• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1997년도 고액공존금속의 성형기술 심포지엄
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• pp.160-173
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• 1997

Microstructure of hypereutectic Al-17wt.% Si alloy, fabricated by mechanical stirring and by reheating at semi-solid state, was investigated by optical microscope. Flow behavior semi-solid metal also was investigated at diffentent mould temperatures 280$^{\circ}C$, 290$^{\circ}C$ and 300$^{\circ}C$. Size of silicon particles were increased over 100$\mu\textrm{m}$ during solidification as a result of stirring. It is considered as microstructural coarsening by bonding between neighbouring primary silion particles during stirring of slurry. In case of reheating at semi-solid state, however, primary silicon particle was not increased at size of 40$\mu\textrm{m}$ and nearly spherical aluminum solde particle also could be obtained uniformly in distribution. The fludity of Al-17wt.% Si alloys at semi-solid state was improved when solid fraction was 0.7 at mould temperature of 300$^{\circ}C$ than other conditions.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.1023-1024
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• 2006

Al-8Fe-2Mo-2V-1Zr alloys were prepared by the gas atomization/hot extrusion and the melt spinning/hot extrusion. For the gas atomized and extruded alloy, equiaxed grains with the average size of 400 nm and finely distributed dispersoids with their particle sizes ranging from 50nm to 200nm were observed. For the melt spun and hot extrusion processed alloy, refined microstructural feature consisting of equiaxed grains with the average size of 200nm and fine dispersoids with their particle sizes under 50nm appeared to exhibit a difference in microstructure. Strength of the latter alloy was higher than that for the former alloy up to elevated temperatures.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 1996년도 춘계학술강연 및 발표대회 강연 및 발표논문 초록집
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• pp.19-19
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• 1996

• 비파괴검사학회지
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• 제20권5호
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• pp.438-444
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• 2000

WC-Co 초경합금의 항자력과 자기포화도를 평가하여 합금조직과 이에 따른 기계적 성질의 예측에 관해 연구하였다. WC 입경이 다르고 탄소함량 및 소결온도가 다른 WC-8%-Co 초경합금을 분말 야금법에 의해 제조하였다. 항자력과 자기포화도와 같은 WC-Co 합금의 자기적 특성은 합금조성 및 조직에 크게 의존하였다. 미소한 합금탄소량의 변화와 WC 입도의 차이에 의해서도 WC-Co 합금의 자기적 특성과 경도 및 항절력이 크게 변화하였다. WC 입도가 미세할수록 소결합금의 항자력과 경도는 증가하였고, 항자력은 경도의 증가와 비례하였다. WC-8%Co 합금의 화학 양론적 조성 아래로 카본함량이 감소하면 자기포화도와 항절력이 떨어지고 $\eta$상의 체적률도 꾸준히 증가하였다. WC-Co 합금에 있어서 자기포화도는 항자력과 반비례하였다.

• 한국분말재료학회지
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• 제10권6호
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• pp.406-414
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• 2003

In order to produce good wear resistance powder metallurgy Al-Si alloys with high strength, addition of glass forming elements of Ni and Ce in $Al_{81}$Si$_{19}$ alloy was examined using SEM, TEM, tensile strength and wear testing. The solubility of Si in aluminum increased with increasing Ni and Ce contents for rapidly solidified powders. These bulk alloys consist of a mixed structure in which fine Si particles with a particle size below 500 nm and very fine A1$_3$Ni, A1$_3$Ce compounds with a particle size below 200 nm are homogeneously dispersed in aluminum matrix with a grain size below 600 nm. The tensile strength at room temperature for $Al_{81}$Si$_{19}$, $Al_{78}$Si$_{19}$Ni$_2$Ce$_{0.5}$, and $Al_{76}$Si$_{19}$Ni$_4$Ce$_1$ bulk alloys extruded at 674 K and ratio of 10 : 1 is 281,521, and 668 ㎫ respectively. Especially, $Al_{73}$Si$_{19}$Ni$_{7}$Ce$_1$ bulk alloy had a high tensile strength of 730 ㎫. These bulk alloys are good wear-resistance bel ter than commercial I/M 390-T6. Specially, attactability for counterpart is very little, about 15 times less than that of the I/M 390-T6. The structural refinement by adding glass forming elements such as Ni and Ce to hyper eutectic $Al_{81}$Si$_{19}$ alloy is concluded to be effective as a structural modification method.d.tion method.

• 소성∙가공
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• 제11권8호
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• pp.682-690
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• 2002

The formation of adiabatic shearband in tungsten heavy alloys(WHA) was studied in this investigation. Five prismatic specimens were loaded by high velocity impacts and treated as plane strain problems. To find out the effect of particle's volume ratio, specimens containing 81%, 93% and 97% volume percents of tungsten particles were used. Also the effects of particle's geometry and size on the formation of shearband were studied for 81% volume percent alloys by small size particle model, large size particle model and undulated particle models, and the results were discussed.be used to diagnose the causes of necking and fracture in industrial practice and to investigate whether these defects were caused by material property variation, changes in lubrication, or incorrect press settings. In non-axisymmetric deep drawing, three modes of forming regimes are found: draw, stretch, plane strain. The stretch mode for non-axisymmetric deep drawing could be defined when the major and minor strains are positive. The draw mode could be defined when the major strain is positive and minor strain is negative, and plane strain mode could be defined when the major strain is positive and minor strain is zero. Through experiments the draw mode was shown on the wall and flange are one of a drawn cup, while the plane strain and the stretch mode were on the punch head and the punch corner area respectively, We observed that the punch load of elliptical deep drawing was decreased according to increase of die corner radius and the thickness deformation of minor side was more large than major side.

• 한국주조공학회지
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• 제17권2호
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• pp.164-169
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• 1997

Mechanical properties of aluminum-matrix composites, fabricated by dispersion of fine SiC particulates of which size was less than 1 ${\mu}m$ into 2024 and 7075 aluminum alloys, have been investigated. Homogeneous mixing between the matrix and SiC particulates could be achieved by jar milling for 8 hours with appropriate processing agent. At temperatures below 473K, high-temperature tensile strength of the composites was higher than that of the 2024 and 7075 aluminum alloys which were used as matrix materials. However, tensile strength of the composites was approximated to that of the matrix materials at 573K. Thus, it could be suggested that effects of particle dispersion on tensile strength of aluminum alloys was diminished at temperatures higher than 573K.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 1997년도 춘계학술강연 및 발표대회 강연 및 발표논문 초록집
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• pp.5-5
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• 1997

Rapidly-solidified P/M aluminium alloys for automobile and home appliance industries were developed. Rapidly-solidification made it possible to refine microstructures and to expand the range of alloy composition. For example, Al-Si alloys containing transition metal have lower thermal expansion coefficient, more excellent wear resistance, higher strength, and better machinability than those of conventional aluminium alloys. Therefore, in Japan, the technologies on powder-extrusion and powder-forging of aluminium alloy powders are developed for fifteen years, and applied to several parts, such as cylinder liners of motor cycle engines, rotors and vanes of compressors for car air conditioner, oil pump rotor for racing car, and so on. In this presentation, applications for automobile are mentioned. In particular, cylinder liners made of particle-dispersed composites with fine alumina and graphite are in detail described.

• 한국주조공학회지
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• 제41권5호
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• pp.434-444
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• 2021

본 연구에서는 미소기공과 Si석출상의 파단으로 구성되는 유효기공 면적분율에 대한 인장특성의 결함민감도 관점에서 Al-Si합금의 인장특성을 공정 Si입자의 분포양상 변화에 대하여 평가하고자 하였다. Al-xSi(x=2,5,8,11)합금의 주방상태 미세조직인 망상구조의 공정 Si입자는 T4처리를 통하여 과립형태로 변형시켰으며, CT분석과 주사전자현미경 관찰을 통하여 미소기공의 분포와 크기를 평가하였다. CT분석과 주사전자현미경의 비교분석을 통하여 인장변형과정에서의 균열성장이 최대 기공율을 포함하는 국부영역에서 발생함을 확인할 수 있었다. 그럼에도 불구하고 이들 분석방법에는 미소기공 인접영역에서의 소성변형집중과 미소기공의 분포양상에 의해 파생되는 실제적인 차이를 포함하기 때문에 정확히 일치된 결과를 얻을 수 없었다. 유효기공 면적분율의 변화에 대한 인장강도와 연신율의 변화는 과립형태보다 망상구조 정출상의 분율변화에 더욱 민감한 의존도를 가진다.

• 한국분말재료학회지
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• 제26권3호
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• pp.201-207
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• 2019

Tungsten heavy alloys (W-Ni-Fe) play an important role in various industries because of their excellent mechanical properties, such as the excellent hardness of tungsten, low thermal expansion, corrosion resistance of nickel, and ductility of iron. In tungsten heavy alloys, tungsten nanoparticles allow the relatively low-temperature molding of high-melting-point tungsten and can improve densification. In this study, to improve the densification of tungsten heavy alloy, nanoparticles are manufactured by ultrasonic milling of metal oxide. The physical properties of the metal oxide and the solvent viscosity are selected as the main parameters. When the density is low and the Mohs hardness is high, the particle size distribution is relatively high. When the density is high and the Mohs hardness is low, the particle size distribution is relatively low. Additionally, the average particle size tends to decrease with increasing viscosity. Metal oxides prepared by ultrasonic milling in high-viscosity solvent show an average particle size of less than 300 nm based on the dynamic light scattering and scanning electron microscopy analysis. The effects of the physical properties of the metal oxide and the solvent viscosity on the pulverization are analyzed experimentally.