Stress analysis in thermal barrier coatings subjected to long-term exposure in simulated turbine conditions

Abstract

In recent years, ruby fluorescence spectroscopy has been demonstrated as a powerful technique for monitoring residual stress evolution in the thermally grown oxide scale in thermal barrier coating (TBC) systems. The measured residual stresses, in turn, can be used to monitor evolution of damage in the coatings. Effective use of this technology for real-time damage monitoring requires the identification of trends in measured stresses that can be used as indicators of damage evolution. The present work focuses on studying the evolution of residual stresses in TBC systems during long-term exposure to turbine operating conditions. The coatings are electron beam physical vapor deposited (EBPVD) and atmospheric plasma sprayed (APS) zirconia. The stress evolution in both EBPVD and APS coatings is analytically modeled by an approach that takes into consideration contributions due to both thermal mismatch and oxide growth. Microstructural changes in the TBC system are correlated with measured stress trends through comparison with the modeled stresses. The stress measurements and modeling provide insight into failure modes and mechanisms, and to identify critical features in the measured stress data that can be used as indicators of failure in TBCs.