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.