The effect on residual stresses of porosity and surface roughness in high temperature insulation coatings on Ag tape for magnet technologies

The main aim of this research is to demonstrate the effect on residual stresses of porosity and surface roughness in high temperature 8% MgO-ZrO₂ and 8% Y₂O₃-ZrO₂ insulation coatings on Ag tape for magnet technologies using classical lamination theory (CLT) and finite element method (FEM). With this regard, the microstructural evolution of MgO-ZrO₂ and Y₂O₃-ZrO₂ coatings was firstly investigated by a scanning electron microscope (SEM). SEM observations revealed that MgO-ZrO₂ and Y₂O₃-ZrO₂ coatings with crack possess mosaic structure. The thermal distribution in the each layer was calculated by using CLT for elastic solution and FEM for elasto-plastic solution in the temperature range of 298 K (25 °C) to 50 K (-223 °C) in liquid helium media. The residual stresses occurred during the manufacturing are neglected. Due to the static equilibrium, Ag substrate is applied tensile force by 8% MgO-ZrO₂ and 8% Y₂O₃-ZrO₂ coatings. We emphasise that the stress component (σ_x) values change rapidly at coating-substrate interface owing to the different modulus of elasticity and thermal expansion coefficient. In spite of the thickness of Ag substrate, the stress components vary from tensile to compressive. In addition, along the thickness of MgO-ZrO₂ and Y₂O₃-ZrO₂ coatings and Ag substrate system, the stress distribution changes linearly.