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기계적합금화로 제조된 Ni-20Cr-20Fe-5Nb 합금에서 PCA로서 H<sub>2</sub>O의 역할과 시효석출거동
김일호,권숙인,이원식,채수원,황선근,김명호,Kim Il-Ho,Kwun S.I.,Lee Won-Sik,Chae S.W.,Hwang S.K.,Kim M.H. 한국분말야금학회 2006 한국분말재료학회지 (KPMI) Vol.13 No.3
The effect of use of $H_2O$ as PCA(process control agent) to prevent the carbon contamination during mechanical alloying process and the precipitation behavior in Ni-20Cr-20Fe-5Nb bulk alloy after aging were investigated. NbC and $Cr_2O_3$ were formed during mechanical alloying and consolidation processes in the Ni-20Cr-20Fe-5Nb alloy in which methanol($CH_3OH$) was added as PCA. Formation of NbC in this alloy decreased the amount of Nb dissolved in the Ni matrix. The use of $H_2O$ as PCA in Ni-20Cr-20Fe-5Nb alloy prevented the formation of NbC and increased the hardness. The increase of hardness in this alloy was attributed to the increased amount of Nb dissolved in the Ni matrix. After aging treatment for 20 hours at $600^{\circ}C\;and\;720^{\circ}C$ of Ni-20Cr-20Fe-5Nb bulk alloy in which $H_2O$ added as PCA, ${\gamma}"$$(Ni_3Nb,\;tetragonal)\;and\;{\delta}\;(Ni_3Nb,\;orthorhombic)$ precipitates were formed, respectively. The precipitation temperatures of ${\gamma}"$ and ${\delta}$ in this bulk alloy were lower than those in commercial IN 718 alloy. It seemed that the lower precipitation temperatures for ${\gamma}"$ and ${\delta}$ in this bulk alloy than in commercial IN 718 alloy were due to severe plastic deformation during mechanical alloying.
광 분배기용 Fiber Array Block의 효율적 제조를 위한 전자동 배면 휠 연삭 시스템의 개발
김명호(M.H. Kim),이동길(D.G. Lee),최금(Kum Choi) 한국생산제조학회 2011 한국생산제조시스템학회 학술발표대회 논문집 Vol.2011 No.4
In this study, for the purpose of reducing the working hours of polishing process and preventing the mix of pollutants for optical splitter FAB(Fiber Array Block), which arrays and connects optical fiber to Planar Waveguide Devices (Chip), which is available to separate optical signal, the backside grinding method of grinding wheel and the automatic polishing machine into which FAB falls had been developed and applied to facilitate chip evacuation, unlike the upper surface grinding method of the conventional polishing pad. As a result, in case of multi bar chip(1ch×10×8ea), the 1st rough grinding at 350㎛ consumed four hours or more before but, now becomes to take less than three minutes to complete, and also prevent mixing of pollutants.
김명호(M.-H. Kim),최정열(J.-Y. Choi),김귀순(K.S. Kim),이기수(G.S. Lee),김유일(Y.I. Kim),임진식(J.S. Lim) 한국전산유체공학회 2001 한국전산유체공학회 학술대회논문집 Vol.2001 No.-
An accelerating flow field through a compressor cascade is studied numerically by unsteady computational simulation. The two-dimensional Navier-Stokes equations for compressible flow is used for the study of unsteady high incidence angle flow, with preconditioning scheme to cover the wide range of Mach number and k-ωmodel for the turbulent viscous flow analysis. A DCA(double circular arc) compressor blade is accelerated artificially in this study to understand the unsteady effect by comparing the present results with the existing steady-state experimental and computational results. Also, the accelerating flow field during the starting phase of gas turbine is studied with actual experimental data for the understanding of flow field and performance characteristics at off-design condition.
김명호(M. H. Kim),배성택(S. T. Bae),안수환(S. W. Ahn) 한국동력기계공학회 2004 한국동력기계공학회 학술대회 논문집 Vol.- No.-
Repeated ribs are used on heat exchange surfaces to promote turbulence and enhance convective heat transfer. Applications include fuel rods of gas-cooled nuclear reactors, inside cavities of turbine blades, and internal surfaces pipes used in heat exchangers. Despite the great number of literature papers, only few experimental data concern detailed distributions of friction factors and heat transfer coefficients in square channels varying the number of rough walls. This issue was tackled by investigating effects of different number of ribbed walls on heat transfer and friction characteristics in square channel. The rough wall had a 45° inclined square rib. Uniform heat flux was maintained on whole inner heat transfer channel area. The heat transfer coefficient and friction factor values increased with increasing the number of rough walls.