Observation of Subcritical Spall Propagation of a Thermal Barrier Coating

Abstract

Observations are reported of the room‐temperature propagation of a spalling failure mode of a thermal barrier coating (TBC) from its bond coat after oxidation. The coating is a Y 2 O 3 ‐stabilized ZrO 2 coating formed by electron‐beam deposition on a Ni‐Co‐Cr‐Al‐Y bond coat. The spall shape evolution and stress redistribution as the spall propagates are reported. The failure propagates primarily as an interface crack between the bond coat and the thermally grown aluminum oxide (TGO) formed on the underside of the TBC during oxidation. The observations are consistent with subcritical propagation of an interface crack between the TGO and bond coat assisted by the presence of moisture. An estimate of 9 J/m 2 is made of the fracture resistance in air of the interface.