• Journal of Powder Materials
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• v.10 no.4
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• pp.270-274
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• 2003

Recently, the fabrication process of W-Cu nanocomposite powders has been researched to improve the sinterability by mechanochemical process (MCP), which consists of ball milling and hydrogen-reduction with W- and Cu-oxide mixture. However, there are many control variables in this process because the W oxides are hydrogen-reduced via several reduction stages at high temperature over 80$0^{\circ}C$ with susceptive reduction conditions. In this experiment, the W-15 wt%Cu nanocomposite powder was fabricated with the ball-milling and hydrogen-reduction process using W and CuO powder. The microstructure of the fabricated W-Cu nanocomposite powder was homogeneously composed of the fine W particles embedded in the Cu matrix. In the sintering process, the solid state sintering was certainly observed around 85$0^{\circ}C$ at the heating rate of 1$0^{\circ}C$/min. It is considered that the solid state sintering at low temperature range should occur as a result of the sintering of Cu phase between aggregates. The specimen was fully densified over 98% for theoretical density at 120$0^{\circ}C$ for 1 h with the heating rate of 1$0^{\circ}C$/min.

• Journal of Powder Materials
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• v.16 no.1
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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 Powder Materials
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• v.30 no.6
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• pp.470-477
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• 2023

The effects of annealing on the microstructure and mechanical properties of Al-Zn-Mg-Cu-Si alloys fabricated by high-energy ball milling (HEBM) and spark plasma sintering (SPS) were investigated. The HEBM-free sintered alloy primarily contained Mg₂Si, Q-AlCuMgSi, and Si phases. Meanwhile, the HEBM-sintered alloy contains Mg-free Si and θ-Al₂Cu phases due to the formation of MgO, which causes Mg depletion in the Al matrix. Annealing without and with HEBM at 500℃ causes partial dissolution and coarsening of the Q-AlCuMgSi and Mg₂Si phases in the alloy and dissolution of the θ-Al₂Cu phase in the alloy, respectively. In both alloys, a thermally stable α-AlFeSi phase was formed after long-term heat treatment. The grain size of the sintered alloys with and without HEBM increased from 0.5 to 1.0 ㎛ and from 2.9 to 6.3 ㎛, respectively. The hardness of the sintered alloy increases after annealing for 1 h but decreases significantly after 24 h of annealing. Extending the annealing time to 168 h improved the hardness of the alloy without HEBM but had little effect on the alloy with HEBM. The relationship between the microstructural factors and the hardness of the sintered and annealed alloys is discussed.

• Journal of Powder Materials
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• v.21 no.5
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• pp.338-342
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• 2014

In the present work, we investigated the mechanical alloying of binary Ga-Se(1:1) and Ga-Te(1;1) sysyems. The high-energy ball-milling was performed at $40^{\circ}C$ where one of constituents (Ga) is molten state. The purpose of the work was to see whether reactions between constituent elements are accelerated by the presence of a liquid phase. During the ball-milling, the liquid Ga phase completely disappeared and the resulting powders consist of nanocrystalline grain of ~20 nm with partly amorphized phases. However, no intermetallic compounds formed in spite of the presence of the liquid phases which has much higher diffusivity than solid constituents. By subsequent heat-treatments, the intermetallic compounds such as GaSe and GaTe formed at relatively low temperatures. The formation temperature of theses compound was much lower than those predicted by equilibrium phase diagram. The comparison of the ball-milled powders with un-milled ones indicated that the easy formation of intermetallic compound or allying occurs at low temperatures.

• Journal of Power System Engineering
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• v.17 no.5
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• pp.78-85
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• 2013

A high thermal conductivity material, namely graphene is treated by planetary ball milling machine to transport the heat by increasing the temperature. Experiments were performed to assess the heat transfer enhancement benefits of coating the bottom wall of copper substrate with graphene. It is well known that the graphene is unable to disperse into base fluid without any treatment, which is due to the several reasons such as attachment of hydrophobic surface, agglomeration and impurity. To further improve the dispersibility and thermal characteristics, planetary ball milling approach is used to grind the raw samples at optimized condition. The results are examined by transmission electron microscopy, x-ray diffraction, Raman spectrometer, UV-spectrometer, thermal conductivity and thermal imager. Thermal conductivity measurements of structures are taken to support the explanation of heat transfer properties of different samples. As a result, it is found that the planetary ball milling approach is effective for improvement of both the dispersion and heat carriers of carbon based material. Indeed, the heat transfer of the ground graphene coated substrate was higher than that of the copper substrate with raw graphene.

• Journal of Powder Materials
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• v.15 no.1
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• pp.1-5
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• 2008

ZnS-$SiO_2$ composite is normally used for sputtering target. In recent years, high sputtering power for higher deposition rate often causes crack formation of the target. Therefore the target material is required that the sintered target material should have high crack resistance, excellent strength and a homogeneous microstructure with high sintered density. In this study, raw ZnS and ZnS-$SiO_2$ powders prepared by a 3-D mixer or high energy ball-milling were successfully densified by spark plasma sintering, the effective densification method of hard-to-sinter materials in a short time. After sintering, the fracture toughness was measured by the indentation fracture (IF) method. Due to the effect of crack deflection by the residual stress occurred by the second phase of fine $SiO_2$, the hardness and fracture toughness reached to 3.031 GPa and $1.014MPa{\cdot}m^{1/2}$, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.648-651
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• 2003

Fine $LaAlO_3$ powders were successfully synthesized from $La_2O_3$ and ${\gamma}-Al_2O_3$ powders milling for $10{\sim}50hrs$ via the high energy milling technique (mechanochemical methode) in room temperature and air. The particle size of $LaAlO_3$ powder were estimated from XRD patterns and SEM images to be $160{\sim}180nm$. The $LaAlO_3$ ceramics are derived for the synthesized powders (milling for 10, 30 and 50hrs) by sintering at $1400^{\circ}C$. The micrographs of grains showed a agglomeration and the degree of agglomeration increased with the milling time. The $LaAlO_3$ made from synthesized powders milling for 30hrs can be sintered to 98% of theoretical density at $1,400^{\circ}C$ for 4hrs.

• Transactions of the Korean hydrogen and new energy society
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• v.12 no.1
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• pp.39-50
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• 2001

Vanadium based solid solution alloys have been studied as a potential negative electrode of Ni/MH battery due to their high hydrogen storage capacity. In order to improve the kinetic property of V-Ti alloy in KOH electrolyte, the ball-milling process with Ni, which has a catalytic effect of hydrogen absorption/desorption, was carried out to modify the surface properties of V-Ti-Cr alloys with high hydrogen storage capacity. Moreover, to overcome the problem of poor cycle life, V-Ti alloy substituted by Cr, V0.68 Ti0.20 Cr0.12, has been developed showing a good cycle performance (keeping about 80 % of initial discharge capacity after 200 cycles). The cycle life of surface-modified V0.68 Ti0.20 Cr0.12 alloy was improved by suppressing the formation of TiO2 layer on the alloy surface while decreasing the amount of dissolved vanadium in the KOH electrolyte. In order to promote the effect of Ni coating on the surface property of V0.68 Ti 0.20 Cr 0.12 alloy by ball-milling, filamentary-typed Ni, which has higher surface coverage area than sphere-typed Ni was used as a surface modifier. Consequently, the surface-modified V0.68 Ti0.20 Cr0.12 alloy electrode showed a improved discharge capacity of 460 mAh/g.

• Journal of Magnetics
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• v.14 no.2
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• pp.71-74
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• 2009

The magnetic and structural properties of FINEMET (the Hitachi product name of the Fe-Si-B-Nb-Cu alloy) nanopowder with a composition of $Fe_{73.5}Si_{13.5}B_9Nb_3Cu_1$ atomic percent were investigated after annealing, chemical etching, and mechanical milling. The primary and secondary crystallization temperatures were 523 and $550^{\circ}C$, respectively. The grain size of the particles was adjusted by annealing time. Optimally annealed particles exhibited a homogenous microstructure composed of nanometer-sized crystalline grains. The grain boundary of the annealed particles was etched preferentially by chemical etching. Chemically etched particles were broken at the grain boundary by high-energy ball milling. As a result, a nanometer-sized FINEMET powder with a uniform size of crystalline grains was fabricated.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.975-976
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• 2006

The present paper is a parameter study of zinc flake production using a Simoloyer CM01 horizontal high energy rotary ball mill. The manufactured flakes have a dimension in thickness (t) < $1{\mu}m$ and diameters (d) 5-100 ${\mu}m$, consequently a ratio d/t up to 200. The flake geometry is mainly controlled by the variation of process parameters such as rotary speed of the rotor, ratio of powder/ball charge, load ratio of the system, process temperature, operating model and the quantity of process control agent (PCA). The Zn flakes were characterized by SEM, tap densitometry, laser diffraction and water coverage measurement.