Finite-element model of the indentation for ybco-based superconductor thin films

Superconducting films with poor mechanical properties are useless even if they possess good transport and flux-pinning properties. Since additive particles as pinning centers are important changes in a microstructure, their effect on the micromechanical properties such as Young's modulus and hardness have to be investigated with respect to the additional-particle type and quantity, using experimental and numerical methods. In this study, films were dip-coated onto (001) SrTiO3 (STO) single-crystal substrates with metalorganic deposition using the trifluoroacetate (TFA-MOD) technique. The phase analysis and the microstructure of the superconducting thin films were determined with an X-ray diffractometer (XRD) and a scanning electron microscope (SEM). The mechanical-property variations of the pure YBCO and the YBCO thin films with Mn (reacting as BaMnO3) were experimentally obtained with nanoindentation techniques. Thus, the BaMnO3 nanoparticle effects on the structural and mechanical properties of the films were observed. According to the nanoindentation results, the Young's modulus and indentation hardness of the films decreased from 88.54 GPa to 76.47 GPa and from 12.51 GPa to 3.88 GPa, respectively, depending on the additive particles. In addition, the finite-element modeling (FEM) of the indentation was applied to estimate the failure stress/stress distribution relation at the contact region between the indenter and the surface of a YBCO-based thin film, obtaining the same force/penetration depth curve as with the indentation experiment. According to these main aims of FEM, the mesh-design effect, material properties and the boundary condition of the axisymmetric model were chosen and optimized to obtain the mechanical results of the instrumented indentation.