Decrement of crack propagation in bulk Bi-2223 superconducting ceramics with Sn-diffusion annealing temperature

Abstract

The effect of Sn diffusion at different annealing temperature on the Bi1.8Pb0.4Sr2.0Ca2.1Cu3.0Oy superconducting materials is performed with the aid of Vickers microhardness (H-v) measurements at different applied loads in the range of 0.245-2.940 N. The measurement results observed show that all the samples exhibit typical indentation size effect behavior, meaning that both the elastic and plastic deformations play dominant role on the inorganic structures owing to the presence of the elastic recovery. Likewise, the mechanical characteristics increase with the Sn additives as a consequence of improvement of the local structural distortions and boundary weak-links between the grains. Furthermore, the increased Sn inclusions in the crystal lattice make the cracks propagate slower than before. This may be related to the fact that the Sn particles prefer to accumulate throughout the grain boundaries (defect locations) similar to the propagation of the cracks in the materials. In other words, the ductility (nondirectional interactions) of the ceramics tends to improve with the increment in the Sn concentration level in the crystal lattice as a consequence of the enhancement of the tensile strength, fracture toughness and especially Griffith critical crack length values. Hence, the mechanical flexibility takes place rapidly in the crystal structure. Moreover, the hardness measurements allow us to discuss the load dependent and independent microhardness, elastic modulus, yield strength and fracture toughness parameters. At the same time, the experimental data of the Vickers hardness are studied by the available models regarding Meyer's law, proportional sample resistance model, elastic-plastic deformation model and Hays-Kendall (HK) approach for the first time. According to the results obtained, the load dependence of Vickers microhardness is fitted with the HK approach rather than the other methods. Based on the electrical and superconducting results observed before, it is to be mentioned here that the significant improvement of electrical performance may contribute to enhancement in mechanical characteristics.