Residual stresses in ceramic plasma-sprayed thermal barrier coatings: measurement and calculation

The present work concerns the residual stresses in plasma-sprayed ZrO2-7Y2O3 thermal barrier coatings deposited on Ni-base superalloy substrates which were kept at different temperatures. The stress measurements were carried out on as-sprayed specimens with X-ray diffraction equipment using the “sin2Ψ” technique. It was found that the residual stresses in the ceramic layer changed from tensile to compressive with increasing substrate temperature during deposition from 75 °C to 500 °C. From microstructural observations and residual stress analysis it followed that the high tensile stresses are responsible for the “segmented structure” formed within the ceramic layer, while high compressive stresses lead to the development of microcracks parallel to the coating-substrate interface. A mathematical model was developed for predicting stress distribution in as-sprayed coating-substrate composites. The experimental data showed good agreement with predicted results.