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가스분무한 Al-8wt.%Fe 합금분말의 급속응고과정에 대한 수치해석
김성균,최회진,나형용 ( Seong Gyoon Kim,Hoi Jin Choi,Hyung Yong Ra ) 한국주조공학회 1993 한국주조공학회지 Vol.13 No.5
N/A A numerical analysis on the microstructural evolutions of microcellular and cellular α -aluminum phase in the gas-atomized Al-8wt. pct droplets was represented. The 2-dimensional non-Newtonian heat transfer and the dendritic growth theory in the undercooled melt were combined under the assumptions of a point nucleation on droplet surface and the macroscopically smooth solid-liquid interface enveloping the cell tips. It reproduced the main characteristic features of the reported microstructures quite well. It predicted a considerable volume fraction of segregation-free region in a droplet smaller than l0㎛ if an initial undercooling larger than 100K is given. The volume fractions of the microcellular region(g_A) and the sum of the microcellular and cellular region(g_a) were predicted as functions of the heat transfer coefficient, h and initial undercooling, ΔT. It was shown that g_A and g_a, in the typical gas-atomization processes with h=0.1-1.0W/㎠K, are dominated by ΔT and h, respectively, but for h larger than 4.0W/㎠K, a fully microcellular structure can be obtained irrespective of the initial undercooling.
수직-수평온도구배법에 의한 200 mm급 사파이어 단결정 성장의 전산모사 연구
김형중 ( Hyung Joong Kim ),차필령 ( Pil Ryung Cha ),김성균 ( Seong Gyoon Kim ),문성환 ( Sung Hwan Moon ),장계원 ( Gye Won Jang ),나복기 ( Bok Kee Na ),김준환 ( Jun Hwan Kim ),김동욱 ( Dong Uk Kim ) 대한금속재료학회(구 대한금속학회) 2015 대한금속·재료학회지 Vol.53 No.1
A sapphire single crystal growth process by the Vertical-Horizontal Gradient Freezing (VHGF) method was studied by a numerical analysis technique. The heater power was controlled in order to follow the given arbitrary target heater temperature profile through the whole series of the process. Due to the influence of radiation heat transfer, the heater had spatial temperature deviation in spite of the fact that the heater power was imposed uniformly through its whole body. As a structural feature of the VHGF method, temperature at the lower part of crucible was lower than that at the upper part of crucible because it was cooler at the bottom of the furnace. Thus, the movement of the solid/liquid interface was driven in the bottom-to-top direction. (Received February 4, 2014)
김성균,나형용,김동익,최회진 대한금속재료학회(대한금속학회) 1995 대한금속·재료학회지 Vol.33 No.5
The effects of cooling velocity, melt weight and purity of copper were reported on copper single-crystal growth by Heat Exchanger Method in this paper. Copper single-crystals could be grown at the cooling velocity lower than 1℃/min. Higher purity(99.995wt%) of copper single crystal less than 7㎝ height(radius 3.5㎝) was grown when the cooling velocity was 0.34℃/min. and the height less than 3.5㎝(radius 3.5㎝) was grown with the plane front of solid-liquid interface and of semi-ellipse, and the free surface of single crystal was solidified in the end. However in the lower purity(99.93wt%) of copper, it should be solidified with plane front at the initial stage, and cell, dendrite formed finally at the cooling velocity lower than 0.5℃/min. The significant segregation were caused when the solid-liquid interface was changed from plane front to cell structure.
김성균,나형용,김동익,최회진 대한금속재료학회(대한금속학회) 1995 대한금속·재료학회지 Vol.33 No.2
The microstructural evolutions during the transition between the supersaturated solid solution and the solutal dendrite in rapid solidification were qualitatively examined using the model of banded structure formation proposed by Carrard et al., It was shown that the positive average temperature gradient at solid-liquid interface is a necessary condition for the banded structure formation, and the banded structure can not be formed during rapid undercooled solidification. Also, it was shown that the banded structure is hardly anticipated in melt-spun aluminum alloy and, on the other hand, it can be formed at the free surface side of the melt-spun Ag-Cu alloy ribbons. These predictions are in good agreement with the reported experimental results on banded structure formation.
김성균,나형용,김동익,최회진 대한금속재료학회(대한금속학회) 1995 대한금속·재료학회지 Vol.33 No.11
Numerical simulations including the fluid flow, conduction and radiation heat transfer have been performed using the geometry of real furnace for the single-crystal growth by heat exchanger method. The finite difference method based on the control volume approach and SIMPLE algorithm were used to solve the momentum and energy equations. Almost all parts of the furnace including the heater, insulating materials and crucible were considered in the calculation domain and the latent heat was accounted by an iterative heat evolution method. Silicon with low thermal conductivity was selected as a model material in order to compare the results with the previous report on the copper single-crystal growth. The effects of cooling rate of the heater, crucible material, crucible shape and melt weight on single-crystal growth were investigated together with the role of natural convection in melt. The optimum process conditions such as the critical cooling rate and the critical ratio of the height to the radius of crystal for the silicon single-crystal growth by heat exchanger method were determined. According to the simulations, among many parameters crucible shape was a dominant processing parameter to control single crystal growth when a thermal conductivity of the specimen was low. The lower the thermal conductivity of base material of crucible was then that of the specimen, the less the region of poly crystal formed at the edge of the crystal was.
Fe40Ni40P14B6 비정질합금에서 공정의 표면결정화와 성장과정에 관한 연구
김성균,나형용 대한금속재료학회(대한금속학회) 1989 대한금속·재료학회지 Vol.27 No.10
The preferential crystallization, microstructure and growth procedure of euctectic crystal in Fe_(40)Ni_(40)P_(14)B_6 metallic glass were investigated in the temperature range of 621∼671 K. When Fe_(40)Ni_(40)P_(14)B_6 metallic glass is annealed, the region that turbulent melt flow has occurred during melt spinning and the void surface crystallize preferentially. This phenomenon is due to the surface oxidation. The eutectic crystals change their morphology from the normal to the degenerate structure with the annealing temperature. This microstructural change of the eutectic can be explained by the difference of the temperature dependence of the interface kinetics between BCT(Fe, Ni)₃(P,B) and γ(Fe, Ni). Assuming that interface kinetics control mechanism dominates the growth of eutectics, the diffusion coefficient estimated from the measured eutectic growth rate agrees relatively well with the directly measured coefficient.
김성균,김동익,최회진 대한금속재료학회(대한금속학회) 1995 대한금속·재료학회지 Vol.33 No.7
A new process for the metal fiber production by the powder extrusion has been developed. Being compared with the conventional processes, such as the bundle drawing method, the shatter machining method and the in-rotating water melt spinning method, the process has two distinctive advantages. One is that the fibers having a diameter below l0㎛ can be easily manufactured, the other is that the diameter, the length and the cross-sectional shape of the fibers can be controlled easily by the selection of the diameter of initial metal powders, extrusion ratios and extrusion die shapes. The silver fibers of 2㎛ wide and 30㎛ long and aluminum fibers of 5-10㎛ wide 1-3㎜ long were demonstrated.
김성균 群山大學校自然科學硏究所 1989 自然科學硏究 Vol.4 No.-
The substitution of plastic magnet roll for the conventional sintered magnet roll in copy machine was examined. EVA 40W and Silane A-189 was the most compatible binder and coupling agent, and the weight per cent of magenetic powder (Sr-ferrite) must be restricted to 90%. By pole thickness control method, it was possible to manufacture the plastic magnet roll whick have nearly the same magnetic properties with the conventional sintered magnet roll.
김성균,나형용,김동익,최회진 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.12
Numerical simulation for copper single crystal growth by a heat exchanger method has been performed including the effects of fluid flow, conduction and radiation heat transfer using the actual geometry of growing furnace. The finite difference method based on a control volume approach and SIMPLE algorithm were used to solve the momentum and energy equations. Almost all parts of the furnace including heater, insulating materials and crucible were considered in the calculation domain and the latent heat was also accounted by an iterative heat evolution method. The effects of cooling rate of heater and crucible position and melt weight were investigated together with the role of natural convection in melt. The optimum process conditions for single crystal growth were determined. The calculated results of critical cooling rate, solidification time and the critical ratio of the height to the radius of crystal were found to be in a good agreement with the experimental results.