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비정질 Spinel Ferrite의 제조와 그 자기적 특성
김태옥(T. O. Kim),김창곤(C. G. Kim) 한국자기학회 1992 韓國磁氣學會誌 Vol.2 No.1
The fundamental research about the amorphous ferrite, which is expected as the important material for electronic and information imdustry in future, was carried out in this work. Because the ferromagnetic amorphous ferrites reported recently are very inferior in magnetic properties than the crystalline ferrites, the development of the more ferromagnetic amorphous ferrites is required.<br/> In order to obtain the fundamental data for the preparation of amorphous ferrites, the hand-made twin-roller quenching apparatus was used for rapid quenching.<br/> Investigation on amorphous ferrite in the system CaO-Bi₂O₃-Fe₂O₃ has been carried out in the composition of 10-50 mole% CaO, 10-50 mole% Bi₂O₃, 40-70 mole% Fe₂O₃. Large magnetization values were obtained near the composition of the mixture of BiFeO₃ and CaFe₄O_7. Especially, an amorphous (CaO)_(20)(Bi₂O₃)_(15)(Fe₂O₃)_(65) specimen has a magmetization value of about 21.84 emu/g at 0K(10 kOe). Fe Mossbauer absorption spectrum indicates that this specimen is compsed of two amorphous phases, antiferromagnetic phase(α-phase) and ferromagnetic phase(β-phase). Crystallization of this amorphous ferrite was happened in steps-550℃ and 775℃, then observed crystal phases were perovskite phase of BiFeO₃ and Fe₂O₃ phase.
김태옥(T. O. Kim),김국주(K. J. Kim),김남용(N. Y. Kim),이진모(J. M. Lee),염종택(J. T. Yeom) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.10
Aerospace engine application needs to stand high temperature and pressure. Because of its mechanical properties such as high strength at high temperature, Alloy 718 is used aerospace engine application about 80%. But ally 718’s mechanical properties cause some problem to manufacturing profile ring like damage of material and mold. In this study, alloy 718’s mechanical properties investigated for knowing its formability and using FE-Simulation for designing profile ring roll process and mold shape. Profile ring rolling processing is designed with “Initial material→Blank→Linear Ring→Profile ring”. Blank’s heating temperature is setting 1100℃ for manufacturing a trial profile ring on the basis of FE-Simulation. As a result of manufacturing alloy 718 profile ring, it is possible to make near target profile shape ring with all of the processing condition which gives in this study.
김태옥(T. O. Kim),권용남(Y. N. Kwon),김상우(S. W. Kim),이정환(J. H. Lee) 한국기계가공학회 2008 한국기계가공학회 춘추계학술대회 논문집 Vol.2008 No.-
Magnesium alloys still have a lot of technical challenges to be solved for more applications. There have been many research activities to enhance formability of magnesium alloys. One is to design new alloy composition having better formability. Also, low formability of wrought alloys can be improved by optimizing the processing variables. In the present study, To understand the effect of as-received microstructure' size, we compared cast billets and extrued billets of three different magnesium alloys such as AZ31, AZ61 and ZK60. For this purpose, a model die configuration was suggested in which both upsetting and extrusion could be exerted throughout forming stage. Firstly, a series of compression tests was carried out to get flow behaviors with temperature. Finally, forged microstructures were observed to find out how Mg alloys evolved with strain accumulation.