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Shin, Keesam,Lee, Sunghak 대한금속재료학회 2003 METALS AND MATERIALS International Vol.9 No.6
This is a study on the fabrication of surface composites of SiC, TiC particulates, and AISI 304 substrate by high voltage electron beam irradiation. Using CaF2 powders as flux, two kinds of surface composites were fabricated for a comparative analysis of the microstructural modification and mechanical properties. Through the employed process, the powders and substrate surface were melted and surface composite layers were successfully formed in both cases. In the specimen fabricated with SiC powders, a volume fraction of Cr_(23)C_(6) particles (~22 vol.%) were homogeneously distributed along solidification cell boundaries. The large amount of Cr_(23)C_(6) particles in combination with solid solution hardening of Si in the matrix resulted in the improved hardness and wear resistance of the surface composite layer, that are 2 to 3 times those of the substrate. In the specimen fabricated with SiC and Ti+SiC powders, TiC and Cr_(23)C_(6) particles were precipitated without precipitation of SiC.
Cavity Formation Mechanism in Inert-Gas-Atomized Superalloy A-286
Shin, Keesam 국립7개대학공동논문집간행위원회 2001 공업기술연구 Vol.1 No.-
Cavity formation mechanism is that of great interest for the possibility of utilizing the cavities as a material strengthening elements and also for the application of the knowledge obtained to suppress the cavity formation upon radiation damage. In this study, the cavity formation mechanism is studied in the inert-gas-atomized superalloy A-286. The powders produced by IGA are rapidly solidified by the rapid heat extraction during atomization. This study focuses the effect solute atoms on the cavity formation.
고에너지 전자빔 투사를 이용한 표면합금화 재료의 미세조직 연구
유정훈,신기삼,윤재홍,이찬규,허성강,오준철,이성학,어광준 국립7개대학공동논문집간행위원회 2002 공업기술연구 Vol.2 No.-
For determination of the mechanism of microstructural modification by surface alloying technique using high energy electron beam (HEEB), surface alloys of carbon steel with TiC, TiB_2 and VC were fabricated and their microstructures were analyzed using optical microscope, XRD (X-ray diffractometer), and SEM (scanning electron microscope). The surface regions of TiC and VC surface alloy consists of 1) melted, 2) interface, and 3) heat affected regions. In the TiC surface alloy precipitates of large primary and fine eutectic TiC were observed. In TiB_2 surface alloy, neither fine precipitates were present nor the TiB_2 shape was changed from the original particles, which was attributed to the high melting temperature of TiB_2. Among the three surface alloys studied, the melted region hardness of VC surface alloy was the highest.
Effect of Shot Peening on Microstructural Evolution of 500-7 Ductile Cast Iron
Zhang, Yubing,Shin, Keesam Korean Society of Microscopy 2018 Applied microscopy Vol.48 No.3
Ductile cast iron is widely used for many automotive components due to its high wear resistance and fatigue resistance in addition to the low cost of fabrication. The improvement of wear resistance and fatigue properties is key to the life time extension and performance increase of the automobile parts. Surface nanocrystallization is a very efficient way of improving the performance of materials including the wear- and fatigue-resistance. Shot peening treatment, as one of the popular and economic surface modification methods, has been widely applied to various materials. In this study, ductile cast iron specimens were ultrasonic shot peening (USP) treated for 5 to 30 min using different ball size. The microstructures were then microscopically analyzed for determination of the microstructural evolution. After the USP treatment, the hardness of pearlite and ferrite increased, in which ball size is more effective than treatment time. With USP treatment, the graphite nodule count near the surface was decreased with grain refinement. The lager balls resulted in an increased deformation, whereas the smaller balls induced more homogenously refined grains in the deformation layer. In addition, formation of nanoparticles was formed in the surface layer upon USP.
Development of the Hybrid Conjugated Polymer Solar Cell Based on GaN Quantum Dots
Kim, Minji,Shin, Min Jeong,Gwon, Dongoh,Ahn, Hyung Soo,Yi, Sam Nyung,Kim, Pan Seok,Yoon, Sung Cheol,Lee, Changjin,Park, Jungsik,Shin, Keesam,Ha, Dong Han,Sawaki, Nobuhiko IOP Publishing 2013 Japanese journal of applied physics Vol.52 No.1
가스터빈용 소재 IN 738LC 합금의 미세조직 열화거동
유정훈,주성욱,신기삼,김의현,정진성,장성호,송기욱,하정수 국립7개대학공동논문집간행위원회 2002 공업기술연구 Vol.2 No.-
IN 738LC, used as gas-turbine for power generation, was heat treated at 750℃, 850℃, 950℃ for 1000, 2000, and 4000 hrs. and the microstructural evolution are examined using optical microscope, XRD, SEM/EDS. For comparison, part of gas turbine used for 18439 hours for power generation was also examined. The results showed γ´, the main strengthening elements in this alloy, was about 300 nm and was about 56% in as-cast samples. The volume fraction of γ´peaked at 2000 hours at 750℃ and then decreased at further or longer heat treatment. The average diameter of the γ´ which was about 200 nm increased to about 1㎛. Carbides were formed at dendrite, cell, or grain boundaries which was ascribed to the segregation caused by solute redistribution during solidification. It was found that the at low temperature, M_6C type carbides formed, whereas carbides of M_23C_6 type formed at higher temperature, or at longer degradation.
Development of High-Temperature Solders: Contribution of Transmission Electron Microscopy
Bae, Jee-Hwan,Shin, Keesam,Lee, Joon-Hwan,Kim, Mi-Yang,Yang, Cheol-Woong Korean Society of Microscopy 2015 Applied microscopy Vol.45 No.2
This article briefly reviews the results of recently reported research on high-temperature Pb-free solder alloys and the research trend for characterization of the interfacial reaction layer. To improve the product reliability of high-temperature Pb-free solder alloys, thorough research is necessary not only to enhance the alloy properties but also to characterize and understand the interfacial reaction occurring during and after the bonding process. Transmission electron microscopy analysis is expected to play an important role in the development of high-temperature solders by providing accurate and reliable data with a high spatial resolution and facilitating understanding of the interfacial reaction at the solder joint.
Microstructural Evolution of Grade 91 Steel upon Heating at 760~1000℃
He, Yinsheng,Chang, Jungchel,Lee, Je-Hyun,Shin, Keesam Materials Research Society of Korea 2015 한국재료학회지 Vol.25 No.11
The microstructural evolution of Grade 91 tempered martensite ferritic steels heat treated at $760{\sim}1000^{\circ}C$ for two hours was investigated using scanning electron microscopy(SEM), energy disperse spectroscopy(EDS), electron backscattered diffraction (EBSD), and transmission electron microscopy(TEM); a microhardness tester was also employed, with a focus on the grain and precipitate evolution process as well as on the main hardening element. It was found that an evolution of tempered martensite to ferrite($760{\sim}850^{\circ}C$), and to fresh martensite($900{\sim}1000^{\circ}C$), occurred with the increase of temperature. Simultaneously, the parabolic evolution characteristics of the low angle grain boundary(LAGB) increased with the increase of the heating temperature(highest fraction of LAGB at $925^{\circ}C$), indicating grain recovery upon intercritical heating. The main precipitate, $M_{23}C_6$, was found to be coarsened slightly at $760{\sim}850^{\circ}C$; it then dissolved at $850{\sim}1000^{\circ}C$. Besides this, $M_3C$ cementite was formed at $900{\sim}1000^{\circ}C$. Finally, the experimental results show that the hardness of the steel depended largely on the matrix structure, rather than on the precipitates, with the fresh martensite showing the highest hardness value.