Hardness and microstructural analysis of Bi1.6Pb0.4Sr2Ca2−xSmxCu3Oy polycrystalline superconductors

Bi1.6Pb0.4Sr2Ca2−xSmxCu3Oy superconductors with nominal substitution parameters x = 0.0, 0.001, 0.005, and 0.1 were prepared by the conventional solid-state reaction powder compacting method. The effects of Sm substitution on the phase formation, microhardness and surface microstructure of the samples were investigated. Phase examination by X-ray diffraction indicated that Sm substitution enhanced the formation of the Bi-2212 phase. Morphological investigations by scanning electron microscope revealed that both the number and size of the voids on the sample surfaces decreased with Sm enrichment. This result was also supported by density measurements of the samples. Additionally, indentation-induced Vickers microhardness testing results in the applied load range 0.245–2.940 N were presented. It was shown that microhardness values decreased non-linearly with increasing applied load in all cases. The experimental results were analyzed using the Kick's law, the Hays–Kendall approach and the modified proportional specimen resistance (PSR) model. The analyses revealed that Kick's law failed to explain the observed variations. Besides, the modified PSR model was more suitable than the Hays–Kendall approach to estimate load independent hardness of BSCCO superconductor.