• Journal of Powder Materials
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• v.16 no.1
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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.

• Journal of Powder Materials
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• v.2 no.1
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• pp.53-62
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• 1995

TLP(Transient-Liquid-Phase) bonding of Fe-base MA956 ODS alloy was performed. As insert metal a commercially available Ni-base alloy(MBF50) and an MA956 alloy with additive elements of 7wt% Si and 1wt% B were used. To confirm the idea that a concurrent use of MA956 powder with Insert metals can enhance the homogenization of constituent elements and thereby reduce the thickness of joint interface, MA956 powder was also inserted In a form of sheet. SEM observation and EDS analysis revealed that Cr-rich phase was formed in the bonded interface in initial stage of isothermal solidification during the bonding process, irrespective of kind of insert metals. Measurement of hardeness in the region of bonded interface and EDS analysis showed that a complete homogenization of composition could not be obtained especially in case of MBF50. Joints using either BSi insert metals only or BSi insert together with MA956 powder interlayer showed, however, a remarkable improvement in a compositional homogenization, even though a rapid grain growth in the bonded interface could not be hindered.

• Journal of Powder Materials
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• v.13 no.6 s.59
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• pp.427-431
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• 2006

Mg-4.3Zn-0.7Y (at%) alloy powders were prepared using an industrial scale gas atomizer, followed by warm extrusion. The powders were almost spherical in shape. The microstructure of atomized powders and those extruded bars was examined using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscope (EDS) and X-ray Diffractometer (XRD). The grain size of the powders was coarsen as the initial powder size increased. After the extrusion, the grain size became fine due to the severe plastic deformation during the extrusion with the ratio of 10:1. Both the ultimate strength and elongation were enhanced with the decrease of initial particle size.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1269-1270
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• 2006

Mg-Zn-RE alloys had a novel lond period stacking ordered (LPO) structure. Their rapidly solidified powder metallurgy (RS P/M) alloys exhibited a combination of high strength and god ductility (tensile yield strength above 550 MPa and elongation above 5%). The LPO Mg-Zn-RE RS P/M alloys had high elevated temperature strength (tensile yield strength above 380 MPa at 473 K) and exhibited a high-strain-rate superplasticity at higher temperatures. In Japan, a national project for developing high strength LPO Mg-Zn-RE RS P/M alloys has started at 2003 for 5 years, which is founded by the Ministry of Economy, Trade and Industry (METI) of Japan. In the national project, project targets in materials performances have been achieved. The developed LPO Mg-Zn-RE RS P/M alloys exhibited higher tensile yield strength, fatigue strength and corrosion resistance than high strength aluminum alloys of extra-super-duralumin (7075-T6).

• Journal of Welding and Joining
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• v.7 no.3
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• pp.55-62
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• 1989

Variation of the spray droplet velocity with spraying distance and the microstructural characteristics of spray deposits fromed by oxy-fuel thermal spraying with Ni-base alloy powder contained chrome boride for hard facing were examined. Measurements of spray droplet velocity as a function of distance from the nozzle tip were inexcellent agreement with computer simulated predictions. Optimum condition for thermal spray deposits in this experiment was found to be under #10kg/cm^2$ of acceleration gas pressure with 15cm of spraying distance. Fine microstructure and higher microhardness of the initial part of the deposits due to rapid solidification were found to be able to maintained in a thickness up to 0.4mm, and this initial microstructure and properties could be maintained throughout the thickness of a thick spray deposits by performing the multipass spraying with 0.4mm thickness of each pass.

• Journal of Powder Materials
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• v.18 no.4
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• pp.340-346
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• 2011

In order to improve the weak mechanical properties of cast Mg alloys, Mg-$Zn_1Y_2$ (at%) alloy powders were synthesized using gas atomization, a typical rapid solidification process. The powders consist of fine dendrite structures less than 3 ${\mu}m$ in arm spacing. In order to fabricate a bulk form, the Mg powders were compacted using magnetic pulse compaction (MPC) under various processing parameters of pressure and temperature. The effects of the processing parameters on the microstructure and mechanical properties were systematically investigated.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.459-460
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• 2006

N-type $Bi_2Te_3-Sb_2Te_3$ solid solutions doped with 1$CdCl_2$ was prepared by melt spinning, crushing and vacuum sintering processes. Microstructure, bending strength and thermoelectric property were investigated as a function of the doping quantity from 0.03wt.% to 0.10wt.% and sintering temperature from $400^{\circ}C$ to $500^{\circ}C$, and finally compared with those of conventionally fabricated alloys. The alloy showed a good structural homogeneity as well as bending strength of $3.88Kgf/mm^2$. The highest thermoelectric figure of merit was obtained by doping 0.03wt.% and sintering at $500^{\circ}C$.

• 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.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2002.11a
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• pp.80-80
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• 2002

Bi-Te게 열전재료는 200~400K 정도의 저온에서 에너지 변환 효율이 가장 높은 재료로써 열전냉각, 발전재료 등에 응용하기 위하여 제조방법 및 특성에 관한 많은 역구가 진행되어 왔다. 현재 산업화에 응용되고 있는 일방향응고법은 기계적 강도가 약하여 회수 율이 낮으며, 결정을 성장시키는데 비교적 장시간을 필요로 하기 때문에 제조 단가가 비싸다. 따라서 이와 같은 문제점을 보완하기 위하여 합금설계 및 가공공정에 대한 연구가 활발히 진행되고 있다. 이에 본 연구에서는 가스분사법을 이용하여 용질원자 편석감소, 고용도의 증가, 균일고용체 형성, 결정립 미세화 등 급속응고 장점을 이용하여 화학적으로 균일한 BI-TerP열전재료 분말을 제조하고, 열간압출 가공을 통하여 이방성의 향상과 함께 미세한 결정립으로 우수한 기계적 강도를 얻을 수 있도록 제조된 분말을 압출 가공하여 열전소자의 기계적 성질과 열전특성을 연구하였다. 그 결과 급속응고 및 압출 공정을 이용한 본 연구에서는 $10\mu\textrm{m}$이하의 미세한 조직과 함께 압출공정을 통하여 이방성을 향상시켰으며, 열전소자는 $2.5{\times}10^{-3}/K$이상의 Figure of merit값을 나타내는 우수한 열전특성을 나타냈다.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1045-1047
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• 2006

Fabrication of $Mg_{95.75}Zn_1Y_3Yb_{0.25}$ bulk alloy has been performed through the consolidation of rapidly solidified ribbons. The $Mg_{95.75}Zn_1Y_3Yb_{0.25}$ bulk alloy exhibited excellent mechanical properties, high tensile yield strength of 530 MPa, and large elongation of 3 %. Microstructure of the alloy was characterized by equiaxed fine grains that consist of -Mg, long period ordered (LPO) structure phase, and $Mg_5RE$-type cubic compound. The strengthening of the alloys may be due to fine grains with LPO structure phase and $Mg_5RE$-type compound.