Analysis of ISE in microhardness measurements of bulk MgB2 superconductors using different models

The indentation load–displacement curves of the MgB2 sample are drawn by different peak load levels ranging from 300 to 1500 mN. Microhardness values are calculated from loading–unloading curves. The results show that the hardness values exhibited peak load dependence, i.e., indentation size effect (ISE) on intermetallic MgB2 superconductors. The peak load dependence is analyzed by using the Meyer's law, the Hays–Kendall approach, the Elastic/Plastic Deformation model, the Proportional Specimen Resistance model (PSR), and the Modified PSR models. As a result, Modified PSR model is found to be the most effective one for microhardness determination of intermetallic MgB2 superconductor.