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Park, Sangwon,Park, Chulho,Na, Youngsang,Kim, Hyoung-Seop,Kang, Namhyun Elsevier 2019 JOURNAL OF ALLOYS AND COMPOUNDS Vol.770 No.-
<P><B>Abstract</B></P> <P>In this study, we investigated the influence of (W, Cr) carbide on the hardness and tensile properties of friction stir welds (FSWs) for CoCrFeMnNi high entropy alloys. FSW without cracks or voids were achieved for rotational speeds of 400–1000 rpm. As the rotational speed increased, the thinning of the weld thickness compared to the thickness of the base metal was increased. Specifically, an abnormal tornado-shaped region was observed in the stir zone at rotation speeds of 600 rpm and above. The tensile strength increased as the rotation speed increased from 400 to 800 rpm and decreased at a rotation speed of 1000 rpm. The abnormal region with a fine (W, Cr) carbide of 0.5 μm or less was dispersed in the grain boundaries. At a rotation speed of 800 rpm, the dispersion of fine (W, Cr) carbide was optimized to produce grain refinement and maximum tensile strength. However, at 1000 rpm, (W, Cr) carbide coarsened due to high heat input, and the number of carbide particles per unit area decreased, thereby decreasing the hardness and tensile strength.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Friction stir welds without crack or void were achieved for CoCrFeMnNi alloy. </LI> <LI> Fine (W, Cr) carbides of 0.5 μm or less were dispersed in the grain boundaries. </LI> <LI> Dispersion of fine carbides produced grain refinement and maximum tensile strength. </LI> <LI> High heat input decreased the number of carbides per unit area. </LI> <LI> High heat input coarsened (W, Cr) carbides, thereby decreasing the tensile strength. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Sanghyeon Park,Hyunbin Nam,Yoona Lee,Nokeun Park,Sunig Hong,Youngsang Na,Cheolho Park,Namhyun Kang 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.8
This study investigated the gas tungsten arc (GTA) weldability of a base metal (BM) Fe60Co15Ni15Cr10medium-entropyalloy (MEA) by applying CoCrFeMnNi and CrFeMnNiCu fillers. Sound welds without macro defects, such as internal poresor cracks, were obtained. The CoCrFeMnNi-based weld consisted of a face-centered cubic (FCC) structure, whereas theCrFeMnNiCu-based weld comprised (Co, Cr, Fe)-rich phase of FCC1 and a Cu-rich phase of FCC2 with the same FCC structureformed by phase separation. In the CrFeMnNiCu-based weld with a Cu-rich phase, the weld metal (WM) was strongerthan that in the CoCrFeMnNi-based weld. The tensile fracture of all specimens occurred in the coarse-grained heat-affectedzone (CGHAZ) at 298 K, while the tensile properties of the CrFeMnNiCu-based weld were improved compared to thoseof the CoCrFeMnNi-based weld, probably because the Cu-rich phase present in WM blocks the movement of dislocations. The WM of all tensile specimens at 77 K exhibited deformation twins, and deformation-induced martensitic transformationoccurred in the BM and CGHAZ, showing improved strength and ductility compared to those at 298 K.
통계적 메타분석을 응용한 미래기술개발로드맵 도출에 관한 연구
유영상(Youngsang Yoo),박정석(Jeong-Seok Park),정내양(Nae-Yang Jeong),박찬근(Chan Keun Park),허태영(Tae-Young Heo) 한국산업정보학회 2008 한국산업정보학회논문지 Vol.13 No.4
본 연구에서는 정보통신 시장의 급격한 변화를 감지하고 경제 및 사회적 미래예측을 통하여 고객의 니즈에 부합하는 미래기술을 발굴하기 위한 방법으로 통계적 메타분석(meta analysis)을 응용하여 미래기술예측을 실시하였다. 특히 미래기술개발을 위한 주요 핵심트렌드를 기술, 고객니즈 차원에서 검토하고, 도출된 동인과 장애요인을 기반으로 하여 통계적 메타 분석을 응용하여 미래기술을 예측하였으며, 정보통신(information and communication technology, ICT)분야에서 메타 분석을 이용하여 예측 가능한 미래기술을 도출하여 미래기술개발 로드맵을 구축하였다. As the information and communications market goes more uncertain, foresight activities becomes more important. A number of foresight activities, such as trend analysis, have been used to predict customer needs. However previous studies tend to lack objectivity and systematization. In this study, we suggest a meta analysis methodology which combines both top-down and bottom-up approach in order to systematize the analysis process. Secondly, we applied this approach to ref market to identify essential future technologies. Based on the result from the meta analysis, we have constructed the future technology roadmap.
Youngsang CHUN,Hyeong Ryeol KIM,Kyung Rae KIM,Eun Jeong KIM,Hah Young YOO,Ja Hyun LEE,Chulhwan PARK,Seung Wook KIM 한국생물공학회 2021 한국생물공학회 학술대회 Vol.2021 No.10
Lipase is well-known as a biocatalyst for the green process to produce biodiesel in charge of a sustainable environment. Enzyme immobilization is a strategy focusing on the application of continuous cycles in the enzymatic process system. In this study, an economical and simple immobilization technique was designed for repeated use of enzymes while stably maintaining enzyme activity through enzyme-metal-phosphate encapsulation. First, the evaluation of lipase activity on metal ions was carried out to determine the substance for encapsulation. As a result, the lipase activity showed the highest in Tris-HCl buffer containing copper ion. In particular, the self-assembled lipase-copper-phosphate (SALCP) in phosphate-buffered saline showed a highly porous and robust inorganic surface by SEM. Immobilized lipase through SALCP showed improved enzyme stability over a wide broad of pH and operating temperatures compared to free lipase. In addition, SALCP succeeded in maintaining more than 80% of lipase activity under the biodiesel conversion process for 10 cycles.