Analysis of Indentation Size Effect on Mechanical Properties of Cu-Diffused Bulk MgB2 Superconductor Using Experimental and Different Theoretical Models

Abstract

This study indicates the change of the electrical, microstructural, physical, mechanical and superconducting properties of Cu-diffused bulk MgB2 superconductors by means of scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), microhardness and dc resistivity measurements. The samples are prepared at different annealing temperatures in the range from 650 to 850 ∘C. Electrical and superconducting properties of samples are estimated from the dc electrical resistivity measurements. Moreover, microhardness measurements are performed to investigate the mechanical properties. Further, phase composition, grain sizes and lattice parameters are determined from the XRD measurements. At the same time, the surface morphology and grain connectivity of the samples are examined by SEM investigations. The measurements conducted demonstrate that both the Cu diffusion into the MgB2 system and the increment in the diffusion-annealing temperature increase the critical transition temperatures. Similarly, microstructure and grain size improve while the voids and porosity decrease with the increase of the diffusion-annealing temperature. In addition, the experimental results of the microhardness measurements are investigated using the Meyer’s law, PSR (proportional specimen resistance), modified PRS (MPSR), elastic-plastic deformation model (EPD) and Hays–Kendall (HK) approach. The obtained microhardness values of the samples decrease with the increase of the diffusion-annealing temperature up to 850 ∘C. The Hays–Kendall approach is found to be the most successful model describing the mechanical properties of the samples studied in this work.