T_g$ 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.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.670-671
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• 2006

We report on the mechanical and structural properties of nanocrystalline 8% and 10% mol yttria stabilized zirconia (YSZ) obtained using mechanical alloying (MA). The as-milled powders show a body-centered cubic structure with grain sizes in the nanometer scale. After uniaxial pressing and sintering the compacts exhibit good mechanical properties. We discuss the correlation of these enhanced properties with the microstructural changes induced by heat treatment.

• 한국재료학회지
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• 제10권8호
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• pp.532-539
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• 2000

Diamond 공구용 Co-0.5C-(15∼20)Cr-20Ni-8W-(2∼7)Fe 합금 결합제를 볼밍링(ball-milling)법과 기계적 합금화(mechanical alloying) 법으로 합성하였다. stearic acid의 첨가 유무에 상관없이 Co-0.5C-(15∼20)Cr-20Ni-8W-(2∼7)Fe 합금의 경우 6시간 동안 합금화된 금속 분말에서 미세 접합(micro welding) 형상이 균일하게 관찰되었다. stearic acid를 첨가하지 않을 때는 부분적으로 조대화된 분말이 형성되었으나 2% 첨가한 경우 미세하고 판상의 분말이 얻어졌다. stearic acid가 첨가된 복합분말을 열간 압축하여 기계적 성질을 평가한 결과 굽힘강도 1100MPa, 경도 46H(sub)Rc의 특성을 나타냈다.

• 한국분말재료학회지
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• 제6권1호
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• pp.27-35
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• 1999

A study was made on the fabrication of nanostructured Fe-Co powders by mechanical alloying and their magnetic properties. Microstrural development during the process of MA was inverstigated by means of X-ray diffraction, differential thermal analyzer, scanning electron microscopy and transmission electron microscopy. The magnetic properties of NS Fe-Co powders were evaluated through the measurements of the saturation magnetization $(M_s)$ as well as the coercivity $(H_c)$. The average grain size calculated from line braodening in XRD peak was about 10nm or less and confirmed by TEM. In this experiment, two different milling methods (cycle opertion and conventional milling) were used. Cycle operation had an advantage over the conventional milling method in that more refined powders can be obtained. Solid state alloying of the components was confirmed from both the change of the saturation magnetization and the change of lattice parameter with Co contentration. Maxium $M_s$ was obtained at the composition of 30at.%Co. Relatively high coercivities of 10~150e were obtained for the compositions investigated, and this seems to be due to the high amount of internal strain introduced during milling.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 추계학술대회 논문집
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• pp.390-393
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• 2008

In this research, we introduce a new process for the consolidation of different types of powders such as metal and ceramic powders by using a magnetic pulsed compaction (MPC). The successful consolidation of many kinds of powers including nanopowder by MPC has been presented. A wide range of experimental studies were carried out for characterizing mechanical properties and microstructure of the MPCed materials. It was found that effective properties of high strength and full density maintaining nanoscal microstructure were achieved. finally, optimization of the compaction parameters and sintering conditions could lead to the good consolidation of powders (metal, ceramic, nano-powder) with higher density, and even further enhanced mechanical properties.

• 한국분말재료학회지
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• 제26권2호
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• pp.101-106
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• 2019

Ni-based oxide dispersion strengthened (ODS) alloys have a higher usable temperature and better high-temperature mechanical properties than conventional superalloys. They are therefore being explored for applications in various fields such as those of aerospace and gas turbines. In general, ODS alloys are manufactured from alloy powders by mechanical alloying of element powders. However, our research team produces alloy powders in which the $Ni_5Y$ intermetallic phase is formed by an atomizing process. In this study, mechanical alloying was performed using a planetary mill to analyze the milling behavior of Ni-based oxide dispersions strengthened alloy powder in which the $Ni_5Y$ is the intermetallic phase. As the milling time increased, the $Ni_5Y$ intermetallic phase was refined. These results are confirmed by SEM and EPMA analysis on microstructure. In addition, it is confirmed that as the milling increased, the mechanical properties of Ni-based ODS alloy powder improve due to grain refinement by plastic deformation.

• 한국세라믹학회지
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• 제35권6호
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• pp.610-618
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• 1998

Alumina were added to ceria based ceramic powders upto 9.7 vol% and composite powders were sprayed by plasma spraying process in order to improve the mechanical properties such as hardness fracture tough-ness and thermal shock resistance. The ceria based coating sprayed without alumina has the typical colum-nar and lamellar structure. Alumina addition has lowered the amount of columnar and lamellar sturcture Added alumina was segreagated in the grain boundary and grain of ceria based crystal accompanied with pore. The maximum value of density and the minimum value of porosity were observed at the sprayed coating with 4.8 vol% alumina. The hardness fracture toughness and thermal shock resistance were increased with alumina addition. The improvement of mechanical properties of plasma sparyed ceria based coatings result-ed from the disapperance of the columnar and lamellar sturcture by addition of alumina.

• Food Science and Biotechnology
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• 제14권6호
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• pp.758-765
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• 2005

Instant powders that only require mixing with water prior to consumption can be produced by extrusion for use in products such as instant beverages. Both extrusion processing conditions and particle size of powder are important to end-product characteristics. In this study, a twin-screw extruder was used under various processing conditions (feed moisture, barrel temperature, and screw speed) to produce extrudates from soft wheat flour, which were ground to powders with particle size ranges of less than 93, 93-145, and $145-249\;{\mu}m$. Effects of adding soy lecithin to wheat flour before extrusion were also investigated. Water absorption, solubility, suspension viscosity, and dispersibility of wheat powders were related to specific. mechanical energy measured during extrusion. Powder particle size was important to instant properties, especially ease of dispersal in water and stability to sedimentation. Addition of lecithin significantly improved dispersibility of powders.

• 한국분말재료학회지
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• 제7권3호
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• pp.154-160
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• 2000

In order to enhance sinterability of W-Cu composites used for heat sink materials, mechanical alloying process where both homogeneous mixing of component powders and fine dispersion of minor phase can be easily attained was employed. Nanostructured W-Cu powders prepared by mechanical alloying showed W grain size ranged of 20-50 nm and were able to be efficiently sintered owing to the fine particle size as well as uniform distribution of Cu phase. The thermal properties such as electrical resistivity, coefficient of thermal expansion and thermal conductivity were evaluated as functions of temperature and Cu content. It was found that the coefficient of thermal expansion could be controlled by changing Cu content. The measured electrical resistivities and thermal diffusivities were also varied with Cu content. The thermal conductivities calculated from the values of resistivities and diffusivities showed similar tendency as a function of temperatures. However, this is in contradiction with thermal conductivities of pure W and Cu which decrease with increasing temperature.