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Lee, Kyong-Whoan,Cho, Gue-Serb,Choe, Kyeong-Hwan,Jo, Hyung-Ho,Ikenaga, Akira,Koroyasu, Sadatoshi The Japan Institute of Metals 2006 MATERIALS TRANSACTIONS Vol.47 No.11
<P>A magnesium alloy was adopted to an evaporative pattern casting (EPC) process to combine advantages of each. In the present study, foam patterns were cast at a top gating system under atmospheric and reduced pressure to evaluate casting characteristics of AZ91D to develop a complete EPC process for high productivity of magnesium alloy castings. Filling time and temperature of molten metal were measured during mold filling. It was recognized that the average filling velocity was affected by the difference of the coating material and the degree of reduced pressure. The grain size of the magnesium alloy was slightly dependent on the degree of reduced pressure. It was considered that the application of the high reduced pressure, which changed the shape of melt surface from convex to concave, was related to the occurrence of internal defects such as cold shut laps or folds in the casting.</P>
백영환,김현경,강석태,황정남,이철주,최대선,정병두 연세대학교 자연과학연구소 1985 學術論文集 Vol.15 No.-
낮은 에너지 가속기를 제작하여 순도가 99.99%인 다결정 Ni에 Li^+ 이온을 7 keV의 에너지로 각 시료에 대한 이온주입율이 1.3×10^16atoms/㎠, 4.0×10^15atoms/㎠, 2.0×10^15atoms/㎠, 1.0×10^15atoms/㎠, 2.0×10^14atoms/㎠ 가 되도록 주입시킨 후 전자총과 억제 전위차형 에너지 분석기를 이용하여 일함수의 변화를 측정하였다. 이온 주입율이 2×10^15atoms/㎠보다 작을 때는 일함수가 1.9 eV까지 감소하였고 이온주입율이 4.0×10^15atoms/㎠보다 많을 때는 일함수가 2.8 eV까지 증가하였다. 이것은 Topping의 이론 및 Bauer의 실험결과와 일치함을 보였다. The changes in the work function of polycrystalline Ni with a purity of 99.99% due to Li^+ ions implanted using a low energy ion accelerator and retarding potential energy analyser(RPEA) have been studied. The implantation energy of the Li^+ ions is 7 keV and the implanted ion dose for the various samples are 1.3×10^16 atoms/㎠, 4.0×10^15 atoms/㎠, 2.0×10^15 atoms/㎠, 1.0×10^15 atoms/㎠ and 2.0×10^14 atoms/㎠. When the ion dose is less than 2×10^15 atoms/㎠ the, work function decreases to 1.9 eV, but when the ion dose is more than 4×10^15 atoms/㎠, the work function increses to 2.8 eV. These results are in good agreement with Topping's theory and Bauer's experiment.
In-Situ Joining of Combustion Synthesized Ni-Al Alloys with Al Casting Alloy
Cho, Gue Serb,Lee, Kang Rae,Choe, Kyeong Hwan,Lee, Kyong Whoan,Ikenaga, Akira Trans Tech Publications, Ltd. 2006 Materials science forum Vol.510 No.-
<P>We focused on the surface reinforcement of Al casting alloys with Ni-Al intermetallic compounds by in-situ combustion reaction to improve the surface properties of Al casting components. Microstructure and phase formation behavior of Ni-Al based intermetallic compounds synthesized by combustion reaction were investigated in terms of thermal and phase analysis using scanning electron microscope(SEM) equipped with energy dispersive x-ray spectrometer (EDS) and x-ray diffractometer(XRD) in Ni-Al intermetallic compounds. Three kinds of nickel aluminides, NiAl3, NiAl and Ni3Al, were synthesized by emission heat from the Al molten metal in order to form a coating layer of intermetallic phase simultaneously on the solidifed Al alloy surface. The synthesized shapes and microstructures of nickel aluminides were varied by casting temperature, Si contents, and the mixing ratio of elemental powders. The synthesized reaction products formed in nickel aluminides were observed to be different depending on the mixing ratio of elemental powders. The reaction layer of about 25m thickness was formed at the interface, and it mainly consisted of NiAl3 phase by the reaction between liquid molten Al alloy and solid Ni powders in green compact. With this information, we successfully produced a coating layer of Ni3Al intermetallic compound onto the casting Al alloy surface using molten metal heat without any additional process. These findings led us to conclude that a near-net shaped nickel aluminide coating layer can be formed using this unique process.</P>
이강래 ( Kang Rae Lee ),최경환 ( Kyeong Hwan Choe ),조규섭 ( Gue Serb Cho ),이경환 ( Kyong Whoan Lee ),김명호 ( Myung Ho Kim ),임경화 ( Kyung Hwa Rim ),김기영 ( Ki Young Kim ) 한국주조공학회 2004 한국주조공학회지 Vol.24 No.5
N/A Vibrational motions of the compaction table were investigated to select the optimal operation conditions of sand filling and compaction for the EPC process. Their modes were measured at the nine points of the table with changing the relative rotation angles between the two eccentric mass vibrators which were attached parallel beneath the table. Well-defined vibration modes were measured at the center of the table but those of left and right sides of the table were distorted regardless of rotational angle differences. The distortion of vibration modes at both sides of the table were caused by the moment generated by offset positions of two eccentric masses. It was found that the uniform vibration modes would be gathered by controlling the relative distances between the rotating axis and the center of gravity in the compaction system at the various conditions of vibration modes and rotational angle differences.
Effect of Si on the Thermal Stability of Ferritic Heat-Resistant Ductile Iron
Choe, Kyeong Hwan,Lee, Kyong Whoan,Kim, Myung Ho Trans Tech Publications, Ltd. 2015 Applied Mechanics and Materials Vol. No.
<P>The effect of silicon (Si) on the stability of heat-resistant ductile iron having ferrite matrix in high temperature was investigated by dilatometric test. Microstructure of heat-resistant ferritic ductile iron consists of ferrite, eutectic carbide at eutectic cell boundaries, precipitated carbide in grain and graphite. Pearlite was found around eutectic carbide in some specimens, however, all pearlite was decomposed by the annealing treatment. As Si content was increased, the number and size of carbide decreased and full ferrite matrix were obtained. The starting temperature of ferrite-austenite transformation and the coefficient of thermal expansion increased with the increase of Si content. The growth of Si 6.0wt% specimen during held at 1,000<SUP> o</SUP>C is lower than other specimens, and it is considered that in the case of Si 6.0wt% specimen, the carbon movement is restrained due to the low solubility of carbon in matrix. In the case of annealed specimens, the contraction during ferrite-austenite transformation was not found when heating. This is because the re-distribution of the graphite was happened through the movement of carbon during annealing treatment.</P>
High Temperature Oxidation Behavior of Si-Mo Ferritic Ductile Cast Iron
Choe, Kyeong Hwan,Lee, Sang Mok,Lee, Kyong Whoan Trans Tech Publications, Ltd. 2010 Materials science forum Vol.654 No.-
<P>High temperature oxidation behavior of Si-Mo ferritic ductile cast iron was investigated in the point of the effect of chromium and vanadium addition. The addition of Cr promoted the formation of as-cast pearlite around carbide which exists in cell boundary, which was eliminated during annealing process. The addition of vanadium promoted the precipitation of tiny carbide and reduced the grain size of ferrite. As the test temperature increased, the change of volume increased, on the other hand, the change of weight decreased above 1173K. In the case of Cr added specimen, the change of weight decreased with the increase of test temperature because of the presence of Cr oxide layer. The vanadium added specimens showed higher increase in the weight and volume change. The oxide layer of vanadium added specimen had very porous structure and showed severe internal oxidation. It is due to the catastrophic oxidation characteristic of vanadium alloyed ferrous alloy. </P>
용체화처리 및 시효처리가 17-4 석출경화형 스테인레스강 정밀주조품의 미세조직 및 기계적 성질에 미치는 영향
유성곤,이경환,나태엽 ( Sung Kon Yu,Kyong Whoan Lee,Tae Yeob Ra ) 한국주조공학회 1992 한국주조공학회지 Vol.12 No.5
N/A The effect of the solution & aging treatment on the tensile strength, yield strength, elongation, reduction of area, hardness was studied in the 17-4 PH stainless steel. SEM pictures were also taken in order to examine the fracture surfaces and precipitated particles. X-ray diffraction patterns for the heat treated samples were also observed. Mechanical properties of the heat treated samples were superior to those of as cast samples. Tensile strength, yield strength, hardeness decreased with the increase of aging temperature. On the other hand, elongation and reduction of area increased as the aging temperature increased.
Al-1 wt % Mg 합금의 일방향응고시 고/액 계면의 형상에 미치는 강화중력의 영향
양영기,강춘식,이진형,이경환,백홍구,윤우영,황장모 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.3
Al-1wt%Mg was unidirectionally solidified to investigate the effect of enhanced gravity on the planar interface morphology. Planar solid/liquid interface morphology became unstable with increasing centrifugal force up to 15G but stabilized again at 20G. Surface stabilization of this alloy with increasing centrifugal force can be explained by thermosolutal convection.
Bi-Mn 공정합금의 일방향응고시 미세조직에 미치는 강화중력의 영향
양영기,강춘식,이경환,황창모 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.4
The microstructure of eutectic MnBi/Bi alloy was investigated after unidirectional solidification under centrifuge process in Bridgman-Stockbarger furnace. Microstructure of the crystals with growth velocity 100 ㎜/h, 25 ㎜/h showed cellular structure and evenly dispersed second phase morphology of MnBi intermetallic compound. The second phase MnBi rod size was varied with acceleration in all growth condition. Numerical analysis was produced to expect fluid flow in rotating system using flow 3d. According to numerical analysis, the fluid flow increased with centrifugal acceleration under constant temperature condition and abrupt increase was expected near centrifugal force is 5G (G = 9.8 m/s: territorial acceleration).