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- 저자 : Jesik Shin (검색결과 4 건)
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Shin, Jesik,Kim, Taehyeong,Kim, DongEung,Kim, Dongkwon,Kim, Kitae Elsevier 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.698 No.-
<P><B>Abstract</B></P> <P>To develop an aluminum alloy that combines excellent mechanical properties with good castability for near-net-shape casting of automotive structural parts, new Cu–free medium Mg 7xxx aluminum alloys with minor Zr (0.1%) and Ti (0, 0.1, and 0.2%) (all contents in wt% unless stated otherwise) elemental content were investigated as potential candidates. The effects of a vulnerable temperature interval and grain refinement on the hot tearing susceptibility (HTS) were investigated in this work to prevent hot tearing. Al–6Zn–(1.3–1.5)Mg–0.1Zr–(0.1–0.2)Ti alloys show 140–150% of ultimate tensile strength (370–390 MPa), 150–180% of elongation (10–12%), 60–80% of medium-thick-wall fluidity, and equivalent thin-wall fluidity, compared to the respective properties of the commercial A356 alloy. Medium-thick-wall fluidity depended on the heat release upon solidification of the alloy investigated, and thin-wall fluidity depended on the surface energy of the alloy in molten state. When the Ti content was increased, a concave variation in the medium-thick-wall fluidity and a monotonic increase in the thin-wall fluidity were observed. In terms of hot tearing, Ti addition led to a decrease in the HTS, which eventually reached zero. By adding 3% Si, hot tearing could be prevented; however, at the same time, elongation was found to decrease to less than 4%. The grain size reduction and morphology alteration due to the combined addition of 0.2% Ti and 0.1% Zr led to an improvement in castability because of a delay in crystal coherency, decrease in solidification time and vulnerable time period, and suppression of Fe-containing intermetallic and T phase crystallization.</P> <P><B>Highlights</B></P> <P> <UL> <LI> New Cu–free medium Mg 7xxx aluminum alloys with minor Ti and Zr are investigated. </LI> <LI> These alloys show an excellent combination of strength, ductility, and castability. </LI> <LI> With increasing Ti content up to 0.2%, the HTS decreases, eventually reaching zero. </LI> <LI> The addition of 0.2% Ti–0.1% Zr improves alloy fluidity and prevents hot tearing. </LI> <LI> The mechanisms of fluidity and HTS dependence on Mg, Si and Ti contents are proposed. </LI> </UL> </P>
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Miranda, Alberto Torres,Bolzoni, Leandro,Barekar, Nilam,Huang, Yan,Shin, Jesik,Ko, Se-Hyun,McKay, Brian John Elsevier 2018 Materials & Design Vol.156 No.-
<P><B>Abstract</B></P> <P>Al matrix composites reinforced with Cu-coated pitch-based carbon fibres (Al/Cu-CFs) were fabricated, using a novel combination of rheocasting and equal channel angular extrusion (ECAE) techniques, in order to exploit the thermal conductivity (<I>K</I>) of the material. Rheocasting allowed the introduction and dispersion of Cu-CFs within the Al<SUB>3</SUB>Mg matrix. The subsequent ECAE processing reduced the porosity of the composites from 3 to 0.03% and induced a high degree of fibre alignment within the matrix, although considerable damage to the fibres occurred during this processing step. After 6 ECAE passes, in which the billet orientation remained constant, the composite with the highest degree of fibre alignment show a thermal conductivity (<I>K</I>) improvement of ~20% with respect to the rheocast composite. The improvement is due to porosity reduction, improved fibre alignment and forced intimate contact of clean CF surfaces with the matrix.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Al/CFs composites TC increased by 19.6% using a novel combination of processing techniques (Rheocasting + ECAE). </LI> <LI> ECAE can be used to align fibres within the Al matrix and maximise the TC of the Al/CF composites. </LI> <LI> It is the first time that this combination of processing has been demonstrated to improve TC. </LI> <LI> Theoretical models are in agreement with experimental findings. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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Jae-Won Jang,Kyung-Eun Min,Cheolhee Kim,Jesik Shin,Jiwoon Lee,Sung Yi 한국정밀공학회 2023 International Journal of Precision Engineering and Vol.24 No.3
The goal of tissue engineering is to replace or regenerate damaged tissue. Scaffold fabrications and biomaterial selections are crucial factors for artificial tissue and bone tissue engineering, which are important due to the limited availability of tissue donors. This paper reviews the scaffold design considerations, manufacturing methods, and biomaterials for bone tissue engineering, and discusses current challenges and future perspectives. Scaffolds are required to have non-hazardous properties such as biocompatibility and biodegradability for the human body, and the necessary mechanical properties to support body weight, or to perform other roles, depending on the type of tissue. Moreover, scaffold structures such as porosity, pore size, and pore shape should be optimized to achieve cell viability and proliferation. Many conventional fabrication methods including thermally induced phase separation, emulsion freeze-drying, solvent casting, gas forming, and electrospinning have been studied and developed, but 3D printing is more suitable for bone tissue engineering because of its ability to manufacture complicated structures. Biomaterials can be divided into four categories: polymer, ceramic, metal, and composites. Composites blend two or more biomaterials to achieve desired properties for matching individual patient conditions. Finding a balance between fabrication method and biomaterial selection, in order to match properties between the scaffold and the target tissue, will be key to the field of bone tissue engineering in the future.
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고압 다이캐스팅법으로 제조한 편상흑연주철-알루미늄 이종소재의 계면접합특성에 미치는 탈흑연 열처리의 영향
양지바름 ( Ji-ba-reum Yang ),김태형 ( Taehyeong Kim ),정재헌 ( Jaeheon Jeong ),김상우 ( Sangwoo Kim ),김윤준 ( Yoonjun Kim ),김동응 ( Dongeung Kim ),신제식 ( Jesik Shin ) 한국주조공학회 2021 한국주조공학회지 Vol.41 No.6
본 연구에서는 주철-알루미늄 이종재료의 계면결합강도를 향상시키기 위하여 탈흑연 열처리를 통해 주철 표면에서 일정 깊이까지의 흑연을 제거하였다. 열처리 시간이 증가함에 따라 흑연이 제거되는 깊이는 증가하였으며, 열처리 시간과 깊이 사이에 선형 관계가 나타났다. 일정 깊이의 흑연이 제거된 주철에 알루미늄을 다이캐스팅 공법으로 주조접합하여 주철에서 흑연이 제거된 공간을 알루미늄으로 채운 후, 계면 반응 및 알루미늄 침투 깊이를 조사하고 계면접합강도를 평가하였다. 다이캐스팅 공법을 통한 알루미늄은 탈흑연 열처리된 주철 표면에서 일정한 깊이까지 채워지는 것으로 확인되었으며, 주철-알루미늄 계면에 금속간화합물이 생성되지는 않은 것으로 확인되었다. 계면접합강도는 열처리 시간과는 큰 관계없이 90MPa 수준의 접합강도를 나타내었으며 이는 탈흑연열처리를 하지 않은 소재의 접합강도 12MPa에 비해 매우 높은 강도이며, 주철의 탈흑연 영역에서 고압 다이캐스팅 공정에 의해 침투된 알루미늄 용탕이 응고되면서 언더컷 구조의 기계적 결합에 의한 것으로 생각된다. In this study, to improve the interfacial bond strength of cast iron-aluminum dissimilar materials, graphite was removed to a certain depth from the cast iron surface through de-graphitization heat treatment. As the heat treatment time increased, the depth at which graphite was removed increased, showing a linear relationship between the heat treatment time and depth. Aluminum was filled to a certain depth on the de-graphitized cast iron surface through die-casting method, and no intermetallic compounds were formed on the cast iron-aluminum interface. The interfacial bonding strength showed a value of 90 MPa regardless of the heat treatment time, which is very high compared to the 12MPa bonding strength of the material without de-graphitization heat treatment. This result is thought to be due to the mechanical bonding of the undercut structure as the liquid aluminum, penetrated by the high pressure die-casting process, solidified in the de-graphitized region of the cast iron.
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