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레이저 직접 용착공정으로 형성된 스테인레스/인코넬 합금 계면의 미세조직 분석
엄영성,김경태,정수호,유지훈,양동열,최중호,심철용,안승준,Eom, Yeong Seong,Kim, Kyung Tae,Jung, Soo-Ho,Yu, Jihun,Yang, Dong Yeol,Choe, Jungho,Sim, Chul Yong,An, Seung Jun 한국분말야금학회 2020 한국분말재료학회지 (KPMI) Vol.27 No.3
The directed energy deposition (DED) process of metal 3D printing technologies has been treated as an effective method for welding, repairing, and even 3-dimensional building of machinery parts. In this study, stainless steel 316L (STS316L) and Inconel 625 (IN625) alloy powders are additively manufactured using the DED process, and the microstructure of the fabricated STS316L/IN625 sample is investigated. In particular, there are no secondary phases in the interface between STS316L and the IN625 alloy. The EDS and Vickers hardness results clearly show compositionally and mechanically transient layers a few tens of micrometers in thickness. Interestingly, several cracks are only observed in the STS 316L rather than in the IN625 alloy near the interface. In addition, small-sized voids 200-400 nm in diameter that look like trapped pores are present in both materials. The cracks present near the interface are formed by tensile stress in STS316L caused by the difference in the CTE (coefficient of thermal expansion) between the two materials during the DED process. These results can provide fundamental information for the fabrication of machinery parts that require joining of two materials, such as valves.
AlSi10Mg 합금분말 크기가 선택적 레이저 용융된 3차원 조형체 특성에 미치는 영향
엄영성,김동원,김경태,양상선,최중호,손인준,유지훈,Eom, Yeong Seong,Kim, Dong Won,Kim, Kyung Tae,Yang, Sang Sun,Choe, Jungho,Son, Injoon,Yu, Ji Hun 한국분말야금학회 2020 한국분말재료학회지 (KPMI) Vol.27 No.2
Aluminum (Al) - based powders have attracted attention as key materials for 3D printing because of their excellent specific mechanical strength, formability, and durability. Although many studies on the fabrication of 3D-printed Al-based alloys have been reported, the influence of the size of raw powder materials on the bulk samples processed by selective laser melting (SLM) has not been fully investigated. In this study, AlSi10Mg powders of 65 ㎛ in average particle size, prepared by a gas atomizing process, are additively manufactured by using an SLM process. AlSi10Mg powders of 45 ㎛ average size are also fabricated into bulk samples in order to compare their properties. The processing parameters of laser power and scan speed are optimized to achieve densified AlSi10Mg alloys. The Vickers hardness value of the bulk sample prepared from 45 ㎛-sized powders is somewhat higher than that of the 65 ㎛m-sized powder. Such differences in hardness are analyzed because the reduction in melt pool size stems from the rapid melting and solidification of small powders, compared to those of coarse powders, during the SLM process. These results show that the size of the powder should be considered in order to achieve optimization of the SLM process.
선택적 레이저 조형된 AlSi10Mg합금의 후열처리에 따른 Si-rich상 형상변화가 기계적 특성에 미치는 영향
남정우,엄영성,김경태,손인준,Nam, Jung-woo,Eom, Yeong Seong,Kim, Kyung Tae,Son, Injoon 한국분말재료학회 (*구 분말야금학회) 2021 한국분말재료학회지 (KPMI) Vol.28 No.2
In this study, AlSi10Mg powders with average diameters of 44 ㎛ are additively manufactured into bulk samples using a selective laser melting (SLM) process. Post-heat treatment to reduce residual stress in the as-synthesized sample is performed at different temperatures. From the results of a tensile test, as the heat-treatment temperature increases from 270 to 320℃, strength decreases while elongation significantly increases up to 13% at 320℃. The microstructures and tensile properties of the two heat-treated samples at 290 and 320℃, respectively, are characterized and compared to those of the as-synthesized samples. Interestingly, the Si-rich phases that network in the as-synthesized state are discontinuously separated, and the size of the particle-shaped Si phases becomes large and spherical as the heat-treatment temperature increases. Due to these morphological changes of Si-rich phases, the reduction in tensile strengths and increase in elongations, respectively, can be obtained by the post-heat treatment process. These results provide fundamental information for the practical applications of AlSi10Mg parts fabricated by SLM.
선택적 레이저 용융공정으로 제조된 Al-Si-Mg 합금의 열처리에 따른 미세조직 및 특성평가
이기승,엄영성,김경태,김병기,유지훈,Lee, Gi Seung,Eom, Yeong Seong,Kim, Kyung Tae,Kim, Byoung Kee,Yu, Ji Hun 한국분말야금학회 2019 한국분말재료학회지 (KPMI) Vol.26 No.2
In this study, Al-Si-Mg alloys are additively manufactured using a selective laser melting (SLM) process from AlSi10Mg powders prepared from a gas-atomization process. The processing parameters such as laser scan speed and laser power are investigated for 3D printing of Al-Si-Mg alloys. The laser scan speeds vary from 100 to 2000 mm/s at the laser power of 180 and 270 W, respectively, to achieve optimized densification of the Al-Si-Mg alloy. It is observed that the relative density of the Al-Si-Mg alloy reaches a peak value of 99% at 1600 mm/s for 180 W and at 2000 mm/s for 270W. The surface morphologies of the both Al-Si-Mg alloy samples at these conditions show significantly reduced porosities compared to those of other samples. The increase in hardness of as-built Al-Si-Mg alloy with increasing scan speed and laser power is analyzed due to high relative density. Furthermore, it was found that cooling conditions after the heat-treatment for homogenization results in the change of dispersion status of Si phases in the Al-Si matrix but also affects tensile behaviors of Al-Si-Mg alloys. These results indicate that combination between SLM processing parameters and post-heat treatment should be considered a key factor to achieve optimized Al-Si alloy performance.
윤지환,엄성현,김상엽,김철연,황홍석,이형화,서지영,김영성,곽동협 대한소화기내시경학회 2007 Clinical Endoscopy Vol.34 No.4
Melanosis ilei is a condition that's characterized by gross greyish-black or brownish-black pigmentation of the mucosa of the terminal ileum. There were several substances that produce gastrointestinal tract pigmentation such as lipofuscin, iron sulphide (FeS), Hemosiderin and exogenous material such as silicates and titanium. We report here on a case of a 58-year-old female who ingested charcoal for a long time, and she was diagnosed with melanosis ilei by colonoscopy. Her condition improved after she stopped ingesting the charcoal. (Korean J Gastrointest Endosc 2007;34:223-226) 회장흑색증이란 회장말단부 점막의 육안적인 회흑색 혹은 흑갈색의 색소 침착으로 정의된다. 일반적인 위장관 색소침착을 일으키는 여러 가지 물질들은 지방갈색소(lipofuscin), 철황화물(iron sulphide), 헤모시데린(hemosiderin), 기타 외인성물질 등이 있다. 저자들은 58세 여자 환자가 장기간 숯을 섭취를 한 후 발생한 회장흑색증 1예를 대장내시경 검사로 경험하였기에 문헌고찰과 함께 보고하는 바이다.
박진일 ( Jin Il Park ),엄성현 ( Sung Hyeon Eum ),김철연 ( Cheul Yeon Kim ),윤지환 ( Ji Hwan Yoon ),황홍석 ( Hong Seok Hwang ),김영성 ( Yeong Sung Kim ),곽동협 ( Dong Hyup Kwak ) 대한내과학회 2006 대한내과학회지 Vol.71 No.6
Most ingested foreign bodies spontaneously pass through the upper and lower intestinal tract. The impaction of an ingested foreign body in the colon is rare. Foreign bodies swallowed inadvertently often cause serious complications, such as perforation, obstruction, abscess formation, enterocolic fistula, or hemorrhage. Physicians should proceed with routine medical care while considering the possibility of the ingestion of a foreign body In cases where abdominal pain of an unknown origin is observed, particularly in elderly patients who wear dentures, alcoholics, mentally disturbed, or rapid eating, and presenting with altered bowel habits. We report a case of a colonoscopically-removed wooden toothpick that impacted the sigmoid colon and was complicated by the formation of a local abscess with a review of the literature. (Korean J Med 71:668-672, 2006)