Influence of thermally grown oxide scale on fatigue resistance of a thermal barrier coated superalloy

Abstract

The life of thermal barrier coating prior to spallation is dominated by micro-cracking in both the thermally grown oxide and the yttria stabilized zirconia top coat. The damage generated by this micro-cracking is expected to be a primary life limiting factor. High temperature force controlled fatigue testing of thermal barrier coated (TBC), bond coated only and bare Superni C263 superalloy was conducted in air. It was observed that the coated materials had higher endurance limits than the bare superalloy and the premature failure for these two materials is possibly due to high stress crack nucleation and growth in the TBC/bond coat layers. Oxidation is also the cause of the reduced life of the bare substrate as compared to the coated substrate while fatigue testing is carried out in an oxidizing environment. Spallation of the ceramic layer was evident at very high fatigue stress and also at low fatigue stress where the TBC composite specimen failed after 5,400,107 cycles during fatigue testing at 800 degrees C in air due to a continuous alumina scale growth (thickness > 3 mu m) at the bond coat/TBC (top coat) interface.