Influence of particle size and residual stresses on the failure mechanisms of plasma-sprayed ZrO2 thermal barrier coatings

Plasma-sprayed duplex thermal barrier coating systems prepared from two Y2O3-stabilized ZrO2 powders of different particle sizes, at different substrate temperatures, were investigated. The coated samples were subjected to thermocyclic oxidation. Before and after thermocyclic oxidation, the microstructure and the residual stresses were analysed. Correlations between damage mechanisms and the states of residual stress are discussed. The thermocyclic oxidation caused the development of residual compressive stresses owing to the formation of an oxide layer between the metal and ceramic. This resulted in the initiation of surface-parallel cracks in those coatings with pronounced laminar porosity, whereas in the coatings with finely dispersed, spherical porosity, the formation of segmentation cracks perpendicular to the surface at high temperatures resulted in stress relaxation.