Effect of aliovalent Si/Bi partial substitution on propagation mechanisms of cracking and dislocation in Bi-2212 crystal system

Abstract

This comprehensive study delves into the differentiation of mechanical performance and mechanical characteristics of Bi-site Si partial substituted Bi2.1-xSixSr2.0Ca1.1Cu2.0Oy superconducting ceramic materials with the assistant of Vickers microhardness measurements performed at the indentation test loads intervals 0.245N-2.940N. It is found that the propagations of voids, dislocations and cracks in the Bi-2212 crystal lattice accelerate dramatically because of the dramatic increment in the sizes of crack-producing omnipresent flaws, crack initiation sites, stress concentration regions, strain fields and stress raisers in the crystal matrix with enhancing the Si/Bi partial substitution level. Hence, the presence of Si inclusions in the Bi-2212 superconducting crystal structure makes the active and independent slip systems cancel immediately, and the cracks locate more rapidly into the critical propagation speed. The load required to break the material diminishes due to the reduced durable tetragonal phase. Namely, the Si inclusions favor considerably the intergranular fracture in the host crystal matrix. Besides, it is noted that the sensitivity to the applied load raises remarkably with the substitution level due to the entanglement of dislocations and cracks with each other. As for the mechanical characterization, all the materials studied exhibit the standard indentation size effect behavior (ISE nature) but in the reduction trend with the substitution level. All the findings are also supported by the bulk density and residual porosity parameters. The bulk density experimental results confirm the regression of elastic properties and fracture strength with the Si/Bi substitution level. At the same time, we survey the original mechanical hardness parameters at the vicinity of plateau limit regions via the Hays-Kendall (HK) and indentation-induced cracking (IIC) approaches for the first time. According to the experimental measurement results, the IIC model is observed to be the best theoretical model to discuss the load-independent Vickers hardness parameters of Bi-site Si partial substituted Bi-2212 ceramic compounds.