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산소 농도에 따른 Alloy 617의 고온헬륨환경에서의 크립 및 산화거동
구자현,김대종,장창희,Koo, Jahyun,Kim, Daejong,Jang, Changheui 한국압력기기공학회 2011 한국압력기기공학회 논문집 Vol.7 No.2
Wrought nickel-base superalloys are being considered as the structural materials in very-high temperature gas-cooled reactors. To understand the effects of impurities, especially oxygen, in helium coolant on the mechanical properties of Alloy 617, creep tests were performed in high temperature flowing He environments with varying $O_2$ contents at 800, 900, and $1000^{\circ}C$. Also, creep life in static He was measured to simulate the pseudo-inert environment. Creep life was the longest in static He, while the shortest in flowing helium. In static He, impurities like $O_2$ and moisture were quickly consumed by oxidation in the early stage of creep test, which prevented further oxidation during creep test. Without oxidation, microstructural change detrimental to creep such as decarburization and internal oxidation were prevented, which resulted in longer creep life. On the other hand, in flowing He environment, surface oxides were not stable enough to act as diffusion barriers for oxidation. Therefore, extensive decarburization and internal oxidation under tensile load contributed to premature failure resulting in short creep life. Limited test in flowing He+200ppm $O_2$ resulted in even shorter creep life. The oxidation samples showed extensive spallation which resulted in severe decarburization and internal oxidation in those environments. Further test and analysis are underway to clarify the relationship between oxidation and creep resistance.
구자현(Koo Jahyun) 한국정보보호학회 2005 情報保護學會誌 Vol.15 No.1
본 연구는 망의 가용성이나 보안성을 확보하는 것이 중요한 통신사업자들에게 전국적인 IT 인프라에서 발생하는 해킹이나 기타 보안 위협에 따른 피해를 최소화하고, 위협에 대해서 능동적으로 방어하기 위하여 구축하는 조기경보 시스템에 대한 연구이다. 이러한 조기경보시스템을 구축함으로서 해킹, 바이러스, 웜 등의 다양한 전자적인 침해사고 등의 이벤트를 수집, 분류하고 빠른 시간 안에 대응할 수 있는 시스템을 갖추게 된다. 본 연구는 통신사업자가 조기 경보시스템(EWIS : Early Warning Information System)을 구축하기 위해서 필요한 프레임워크를 제시하는데 있다.
김동훈,구자현,김대종,유영성,장창희,Kim, Donghoon,Koo, Jahyun,Kim, Daejong,Yoo, Young-Sung,Jang, Changheui 한국압력기기공학회 2011 한국압력기기공학회 논문집 Vol.7 No.2
To evaluate steam oxidation behaviours of Alloy 617 and Haynes 230, oxidation test were performed at $900^{\circ}C$ in steam and $steam+20\;vol.-%\;H_2$ environments. Oxidation rate in steam condition was similar to that in air for Alloy 617, while it was slightly lower for Haynes 230. When hydrogen was added to steam, oxidation rate was enhanced. Isolated $MnTiO_3$ particle were formed on $Cr_2O_3$ oxide layer and sub layer $Cr_2O_3$ were formed in steam and $steam+20\;vol.-%\;H_2$ for Alloy 617. On the other hands, $MnCr_2O_3$ layer were formed on top of $Cr_2O_3$ oxide layer for Haynes 230. The extensive sub layer $Cr_2O_3$ formation was resulted from the oxygen inward diffusion in such environments. When hydrogen was added, the oxide morphology was changed from polygonal to platelet because of the accelerated diffusion of cations under the oxide layer. In addition, decarburized zone was extended as hydrogen participated into the reactions causing carbide dissolution.