Browsing by Author "Cetinkara H.A."

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Investigation of mechanical and superconducting properties of iron diffusion-doped Bi-2223 superconductors
(2011-09-01) Ozturk O.; Cetinkara H.A.; Asikuzun E.; Akdogan M.; Yilmazlar M.; Terzioglu C.
The mechanical and superconducting properties of the Fe diffusion-doped (Bi-Pb)-2223 superconductor have been investigated. First, iron was evaporated on Bi-2223 superconductor and then the Fe layered superconductor was annealed at 830 °C for 10, 30 and 60 h. Static Vickers hardness, dc electrical resistivity, X-ray diffraction and scanning electron microcopy have been carried out to assess the effects of Fe doping. These measurements indicates that Fe doping, in comparison with the undoped samples, increased the critical transition temperature, and improved formation of high Tc phase, while decreasing the number and size of voids. Moreover, both microhardness and grain size were also enhanced by increasing the amount of diffusion. The values of microhardness were found to be load dependent. In addition, we have investigated the indentation size effect (ISE) behavior using some models such as the Kick's law, modified proportional specimen resistance (MPRS) model and the Hays- Kendall (HK) approach. Among them, both HK and MPRS models are successful. In this study, the possible reasons of noticed improvement on mechanical and physical properties due to iron diffusion are discussed. © Springer Science+Business Media, LLC 2011.
The influence of cooling rates on microstructure and mechanical properties of Bi1,6Pb0,4Sr2Ca2Cu 3Oy superconductors
(2009-01-01) Cetinkara H.A.; Yilmazlar M.; Ozturk O.; Nursoy M.; Terzioglu C.
We investigated the effect of cooling rates on the microstructure and mechanical properties of Bi1,6Pb0,4Sr2Ca 2Cu3Oy superconductors prepared by standard solid state reaction methods. The samples were annealed under identical condition and cooled with different cooling rates. The investigations consisted of Vickers microhardness, SEM and XRD measurements. XRD examination of the samples showed that high percentage of Bi-2212 phase was observed and low-T c phase increased with increasing the cooling rates. From SEM analysis, flake-like grains were more pronounced with increasing cooling rates. The indentation load versus diagonal length of the samples under different indentation loads in the range of 0.245-2.940 N were presented. We calculated Vickers hardness, Young's modulus, yield strength, fracture toughness values. These mechanical properties of the samples were found to be load and cooling rate dependent. In addition, we calculated the load independent microhardness, Young's modulus, and yield strength and fracture toughness of the samples using different models. The possible reasons for the observed changes in microstructure and mechanical properties of the samples due to cooling rates were discussed. © 2009 IOP Publishing Ltd.
Vickers hardness measurements and some physical properties of Pr2O 3 doped Bi-2212 superconductors
(2012-05-01) Asikuzun E.; Ozturk O.; Cetinkara H.A.; Yildirim G.; Varilci A.; Ylmazlar M.; Terzioglu C.
This study deals with the effect of Pr 2O 3 addition on the structural, superconducting and mechanical properties of Bi-2212 superconductor by means of X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), electron dispersive X-ray (EDX), Vickers microhardness and resistivity measurements. The samples studied are prepared using the standard solid-state reaction method. Onset transition temperatures (T conset) of the samples are estimated from the dc resistivity measurements. Furthermore, the phase ratio and lattice parameters a and c are determined from XRD patterns when the microstructure, surface morphology and element composition analyses of the samples are investigated by SEM and EDX measurements, respectively. Additionally, vickers microhardness, elastic modulus, yield strength and fracture toughness values of the samples are deduced from microhardness measurements. It is found that T conset values of the samples increase from 87 to 97 K with the Pr 2O 3 addition. According to the refinement of cell parameters done by considering the structural modulation, the doping is confirmed by both an increase of the lattice parameter a and a decrease of the cell parameter c of the samples in comparison with that of the pure sample. As for SEM measurements, it is obtained that the surface morphology and grain connectivity degrade with the increase of the Pr 2O 3 addition. Moreover, EDX images show that the elements used for the preparation of samples distribute homogeneously and the Pr atoms enter into the crystal structure by replacing Sr atoms. To sum up, the Pr 2O 3 addition is found to suppress the mechanical, microstructural and superconducting properties of the Bi-2212 superconductor. © 2011 Springer Science+Business Media, LLC.