• 한국세라믹학회지
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• 제31권4호
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• pp.347-358
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• 1994

Creep densification and grain growth of alumina powder compacts during high temperature processing were investigated. The creep densification and grain growth of alumina powder compacts during various sintering processes were analyzed by employing the consitutive model by Kwon and Kim. Theoretical results from the constitutive model were compared with various experimental data of alumina powder compacts in the literature including pressureless sintering, sinter forging and hot pressing. The proposed constitutive equations were implemented into finite element analysis program (ABAQUS) to simulate densification for more complicated geometry and loading conditions. The effects of friction between die and powder compact or punch and powder compact during sinter forging and hot pressing are investigated by using the finite element method. Also, high temperature forming processing of alumina compact with complicated shape was simulated.

• 한국세라믹학회지
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• 제47권5호
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• pp.419-425
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• 2010

In order to examine the P.H.C pile raw material using glass forming ceramic. The used materials is ordinary portland cement, waste TFT-LCD glass powder and reactive agent(Ca$(OH)_2$). The first experiment is characteristics analysis of the waste TFT-LCD glass powder, For the second experiment is mortar and concrete compressive strength for using of the concrete file raw material for waste TFT-LCD glass powder. The results of experiment showed that the substitution ratio of 10% waste TFT-LCD glass powder and 1% reactive agent(Ca$(OH)_2$) was excellent at a point of view for the physical characteristic. The study's most important finding is that the recycling of waste TFT-LCD glass powder.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 춘계학술대회 논문집
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• pp.258-261
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• 2005

In this paper, experimental and numerical attempts are made fur application of powder metallurgy forming technology to making the cylinder block of a hydraulic pump of which height reaches nearly 70 mm and is ten times larger than the wall thickness. Leak tests with several compositions are carried out in order to find allowable powder composition to prevent leak under high pressure in service and CAE techniques are applied to finding proper process conditions. Through the research, the possibility of the powder formed cylinder block that is very competitive from the point of both cost and mass production has been shown, even though its thickness exceeds the recommended limit considering heterogeneous density distribution caused by the friction between a powder compact and dies.

• 한국식품영양과학회지
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• 제24권6호
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• pp.837-842
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• 1995

고추가루 첨가 식이가 체액성 면역기능에 미치는 영향을 조사하였다. 실험동무로 흰쥐를 사용하여 대조군과 2%, 5%, 10% 고추가루 첨가 식이군을 설정한 후 27일간 실험식이로 사육하였다. 실험종료 10일 전에 각군의 흰쥐를 면양적혈구로 세차례 면역시킨 후 항체생성 세포수 및 혈청 중 항체 농도 등 체액성 면역기능을 중심으로 조사하였다. 그 결과, 대조군에 비해 고추가루 첨가 식이군의 항체 생성 세포수, 적혈구 응집반응 및 혈청중 항체 농도가 높은 것으로 나타났으며, 또한 이때 고추가루 첨가식이군의 각 장기조직 중 AsA 함량은 대조군에 비해 높은 것으로 나타났다. 이들 결과로 보아, 고추성분은 체액성 면역기능의 활성화에 기여하는 물질을 함유하고 있을 뿐만이 아니라, AsA의 공급효과가 뛰어난 것이 확인되었다.

• 한국분말재료학회지
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• 제9권6호
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• pp.394-408
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• 2002

Nanostructured high strength metastable Al-, Mg- and Ti-based alloys containing different amorphous, quasicrystalline and nanocrystalline phases are synthesized by non-equilibrium processing techniques. Such alloys can be prepared by quenching from the melt or by powder metallurgy techniques. This paper focuses on one hand on mechanically alloyed and ball milled powders containing different volume fractions of amorphous or nano-(quasi)crystalline phases, consolidated bulk specimens and, on the other hand. on cast specimens containing different constituent phases with different length-scale. As one example. $Mg_{55}Y_{15}Cu_{30}$- based metallic glass matrix composites are produced by mechanical alloying of elemental powder mixtures containing up to 30 vol.% $Y_2O_3$ particles. The comparison with the particle-free metallic glass reveals that the nanosized second phase oxide particles do not significantly affect the glass-forming ability upon mechanical alloying despite some limited particle dissolution. A supercooled liquid region with an extension of about 50 K can be maintained in the presence of the oxides. The distinct viscosity decrease in the supercooled liquid regime allows to consolidate the powders into bulk samples by uniaxial hot pressing. The $Y_2O_3$ additions increase the mechanical strength of the composites compared to the $Mg_{55}Y_{15}Cu_{30}$ metallic glass. The second example deals with Al-Mn-Ce and Al-Cu-Fe composites with quasicrystalline particles as reinforcements, which are prepared by quenching from the melt and by powder metallurgy. $Al_{98-x}Mn_xCe_2$ (x =5,6,7) melt-spun ribbons containing a major quasicrystalline phase coexisting with an Al-matrix on a nanometer scale are pulverized by ball milling. The powders are consolidated by hot extrusion. Grain growth during consolidation causes the formation of a micrometer-scale microstructure. Mechanical alloying of $Al_{63}Cu_{25}Fe_{12}$ leads to single-phase quasicrystalline powders. which are blended with different volume fractions of pure Al-powder and hot extruded forming $Al_{100-x}$$(Al_{0.63}Cu_{0.25}Fe_{0.12})_x$ (x = 40,50,60,80) micrometer-scale composites. Compression test data reveal a high yield strength of ${\sigma}_y{\geq}$700 MPa and a ductility of ${\varepsilon}_{pl}{\geq}$5% for than the Al-Mn-Ce bulk samples. The strength level of the Al-Cu-Fe alloys is ${\sigma}_y{\leq}$550 MPa significantly lower. By the addition of different amounts of aluminum, the mechanical properties can be tuned to a wide range. Finally, a bulk metallic glass-forming Ti-Cu-Ni-Sn alloy with in situ formed composite microstructure prepared by both centrifugal and injection casting presents more than 6% plastic strain under compressive stress at room temperature. The in situ formed composite contains dendritic hcp Ti solid solution precipitates and a few $Ti_3Sn,\;{\beta}$-(Cu, Sn) grains dispersed in a glassy matrix. The composite micro- structure can avoid the development of the highly localized shear bands typical for the room temperature defor-mation of monolithic glasses. Instead, widely developed shear bands with evident protuberance are observed. resulting in significant yielding and homogeneous plastic deformation over the entire sample.

• Journal of Welding and Joining
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• 제8권4호
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• pp.35-45
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• 1990

Casting are widely used nodays as complicated and diversified forming materials due to its superior castability. However the welding of cast iron has not been accompaniced satisfactory resulting in an microstructure change happened in the heat affected zone (HAZ), especially the graphite are formed and shaped consecutively in the area and it has great impact on the crack occuring and growth together with martensite forming in this area. It case of gray cast iron welding, it is required for pre-heat treatment or specific welding consumables to restrain forming the martensite in the HAZ. In this study, by applying the plasma surface overlaid welding. Fe-Mn-Al steel powder has been used for improvement of anti-crackability in the HAZ and much attention has been paid to establish the overlaid welding method for gray cast iron so that optimum welding conditions may prevent the cracking. With our experiments, we have found that to prevent defects which may occur in the HAZ, the overlaid welding technique for gray cast iron has been developed.

• 대한기계학회논문집A
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• 제20권7호
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• pp.2182-2195
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• 1996

Densification characteristics and behavior of tool steel powder compact during high temperature forming processes were investigated under pressure less sintering, sinter forging and hot isostastic pressing. In pressureless sintering, full density was obtained at a closely controlled temperature near the solidus of the material. Finite element calculations from constitutive model for densification by power law creep and diffusional flow were compared with experimental data. Agreements between theoretical calculations and experimental data were good in hot isostatic pressing but not as good in sinter forging.

• 연구논문집
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• 통권34호
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• pp.131-138
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• 2004

Porous silicon nitride ceramics were prepared by Self-propagating High Temperature Synthesis from silicon powder, silicon nitride powder and the pore-forming precursor. The microstructure, porosity and the flexural strength of the porous silicon nitride ceramics were varied according to the Si/$Si_3N_4$ ratio, size and amount of the pore-forming precursors. Some samples exhibited as high flexural strength as $162\pm24$ MPa. The high strength is considered to result from the fine pore size and the strong bonding among the silicon nitrid particles.

• 한국분말재료학회지
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• 제1권1호
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• pp.85-94
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• 1994

In order to predict droplet velocity and temperature profiles and fractional solidification with flight distance during spray forming, the Newtonian heat transfer formulation has been coupled with the classical heterogeneous nucleation and the specific solidification process. It has been demonstrated that the thermal profile of the droplet in flight is significantly affected by process parameters such as droplet size, initial gas velocity, undercooling. As the droplet size and/or the initial gas velocity increase, the onset and completion of solidification are shifted to greater flight distances and the solidification process also extends over a wider range of flight distances. The amounts of solid fractions formed during recoalescence, segregated solidification and eutectic solidification are insensitive to droplet size and initial gas velocity whereas those are strongly affected by the degree of undercooling. There are good linear relations between the undercooling and the corresponding solid fractions generated during recoalesced, segregated and eutectic stages.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.236-237
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• 2006

Cold spraying is a fairly new coating technique, which within the last decade attracted serious attention of research groups and spray companies. As compared to thermal spraying, the low process temperatures in cold spraying result in unique coating properties, which promise new applications. Since particles impact with high kinetic energy in the solid state, new concepts to describe coating formation are requested to enable the full potential of this new technology. The present contribution gives a brief review of current models concerning bonding, supplying a description of the most influential spray parameters and consequences for new developments. With respect to spray forming by cold cold spraying, microstructures and thick, further machineable structures are presented.