• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.4
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• pp.440-446
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• 2009

This paper was designed to fabricate the miniature spur gear with pitch circle of 2.25mm using extrusion process of a mechanically alloyed Al-78wt%Zn powder. The mechanical alloying of the powder particles were performed for ball milled times of 4h, 8h, 16 and 32h by the planetary ball milling. The mechanical properties of these alloyed powders, which were compacted and sintered-cylindrical preforms, were estimated using compression test. The results showed that the alloyed powder with average particle size of $10{\mu}m$ milled for 32h has the highest compressive(fractured) strength(288MPa). Extrusions of the miniature spur gear using the alloyed powder were carried out at different extrusion temperatures. Extrusion temperature of $300^{\circ}C$ provided the spur gear with the highest relative density and Vickers hardness and without any surface defects.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.1
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• pp.21-27
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• 2018

Synthesis of ferromagnetic composite materials for the $Cu-BaFe_{12}O_{19}$ system by mechanical alloying (MA) has been investigated at room temperature. A mixture of copper and barium ferrite with a weight ratio of $Cu:BaFe_{12}O_{19}=4:1$, 3 : 2, 2 : 3 and 1 : 4 was used. It is found that $Cu-BaFe_{12}O_{19}$ composite powders in which $BaFe_{12}O_{19}$ is dispersed in copper matrix are successfully produced by mechanical alloying of $BaFe_{12}O_{19}$ with Cu for 80 min. in all composition. The change in X-ray diffraction patterns and magnetic properties reflects the details for the formation of ferromagnetic metal matrix composite of pure Cu and $BaFe_{12}O_{19}$ during mechanical alloying. Magnetization of $Cu-BaFe_{12}O_{19}$ composite powders gradually increases with increasing the amounts of barium ferrite, whereas coercive force of MA powders gradually decreases due to the refinement of barium ferrite powders with ball milling. However, it can be seen that the coercivity of $Cu-BaFe_{12}O_{19}$ MA composite powders with a weight ratio of $Cu:BaFe_{12}O_{19}=4:1$ and 3 : 2 ball-milled for 80 min. is still high value of 1400 Oe and 1450 Oe, respectively suggesting that the refinement of barium ferrite powders during ball milling process tend to be suppressed due to the ductile copper.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2001.11a
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• pp.8-9
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• 2001

• Proceedings of the Materials Research Society of Korea Conference
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• 1996.11a
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• pp.43-43
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• 1996

• Journal of Powder Materials
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• v.12 no.2 s.49
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• pp.136-145
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• 2005

Graphite-Ni composite powders were synthesized by mechanical alloying(MA) and spray drying(SD). Fabricated powders as well as commercial graphite-Ni powders were thermally sprayed on mild steel substrates using high velocity oxygen fuel (HVOF) thermal spray process and flame thermal spray process. The effects of several process parameters on related properties in thermally sprayed coatings have been investigated and correlated with microstructures in this study. The results indicated that the desired properties can be obtained when commercial powders were applied using HVOF process, while coating properties in case of MA powder application were inferior to those in HVOF process in so far. However, it is suggested that property enhancement can be obtained if the fraction of hexagonal graphite phase can be increased in mechanically alloyed powders.

• Korean Journal of Materials Research
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• v.14 no.10
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• pp.743-748
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• 2004

Modified Ni/YSZ cermets for high temperature electrolysis were synthesized by the direct ball milling of Ni and YSZ powder. The ball milling was carried out in dry process and in ethanol with varying milling time. While the dry-milling decreased the average size from 65 to $80{\mu}m$, the wet-milling decreased the average size down to $10{\mu}m$. In addition, very fine particles less than $0.1{\mu}m$ were observed in the wet-milling condition. The subsequent process of cold-pressing and sintering at $900^{\circ}C$ for 2 h did not affect the particle size of dry-milled powder. The electrical conductivity of the dry-milled Ni/YSZ cermet showed the value of $5{\times}10^{2}\;S/cm$ and this value was increased to $1.4{\times}10^{4}\;S/cm$ after the sintering at $900^{\circ}C$ for 2 h.

• Journal of Ceramic Processing Research
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• v.20 no.6
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• pp.582-588
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• 2019

FeVSb1-xTex (0.02 ≤ x ≤ 0.10) half-Heusler alloys were fabricated by mechanical alloying process and subsequent vacuum hot pressing. Near single half-Heusler phases are formed in vacuum hot pressed samples but a second phase of FeSb2 couldn't be avoided. After doping, the lattice thermal conductivity in the system was shown to decrease with increasing Te concentration and with increasing temperature. The lowest thermal conductivity was achieved for FeVSb0.94Te0.06 sample at about 657 K. This considerable reduction of thermal conductivities is attributed to the increased phonon scattering enhanced by defect structure, which is formed by doping of Te at Sb site. The phonon scattering might also increase at grain boundaries due to the formation of fine grain structure. The Seebeck coefficient increased considerably as well, consequently optimizing the thermoelectric figure of merit to a peak value of ~0.24 for FeVSb0.94Te0.06. Thermoelectric properties of various Te concentrations were investigated in the temperature range of around 300~973 K.

• Journal of Korea Foundry Society
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• v.14 no.3
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• pp.240-247
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• 1994

TiC particulate reinforced magnesium matrix composites were fabricated by melt stirring method. The effect of alloying elements on TiC particulate dispersion into molten magnesium and mechanical properties were investigated. The incorporation time is defined as the time required for dispersion of solid particles into molten metal. The incorporation time of TiC particles into molten pure magnesium was remarkably shorter and the particulated dispersion was more uniform than that of pure aluminum which was reported previously. The incorporation time was, prolonged by the addition of Al, Bi, Ca, Ce, Pb, Sn or Zn. The tensile strength increased and elongation decreased by the addition of Cu or Sn into the matrices and composites. Although, the tensile strength of the matrices and composites increased by alloying with Ca or Ce, the maximum elongation was observed at a content of about 1% for the matrices. By alloying with Zn, the tensile strength increased for the matrices and composites, but the elongation of the matrices increased. The pure magnesium and its alloy matrix composites reinforced with 20vol% TiC have the tensile strength of about 400MPa. This value is compared with the tensile strength of SiC whisker reinforced magnesium matrix composites fabricated by liquid infiltration method at the same volume fraction. There fore, the melt strirring method which has the advantages of simple process is considered to be efficient in fabricating magnesium matrix composites.

• Progress in Superconductivity
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• v.1 no.1
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• pp.61-67
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• 1999

We evaluated the effect of alloying element additions to Ag sheath on mechanical, electrical and thermal properties of Bi-2223. Additions of Au, Pd and Mg to Ag sheath increased hardness and strength, while reduced elongation and electrical and thermal conductivity. In addition, microstructural investigation showed that the grain size of Ag significantly decreased with increasing content of alloying elements. The improvements in strength and hardness are believed to be due to the presence of alloying elements that lead to strengthen materials by combined effects of solid-solution, dispersion hardening and grain size hardening. Thermal conductivity of Ag and Ag alloys was evaluated in the temperature range from 77 K to 300 K, and com-pared to calculated value obtained by Wiedermann-Franz law. It was observed that the thermal conductivity decreased with increasing the content of alloying elements. Specifically, the thermal conductivity of $Ag_{0.92}Pd_{0.06}Mg_{0.02}$ alloy was measured to be $48.2W/(m{\cdot}K)$ at 77 K, which is about 6 times lower than that of $Ag(302.6W/(m{\cdot}K))$.

• Korean Journal of Materials Research
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• v.11 no.5
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• pp.378-384
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• 2001

In this study, nanostructured Fe-Ce powder with grain size of 10nm was produced by MA (mechanical alloying) process and was consolidated by PECS (pulse electric current sintering) process for the fabrication of bulk nanostructured Fe-Co softmagnetic alloy. PECS process was performed at 700, 800, 900 and $^1000{\circ}C$ with holding time ranging from 0 to 15min. The effectiveness of PECS Process to Produce nanostructured bulk specimens was estimated. The optimal PECS process condition for nanostructured Fe-Co powders was found through observing the change of relative density and microstructure with sintering temperature and holding time. The magnetic properties of the sintered specimens were evaluated through the measurement of coercivity and saturation magnetization.