Uzun, Oguzhan; Abdioglu, Murat; Ozturk, U. Kemal

This study investigates flux trapping in bulk YBaCuOx (YBCO) high-temperature superconductors (HTS) under various permanent magnet configurations (PMCs) through both experimental and numerical methods. A finite element method (FEM) based on the H-formulation of Maxwell's equations is employed to simulate the HTS-PM interaction, showing good agreement with experimental results in peak trapped flux density values. The maximum trapped flux densities for PMC-1, PMC-2, PMC-3, and PMC-4 were measured as 207 mT, 359 mT, 392 mT, and 478 mT, respectively, demonstrating the significance of PMC design in optimising flux trapping in HTS materials. Enhanced flux trapping was observed with configurations including additional permanent magnets, such as PMC-2 and PMC-4, yielding trapped flux efficiencies of 77.5 % and 55.0 %, respectively. Obtained results in trapped flux efficiency are very impressive as compared to a value of 23 % trapped flux efficiency in literature in which a solenoid magnet with a 3 T peak value of magnetic flux density is used to trap a magnetic field in the HTS. The magnetic flux trapping methodology of this research is very effective for magnetic bearing applications with self-stabilisation in which high magnetic fields are not needed since it doesn't need any magnetic field sources with complex structures, such as coils, to facilitate the magnetic field trapping in the HTSs.

AtıfScopus3·WoS3·OpenAlex2

İncele

Sakar, E.; Guler, O.; Alim, B.; Guler, S.H.; Dikici, B.; Lampke, T.

This study presents the production and comprehensive assessment of a Refractory High Entropy Alloy (RHEA) with a ZrNbTaMoW composition for possible usage nuclear reactor applications. The alloy was synthesized using the mechanical alloying (MA) method, and its radiation properties were examined. Elemental powders of Zr, Nb, Ta, Mo, and W were utilized in equimolar quantities during the 120-hour MA process, conducted under a high-purity Ar atmosphere to prevent oxidation. The obtained HEA was then subjected to a mechano-thermal process to transform it into Refractory High-Entropy Oxide (RHEO) for comparing their radiation-shielding performance under oxide conditions. The characterization of the produced alloys through X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron dispersive spectroscopy (EDS). The photon shielding parameters of the alloys were experimentally obtained for various energies emitted from a 133Ba radioactive source, employing a Canberra UltraLEGe semiconductor detector. Furthermore, theoretical calculations were performed to validate the experimental data and to evaluate the alloys' photon shielding capabilities comprehensively. For this purpose, Phy-X/PSD software was employed to determine mass attenuation coefficients, half-value layer, effective atomic number, and effective electron density. Fast neutron absorption capabilities were determined through the calculation of average absorption cross-sections in the 2–12 MeV energy range. The results showed that the oxidation process significantly diminished the photon absorption capacity of RHEA.

AtıfScopus34·WoS33·OpenAlex37

İncele

Savaskan, B.; Ozturk, U. K.; Guner, S. B.; Abdioglu, M.; Bahadir, M. V.; Acar, S.; Somer, M.; Ionescu, A. M.; Locovei, C.; Enculescu, M.

Bulk MgB2 discs were prepared by an in situ route from mixtures of magnesium and boron powders. The boron powders were produced by two methods. The first one consisted of a self-propagating high tem-perature magnesiothermic synthesis (SHS) process followed by acid and fluorine cleaning and a heat treatment in inert atmosphere. This approach produced boron with purities between 86 % and 97 %, where the main impurity was Mg. Depending on the final heat treatment, these boron powders were amorphous or crystalline. In the second route, high purity nano powders (99 %) of boron were obtained by a diborane pyrolysis process. Bulks of MgB2 were characterized by structural, microstructural, and magnetic mea-surements. Critical current density, pinning force aspects and levitation force (including guiding force) details were assessed. Amorphous lower purity boron (86-97 %) obtained by the first processing route was found to promote the largest levitation forces of the MgB2 bulks and, among these samples, the best le-vitation results were recorded when using boron with a purity of 95-97 %. Use of a lower purity boron that decreases the cost of MgB2 promotes large scale production at industrial level of bulk MgB2 super-conducting magnets for levitation applications and enhances the applicability potential of MgB2 super-conductor. The relationship between levitation force and specific features of the samples such as pinning force details are discussed.& COPY; 2023 Elsevier B.V. All rights reserved.

AtıfScopus10·WoS10·OpenAlex12

İncele

Sakar, Erdem; Guler, Omer; Alım, Bünyamin; Say, Yakup; Dikici, Burak

It is well known that high entropy alloys (HEAs) have a wide range of potential applications as radiation shielding due to their superior properties. The CoNiFeCr-Ti/Al compositions were chosen for their low cost as HEA in this study. The HEAs were successfully produced using the mechanical alloying (MA) method with equimolar CoNiFeCr, CoNiFeCrAl, and CoNiFeCrTi compositions. The production and structural properties of the alloys were investigated in detail. Besides, the photon and particle radiation shielding properties of the HEAs were calculated with the help of Phy-X/PSD, SRIM (10 keV-20 MeV), and ESTAR (10 keV-20 MeV) programs. The photon-matter interaction parameters were calculated in both specific photon energies emitted from 241Am, 133Ba, 109Cd, 60Co, 137Cs, 131I, and 22Na nuclides and a continuous energy range of 15 keV-15 MeV. The characterization of the alloys was investigated by using X-ray diffraction (XRD) and scanning electron microscopes (SEM) attached to an energy dispersive spectroscopy (EDX). It was found that the HEAs have a highly amorphous structure due to the selected production method. The crystal size of the alloys was calculated as 70, 35, and 20 nm for CoNiFeCr, CoNiFeCrAl, and CoNiFeCrTi, respectively. In terms of shielding properties, it has been determined that the produced HEAs have better shielding characteristics for photon and particle radiations than standard shielding concretes. In addition, the results demonstrated that CoNiFeCr alloy, which has the best shielding ability among the HEA alloys, can be used as a shielding material application requiring photon, electron, proton, alpha, and neutron radiations.

AtıfScopus30·WoS32·OpenAlex32

İncele

Güner, Sait Barış; Abdioğlu, Murat; Öztürk, Kemal; Çelik, Şükrü

In this work, in the first time, we have investigated the levitation and lateral force properties of bulk and cut-pasted bulk GdBCO samples at different temperatures and different cooling heights (CH) to determine the effect of cut-pasted process on the magnetic levitation force behaviour. The measurements of superconducting characteristics indicated that the attractive and repulsive force values of cut-pasted GdBCO sample are slightly lesser than those of GdBCO bulk sample. The maximum repulsive and attractive force values obtained as 15.45 N and −4.56 N for GdBCO bulk and as 14.78 N and −3.92 N for cut-pasted GdBCO samples at 37 K. Although there are many fabrication methods as melt-textured growth (MTG), top seeded infiltration growth (TSIG) and TSMG to produce large HTS samples, the desired large sample size and the sample shape compatible with the superconducting magnetic bearing systems are not still sufficient for the technological applications. In this study, the performed cut-pasted process and obtained magnetic levitation force data can be using for the increment sample size and the desired sample shape in the needed different geometry and size for superconducting magnetic bearing systems.

AtıfScopus8·WoS8·OpenAlex9

İncele

Savaskan, Burcu; Abdioglu, Murat; Ozturk, Kemal

In our study as different from the literature, the magnetic levitation force between a bulk MgB2 and two different permanent magnetic guideway (PMG) arrangements, which are Halbach and Conventional PMGs, were investigated in different cooling heights (CHs) and Field-Cooled (FC) condition at the temperatures of 37 K and 33 K. The cylindrical bulk MgB2 superconductor was fabricated by in-situ solid state reaction process with the diameter of 18 mm and the height of 5 mm. The XRD data indicates well developed MgB2 phase and the Jc value was obtained as 68 kA/cm2 at 30 K in the self-field. Experimental results show that MgB2 bulk above the Halbach PMG can exhibit better load capability at all the cooling heights between the bulk MgB2 and the PMG due to a more suitable magnetic field distribution. The maximum levitation force for Halbach PMG corresponds to 16.86 N whereas the conventional PMG shows 9.02 N at 37 K in cooling height of 77 mm. Additionally, the maximum levitation force increases while the CH increases because flux exclusion is more effective for larger CHs. It is considered that the experimental results obtained in study are very useful for future Maglev applications, because there are limited number of studies on magnetic levitation force of MgB2 bulk for different MgB2-PMG arrangements.

AtıfScopus17·WoS14·OpenAlex20

İncele

Ozturk, K.; Guner, S.B.; Abdioglu, M.; Demirci, M.; Celik, S.; Cansiz, A.

The higher magnetic levitation force and related stiffness values are very important for Maglev and magnetic bearing applications. Also, larger superconducting surface area is needed for continuous and larger magnetic mediums with different geometries and dimensions in real scale industrial applications of superconducting systems. In this study, the cylindrical YBCO superconductors were fabricated by top−seeded melt growth (TSMG) method in single and two−seeded forms with different seed distances and then the magnetic force and stiffness measurements were carried out by three axes magnetic force measurement system in different cooling heights (CH) of 20 mm and 75 mm. Additionally, a new analytical method, based on the magnetic dipole approximation, is proposed to calculate the levitation force in this study, named as Modified Advanced Frozen Image Method (MAFI), since although the Advanced Frozen Image Method in literature can calculate the levitation force with hysteresis, this method does not include the size effect of the superconductor. In the experimental studies, it is seen that the maximum levitation force values obtained by PMG with three PMs (named PMG−1) are more than two times higher than that of obtained with single PM for all samples with different distance of seeds, because of the higher magnetic flux distribution of related PMG arrangement than the single PM. In addition, the maximum magnetic levitation force value firstly increased and then decreased due to current coupling effect weakness by increasing distance of seeds. The calculated analytical levitation force results are not compatible with the experimental results without current coupling effect, but a well agreement is observed when the current coupling effect is taken into account in calculations. Also the MAFI method was tested with different dimensions of superconductors and the obtained results indicated the success of the proposed method. The maximum levitation force values obtained with MAFI method increased with increasing dimensions of HTS and PMs. Thus, one can say that the MAFI method is useful for the levitation force calculations between multi−seeded superconductors and PMGs with different dimensions and for different CHs. As a result, the analytical levitation force values obtained with the MAFI method are agree with the experimental levitation force sufficiently and this method can give fast calculation results without any divergence problem. This method can be thought as an alternative to the numerical calculation methods, having serious divergence problems for much amount and bigger size superconducting samples, therefore it will be useful to clarify bulk superconducting properties as supporter to the experimental studies.

AtıfScopus19·WoS18·OpenAlex22

İncele

Purcek, G.; Yanar, H.; Shangina, D.V.; Demirtas, M.; Bochvar, N.R.; Dobatkin, S.V.

Effects of ultrafine grain formation via high pressure torsion (HPT) and precipitation during aging on the microstructure, mechanical and tribological properties of a Cu-Cr-Zr alloy have been investigated systematically. HPT results in the formation of ultrafine-grained (UFG) structure in the alloy with an average grain/subgrain size of 155 nm which leads to remarkable improvement in its hardness and strength along with a reduction in elongation to failure. Aging of UFG alloy brings about further strengthening due to the precipitation. UFG formation by HPT increases substantially the wear resistance of Cu-Cr-Zr alloy and reduces the friction coefficient. The highest wear resistance and the lowest friction coefficient are obtained on the sample processed by HPT and subsequent aging. The dominant wear mechanism of the alloy varies depending on the applied processes. Adhesion with smearing is the predominant wear mechanism for the initial (warm extruded) samples having coarse-grained (CG) structure. UFG samples show less adhesional effect with less smearing, and a higher tendency to the formation of cracks, abrasion and delamination seem to be dominant in those samples. Oxidative wear mechanism is also operative in both CG and UFG alloy samples. It may be concluded from this study that a combined process including UFG formation by HPT and subsequent precipitation by artificial aging provides a simple and effective processing procedure for improving the strength, hardness and wear resistance of Cu–Cr–Zr alloys without modification of the chemical composition.

AtıfScopus96·WoS91·OpenAlex99

İncele

Uğurlu, Mine; Alım, Bünyamin; Han, İbrahim; Demir, Lütfü

Kβ-to-Kα X-ray intensity ratios of Fe, Ni, Co, Ti, V in pure form and PERMENDUR49 (Fe49Co49V2), KOVAR (Fe54Ni29Co17) and Ti50Co50 alloys were calculated in order to determine valence-electron structure of the samples. The obtained experimental Kβ-to-Kα X-ray intensity ratios were found to be 0.1252 ± 0.0025, 0.1256 ± 0.0027, 0.1298 ± 0.0026, 0.1327 ± 0.0028, 0.1346 ± 0.0027 for pure Ti, V, Fe, Co and Ni, respectively. These values of present pure metals have increased with the increment in atomic number of these pure metals. Also, although the obtained these values for metal atoms in PERMENDUR49, Ti50Co50 and for Fe, Ni metal atoms in KOVAR approximately compatible with respect to results same pure metals, the obtained experimental Kβ-to-Kα X-ray intensity ratios for Co in KOVAR are significantly different from the appropriate values for pure Co metal. Then, the valence-electron populations of these alloys were calculated in order to answer as to why the characteristic properties of the studied alloys are distinct from each other. The valence-electron structures of these metals in pure form and alloys were determined by comparison of the calculated Kβ-to-Kα X-ray intensity ratios with the results of multi-configurations Dirac-Fock (MCDF) calculations to understand the charge-transfer and/or delocalization phenomena of these alloys. The experimental n3d values were found to be 3.2694, 4.7905, 7.7941, 7.9618, 8.500 for pure Ti, V, Fe, Co and Ni, respectively. The calculated 3d and 4s, 4p electron population values for Ti, V and Co in pure form have shown very little deviation from the appropriate values of Ti in Ti50Co50 and Co, V in PERMENDUR49. Also, the deviation for these values is greater for Fe, Ni, in KOVAR, Co in Ti50Co50, Fe in PERMENDUR49 with respect to the corresponding values of pure metals and the largest deviation for these values is observed for Co metal atoms in KOVAR alloy. We have also calculated the weighted average numbers of 3d and 4s, 4p electrons per one atom as well as the superposition of 3d and 4s, 4p electrons, as obtained from pure metal values. While the obtained superposition 3d electron numbers of present alloys exhibit a decreasing tendency as S3d(Ti50Co50) < S3d(PERMENDUR49) < S3d(KOVAR), the obtained weighted average 3d electron numbers of present alloys has opposite tendency (A3d(KOVAR) < A3d(PERMENDUR49) < A3d(Ti50Co50)). The analysis show that valance-electron population of elements in these alloys indicated differences with respect to the pure metal and each other. These differences can be related to type of alloy elements, concentration of alloy elements, charge transfer and/or delocalization phenomena between of individual metal atoms in alloys. Also, the obtained results show that there are alloying effect on valence-electron population due to charge transfer and/or delocalization phenomena.

AtıfScopus15·WoS15·OpenAlex16

İncele

Erdem, O.; Abdioglu, M.; Guner, S.B.; Celik, S.; Kucukomeroglu, T.

The effect of coronene (C24H12) addition on the levitation force properties of MgB2 superconductor has been investigated for the first time in this study. The polycrystalline disk-shaped MgB2 + y wt % C24H12 samples (y = 0, 2, 4, 6, 8, 10), were synthesized by a pellet/closed tube method at 850 °C under Ar atmosphere, after hot pressing at 200 °C. XRD analysis indicates a decrease in lattice parameters of coronene added samples and confirms substitution of carbon in boron sites. An increase in lattice strain and a decrease in grain size are observed due to the carbon substitution effect. Vertical and lateral levitation force measurements under zero-field-cooled and field-cooled regimes were carried out at different temperatures of 20, 25 and 30 K. It was found that the coronene addition significantly increases the high-field critical current density of MgB2. The Jc values were obtained as 4.6 × 103 Acm−2 and 1.3 × 104 Acm−2 for pure and 4 wt % coronene added samples at 20 K and 4 T. In addition, the levitation force measurements show that 4 wt % coronene adding is very effective in increasing both the vertical and lateral levitation force performances at 20 K. The maximum levitation force for 4 wt % coronene added sample corresponds to 7.58 N/g whereas the reference sample shows 6.73 N/g at 20 K in ZFC regime. The results point out that the hydrocarbon of C24H12 is an effective carbon-containing additive for MgB2 and can be useful for optimizing the levitation performance of MgB2 superconductors for potential applications.

AtıfScopus25·WoS21·OpenAlex27

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