Numerical analysis of the influence of buffer layer thickness on the residual stresses in YBCO/La₂Zr₂O₇/Ni superconducting materials

The present paper addresses a numerical investigation of the influence of buffer layer thickness on the residual stress in YBCO/La₂Zr₂O₇/Ni architectured materials under cryogenic conditions by using classical lamination theory (CLT) and finite element method (FEM) for coated conductor applications. YBCO/La₂Zr₂O₇ multilayer films were fabricated on Ni tape substrate using reel-to-reel sol-gel and pulse laser deposition (PLD) systems. The microstructural evolution of high temperature superconducting YBCO film and buffer layers with La₂Zr₂O₇ configuration grown on textured Ni tape substrates was investigated by using a scanning electron microscope (SEM). Thermal stress analysis of YBCO/La₂Zr₂O₇/Ni multilayer sample was performed by using CLT in the temperature range of 298-175 K in liquid helium media. The YBCO/La₂Zr₂O₇/Ni sample strip was solved by using FEM for linear or nonlinear cases in the temperature range of 298-3 K in liquid helium media. SEM observations revealed that crack-free, pinhole-free, continuous superconducting film and buffer layer were obtained by sol-gel and PLD systems. In addition to microstructural observations, it was found that the largest compressive stresses and failure occur in La₂Zr₂O₇ buffer layer due to its smallest thermal expansion coefficient. The thickness of La₂Zr₂O₇ buffer layer affects the failure. The stress component of σ_x is the smallest in Ni tape substrate due to its largest thickness.