Effect of Diffusion Annealing Temperature on Crack-initiating Omnipresent Flaws, Void/crack Propagation and Dislocation Movements Along Ni Surface-layered Bi-2223 Crystal Structure

Abstract

This study aims to find out the crucial variations in the mechanical performance and characterization of Bi-2223 superconducting compounds with the diffusion annealing temperatures interval 650 °C-850 °C by means of Vickers hardness measurements exerted at the different applied indentation test loads ( 0.245 N-2.940 N) and derived theoretical findings. All the experimental measurement results and theoretical evidences declare that the mechanical characterization and performance are obtained to improve with the increment in the diffusion annealing temperature up the value of 700 °C as a consequence of decrement in the grain boundary coupling problems, local structural distortions, grain misorientations, lattice strains, lattice defects, disorders and dislocations in the adjacent layers. Namely, the optimum annealing temperature of 700 °C resulting in the optimum penetration of Ni impurities into both the superconducting grains and over the grain boundaries develops the crystallinity of Bi-2223 crystal structure. In other words, the surface energy related to the crack-initiating omnipresent flaws, void/crack propagation and dislocation movement reduces due to the augmented critical stress value. In this respect, the diffusion annealing temperature of 700 °C develops the mechanical durability, stiffness, ideal fracture and flexural strength. However, after the certain diffusion annealing temperature value of 700 °C, the crystallinity tends to degrade considerably and in fact dwelling in the worst crystal structure for 850 °C annealing temperature . Accordingly, t he initial crack growths, sizes of crack-producing flaws, void/crack propagation and dislocation movement in the copper-oxide consecutively stacked layers reac h much more rapidly to the critical speeds due to the increased stress amplification so that the Bi-2223 compound with the augmented brittle behavior breaks at even lower test load. Moreover, it is observed that the presence of optimum nickel impurities in the crystal structure strengthens the standard indentation size effect behavior.