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Effect of Al and Cu Additions on Microstructure and Magnetic Properties of NdTb-FeCo-B Magnets

100%
Sadullahoğlu G., Altuncevahir B., Addemir O.
Acta Physica Polonica A
|
2014
|
vol. 125
|
issue 5
1172-1175
EN
With the addition of Al and/or Cu into the NdFeB based magnet, the soft free iron phase was not observed in the cast alloys while it exists in the microstructure of the undoped NdFeB ingots. For the undoped sample, free iron disappeared after hot deformation process. Grain orientation is not good and there are deviations in the growth direction of the lamellar grains which are not perpendicular to the pressing direction. On the other hand, there is a striking change that the intergranular chemistry of Al added ingot separated into Nd-rich phase and a ternary FeNdAl composition most probably formed at the pressing temperature of 750°C. The highest remanent magnetization of 7.47 kG obtained for this sample, it might be due to the hard magnetic properties of this ternary composition. For the Al-Cu added sample, the high H_{c} and B_{r} values of 7.71 kOe and 7.33 kG, respectively, can be attributed to the homogeneous distribution of the intergranular composition and good orientation of the magnetic grains by hot deformation process.
2
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Investigation of Grain Boundary Compositions and Magnetic Properties of Hot-Worked Nd_{18}Tb_1Fe_{66.5}Co_5Al_{1.5}B_8 Magnets

100%
Sadullahoğlu G., Altuncevahir B., Okan Addemir A.
Acta Physica Polonica A
|
2013
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vol. 123
|
issue 2
233-234
EN
Magnetic properties which are related to the compositions on the grain boundaries of the NdFeB permanent magnets were studied at different hot working temperatures applied to the cast Nd_{18}Tb_1Fe_{66.5}Co_5Al_{1.5}B_8 ingots. Since the addition of Al caused the formation of hard magnetic μ phase between the magnetic NdFeB crystals after the pressing 800C H_{c} value increased to the highest value of 8.21 kOe. According to the SEM micrographs and EDS analysis, the increase in pressing temperature, the atomic ratios in the NdFeAl compositions approached to hard magnetic μ phase with the increase in pressing temperature and its exact composition was obtained in the sample hot deformed at 800°C. Although the secondary μ phase with a high melting temperature is detremental to the alignment of c axis of the magnetic NdFeB grains along the pressing direction, we found that the magnetic properties of the magnets improve due to the presence of this hard magnetic phase on the grain boundaries.
3
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The Effect of Mechanical Alloying on the Microhardness and Fracture Toughness of BaTiO_3

76%
Ertuğ B., Çetiner B., Sadullahoğlu G., Gökçe H., Erkmen Z., Öveçoğlu M.
Acta Physica Polonica A
|
2013
|
vol. 123
|
issue 2
188-190
EN
In this work, the effects of mechanical alloying on the mechanical properties of BaTiO_3 were investigated. In order to examine the milling conditions and sintering parameters on the solid state formation of BaTiO_3, X-ray diffraction technique was used. After mechanical alloying process, nanosized powder mixtures were produced. Sintering temperatures were 600, 700, 800, 900, 1000, and 1200C and sintering duration was 1 h. Besides X-ray diffraction examinations, mechanical properties of the BaTiO_3 samples were determined by Vickers microhardness test.
4
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The Effect of Milling Time and Sintering Temperature on Crystallization of BaFe₁₂O₁₉ Phase and Magnetic Properties of Ba-Hexaferrite Magnet

64%
Sadullahoğlu G., Ertuğ B., Gökçe H., Altuncevahir B., Öztürk M., Topkaya R., Akdoğan N., Öveçoğlu M., Addemir O.
Acta Physica Polonica A
|
2015
|
vol. 128
|
issue 3
377-382
EN
Barium hexaferrite samples were prepared by mechanical alloying using the stoichiometric amounts of BaCO₃ and Fe₂O₃ precursors followed by heat treatment applied in the temperature range 700-1150°C. It was found that the high energy ball mill with a milling rate enabled to obtain powders with the finer particles at the reduced milling time mechanical alloying of the initial powders linked to the formation of barium hexaferrite phase. The exothermic reaction peaks corresponding to the formation of BaFe₁₂O₁₉ phase shift from 928°C to 793°C for the increased milling time up to 6 h. This was resulted in improved magnetic properties that the Mₛ value of the as-blended sample sintered at 800°C rised from 31.16 emu/g to 53.46 emu/g after milling for 6 h. The saturation magnetization and remanence values of the samples mechanically alloyed for 3 h and sintered at 1150°C also increased to 63.57 emu/g and 31.26 emu/g, respectively, more than for 800°C and 900°C. The increase in the annealing temperature favours the formation of BaFe₁₂O₁₉ phase in the samples.
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