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    Reveal of relationship between microscopy architecture and mechanical performance of Y/Bi substituted Bi-2212 engineering ceramics
    (John Wiley and Sons Inc, 2025) Yilmaz, Tolgahan; Kurtul, Gülnur; Ülgen, Asaf Tolga; Erdem, Ümit; Mercan, Ali; Turgay, Tahsin; Yildirim, Gürcan
    This study aims to find out how the crystallinity quality, surface morphology, and mechanical performances change with the substitution of yttrium (Y) for bismuth (Bi) impurity within molar ratios of 0.00 ? x ? 0.12 in the Bi2.0?xYxSr2.0Ca1.1Cu2.0Oy (Bi-2212) cuprates to reveal the dependence of micro surface topology on the substitution mechanism and achieve a strong relation between the impurity ions and crystallization mechanism. The materials are prepared by ceramic method. It is found that all the experimental findings improve remarkably with increasing yttrium impurity molar ratio of x = 0.01. Scanning electron microscopy (SEM) images indicate that the optimum Y ions strengthen the formation of flaky adjacent stacked layers due to the changes of thermal expansion, vibration amplitude of atoms, heat capacitance, reaction kinetics, activation energy, nucleation temperature, thermodynamic stability, and intermolecular forces. Besides, new engineering novel compound produced by optimum Y ions presents the best crystallinity quality, uniform surface view, greatest coupling interaction between grains, largest particle size distributions/orientations, and densest/smoothest surface morphology. Hardness measurement results totally support the surface morphology view. Moreover, mechanical design properties and durability of the tetragonal phase improve significantly with increasing replacement level of x = 0.01 due to the induction of new surface residual compressive stress areas, slip systems, and chemical bonding between the foreign and host atoms. Besides, the same sample exhibits the maximum strength and minimum sensitivity to loads depending on reduction of stored internal strain energy and degree of granularity. Consequently, cracks tend to propagate predominantly within the transcrystalline regions. Furthermore, each material investigated exhibits the characteristic behavior of the indentation size effect. In summary, the optimum Y-doped Bi-2212 sample paves the way for the expanded use of engineering ceramics across various applications based on the enhanced service life. Research Highlights: The presence of the optimum yttrium impurity significantly decreases the Ea value. As the Y/Bi replacement increases up to the molar substitution level of x = 0.01, the mechanical design properties and durability of the tetragonal phase enhance significantly. © 2024 Wiley Periodicals LLC.
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    Öğe
    Role of active slip systems induced with holmium impurity in Bi-2212 ceramics on mechanical design performance and morphological properties
    (Elsevier Sci Ltd, 2022) Ülgen, Asaf Tolga; Çetin, Samet; Zalaoglu, Y.; Turkoz, M. B.; Erdem, Ümit; Yıldırım, Gürcan
    Effect of Ho/Bi partial replacement in Bi2.1-xHoxSr2.0Ca1.1Cu2.0Oy (Bi-2212) superconductors on the fundamental structural, morphological and mechanical performance properties are investigated by Scanning Electron Mi-croscopy (SEM) and Vickers hardness (Hv) measurement techniques. Crystallinity quality and surface morphology including the microcrystal coalescence orientations, grain alignment distributions, microscopic structural problems, microvoids, internal defects, uniform surface view, porosity and particle growth distribution are visually examined with the aid of SEM. Basic mechanical performance and characteristic features of Bi/Ho substituted Bi-2212 superconducting ceramics (0.00 <= x <= 0.10) are also determined with Vickers tests con-ducted at various loads intervals 0.245-2.940 N. Experimental findings show that the characteristic features enhance seriously in case of x = 0.01 due to refinement of crystallinity quality and slip systems. Thus, the op-timum Ho concentration presents the highest mechanical fracture strength to the load applied as a result of better uniform surface appearance and grain orientations, well-connected flaky layers, larger particle size distribution and denser structure, confirmed by the SEM investigations. Namely, much more load is required to accelerate the dislocation movement and crack propagation to the terminal velocity for critical size growth. The fracture predominantly takes place in the transcrystalline regions and hence the propagations are easily controlled with the optimum Ho dopant ions. On the other hand, the increase in the Ho ions in Bi-2212 structure induces the crack-initiating defects for new stress concentration sites. In conclusion, the permanent and non-recoverable deformations appear at even lower indentation test loads. All samples present indentation size effect feature depending on the dominant character of elastic recovery mechanism. Further, original hardness parameters are semi-empirically analyzed in the plateau limit regions using mechanical modelling approaches for the first time. Based on the analyses, Hays-Kendall model exhibits the closest results to the experimental findings.