Investigation of the influence on residual stresses of porosity in high temperature ZrO2 coatings on Ag tape for magnet technologies

The present paper reports on the effect on residual stresses of porosity in high temperature ZrO2 coatings on Ag tape for magnet technologies. ZrO2 coatings were fabricated on Ag tape substrate using a reel-to-reel sol–gel system. The microstructural evolution of high temperature ZrO2 coatings was investigated by a scanning electron microscope (SEM). SEM observations revealed that ZrO2 coatings with crack had some porosity and mosaic structure. Stress analysis was carried out on ZrO2 coatings with porosity on Ag tape substrates under cryogenic conditions by using classical lamination theory (CLT) for elastic solution and finite element method (FEM) for elasto-plastic solution in the temperature range of 0 °C to −223 °C in liquid helium media. Because of the static equilibrium, tensile force is applied to the Ag substrate, by ZrO2 coating. The stress component (σx) values change rapidly at coating-substrate interface owing to the different moduli 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 ZrO2 coating and Ag substrate system, the stress distribution changes linearly. FEM results demonstrate that the failure does not occur in ZrO2 coating for all porosities due to its high yield strength.