Application and comparison of theoretical approaches to mechanical properties of bulk YBCO-358 ceramic superconductors

Co nanopowder substituted YBCO-358 (Y3Ba5Cu8-xCoxO18-δ) bulk ceramics were prepared with weight ratios of x=0, 0.05, 0.10 and 0.15 using the SSR (Solid State Reaction) method in tube furnace at oxygen (O2) atmosphere. The impact of partially replacing Cu with Co impurities on the load-independent (or true) microhardness parameters of YBCO-358 have been examined using five theoretical models: Meyer's law (ML), Hays-Kendall (HK), elastic/plastic deformation (EPD), proportional sample resistance (PSR) and the last is indentation-induced cracking (IIC). These models were applied to results that obtained by experimental microhardness tests conducted at various loads. Vicker’s Microhardness analysis shown that each samples has reverse indentation size effect (RISE). The results showed that partial Co nanoparticle doping affected the mechanical behavior/properties of produced YBCO-358 ceramics due to an enhance in crystal structural defects. Additionally, the degradation of the crystal structure led to a reduce in the typical RISE behavior of YBCO-358 superconducting ceramics. It has found that the IIC model was the best fit as it was the only one that produced results close to the saturation point, while the other models did not.