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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>
Vibration Characteristics of Ni Thin Film Diaphragm by Acoustic Wave
Cho, Gue Serb,Lee, Won Sik,Ko, Se Hyun,Son, Seong Ho,Lee, Chang Woo,Kim, Jun Ki Trans Tech Publications, Ltd. 2010 Advanced materials research Vol.97 No.-
<P>Vibration characteristics of 5μm- thick Ni film were investigated with applying acoustic wave to the Ni diaphragm of 2mm x 2mm unit size. In the modal analysis, the first resonance mode of the diaphragm showed an out-of-plane piston-like movement and the first natural frequency was 1,643 Hz, whereas in this experiment, the first natural frequency appears at about 1,300 Hz under sound pressure of 0.2 Pa. The amplitudes of diaphragm increase with increase of sound pressure level in the applied frequency range from 300 Hz to 1,000 Hz, indicating that area of diaphragm influences directly the amplitude.</P>
Cho, Gue-Serb,Kim, Jin-Wook,Choe, Kyeong-Hwan,Kim, Sang-Sub American Scientific Publishers 2014 Journal of Nanoscience and Nanotechnology Vol.14 No.10
<P>Copper (Cu) coated carbon nanotubes (CNTs) were prepared and investigated by chemical reduction or cementation method. The morphology changes of Cu nanoparticles deposited onto the multiwall carbon nanotubes with metallic zinc (Zn) as a reducing agent have been examined at different cementation factors. The precipitated Cu nanoparticles from the copper ion in the reaction solution were deposited onto and entangled with the CNT substrates. CNTs used were multi-wall carbon nanotubes with average diameter of 10-20 nm and length of 10-50 μm. As-prepared CNTs products were purified by nitric acid solution, and then the CNTs were washed several times with distilled water, and dried in vacuum. The pre-treated CNTs were suspended in solvent. Then, the copper salt was dissolved in the suspension containing the CNTs. The deposited morphology and distribution of copper particles on the CNTs substrate were investigated by changing the solute, solvent and reducing agent. The Cu/CNTs agglomerates were obtained in the presence of copper chloride and copper sulphate salts, and water and ethanol were used as the solvents. And the raw CNTs were pretreated with glacial acetic acid for increasing the coverage rate of copper particles over the CNTs surface at different acid concentrations. The Cu deposited CNTs were characterized in respect of morphology and distribution of CNTs and Cu particles with field emission scanning electron microscopy (FESEM). The copper crystals were identified by X-ray diffraction patterns.</P>
조규섭 ( Gue Serb Cho ),임정규 ( Jung Kyu Lim ),장훈 ( Hoon Jang ),최경환 ( Kyeong Hwan Choe ) 대한금속재료학회 ( 구 대한금속학회 ) 2010 대한금속·재료학회지 Vol.48 No.5
Carbon Nanotubes (CNTs) have recently emerged as a material with outstanding properties. It has shown promising potential for applications in many engineering fields as electronic devices, thermal conductors, and light-weight composites. Researchers have investigated their use as reinforcements in themetal matrix composites of CNTs. In the present work, we decorated CNTs with Ni particles by electroless plating. The CNTs were wet-ball milled for various milling times with a nickel sulfate solution. The precipitated Ni particles were observed mainly by FESEM. In this study, the dispersion of the CNTs and Ni particles was improved with the addition of the surfactant. Also, as the CNTs were shortened and widened by an increased ball milling time, the size of the precipitated Ni particles increased. It was estimated that the CNTs were deformed and caused some defects on their surface during the ball milling process. Those defects were assumed to be heterogeneous nucleation sites for the Ni particles.
Fe-15Cr-5V-1.2C 합금의 응고 및 상변태에 따른 용질원자의 분배
오규환,조규변,김창섭,라형용 대한금속재료학회(대한금속학회) 1997 대한금속·재료학회지 Vol.35 No.2
Transformation sequence and subsequent solute redistribution behaviors of Fe-15Cr-5V-1.2C alloy during solidification have been discussed. Specimens were quenched interruptly, as they were solidified and transformed. Primary δ-ferrite was not completely transformed into γ-austenite during δ→γ peritectic reaction. During the peritectic reaction V was enriched to the retained δ-ferrite, but Cr was not. When the retained δ-ferrite was directly changed into α-ferrite. V was diffused from δ-ferrite into the surrounding γ-austenite due to the decrease of V-solubility in the α-ferrite. As heating the as-cast specimen up to 1000℃, precipitated iron complex carbides were dissolved into the newly formed γ-austenite. The iron carbides were inferred as M_(23)C_6 carbides from the mole fraction change of each phases existing at the heating temperatures and microstructure change with increasing heating temperatures.
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>
급속응고법으로 제조한 과공정 Al-Si 합금분말 압출재의 마멸특성
안영남,조규섭,나형용 ( Young Nam Ahn,Gue Serb Cho,Hyung Yong Ra ) 한국주조공학회 1994 한국주조공학회지 Vol.14 No.5
N/A Wear resistance and wear mechanism of hypereutectic Al- (15∼40 ) wt%Si alloys were investigated. Primary Si particles under 20㎛ size were formed in hypereutectic Al-Si alloy powders due to rapid solidification. But the Si particles of extruded bars were finely distributed in smaller size than that of atomized powders. The wear mechanism of hypereutectic Al-Si alloys was divided into three types of wear phenomena, which were abrasive wear, delamination wear and severe adhesive wear according to sliding speed and load. At low sliding speed and load, wear mechanism was abrasive wear, so Al-15wt%Si alloy showed the best wear resistance. At high sliding speed and load, wear mechanism was adhesive wear, and Al-40wt%Si alloy showed the best wear resistance.
저탄소강에 접합된 Fe-13Cr-5V-1.2C 합금의 초기 응고층 조직 변화
오규환,이희춘,조규섭,라형용 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.9
Liquid Fe-13Cr-5V-1.2C alloy and solid low carbon steel were solidified and bonded in a tube after holding at temperatures for 285sec. The effects of mutual diffusion between two alloys on the microstructural change was investigated. Primary solidified layer bonded on the low carbon steel surface was formed as planar type. Alloy contents and hardness values droped nearby the bonded interface within primary solidified layer. Reaction layer formed in the vicinity of the bonded interface within 30∼40㎛ distance had lower alloy contents than cellular type structure. It is suggested that uphill diffusion of carbon from low carbon Fe-0.2C steel into the Fe-13Cr-5V-1.2C alloy at 1200℃ had produced low Cr content austenite. The austenite was transformed to auto-tempered martensite, which were identified as reaction layer.
기계적 합금화한 Cu-Cr 합금 분말 압출재의 미세조직 및 기계적 성질
김동훈,나형용,조규섭 대한금속재료학회(대한금속학회) 1992 대한금속·재료학회지 Vol.30 No.5
Cu-Cr alloys have been used as precipitation hardened alloys, due to low solubility of Cr in Cu. The strength of copper alloys is known to decrease as precipitates and grain size get coarser as service temperature is increased. Meanwhile, using MA process, higher strengths could be obtained through uniform distribution of fine Cr-particles. In this study, Cu-Cr powder mixtures were mechanically alloyed in order to develop high strength Cu alloys. The properties of extruded bars were investigated using various analytical techniques. The ratio of pre-alloyed powders to steel balls was 1 : 20 and the mechanical alloying was performed for 10hours in Ar atmosphere. TEM observations showed that the Cr-particles were distributed in Cu-matrix, and grain size of the extruded bars was about 100㎚. The tensile strength of extruded bars was found to increase with the volume fraction of Cr and its maximum value was 500㎫ in Cu-4vol%Cr-alloy. The tensile strength was slightly decreased after annealing at 800℃ far 1hours, but greatly decreased after annealing at 900℃ for 1hour. As the result of this study, the strength of Cu-Cr alloys was dependent on the volume fraction of Cr and grain size.