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        • KCI등재

          고에너지 전자빔 투사방법으로 제조된(TiC, SiC)/Ti-6A1-4V 표면복합재료의 연삭 및 미끄럼 마모특성

          吳俊喆,李聖鶴 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.12

          This study is concerned with the improvement of abrasive and sliding wear properties of (TiC, SiC)/Ti-6Al-4V surface composites fabricated by high-energy electron beam irradiation. The mixtures of TiC, SiC, SiC+Ti, or SiC+TiC powders and CaF_2 flux were deposited on a Ti-6Al-4V substrate, and then electron beam was irradiated on these mixtures. The surface composite layers of 1.2∼2.1 ㎜ in thickness were homogeneously formed without defects, and contained a large amount (30∼66 vol.%) of hard phases such as TiC and Ti_5Si_3 in the martensitic matrix. This microstructural modification including the formation of hard phases in the surface composite layer improved hardness and abrasive wear resistance. Particularly in the surface composite fabricated with TiC+SiC powders, the abrasive wear resistance was greatly enhanced by 25 times higher than that of the Ti alloy substrate because of the formation of 66 vol.% of TiC and Ti_5Si_3 in the hardened martensitic matrix. During the sliding wear process, hard and coarse TiC and Ti_5Si_3 were fallen off from the matrix, and their wear debris worked as abrasive particles, thereby reducing the sliding wear resistance. On the other hand, needle-shaped Ti_5Si_3 decelerated the sliding wear because their wear debris were fine and worked as solid lubricants instead of abrasive particles. These findings indicated that high-energy electron beam irradiation was economical and useful for the development of Ti-base surface composites with improved abrasive and sliding wear properties, although the abrasive and sliding wear data should be interpreted by different wear mechanisms.

        • KCI등재후보

          대북제재가 북한 군사력에 미치는 영향

          오준철 고려대학교세종캠퍼스 공공정책연구소 2017 Journal of North Korea Studies Vol.3 No.1

          In 1993 DPRK(Democratic People’s Republic of Korea) declared withdrawal from the NPT(Non-Proliferation Treaty) and UNSC(United Nations Security Council) adopted resolution No. 825 to call upon DPRK to reconsider its decision and allow weapon inspectors from the IAEA(International Atomic Energy Agency) into the country. Since then DPRK has been improving its military capacities especially on asymmetric power of nuclear weapon and long range missile, UNSC and multi-country such as United States, Japan, China and Republic of Korea have been imposing economic sanctions on this action but DPRK have been carrying on regardless. It focused its national capacities and resources on military due military-first ideology and Economy-Nuclear Parallel Policy. However DPRK could not exceed its limit on capacities, this resulted in reduction in defense expenditure when DPRK economy is in deep recession. Which means effective economic sanction which would drag economy down to recession, DPRK would not have enough input due lack of its resources. To achieve this aim, China must take an important part because China is the one main trade partner to DPRK. Thus we must persuade China to consider that to sanction DPRK will be in China’s interest in the future.

        • KCI등재

          고에너지 전자빔 투사방법에 의한 2층 VC/Ti-6Al-4V 표면복합재료의 제조와 마모 및 파괴특성

          吳俊喆,李昌燮,李聖鶴 대한금속재료학회 2001 대한금속·재료학회지 Vol.39 No.12

          This study is concerned with the analysis of microstructure, hardness, wear resistance, and fracture toughnes of two-layered VC/Ti-6Al-4V surface composites fabricated by high energy electron beam irradiation. The mixture of VC powders and CaF_2 flux was deposited on a Ti-6Al-4V substrate, and then electron beam was irradiated on these powder mixture to fabricate a one-layered surface composite. A two-layered surface composite was also fabricated by irradiating electron beam again onto the powder mixture deposited on the one-layered surface composite. The composite layers of 1.2∼1.5 ㎜. in thickness were homogeneously formed without defects, and contained a large amount (25∼40 vol.%) of (Ti, V)C precipitates in the martensitic or V-rich β-Ti matrix. This microstructural modification including the formation of hard carbides and hardened matrices in the surface composite layers improved hardness and wear resistance. Particularly in the two-layered surface composite containing more carbides, the wear resistance was greatly enhanced by seven times higher than that of the Ti-6Al-4V substrate. In-situ observation of fracture process showed that microcracks were initiated at carbides and propagated along these microcracked carbides, and that in the two-layer surface composite, more microcracks were easily formed at carbides than in the one-layed composite, thereby showing lower fracture toughness.

        • KCI등재

          고에너지 전자빔 투사방법으로 제조된(TiC, SiC)/Ti-6Al-4V 표면복합재료의 미세조직과 마모 및 파괴특성(1. 미세조직 형성과정)

          오준철,윤은섭,이성학 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.11

          The present study is concearned with microstructural analysis of (TiC, SiC)/Ti-6Al-4V surfaces composites fabricated by high-energy electron beam irradiation. The mixtures of TiC, SiC, Ti+SiC, and TiC+SiC powders and CaF_2 flux were evenly deposited on a Ti-6Al-4V substrate, and then electron beam was irradiated on these mixtures using an electron beam accelerator. In the specimens processed with flux addition, the surface-alloyed layers of 1.2∼2.1 ㎜ in thickness were homogeneously formed without defects, and contained a large amount (30∼66 vol.%) of precipitates such as TiC and Ti_5Si_3 in the martensitic matrix. Upon electron beam irradiation, (TiC, SiC)/flux powder mixtures and part of the substrate were melted to form a molten metal containing Ti, Si, and C. Here, C and Si atoms interacted with Ti atoms to form TiC and Ti_5Si_3, respectively, and the matrix was composed of martensite because of fast cooling during solidification. Microstructural modifications including melting, solidification, precipitation, and phase transformation processes could be explained well from a Ti-Si-C ternary phase diagram.

        • O-ring의 마찰, 마모 특성에 관한 실험적 고찰

          오준철(Jun-Chul Oh),김대은(Dae-Eun Kim),김현준(Hyun-Jun Kim),김문환(Mun-Hwan Kim),김춘일(Chun-Il Kim) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5

          O-rings are commonly used in machines as a seal. Due to prolonged use the surface of an O-ring can degrade which can lead to leakage as well as contamination. Damage of O-rings used in vacuum applications such as sputter is caused by various mechanisms. Particles detached from the O-ring may cause significant problems on the performance of the system in the vacuum chamber. Therefore, understanding the tribological behavior of O-rings is important to tackle the damage caused by repeated contact. In this work, FKM rubber was used for friction and wear tests conducted to investigate the tribological behavior of O-rings. A reciprocating type of a tribo-tester was used for the tests. The friction coefficient between the steel ball and the FKM specimen was quite high. Also, in order to identify the wear behavior, the surface of the FKM specimen was characterized using both optical and scanning electron microscopes. Evidence of wear due to adhesion and extrusion could be found. The results of this work will aid in improving the durability of O-rings.

        • KCI등재

          O-ring의 마찰, 마모 특성에 관한 실험적 고찰

          오준철(Jun-Chul Oh),김대은(Dae-Eun Kim),김현준(Hyun-Jun Kim),김문환(Mun-Hwan Kim),김춘일(Chun-Il Kim) 대한기계학회 2009 大韓機械學會論文集A Vol.33 No.10

          O-rings are commonly used in machines as a seal. Due to prolonged use the surface of an O-ring can degrade which can lead to leakage as well as contamination. Damage of O-rings used in vacuum applications such as sputter is caused by various mechanisms. Particles detached from the O-ring may cause significant problems on the performance of the system in the vacuum chamber. Therefore, understanding the tribological behavior of O-rings is important to tackle the damage caused by repeated contact. In this work, FKM rubber was used for friction and wear tests conducted to investigate the tribological behavior of O-rings. A reciprocating type of a tribo-tester was used for the tests. The friction coefficient between the steel ball and the FKM specimen was quite high. Also, in order to identify the wear behavior, the surface of the FKM specimen was characterized using both optical and scanning electron microscopes. Evidence of wear due to adhesion and extrusion could be found. The results of this work will aid in improving the durability of O-rings.

        • KCI등재

          고에너지 전자빔 투사방법으로 제조된 Ti-6Al-4V 표면합금화 재료의 미세조직과 마모특성

          이성학,오준철 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.5

          The present study is concerned with the microstructural analysis and the evaluation of hardness and wear properties of Ti-6Al-4V surface-alloyed materials fabricated by high-energy electron beam. The mixtures of TiC, TiN, or TiC+TiN powders and CaF₂ flux were deposited on a Ti-6Al-4V substrate, and then electron beam was irradiated on these mixtures using an electron beam accelerator. In the specimens processed with a flux mixing ratio of 50 wt.%, the surface-alloyed layers of 1 ㎜ in thickness were homogeneously formed without defects, and contained a large amount (over 30 vol.%) of precipitates such as TiC, TiN, (Ti_xAl(1-x).)N, and TiC_xN(1-x) in the martensitic or N-rich acicular α-Ti matrix. This microstructural modification including the formation of hard precipitates and hardened matrices in the surface-alloyed layers improved hardness and wear resistance. Particularly in the TiN/Ti surface-alloyed material, the wear resistance was greatly enhanced by ten times higher than that of the Ti alloy substrate. These findings suggested that the surface-alloying using high-energy electron beam irradiation was economical and useful for the development of titanium-base surface-alloyed materials with improved hardness and wear properties.

        • KCI등재

          고에너지 전자빔 투사방법으로 제조된 (TiC, TiB)/Ti-6Al-4V 표면합금화 재료의 미세조직과 마모특성

          이창섭,오준철,이성학 대한금속재료학회 2002 대한금속·재료학회지 Vol.41 No.2

          The present study is concerned with the microstructural analysis and the evaluation of hardness and wear properties of (TiC,TiB)/Ti-6Al-4V surface-alloyed materials fabricated by high-energy electron beam irradiation. The mixtures of Ti+C, TiC+TiB_2, and Ti+B_4C powders and CaF_2 flux were deposited on a Ti-6Al-4V substrate, and then electron beam was irradiated on these mixtures using an electron beam accelerator. The surface-alloyed layers of 0.9∼1.6mm in thickness were formed without defects, and contained a large amount (30∼44vol.%) of precipitates such as TiC and TiB in the martensitic matrix. This microstructural modification including the formation of hard precipitates and hardened matrix in the surface-alloyed layers resulted in the improvement hardness and wear resistance. Particularly in the surface-alloyed material fabricated with Ti+B_4C powders, the wear resistance was greatly enhanced by nine times higher than that of the Ti alloy substrate because a 44 vol.% of TiB and TiC was precipitated homogeneously in the martensitic matrix. These findings suggested that the surface-alloying using high-energy electron beam irradiation was useful for the development of titanium-base surface-alloyed materials with increased surface hardness and improved wear properties.

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