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

Plasma-sprayed duplex thermal barrier coating systems prepared from two Y2O 3-stabilized ZrO2 powders of different particle sizes, at different substra te temperatures, were investigated. The coated samples were subjected to th ermocyclic oxidation. Before and after thermocyclic oxidation, the microstr ucture and the residual stresses were analysed. Correlations between damage mechanisms and the states of residual stress are discussed. The thermocycl ic oxidation caused the development of residual compressive stresses owing to the formation of an oxide layer between the metal and ceramic. This resu lted in the initiation of surface-parallel cracks in those coatings with pr onounced laminar porosity, whereas in the coatings with finely dispersed, s pherical porosity, the formation of segmentation cracks perpendicular to th e surface at high temperatures resulted in stress relaxation.