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김유찬 ( Y. C. Kim ),김기배 ( K. B. Kim ),이재철 ( J. C. Lee ),이병주 ( B. J. Lee ),에릭플러리 ( E. Fleury ) 대한금속재료학회 ( 구 대한금속학회 ) 2005 재료마당 Vol.18 No.5
The purpose of this paper is to present recent results obtained from a project aimed at enhancing the plastic deformation of bulk metallic glasses (BMGs). Inhomogeneities of micro- and nanometer-sized introduced in the amorphous matrix resulted in BMGs composites with both high strength and extended plastic deformation.
윤의박,김기배,차정민,조순형,위당문,남태운 대한금속재료학회(대한금속학회) 1985 대한금속·재료학회지 Vol.23 No.7
In this paper decomposition and thermal stability of the supersaturated solid solution of Al-Cr alloys were investigated. Al-1.2 wt%Cr alloys were rapidly solidified by using a small droplet chill quenching method. The decomposition process of the supersaturated Al-Cr solid solution by annealing at 350℃ to 600℃ and up to 60 hours was examined by means of microhardness and X-ray diffraction analysis. Hardness measurements on supersaturated Al-Cr solid solution annealed isothermally showed no sign of age hardening. The activation energy for decomposition was estimated to be 52.6㎉ and the thermal stability to be 0.76. The microstructural change during isothermal aging was that the fine, globular particles, which were nucleated heterogeneously along the cell boundary, were grown into chunky particles. The decomposition process was considered by establishing a cylindrical cell model and by using Johnson-Mehl equation. At the initial stage of the decomposition process the decomposition was governed by the diffusion controlled growth of a fixed number of particles (that was, the time exponent of Johnson-Mehl equation n=3/2), and at the middle and final stage the decomposition was governed by the combination of the diffusion controlled growth of cylinders in axial direction only and growth on dislocation (that was, n=1∼2/3).
Bi/MnBi 공정합금의 일방향응고조직 및 자기적 특성에 관한 연구
이호인,윤의박,김기배,조순형,나형용,심진섭,박종완 대한금속재료학회(대한금속학회) 1991 대한금속·재료학회지 Vol.29 No.7
Microstructure and magnetic property correlations have been sought for unidirectionally solidified Bi/MnBi eutectic alloys. The growth rate was varied from 0.5 to 60 ㎝/h and the temperature gradient was varied from 56 to 256 K/㎝. Annealing for 60 hours at 248℃ was necessary for enhancing the magnetic property. The MnBi phase morphology under various growth conditions was characterized by four types;rod, trinangular, V letter and broken lamellar type. The slope of a logarithmic plot of MnBi phase spacing with respect to growth rate was 0.5148, which was nearly in agreement with the theoretical slope of a nf/nf eutectic alloy. This means the MnBi phase to be independent of temperature gradient. The coercivity of the Bi/MnBi eutectic alloy solidified unidirectionally were greatly imporved by annealing. This seems to be caused by the transformation of the MnBi phase from HTP to LTP. The more increased the growth rate, the more the intrinsic coercivity improved. As a result, the maximum intrinsic coercivity of 27.8 kOe was obtained at the growth rate of 60 ㎝/h.
침적 피복법에 의한 Al2O3 와 Al 과의 젖음성에 미치는 Al2O3 에 첨가된 SiO2 의 영향
윤의박,김기배,조순형,김경민,김헌주 대한금속재료학회(대한금속학회) 1991 대한금속·재료학회지 Vol.29 No.11
In this study wettability between Al₂O₃ and Al to the variation of SiO₂ concentration in Al₂O₄ was investigated. Alumina specimens containing from 0 Lo 20wt%SiO₂ were prepared by using the coventional ceramic processing techniques. Wettability was measured by using the dip coverage method and was compared with wettability measured by using the sessile drop method. Also the distributions of Al and Si element around the interface were investigated. As the results of these investigation, wetting process in the dip coverage method was shorter than that of the sessile drop method, and the equation of reaction rate for wetting process between alumina and aluminium was almost agreed with the following equation. Qn[ 1/(1- α)]=K_0(t-τ²) Both the started time and the completed time of wetting became short with SiO₂ concentration and this tendency bacame severe with higher melt temperature. The Si content around the interface did not change.
윤의박,김기배,조순형,김경민,김헌주 대한금속재료학회(대한금속학회) 1991 대한금속·재료학회지 Vol.29 No.11
In order to investigate the interface phenomena, namely wettability, interface reaction, interfacial bonding, between Al₂O₃, and various Al alloys, wettability with the addition of alloying elements was measured by the dip coverage method, and the distribution of alloying elements and interfacial compounds at the interface were examined by using SEM-EDAX, Auger electron spectroscope and X-ray diffractometer. The interfacial bonding strength was also estimated by the indentation method. Wettability of Al was considerably improved by addition of Mg, Cu, Ni or Si. Among the four elements, Mg was the most effective. Mg was segregated at the interface of AC8A/Al₂O₃-20%SiO₂;the segregated Mg formed MgAl₂O₄, an interfacial compound. In pure Al/Al₂O₃ the inierface bonding strength was not affected by the concentration of SiO₂ in A1₂O₃ but in AC8A/Al₂O₃ the interface bonding strength increased with SiO₂ concentration and was 6.05 kgf/㎟ at 20%SiO₂.