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- 저자 : Insup Lee (검색결과 75 건)
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Insup Lee 한국표면공학회 2017 한국표면공학회지 Vol.50 No.4
The response of AISI 310 type austenitic stainless steel to the novel low temperature plasma carburizing process has been investigated in this work. This grade of stainless steel shows better corrosion resistance and high temperature oxidation resistance due to its high chromium and nickel content. In this experiment, plasma carburizing was performed on AISI 310 stainless steel in a D.C. pulsed plasma ion nitriding system at different temperatures in H₂-Ar-CH₄ gas mixtures. The working pressure was 4 Torr (533Pa approx.) and the applied voltage was 600 V during the plasma carburizing treatment. The hardness of the samples was measured by using a Vickers micro hardness tester with the load of 100 g. The phase of carburized layer formed on the surface was confirmed by X-ray diffraction. The resultant carburized layer was found to be precipitation free and resulted in significantly improved hardness and corrosion resistance
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Lee, Insup,Park, Ikmin Elsevier 2007 Materials science & engineering. properties, micro Vol.449 No.-
<P><B>Abstract</B></P><P>Plasma radical nitriding was performed to harden the surface of SKD 61 steel for 1–10h at temperature range of 450–550°C. The microstructures and material properties of the radical nitrided layer were characterized in order to investigate the effects of various radical nitriding processing parameters. No compound layer was formed during this process except the experiment carried out at 500°C for 10h. A diffusion depth increased with increasing treatment temperature and time (up to about 150μm). The surface hardness of radical nitrided layer was two times higher than that of the untreated surface. The main phases produced in the diffusion zone were identified to be ϵ-Fe<SUB>2-3</SUB>(N,C) and γ′-Fe<SUB>4</SUB>(N,C). The residual stress of the diffusion layer also increased with increasing treatment temperature and time due to the increase of precipitates. In addition, plasma radical nitriding produces better surface roughness, compared with conventional ion nitriding.</P>
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Insup Lee 한국물리학회 2009 Current Applied Physics Vol.9 No.3
The effect of molybdenum in the surface characteristics on low temperature plasma nitrocarburized layer of austenitic stainless steel was investigated. A low temperature nitrocarburized layer of AISI 316L steel (Fe–17Cr–12Ni–2.5Mo) was compared with that of AISI 304L steel (Fe–19Cr–10Ni) to evaluate the influence of molybdenum on nitrocarburizing. The low temperature plasma nitrocarburizing was performed in a gas mixture of N2, H2 and carbon-containing gas such as CH4. The influence of processing temperature (380–480 ℃) on the surface properties of the nitrocarburized layer was investigated. The resultant nitrocarburized layer produced on both 316L steel and 304L steel is a dual-layer structure, which comprises a N-enriched layer (γN) with a high nitrogen content on top of a C-enriched layer (γC) with a high carbon content, leading to a significant increase in surface hardness (about 1200 HV0.01). The chromium nitride was formed in the N-enriched layer for 316L steel treated at temperatures above 480 ℃ compared with 304L steel treated at temperatures above 430 ℃. The thickness of the hardened layer without precipitation of chromium nitride of both 316L steel and 304L steel increased with increasing temperature, and reached up to 25 ㎛ in 316L steel at 450 ℃, 10 ㎛ in 304L steel at 400 ℃, respectively. However, at same treatment temperature, the thickness of the hardened layer formed on nitrocarburized 316L steel was larger than that produced on nitrocarburized 304L steel. The specimens treated at 400 ℃ showed much enhanced corrosion resistance in terms of lower corrosion current density and a higher corrosion potential as compared to the untreated steel. The loss in corrosion resistance was observed for the specimens treated at 430 ℃ for 304L steel and 480 ℃ for 316L steel, due to the formation of chromium nitrides in the nitrogen-enriched layer. The effect of molybdenum in the surface characteristics on low temperature plasma nitrocarburized layer of austenitic stainless steel was investigated. A low temperature nitrocarburized layer of AISI 316L steel (Fe–17Cr–12Ni–2.5Mo) was compared with that of AISI 304L steel (Fe–19Cr–10Ni) to evaluate the influence of molybdenum on nitrocarburizing. The low temperature plasma nitrocarburizing was performed in a gas mixture of N2, H2 and carbon-containing gas such as CH4. The influence of processing temperature (380–480 ℃) on the surface properties of the nitrocarburized layer was investigated. The resultant nitrocarburized layer produced on both 316L steel and 304L steel is a dual-layer structure, which comprises a N-enriched layer (γN) with a high nitrogen content on top of a C-enriched layer (γC) with a high carbon content, leading to a significant increase in surface hardness (about 1200 HV0.01). The chromium nitride was formed in the N-enriched layer for 316L steel treated at temperatures above 480 ℃ compared with 304L steel treated at temperatures above 430 ℃. The thickness of the hardened layer without precipitation of chromium nitride of both 316L steel and 304L steel increased with increasing temperature, and reached up to 25 ㎛ in 316L steel at 450 ℃, 10 ㎛ in 304L steel at 400 ℃, respectively. However, at same treatment temperature, the thickness of the hardened layer formed on nitrocarburized 316L steel was larger than that produced on nitrocarburized 304L steel. The specimens treated at 400 ℃ showed much enhanced corrosion resistance in terms of lower corrosion current density and a higher corrosion potential as compared to the untreated steel. The loss in corrosion resistance was observed for the specimens treated at 430 ℃ for 304L steel and 480 ℃ for 316L steel, due to the formation of chromium nitrides in the nitrogen-enriched layer.
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Challenges and Research Directions in Medical Cyber–Physical Systems
Insup Lee,Sokolsky, O.,Sanjian Chen,Hatcliff, J.,Eunkyoung Jee,BaekGyu Kim,King, A.,Mullen-Fortino, Margaret,Soojin Park,Roederer, A.,Venkatasubramanian, K. K. IEEE 2012 Proceedings of the Institute of Electrical and Ele Vol.100 No.1
<P>Medical cyber-physical systems (MCPS) are life-critical, context-aware, networked systems of medical devices. These systems are increasingly used in hospitals to provide high-quality continuous care for patients. The need to design complex MCPS that are both safe and effective has presented numerous challenges, including achieving high assurance in system software, intoperability, context-aware intelligence, autonomy, security and privacy, and device certifiability. In this paper, we discuss these challenges in developing MCPS, some of our work in addressing them, and several open research issues.</P>
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Duplex Surface Treatments of Plasma Nitrocarburizing and Plasma Oxidation of SKD 11 Steel
Insup Lee,Kwang Ho Jeong,Young-Rae Cho 한국표면공학회 2007 한국표면공학회지 Vol.40 No.6
Plasma nitrocarburizing and plasma oxidizing treatments were performed to improve the wear and corrosion resistance of SKD 11 steel. Plasma nitrocarburizing was conducted for 12 h at 520℃ in the nitrogen, hydrogen and methane atmosphere to produce the ε-Fe₂?₃(N,C) phase. It was found that the compound layer produced by plasma nitrocarburising was predominantly composed of ε-phase, with a small proportion of γ'-Fe₄(N,C) phase. The thickness of the compound layer was about 5 μm and the diffusion layer was about 150 ㎛ in thickness, respectively. Plasma post oxidation was performed on the nitrocarburized samples with various oxygen/hydrogen ratio at constant temperature of 500℃ for 1 hour. The very thin magnetite (Fe₃O₄) layer 1-2 ㎛ in thickness on top of the compound layer was obtained by plasma post oxidation. It was confirmed that the corrosion characteristics of the nitrocarburized compound layer could be further improved by the application of the superficial magnetite layer.
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Insup Lee 한국표면공학회 2015 한국표면공학회지 Vol.48 No.6
In this experiment, post-nitriding treatment was performed at 400℃ on AISI 316 stainless steel which was plasma carburized previously at 430℃ for 15 hours. Plasma nitriding was implemented on AISI 316 stainless steel at various gas compositions (25% N₂, 50% N₂ and 75% N₂) for 4 hours. Additionally, during post nitriding Ar gas was used with H2 and N2 to observe the improvement of surface properties. After treatment, the behavior of the hybrid layer was investigated by optical microscopy, X-ray diffraction, and micro-hardness testing. Potentiodynamic polarization test was also used to evaluate the corrosion resistance of the samples. Meanwhile, it was found that the surface hardness increased with increasing the nitrogen gas content. Also small percentage of Ar gas was introduced in the post nitriding process which improved the hardness of the hardened layer but reduced the corrosion resistance compared with the carburized sample. The experiment revealed that AISI 316L stainless steel showed better hardness and excellent corrosion resistance compared with the carburized sample, when 75% N2 gas was used during the post nitriding treatment. Also addition of Ar gas during post nitriding treatment degraded the corrosion resistance of the sample compared with the carburized sample.
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MC-ADAPT : Adaptive Task Dropping in Mixed-Criticality Scheduling
Lee, Jaewoo,Chwa, Hoon Sung,Phan, Linh T. X.,Shin, Insik,Lee, Insup Association for Computing Machinery 2017 ACM transactions on embedded computing systems Vol.16 No.s5
<P>Recent embedded systems are becoming integrated systems with components of different criticality. To tackle this, mixed-criticality systems aim to provide different levels of timing assurance to components of different criticality levels while achieving efficient resource utilization. Many approaches have been proposed to execute more lower-criticality tasks without affecting the timeliness of higher-criticality tasks. Those previous approaches however have at least one of the two limitations; i) they penalize all lower-criticality tasks at once upon a certain situation, or ii) they make the decision how to penalize lower-criticality tasks at design time. As a consequence, they under-utilize resources by imposing an excessive penalty on low-criticality tasks. Unlike those existing studies, we present a novel framework, called MC-ADAPT, that aims to minimally penalize lower-criticality tasks by fully reflecting the dynamically changing system behavior into adaptive decision making. Towards this, we propose a new scheduling algorithm and develop its runtime schedulability analysis capable of capturing the dynamic system state. Our proposed algorithm adaptively determines which task to drop based on the runtime analysis. To determine the quality of task dropping solution, we propose the speedup factor for task dropping while the conventional use of the speedup factor only evaluates MC scheduling algorithms in terms of the worst-case schedulability. We apply the speedup factor for a newly-defined task dropping problem that evaluates task dropping solution under different runtime scheduling scenarios. We derive that MC-ADAPT has a speedup factor of 1.619 for task drop. This implies that MC-ADAPT can behave the same as the optimal scheduling algorithm with optimal task dropping strategy does under any runtime scenario if the system is sped up by a factor of 1.619.</P>
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