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Al-Mg-Si 합금의 응고편석과 (凝固偏析) 균질화거동에 (均質化擧動) 미치는 Cr 및 Ti 의 영향
최정철,수총유강 (手塚裕康),신미창언 (神尾彰彦),고고항부 (高稿恒夫),윤의박 ( J . C . Choe,H . Tezuka,A . Kamio,T . Takahashi,E . P . Yoon ) 한국주조공학회 1988 한국주조공학회지 Vol.8 No.1
Microsegregation and its homegenization behavior of magnesium and silicon in Al-1, 1wt %Mg-0.68wt%Si alloy as well as those of chromium and titanium in the alloy have been investigated. Minimum magnesium and silicon concentrations in alpha-dendrite arm are 0.4wt% and 0.2wt% that are one half and one third of each composition, respectively. The concentrations are, however, rapidly homogenizecl at 530℃. Titanium and chromium elements make grain size be greatly refined in Al-Mg-Si alloys but they are remarkably concentrated at the center of alpha-dendrite arm and from a cored structure. The maximum concentrations increase two to three times for titanium and one and a half times for chromium. The concentration of titanium does not appear outside the cored structure but that of chromium is approximately one half of the total ahromium amount. These do not disappear at 530℃ for 100 hours. During homogenization treatment, chromium is deposited as E phase of Al_(18)Mg₃Cr₂ around crystallized compounds and its distribution becomes inhomogeneous.
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.
Ni 기 초내열합금의 급속응고조직 및 열처리 조직 (1)
윤의박,나형용,장재규,정홍철 대한금속재료학회(대한금속학회) 1990 대한금속·재료학회지 Vol.28 No.1
Raipdly solidified powders of Ni-6.61%Al-3.35 %Ti-0.019%C and Ni-6.49%Al-1.98%Ti-5.34%Mo-0.028%B-0.33%Fe-0.084%C were investigated ; microstructures of the powders had been investigated at as-rapidly-solidified state and after annealing at 800℃ and 1,000℃. After rapid solidification by Ar gas atomization, the microstructure of the powder particles showed dendritic or equiaxed poly-grain morphology irrespective of the particle size. The elongated γ' phase has been precipitated next to grain boundaries in the direction perpendicular to the grain boundary, and ultrafine γ' particles were dispersed within the grains. When the alloy powders were annealed at 800℃ and 1,000℃, the elongated γ' phase had grown to an irregular shape, and the ultrafine γ' particles inside the grains had grown to a cubic shape.
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).