• Journal of Powder Materials
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• v.12 no.5 s.52
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• pp.362-368
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• 2005

The structural and magnetic properties of nanostructued Fe-20 ;wt.%Si alloy powders were investigated. Commercial Fe-20 wt.%Si alloy powders (Hoeganaes Co., USA) with 99.9% purities were used to fabricate the nanostructure Fe-Si alloy powders through a high-energy ball milling process. The alloy powders were fabricated at 400 rpm for 50 h, resulting in an average grain size of 16 nm. The nanostructured powder was characterized by fcc $Fe_{3}Si$ and hcp $Fe_{5}Si_3$ phases and exhibited a minimum coercivity of approximately 50 Oe.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1264-1265
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• 2006

Study about the feasibility and effect of high-energy ball milling on a specific Mg alloy under protection medium of alcohol was presented via comparing with conventional vacuum milling. More fine particles with wider powder size distribution but more irregular shape were shown of the powder milled under alcohol. No obvious oxide was revealed from the two kinds of Mg alloy powders with limited milling time. And since slip induced in a preferential direction, the (002) texture was formed in the Mg alloy powders at the initial stage of alcohol milling. More O and Fe contaminants were introduced into the powders milled under alcohol according to the EDS analysis.

• Journal of Powder Materials
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• v.6 no.3
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• pp.231-237
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• 1999

In this study, the characteristics of gas atomized Mg-3wt%Al-1wt%Zn-1wt%MM alloy powders under vacuum condition were investigated. In spite of the low fluidity and easy oxidation of the molten magnesium, the spherical powders could be successfully produced by using a modified three pieces nozzle attached to the gas atomization unit. It was found that most of the solidified powders less than 50$\mu$m in diameter were single crystal and the solidified structure showed a typical dendritic morphology due to supercooling prior to nucleation. The secondary dendrite arm spacing decreased as the size of powders decreased. The Mg-Al-Ce intermetallic compounds with chemically stable phase were found in the interdendritic regions of $\alpha$-Mg. It is considered that formation of the chemically stable phase may possibly affect to improve the corrosion resistance. Therefore, it is expected that the materials formed of these Mg-Al-Zn-MM alloy powders shows better mechanical properties and corrosion resistance due to the structural refinement.

• Korean Journal of Materials Research
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• v.15 no.3
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• pp.166-171
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• 2005

Fe-6Al-9Si(N) alloy powders were synthesized by hybrid process of chemical nitrification and mechanical milling. The nitriding treatment on Fe-6Al-9Si alloy powders formed $\gamma'-Fe_4N$ phase on the powders surface. The nitriding-treated powders were pulverized by horizontal high-energy ball milling machine. The longer ball milling time tended to reduce the size of alloy powders. In ball milling for 36h, extremely fine powders with about $7\~9wt\%$ nitrogen were obtained. Through X-ray diffraction analysis on the powders, it was found out that the longer milling time caused a disappearance of the crystallinity of $\alpha-Fe$ in the powders. TEM study confirmed that the powders is comprised of a few tens nano-meter sized crystals, including $\alpha-Fe$ phase with partially $\gamma'-Fe_4N$ phase. Hysteresis curves of the synthesized powders measured by VSM revealed lower saturation magnetization and higher coercivity, which seemed to be attributed to nitrogen-impregnation and severe residual stress developed during the high energy milling. Microstructure observation on the powder annealed at 873 K for 1 h showed 10 to 20 nm sized $\alpha-Fe$ crystal. Such a enhanced crystallinity significantly increased the magnetization and decreased the coercivity, which was attributed to not only the crystallinity but also residual stress relaxation.

• Journal of Welding and Joining
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• v.15 no.5
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• pp.92-103
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• 1997

The purpose of this study is to improve the wear resistance and hardness of Al alloy by making a formation of the thick surface hardening layers. The thick surface hardening layers were formed by PTAW(Plasma Transferred Arc Welding), with the addition of metal powders (Cu), ceramics powders (NbC, TiC), and mixture powders (Cu+NbC) in Al alloy (A1050, A5083). Mechanical properties of overlaid layers (wear resistance, hardness) were investigated in relation to the microstructure. The results obtained are summarized as follows: The depth of penetration was increased with increasing powder feeding rate. It is considered that these increase were due to the thermal pinch effect by the addition of powders, especially, for the Cu powders, were due to the heat of reaction with the matrix. The hardness and wear resistance of overlaid layers were improved with increasing powder feeding rate. For the Cu powders, it is considered that these increase were due to the increase of the formation of ${\theta}(CuAl_2)$ phase with increasing feeding rate of Cu powers.

• Clean Technology
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• v.19 no.2
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• pp.75-83
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• 2013

In the present paper, we review recycling and applications of titanium binary alloy scraps. The recycling techniques are to successfully prepare low oxygen content ingots using hydrogen plasma arc melting (HPAM) and to produce low oxygen content titanium alloy powders by Hydrogenation-dehydrogenation (HDH) and Deoxidation in solid state (DOSS) process. In addition, as applications of the titanium binary alloy scraps, Ti based solid-solution carbide powders, which would be used for producing Ti based solid-solution cermets with high toughness, were prepared using the titanium binary alloy scraps. These results confirmed that the titanium alloy scraps could be recycled and refined using the HPAM. The resulting oxygen content of the titanium alloy powders were below 1,000 ppm after powderizing. Finally, we had confirmed that the refined titanium alloy powders were able to be utilized as raw materials for preparing the toughened cermets.

• Transactions of Materials Processing
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• v.6 no.2
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• pp.145-151
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• 1997

In order to obtain high quality products in powder metallurgy, it is important to control and understand the densification behavior of metal powders. The effect of the characters of powders on the compaction behavior was studied in this study by using three types of powders produced by the gas atomization, the centrifugal atomization and the twin roll-pulverization. The shape of the powders was a major factor in the apparent or tap density, and the deformation resistance of the matrix of the powders was a major factor in compactibility. Han's yield function (eq.2) for metal powders was simplified from the relationship based on the experimental results of copper powders. In spite of some assumptions, the calculated compaction curves using a new yield functionw was in accordance with the experimental results.

• Journal of Powder Materials
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• v.15 no.3
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• pp.234-238
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• 2008

Al-Cu alloy nano powders have been produced by the electrical explosion of Cu-plated Al wire. The porous nano particles were prepared by leaching for Al-Cu alloy nano powders in 40wt% NaOH aqueous solution. The surface area of leached powder for 5 hours was 4 times larger than that of original alloy nano powder. It is demonstrated that porous nano particles could be obtained by selective leaching of alloy nano powder. It is expected that porous Cu nano powders can be applied for catalyst of SRM (steam reforming methanol).

• Journal of Korea Foundry Society
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• v.31 no.1
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• pp.26-30
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• 2011

For the fabrication of bulk near-net-shape Ti-Ni-Cu shape memory alloys, consolidation of Ti-Ni-Cu alloy powders are useful because of their brittle property. In the present study, $Ti_{50}Ni_{30}Cu_{20}$ shape memory alloy powders were prepared by gas atomization and martensitic transformation temperatures and microstructures of those powders were investigated as a function of powder size. The size distribution of the powders was measured by conventional sieving, and sieved powders with the specific size range of 25 to $150\;{\mu}m$ were chosen for this examination. XRD analysis showed that the B2-B19 martensitic transformation occurred in the powders. In DSC curves of the as-atomized $Ti_{50}Ni_{30}Cu_{20}$ powders as a function of powder size, only one clear peak was found on each cooling and heating curve. The martensitic transformation start temperature($M_s$) of the $25-50\;{\mu}m$ powders was $31.5^{\circ}C$. The $M_s$ increased with increasing powder size and the difference of $M_s$ between $25-50\;{\mu}m$ powders and $100-150\;{\mu}m$ powders is only $1^{\circ}C$. The typical microstructure of the rapidly solidified powders showed cellular morphology and very small pores were observed in intercellular regions.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.35-37
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• 2008

The light Mg alloys bearing the remarkably high strength, corrosion resistance and elevated temperature stability stand on the center of interest. The accomplishment so far is, however, only by alloy modification without any consideration on the rapid solidification effect. This work is to report not only the effect of rapid solidification of $MgZn_{4.3}Y_{0.7}$ alloy powders, but the extrusion behavior on the materials properties. The average grain size of the atomized powders was about $3-4{\mu}m$. The extrusion was carried out with the area reduction ratio of 10:1 to 15:1. As the ratio increased, homogeneous microstructure was obtained, and the mechanical properties such as tensile strength and elongation were simultaneously increased.