Modeling oxidation induced stresses in thermal barrier coatings

Oxidation of the bond coat of a thermal barrier coating (TBC) is an important contributing factor to spallation of the ceramic top coat during service. However, the mechanisms by which oxidation facilitates TBC failure are poorly understood. It is also unclear how oxidation may interact with other potential degradation mechanisms. A finite element model was developed to evaluate stresses induced by thermal cycling of a typical plasma sprayed TBC system. It was found that oxidation of the bond coat had a strong effect on ceramic layer stresses and that oxidation induced stresses were influenced by other factors, such as bond coat creep, top coat creep and bond coat roughness. Material discussed: a Waspaloy rod with a NiCrAlY bond coat covered with a zirconia top coat.