Browsing by Author "Aksoy C."

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Changes in mechanical and structural properties of Bi-2212 added MgB2 superconductors
(2016-06-01) Koparan E.; Savaskan B.; Ozturk O.; Kaya S.; Aksoy C.; Wang J.; Speller S.; Grovenor C.; Gencer A.; Yanmaz E.
In the present study, we investigate the effects of Bi2Sr2Ca1Cu2O8+κ (Bi-2212) addition on structural and mechanical properties of bulk MgB2 obtained by hot-press method by means of X-ray diffraction, the Scanning Electron Microscopy and Vickers microhardness measurements. The amount of Bi-2212 was varied between 0 and 10 wt% (0, 2, 4, 6, 8 and 10 wt%) of the total MgB2. All samples were prepared by using elemental magnesium (Mg) powder, amorphous nano boron (B) powder and Bi-2212 powder which are produced by hot-press method. As a result of the hot-press process, the compact pellet samples were manufactured. The microhardness results were analyzed by Meyer’s law, Proportional Sample Resistance Model, Elastic–Plastic Deformation Model, Hays Kendall Approach, and Indentation Induced Cracking (IIC) Model. IIC model was identified as the most appropriate model for samples exhibiting the reverse indentation size effect behavior.
Influence of Sr/Nd partial replacement on fundamental properties of Bi-2223 superconducting system
(2021-03-01) Dogruer M.; Aksoy C.; Yildirim G.; Ozturk O.; Terzioglu C.
This comprehensive work aims to examine the change in flux pinning mechanism, physical, mechanical, and structural characteristics of pure and Sr-site Nd-substituted Bi1.8Pb0.35Sr1.9−yNdyCa2.2Cu3Ox (Bi-2223) systems. The magnetoresistivity performances for all the samples are carried out by magnetotransport experiments in the existence of external magnetic field strength intervals 0–7 T. It is found that the increment of Nd/Sr substitution amount in bulk Bi-2223 system retrogrades the pinning capability of thermal flux motions for interlayer Josephson junction between the isolated grains. Similarly, the coupling probabilities of copper pairs and potential energy barriers are significantly diminished by increasing Nd impurity. This is in association with the enhancement of permanent structural problems in the crystal structure. Therefore, the excessive Nd inclusions improve the reattached linear/split pancake-like nature. In this regard, the best magnetic performance quantities are obtained for the pure sample. Besides, the SEM images show that the grain connectivity and surface morphology damage significantly with the Nd impurity. Additionally, the experimental microhardness findings conducted at various external loads (0.245–2.940 N) display that the Nd purity in the superconducting system degrades dramatically the key design mechanical features. Besides, we analyze the mechanical characteristic properties founded on the theoretical approaches with the proportional sample resistance, elastic/plastic deformation, and Hays–Kendall methods. The results obtained show that the Nd purity causes the indentation size effect behavior to decrease dramatically for all the samples. Furthermore, the findings of Hays–Kendall method are noticed to much more agree with the real hardness parameters. Thus, the Hays–Kendall model is the best methods to find the load-independent Vickers hardness values for the Sr-site Nd-substituted Bi1.8Pb0.35Sr1.9−yNdyCa2.2Cu3Ox (Bi-2223) systems. Moreover, in the dynamic microhardness measurements, the contact depth (hc), elastic modulus (Er), and load (Pmax) of all the samples are experimentally recorded for the first time. The results reveal that the mechanical properties depend strongly on the load and Nd impurity level.