• 한국분말재료학회지
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• 제11권6호
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• pp.528-534
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• 2004

Using the nano Fe powders having 50 nm in diameter, Fe compact bodies were fabricated by injec-tion molding process. The relationship between microstructure and material properties depending on the volume ratio of powder/binder and sintering temperature were characterized by SEM, TEM techniques. In the compact body with the volume percentage ratio of 45(Fe powder) : 55(binder), which was sintered at $700^{\circ}C,$ the relative density was about $97{\%},$ and the values of volume shrinkage and hardness were about $66.3{\%}$ and 242.0 Hv, respec-tively. Using the composition of 50(Fe powder) : 50(binder) and sintered at $700^{\circ}C,$ the values of relative density, volume shrinkage and hardness of Fe sintered bodies were $73.3{\%},\;47.6{\%}$ and 152.8 Hv, respectively. They showed brittle fracture mode due to the porous and fine microstructure.

• 한국분말재료학회지
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• 제16권4호
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• pp.275-279
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• 2009

The aging characteristics of gas atomized Mg-6 wt.% Al-1 wt.% Zn alloy were investigated and compared to those of cast Mg-6 wt.% Al alloy. The gas atomized Mg-6 wt.% Al-1wt.% Zn alloy powders had spherical morphology between 1 and 100 $\mu m$ in diameter. After compaction under the pressure of 700 MPa at $320^{\circ}C$ for 10 min, the Mg-6 wt.% Al-1 wt.% Zn alloy showed a grain size of approximately 40 $\mu m$ which is smaller than that of the cast Mg-6 wt.% Al alloy, and a relative compact density of approximately 93%. After ageing, the Mg-6 wt.% Al-1 wt.% Zn alloy showed much faster peak hardness than cast Mg-6 wt.% Al alloy. The Mg-6 wt.% Al-1 wt.% Zn alloy showed the new fine precipitations with ageing time, while the cast Mg-6 wt.% Al alloy was almost similar morphology.

• 한국분말재료학회지
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• 제15권1호
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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.

• 한국분말재료학회지
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• 제5권4호
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• pp.250-257
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• 1998

The synthesis of titanium silicides ($Ti_3Si$, $TiSi_2$, $Ti_5Si_4$, $Ti_5Si_3$ and TiSi) by mechanical alloying has been investigated. Rapid, self-propagating high-temperature synthesis (SHS) reactions were observed to produce the last three phases during room-temperature high-energy ball milling of elemental powders. Such reactions appeared to be ignited by mechanical impact in an intimate, fine powder mixture formed after a critical milling period. During the high-energy ball milling, the repeated impact at contact points leads to a local concentration of energy which may ignite a self-propagating reaction. From in-situ thermal analysis, each critical milling period for the formation of $Ti_5Si_4$, $Ti_5Si_3$ and TiSi was observed to be 22, 35.5 and 53.5 min, respectively. $Ti_3Si$ and $TiSi_2$, however, have not been produced even till the milling period of 360 min due to lack of the homogeneity of the powder mixtures. The formation of titanium silicides by mechanical alloying and the relevant reaction rates appeared to depend upon the critical milling period, the homogeneity of the powder mixtures, and the heat of formation of the products involved.

• 한국분말재료학회지
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• 제5권4호
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• pp.334-339
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• 1998

In purpose of introducing the inverse magnetostrictive properties into the structural ceramics, $Al_2O_3$ based nanocomposites dispersed with nano-sized Ni-Co particles were studied. The composites were fabricated by the hydrogen reduction and hot-pressing of $Al_2O_3$ and NiO-CoO mixed powders. The mixtures were prepared by using Ni- and Co-nitrate $(Ni(NO_3)_2\;{\cdot}\;6H_2O\;and\;Co(NO_3)_2\;{\cdot}\6H_2O)$ as source materials for the Ni-Co particles. Microstructural observations revealed that nano-sized Ni-Co particles were dispersed homogeneously at $Al_2O_3$ grain boundaries. High strength above 1 GPa was obtained for the $Al_2O_3/10$ wt% Ni-Co nanocomposite fabricated by a controlled powder preparation process. The inverse magnetostrictive response to applied stress was obtained due to the presence of dispersed Ni-Co particles, which indicates a possibility to incorporate new functions into the structural ceramics without loosing the mechanical properties.

• 한국분말재료학회지
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• 제10권1호
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• pp.15-20
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• 2003

Hybrid $A1_2O_3-TiC$ ceramic particle reinforced 6061 and 5083 Al composite powders were prepared by the combination of twin rolling and stone mill crushing process, followed by consolidating processes of cold compaction, degassing and hot extrusion. The composite bar consists of lamellar structure of ceramic particle rich area and matrix area, in which the hybrid was decomposed into each TiC of about $3-4\mutextrm{m}$ and $AI_2O_3$ particles of about $1-2\mutextrm{m}$ in diameter. It also found that fine $Mg_2Si$ precipitates of about 30 nm were embedded in the matrix, which have grains of about 3 $\mutextrm{m}$. Higher UTS was measured at the 5083 composite bar compared to the conventionally fabricated composite, due to again refinement effect by the rapid solidification. No particle was shown to form in the interface between the matrix and reinforcement, whereas carbon was diffused into the matrix.

• 한국분말재료학회지
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• 제16권1호
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• pp.63-67
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• 2009

In order to investigate the effect of rapid solidification on the microstructure and the mechanical properties of Al-Zn-Mg system alloys, water atomization was carried out, since the water atomization beared the highest solidification rate among the atomization processes. The as atomized alloy powders consisted of fine grains less than 4 ${\mu}m$ in diameter, and the second particles were not detected on XRD. The microstructure as solidified was maintained even after the spark plasma sintering at the heating rate of 50 K/min. On the other hand, lower rate of 20 K/min induced a formation of $MgZn_2$ particles, resulting in strengthening of the matrix. The density was almost constant at the temperature above 698K. The sintering temperature above 698K had no effect on the strength of the sintered materials.

• 품질경영학회지
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• 제42권4호
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• pp.579-590
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• 2014

Purpose: Ball milling is a popular process for obtaining fine powders in the part and material industry. One of important issues in the ball milling is to produce particles with a uniform size. Although many factors affect uniformity of particles, this paper focuses on the choice of ball diameter. Consider a ball milling where balls can be taken with three different diameters. The purpose of this paper is to find a ball mix which minimizes the average particle size. Methods: Ball diameters are selected as 10mm, 3mm, and 0.5mm. In order to find an optimum mixing ratio, the method of mixture experiments is employed in this paper. Taguchi's signal-to-noise ratio (SNR) for smaller-the-better type is also used to analyze experimental data. Results: According to the experimental result, SNR is maximized when the ball mix is taken as either 7:3:0 or 6:4:0. Such mixing ratios can be technically validated in terms of porosity reduction. Conclusion: The ball mixing technique presented in this paper provides a useful way to improve the production efficiency with a low cost.

• 한국세라믹학회지
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• 제27권7호
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• pp.851-860
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• 1990

The hydrolysis-precipitation reaction of mixed aluminum salt solutions of aluminum sulfate, aluminum nitrate, and urea has been investigated to obtain narrow-sized and unagglomerated fine spherical precipitates of aluminum hydroxide required for coating core particles. The hydrolysis-precipitatin reaction could be controlled to be appropriate to coating processes by usign urea as a pH control-agent. As the concetration of total Al3+ ion and the molar ratio of SO42-/Al3+ in starting solutions became smaller and also as the vol. ratio of water/solution for hydrolyzing mixed aluminum salt solution became larger, the morphology of precipitates tended to be more unagglomerated and spherical, while their size(0.5longrightarrow0.05${\mu}{\textrm}{m}$) to be smaller. The optimum hydrolysis condition for coating processes was to hydrolyze the mixed aluminum salt solution, in which the molar ratio of SO42-/Al3+ was 0.75, while the amount of water corresponding to the vol. ratio of water/solution of 15. The precipitate was the aluminum hydroxide which sulfate ions were strongly adsorbed on and the maximum yield in the hydrolysis-precipitation reaction was about 20%.

• Progress in Superconductivity
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• 제7권1호
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• pp.52-57
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• 2005

[ $YBa_{2}Cu_{3}O_y$ ] superconducting films were prepared on $LaAlO_3$(100) single crystal substrate by spray pyrolysis method. The precursor solution was prepared by dissolving nitrate powders in de-ionized water. Both of ultrasonic and concentric nebulizers were used in order to generate fine droplets of precursor solution. C-axis oriented films were obtained at deposition temperature of $750\~850^{\circ}C$ and working pressure of 100 Torr and 500 Torr. In case of ultrasonic nebulizer, films showed rough and porous surface morphology due to formation of enormous droplets, while smooth and dense films were obtained for concentric nebulizer. A transport $J_c$ value of $0.43\;MA/cm^2$ at 77 K and self field was achieved on $LaAlO_3$(100) single crystal substrate.