Improvement of mechanical performances and characteristics of bulk Bi-2212 materials exposed to Au diffusion and stabilization of durable tetragonal phase by Au. Issue 9 (15th June 2017)

• Record Type: Journal Article
• Authors: Zalaoglu, Y.; Karaboga, F.; Terzioglu, C.; Yildirim, G.
• Is Part Of: Ceramics international. Volume 43:Issue 9(2017)
• Page Start: 6836
• Page End: 6844
• Publication Date: 2017-06-15
• Subjects: Ceramics -- Sintering -- Hardness measurement -- Mechanical characterization -- Fracture -- Dislocations; Ceramics -- Periodicals; Céramique industrielle -- Périodiques; Ceramics; Periodicals; Electronic journals; 666
• DOI: 10.1016/j.ceramint.2017.02.104
• Languages: English
• ISSNs: 0272-8842

Abstract

Abstract: This study centers sensitively on the determination of optimum diffusion annealing temperature (650–850 °C) for the electrical, superconducting, crystal structure, and especially mechanical characteristics of Au surface-layered Bi-2212 superconducting materials with the aid of dc electrical resistivity, powder X-ray diffraction and microhardness measurements. The experimental results show that all the characteristic properties (normal state resistivity, critical transition temperatures, degree of broadening, phase fractions, lattice cell parameters, elastic modulus, yield strength, fracture toughness, brittleness index and flexural strength parameters) improve considerably with the increment in the annealing temperature up to 800 °C as a consequence of the decreased local structural distortions, lattice strains, disorders, defects and grain boundary interaction problems in the Cu-O2 consecutively stacked layers. After the critical annealing temperature value of 800 °C, the parameters immediately recrudesce towards their global minimum points. Similarly, the highest Bi-2223 phase fraction and c -axis length are observed at the 800 °C annealing temperature due to the best crystallinity and crystal plane alignments. Additionally, the optimum value strengthens the mechanical durability and ideal flexural strength as a result of the stabilization of durable tetragonal phase. Thus, the presence of Au impurities increases the critical stress value so that the crack-producing flaws and cracks propagation divert or slow down rapidly. On the other hand, the excess temperature value such as 850 °C leads to the deleterious effect on the mechanical performances of Au surface-layered Bi-2212 compound because of the increased residual porosity and omnipresent flaws (stress raisers and crack initiation sites). Further, it is at least equally important that the crack propagation or dislocation movement more proceeds through the transgranular regions instead of along the intergranular regions with increasing temperature up to the optimum value beyond which the limited number of operable slip systems enhances noticeably and the intergranular fracture becomes more dominant.