R. J. Visher, W. A. Ellingson, M. D. Shields, Argonne National Laboratory, Argonne, IL; A. Feuerstein, Praxair Surface Technologies, Inc., Indianapolis, IN
The condition of the interface between the metallic bond coat and Yttria-stabilized Zirconia thermal barrier coating (TBC) has been shown to be a potentially critical indicator of prediction of spallation. The optical properties of these ceramic coatings allow laser light of certain wavelengths to penetrate the TBC allowing probing of the sub-surface interface. A laser system in a backscatter configuration has been developed at Argonne National Laboratory (ANL). In cooperation with Praxair Surface Technologies, this system has investigated thermally cycled TBCs produced using electron beam-physical deposition (EB-PVD) and Air Plasma Spray (APS). A series of EB-PVD TBC samples was thermally cycled until failure and backscatter data were acquired after set numbers of thermal cycles. Analysis of the resulting data strongly suggests that bakcscatter parameters can be used to predict failure. Trends in these parameters for the APS samples are similar.
Summary: Elastic optical scattering has been used to study the interface between the bond coat and thermal barrier coating. Analysis of backscattered laser light suggests that this technique is capable of failure prediction and detection of sub-surface defects. Data obtained from the laser backscatter technique will be presented.
