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고온 부품용 Ti-6Al-4V 합금의 미세조직과 고온 인장 특성과의 상관관계
이정섭(Jungsub Lee),송전영(Jeon Young Song),한정민(Jung Min Han),구지호(Ji Ho Gu),마영화(Young Wha Ma) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
AM(Additive Manufacturing) has columnar prior beta grain with α’-martensite due to vertical direction temperature gradient and rapid cooling rate (10³~10⁴ K/s), and most AMed part performs the heat treatment to remove the crystallographic texture. After heat treatment of AMed Ti-6Al-4V alloy, α’-martensite transform to α+β mixture phase that reduce the anisotropy and maintain the strength stability at elevated temperature. However, Ti-6Al-4V alloy occurs degradation of tensile properties above 300 °C. It is necessary to study on life prediction at elevated temperature and build the database of AMed Ti-6Al-4V alloy to apply low-pressure and compressor turbine blades. In this study, horizontal and vertical specimen manufacture by L-PBF and elevated temperature tensile test conducted at 25~700 °C with analysis of microstructure and fractography. Tensile properties are decreased with increasing testing temperature. In fractographs, V series specimen has larger dimple size that indicates decreasing of strength due to Hall-Petch relationship. However, V series specimen has similar axis of tensile load and columnar grain that result in higher elongation at elevated temperature.
이정섭(Jungsub Lee),최원준(Won June Choi),김민기(Min Ki Kim),문기현(Ki Hyun Moon),송승환(Seong Hwan Song),권세진(Sejin Kwon) 한국추진공학회 2008 한국추진공학회 학술대회논문집 Vol.2008 No.11
본 연구에서는 과산화수소 분해 반응을 이용하여 세계 최초로 10뉴턴 급의 추진력을 갖는 액체 추진 소형 모델 로켓을 제작하고 발사 시험을 하였다. 일련의 설계를 통해 인젝터에 지름 200㎛의 오리피스를 7개 만들었고, 목의 지름이 2.5mm 이고 면적비가 2.56인 노즐을 제작하였다. 촉매로 백금을 코팅한 아이솔라이트(Isolite)를 사용하였다. 90wt% 과산화수소를 질소 가스를 통해 20bar로 가압하여 촉매 베드의 길이와 베드에 올린 백금의 적재량을 변수로 하여 추력 실험을 행하였다. 그 결과, 5wt%의 백금을 4cm의 베드에 올렸을 때 가장 높은 c* 효율과 추력 안전성을 보여주었다. 경량화를 위해 로켓의 몸체는 알루미늄으로 만들었으며, 제작한 로켓에서는 솔레노이드 벨브를 통해 유량을 조절하였다. 발사 시험을 행한 결과 비교적 일정한 속도로 10m 가량을 올라갔다. In this paper, a 10N class liquid propellant rocket utilizing a dissolving reaction of hydrogen peroxide is constructed and tested. Through a series of designs, seven orifices with a diameter of 200㎛ and a nozzle with a neck of 2.5mm in diameter and area ratio of 2.56 were made. The platinum coated on Isolite was used for catalyst. 90wt% peroxide pressed at 20 bar by nitrogen gas was used for performance evaluation. The length of the catalyst bed and the load of platinum was taken as the parameters for this experiment. For the catalyst support length of 4cm loaded on 5wt% platinum, satisfactory c* efficiency and stable thrust was observed. The light weight body of the rocket was composed of aluminum. Rocket rose about 10m with relatively constant velocity in launching test.
이정섭(Jungsub Lee),장태우(Tai-Woo Chang),신기태(Kitae Shin),박진우(Jinwoo Park) 한국IT서비스학회 2009 한국IT서비스학회지 Vol.8 No.4
In today's changing environment where the product life-cycle is becoming shorter, enterprises are forced to introduce new products as rapidly as possible and to score a success in a market. It is important to manage suppliers who supply part of the new products to satisfy variable demands. We suggest performance measures of flexibility for suppliers in new products environments. We analyzed the measures from literatures, SCOR (Supply Chain Operations Reference) model and several scorecards. A simulation study was made with the measures in order to understand adaptability of a supply chain. It could help a manufacturer make a decision of purchasing and find a bottleneck supplier.
적층 제조된 H13 공구강의 미세조직과 기계적 특성간의 상관관계
안우진,박준혁,이정섭,최중호,정임두,유지훈,김상식,성효경,An, Woojin,Park, Junhyeok,Lee, Jungsub,Choe, Jungho,Jung, Im Doo,Yu, Ji-Hun,Kim, Sangshik,Sung, Hyokyung 한국재료학회 2018 한국재료학회지 Vol.28 No.11
H13 tool steels are widely used as metallic mold materials due to their high hardness and thermal stability. Recently, many studies are undertaken to satisfy the demands for manufacturing the complex shape of the mold using a 3D printing technique. It is reported that the mechanical properties of 3D printed materials are lower than those of commercial forged alloys owing to micropores. In this study, we investigate the effect of microstructures and defects on mechanical properties in the 3D printed H13 tool steels. H13 tool steel is fabricated using a selective laser melting(SLM) process with a scan speed of 200 mm/s and a layer thickness of $25{\mu}m$. Microstructures are observed and porosities are measured by optical and scanning electron microscopy in the X-, Y-, and Z-directions with various the build heights. Tiny keyhole type pores are observed with a porosity of 0.4 %, which shows the lowest porosity in the center region. The measured Vickers hardness is around 550 HV and the yield and tensile strength are 1400 and 1700 MPa, respectively. The tensile properties are predicted using two empirical equations through the measured values of the Vickers hardness. The prediction of tensile strength has high accuracy with the experimental data of the 3D printed H13 tool steel. The effects of porosities and unmelted powders on mechanical properties are also elucidated by the metallic fractography analysis to understand tensile and fracture behavior.