Damage resistance of a thermal barrier coated superalloy for combustor liners in aero turbines during fatigue and creep

Abstract

This paper deals with an evaluation of the lifetime of a thermal barrier coated (TBC) C263 superalloy under fatigue and creep loading. Results revealed that both TBC and bond-coated substrate had higher endurance limits than the base alloy, while the opposite was found for high stress, low cyclic lifetimes. At high stress, the premature failure for these two materials is possibly due to high stress crack initiation/growth in the TBC/bond coat layers. Oxidation is the cause of the reduced life of the bare substrate as compared to the coated substrate while fatigue and creep experiments are carried out in an oxidizing environment. During 800 degrees C fatigue, the bare specimens behave differently from the coated specimens, but both the bond-coated only and bond coat + TBC specimens seem to exhibit very similar results that are within experimental scatter. Delamination of the bond coat, oxidation of the substrate and spallation of the ceramic layer were evident at very high fatigue and creep stresses. Lateral cracks that grew in the ceramic layer parallel to the stress axis were responsible for spallation of the top coat (TBC) at a very high fatigue stress, whereas, at low creep stress, spallation of the top coat was due to the growth of alumina scale (of thickness >3 mu m) at the top coat (TBC)/bond coat interface