Failure mechanisms of dense vertically-cracked thermal barrier coatings

Failure lives and failure mechanisms of samples coated with dense vertically-cracked (DVC) thermal barrier coatings (TBCs) were studied in cyclic furnace tests using 1-h cycles at three different temperatures: 1100 °C, 1121 °C and 1151 °C. Average failure life at 1100 °C cycles was six times longer than at 1151 °C. At all the three temperatures in the 1-h cycle tests, progressive cracking of the TBC near and parallel to the interface with the bond coat was observed beginning typically at 25% of the expected failure life. The measured density of such cracks increased almost linearly with cycles. Strains imposed on the TBC by progressive distortion of the bond coat (rumpling) are believed to be primarily responsible for the observed cracking with a secondary role played by the formation of chromia in the bond coat.