Hydrogen Detection in Buried Layers of Thermal Barrier Coatings

Abstract

Thermal barrier coatings used in airplane engines or land-based gas turbines can show catastrophic failure (i. e. spallation) typically during cooldown due to thermal expansion mismatch stresses. However, it is also often noted that spallation occurs minutes, hours, or even days after the sample is cold. This type of delayed failure, called “desk top spallation” is, up to now, not fully understood and therefore a field of great interest. Because desk top failure occurs in ambient air, the working hypothesis is that water vapor from the office environment plays a role. Consequently, a number of experiments have been designed to verify this hypothesis. The experiments include more traditional approaches like acoustic emission measurements during cyclic oxidation, but also innovative new approaches like acoustic emission during water drop testing, and hydrogen detection at the interface to the thermally grown oxide using ion beam techniques.