• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.1203-1204
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• 2006

Cu-$TiB_2$ nanocomposite powders were synthesized by combining high-energy ball-milling of Cu-Ti-B mixtures and subsequent self-propagating high temperature synthesis (SHS). Cu-40wt.%$TiB_2$ powders were produced by SHS reaction and ball-milled. The milled SHS powder was mixed with Cu powders by ball milling to produce Cu-2.5wt.%$TiB_2$ composites. $TiB_2$ particles less than 250nm were formed in the copper matrix after SHS-reaction. The releative density, electrical conductivity and hardness of specimens sintered at $650-750^{\circ}C$ were nearly 98%, 83%IACS and 71HRB, respectively. After heat treatment at 850 to $950^{\circ}C$ for 2 hours under Ar atmosphere, hardness was descedned by 15%. Our Cu-$TiB_2$ composite showed good thermal stability at eleveated temperature.

• Progress in Superconductivity
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• 제10권1호
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• pp.23-28
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• 2008

We report refinement of crystalline boron by an attrition ball milling system and the superconducting properties of the $MgB_2$ pellets prepared from the refined boron. In this work, we have conducted the ball milling with only crystalline boron powder, in order to improve homogeneity and control the grain size of the $MgB_2$ that is formed from it. We observed that the crystalline responses in the ball-milled boron became broader and weaker when the ball-milling time was further increased. On the other hand, the $B_{2}O_{3}$ peak became stronger in the powders, resulting in an increase in the amount of MgO within the $MgB_2$ volume. The main reason for this is a greater oxygen uptake. From the perspective of the superconducting properties, however, the sample prepared from boron that was ball milled for 5 hours showed an improvement of critical current density ($J_c$), even with increased MgO phase, under an external magnetic field at 5 and 20 K.

• 한국기계가공학회지
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• 제20권4호
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• pp.87-93
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• 2021

The mold industry is competitive, and mold should be processed under optimal conditions for efficient processing. However, the cutting conditions of the ball-end mill, which are a major factor in mold processing, are mostly set empirically, and considerable research is required for increasing the tool life and processing accuracy. In this study, a tool dynamometer and an eddy current sensor were used along with NI-DAQ, a data acquisition device, to obtain characteristic values of the cutting force and tool deformation during the ball end-mill machining of inclined surfaces at a machining center. The cutting force and tool deformation were measured in an experiment. It was found that the tool received the greatest cutting force at the end of the machining process, and the deformation of the tool increased rapidly. Furthermore, the cutting force tended to increase with the angle and number of rotations. The deformation increased rapidly during the machining of a 45° inclined surface.

• 한국분말재료학회지
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• 제16권1호
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• pp.9-15
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• 2009

Amorphization and crystallization behaviors of $Ti_{50}Cu_{50}Ni_{20}Al_{10}$ powders during high-energy ball milling and subsequent heat treatment were studied. Full amorphization obtained after milling for 30 h was confirmed by X-ray diffraction and transmission electron microscope. The morphology of powders prepared using different milling times was observed by field-emission scanning electron microscope. The powders developed a fine, layered, homogeneous structure with prolonged milling. The crystallization behavior showed that the glass transition, $T_g$, onset crystallization, $T_x$, and super cooled liquid range ${\Delta}T=T_x-T_g$ were 691,771 and 80 K, respectively. The isothermal transformation kinetics was analyzed by the John-Mehn-Avrami equation. The Avrami exponent was close to 2.5, which corresponds to the transformation process with a diffusion-controlled type at nearly constant nucleation rate. The activation energy of crystallization for the alloy in the isothermal annealing process calculated using an Arrhenius plot was 345 kJ/mol.

• Journal of the Korean Physical Society
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• 제73권9호
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• pp.1340-1345
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• 2018

Mo-10 at.% Cu nanocomposite powders were fabricated by using planetary ball-milling (PBM), a mechanical alloying technique for preparing nanocomposite alloy powders of metals with mutual insolubility, and the variations in the physical and the chemical characteristics with the process conditions were investigated. We observed that Mo-10 at.% Cu was an appropriate composition to ensure a good alloying grade and minimal welding between particles. The influences of the temperature and the milling conditions on the mechanical alloying process and the phase change of Mo-10 at.% Cu composite powders were investigated, and the particle and the grain sizes of the powders after mechanical alloying were confirmed. The Mo-10 at.% Cu powders showed homogeneous elemental distributions and no phase changes up to $1200^{\circ}C$; their compositions were retained after the mechanical alloying process. The finest grain size obtained was about 5 nm for powders processed using optimum PBM processing conditions: ball-to-powder weight ratio of 5 : 1, ambient air atmosphere, a milling time of 20 h, a rotation speed of 200 rpm, and a stearic acid content of 4 wt.% produced superfine-grained Mo-10 at.% Cu nanocomposite powders with an average grain size of 5 nm (which is smaller than that of other similar materials reported in the literature). The analytical results confirmed that the PBM technique presented here is a promising method for preparing superfine-grained Mo-10 at.% Cu powders with improved properties.

• 한국재료학회지
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• 제33권2호
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• pp.63-70
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• 2023

In this study, crystallization was effectively suppressed in Al-based metallic glasses (Al-MGs) during pulverization by cryo-milling by applying an extremely low processing temperature and using a surfactant. Before Al-MGs can be used as an additive in Ag paste for solar cells, the particle sizes of the Al-MGs must be reduced by milling. However, during the ball milling process crystallization of the Al-MG is a problem. Once the Al-MG is crystallized, they no longer exhibit glass-like behavior, such as thermoplastic deformation, which is critical to decrease the electrical resistance of the Ag electrode. The main reason for crystallization during the ball milling process is the heat generated by collisions between the particles and the balls, or between the particles. Once the heat reaches the crystallization temperature of the Al-MGs, they start crystallization. Another reason for the crystallization is agglomeration of the particles. If the initially fed particles become severely agglomerated, they coalesce instead of being pulverized during the milling. The coalesced particles experience more collisions and finally crystallize. In this study, the heat generated during milling was suppressed by using cryo-milling with liquid-nitrogen, which was regularly fed into the milling jar. Also, the MG powders were dispersed using a surfactant before milling, so that the problem of agglomeration was resolved. Cryo-milling with the surfactant led to D50 = 10 um after 6 h milling, and we finally achieved a specific contact resistance of 0.22 mΩcm² and electrical resistivity of 2.81 μΩcm using the milled MG particles.

• 한국재료학회지
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• 제16권2호
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• pp.116-122
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• 2006

The effects of milling time in argon and hydrogen atmospheres on the hydrogen sorption speed of a getter alloy, $Zr_{57}V_{36}Fe_{7}$, was studied. The hydrogen sorption speed of milled alloys was evaluated at room temperature. In argon, as the oxygen content increased with milling time, the hydrogen sorption speed decreased accordingly. In hydrogen, on the other hand, the oxygen content decreased at first with milling time but started increasing after 5 hrs of milling time. Similar to the case of argon, however, the hydrogen sorption speed changed exactly in the opposite direction with the oxygen content, exhibiting the maximum rate at 5 hrs. These results suggest that in both atmospheres the hydrogen sorption speeds are inversely related with the oxygen contents.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 1993년도 추계학술강연 및 발표대회강연 및 발표논문 초록집
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• pp.18-19
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• 1993

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 1993년도 추계학술강연 및 발표대회강연 및 발표논문 초록집
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• pp.20-21
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• 1993

• 한국자기학회지
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• 제5권6호
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• pp.928-936
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• 1995

원료$(NiO,\;CuO,\;ZnO,\;Fe_{2}O_{3})$를 사용하여 원하는 조성의 NiCuZn Ferrite 를 제조하기 위해서는, 가능한 고농도 원료슬러리를 균일 혼합 및 효율적인 분쇄를 하여야 한다. 본 연구에서는 습식 볼밀을 사용하여 혼합원료 입자들의 분산상태를 유지하며, 최적의 혼합 및 분쇄조건을 확립하고자 한다. 먼저 혼합원료의 분산특성을 조사한 후, 볼밀링시 사용하고자 하는 pH 영역을 결정하고, 이 때 사용 가능한 분산제를 선택하였다. 또한, 분산제의 양, 분쇄시간, 볼밀링 가능한 슬러리의 농도 등을 조사하였다. 혼합원료의 분산거동을 조사한 결과, 혼합 및 분쇄할 때 음이온성 고분자전해질(poly acrylic ammonium salt)이 적절한 분산제였으며, 분산제 양은 0.7 wt%가 적절하였다. 이 때 최적 볼밀링 시간은 18시간이었으며 볼밀링이 가능한 슬러리의 최대 농도는 약 55 vol%이었다. 혼합원료 30 vol%슬러리에 음이온성 고분자전해질을 0.7 wt% 첨가하여 18시간 볼밀링한 결과, 혼합원료의 평균입자경은 약 $0.54\mu\textrm{m}$, 비표면적은 $12.92m^{2}/cc$이었다. 이를 $700^{\circ}C$에서 3시간 동안 하소하면 단일상의 NiCuZn Ferrite가 얻어졌다.