A methodology, based on sintering-induced stiffening, for prediction of the spallation lifetime of plasma-sprayed coatings

This study concerns the effect of sintering-induced stiffening in promoting spallation of plasma-sprayed yttria-stabilized zirconia thermal barrier coatings. Coatings with thickness in the range 350–800 μm were sprayed onto dense alumina substrates. In order to ensure a tough interface, the surface of the alumina substrates were first roughened by laser treatment. Specimens were heat treated at 1500 °C and periodically quenched to ∼100 °C, using nitrogen jets. During cooling, specimens were monitored for spallation via a webcam. Spallation lifetimes were observed to be shorter for thicker coatings. Using a simple fracture mechanics approach, with the strain energy release rate obtained using measured coating stiffness values, the behaviour was found to be consistent with an approximately constant interfacial fracture energy value of the order of 300 J m−2. If this interfacial toughness had been known beforehand, then the rationale presented here could have been used for prediction of coating lifetime. While the experiments are based on use of a ceramic substrate, the approach could be applied to conventional metallic substrate systems.