• 소성∙가공
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• 제21권7호
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• pp.412-419
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• 2012

The ingot-breakdown scheme of a tower flange material (low-alloy steel) for offshore wind turbine was investigated using finite element (FE) simulations and experimental analyses. Based on compression test results of the low-alloy steel, a deformation processing map was generated using the superposition approach between the dynamic materials model (DMM) and Ziegler's instability criterion. The deformation processing map allowed determination of the optimum process conditions for the tower flange material. Within the FE simulations of the ingot breakdown process, the Cockcroft-Latham criterion, which considers ductile fracture, was used to predict the possibility of forming defects during the hot working process. In general, the critical value for the ductile fracture of steel is 0.74. During the ingot-breakdown under optimum process conditions, the actual tower flange forgings exhibited a relatively uniform shape without any forming defects.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2006년도 춘계학술대회 논문집
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• pp.377-380
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• 2006

Manufacturing process of Ti-6Al-4V alloy billet was investigated with FEM simulation and experimental analysis. Before the breakdown process of Ti-6Al-4V alloy ingot, FEM simulation for the breakdown processes of Ti-6Al-4V alloy ingot was used to calculate the forging load and state variables such as strain, strain rate and temperature. In order to breakdown the ingot structure and make an equiaxed structure billet, two different processes were employed for a VAR/VAR processed Ti-6Al-4V alloy ingot. Firstly, the ingot was cogged in single-phase $\beta$ field at the temperature of $1,100^{\circ}C$. In the process, the coarse and inhomogeneous structure developed by the double melting process was broken down. The second breakdown was performed by upsetting and cogging processes in $\alpha+\beta$ phase field to obtain the microstructure of fine equixed $\alpha$ structure in the matrix of transformed $\beta$. Finally, the mechanical properties of Ti-6Al-4V alloy billet made in this work were compared with those of other billet and ring product.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 추계학술대회 논문집
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• pp.42-45
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• 2007

Recrystallization behavior during ingot-breakdown process of Alloy 718 was investigated with finite element analysis and experimental approaches. In order to analyze microstructural changes during the cogging process of an Alloy 718 ingot, the side-pressing and heat treatment tests were performed at different temperatures and ram speed. From the side-pressing and heat treatment test results, it was found that microstructural changes during hot forging of Alloy 718 ingot greatly influenced on a close interaction between dynamic and static-recrystallization behaviors. A recrystallization model of Alloy 718 was used to predict the complex microstructural variation during continuous heating and forging processes of the cogging, and the predicted grain size and its distribution were compared with the actual cogged Alloy 718 billet.

• 한국방사성폐기물학회:학술대회논문집
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• 한국방사성폐기물학회 2005년도 춘계 학술대회
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• pp.426-427
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• 2005

Advanced Spent Fuel Conditioning Process (ACP) is a pyrochemical process in which the spent fuel of PWR is transformed into the uranic metal ingot. Through this process, which has been developed in KAERI since 1998, the radioactivity, the radiotoxicity, the heat and the volume of the PWR spent fuel are reduced by a quarter of the original. To demonstrate a lab-scale process and extract the data for the later pilot-scale process, a demonstration facility of ACP (ACPF) is under construction and the lab-scale demonstration is slated for 2006. To establish the safeguardability of ACPF, a safeguards system including a neutron counter based on non-destructive assay, which is named as ACP Safeguards Neutron Counter (ASNC), the ACP Safeguards Surveillance System (ASSS) which consists of two neutron monitors and five IAEA cameras, and Laser Induced Breakdown System (LIBS) have been developed and are ready to be installed at ACPF. The target materials of ACP to assay with ASNC are categorized into three types among which the first is the uranic metal ingot, the second is the salt waste and the last is $UO_2$ and $U_{3}O_8$ powders, rod cuts and hulls. The Pu content of process nuclear materials can be accounted with ASNC. The ASSS is integrated in the ACP Intelligent Surveillance Software (AISS) in which the IAEA camera images and background signals at the rear doors of ACPF are displayed. The composition of special nuclear materials of ACP can be measured with LIBS which can be a supporting measurement tool for ASNC. The conceptual picture of safeguards system of ACPF is shown in Fig. 1.

• 한국결정성장학회지
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• 제32권4호
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• pp.121-127
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• 2022

초광역대 반도체인 β-Ga₂O₃은 고전력 반도체 소재에 대한 유망한 응용으로 인해 큰 주목을 받고 있다. 5가지 다른 다형 중 가장 안정적인 상인 β-Ga₂O₃는 4.9 eV의 넓은 밴드갭과 8 MV/cm의 높은 항복 전계를 갖는다. 또한, 이는 용융 소스로부터 성장될 수 있어 전력반도체용 SiC, GaN 및 다이아몬드와 같은 다른 와이드 밴드갭 반도체보다 더 높은 성장률과 더 낮은 제조 비용으로 성장이 가능하다. 이 연구에서 β-Ga₂O₃ 단결정 성장은 EFG(edge-defined film-fed growth) 방법에 의해 성장되었다. 성장 방향과 주면을 각각 β-Ga₂O₃ 결정의 [010] 방향과 (100)면으로 성장하였다. Raman 분석의 스펙트럼으로 β-Ga₂O₃ 잉곳의 결정상과 불순물을 확인하였고, 고해상도 X선 회절(HRXRD)을 이용하여 결정 품질과 결정 방향을 분석하였다. 또한 EFG 방법으로 성장한 β-Ga₂O₃ 리본형태의 잉곳을 각 위치별로 결정 품질과 다양한 특성을 체계적으로 분석하였다.