Effect of temperature on rumpling and thermally grown oxide stress in an EB-PVD thermal barrier coating

One hour thermal cyclic tests were conducted on EB-PVD 7YSZ/ (Ni,Pt)Al/ CMSX-4 TBCs at three temperatures (1151 °C, 1121 °C and 1100 °C). Stress in the thermally grown oxide was measured using a non-destructive optical method photoluminescence piezospectroscopy (PLPS). The progression of damage was also documented using destructive sectioning and SEM characterization. Progressive rumpling of the bond coat was observed and quantified while simultaneously non-destructive measurements of the stress in the thermally grown oxide were made. Consistent with previous experiments, the cyclic life decreased and the rumpling rate increased with increasing temperature. The rumpling increased monotonically with cycling while the measured TGO stress decreased monotonically. Contrary to some experiments and theory, power spectra of the evolving bond coat surface did not show a dominate wavelength. The rumpling amplitude was found to be a single valued function of TGO thickness, independent of temperature and an associated six-fold variation in rumpling rate. The experimental results reinforce a connection between the observed failure due to rumpling and the decrease in stress measured non-destructively, providing a strong basis for the use of PLPS measurements to predict remaining life in such systems.