Abstract

Delamination- spallation was well identified as the thermal barrier coating (TBC) failure mode.  TBC failed at or close to TBC/bond coat interface when thermally grown oxide (TGO) grew to a critical thickness. Aim of the investigation is to increase understanding of progressive damage of TBC. Experiments were designed to closely monitor cracking and delamination progressing by thermal wave imaging (TWI) and microscope at thermal cycling intervals.  It was revealed that microcracking occurred in TBC at close to TBC/bond coat interface at early stage of TBC life time. Those crocks could continuously propagate with thermal cycling or stop by the ridge atTBC/ bond coat interface.   TBC spalled when TGO failed at those ridges and made cracks connected each. The role of bond coat oxidation and its surface roughness will also be discussed.