Measurement of residual stress in air plasma-sprayed Y2O3-ZrO2 thermal barrier coating system using micro-Raman spectroscopy

Residual stress in air plasma-sprayed Y2O3 stabilized ZrO2 thermal barrier coating (TBC) has been measured using micro-Raman spectroscopy. The frequency shift of Raman peak from tetragonal phase (approximate to 640 cm(-1)) is used for determination of local stress in TBC. The relation between Raman peak shift and applied uniaxial stress is measured using a freestanding specimen. The relation is used to determine actual residual stress of the TBC layer coated on a stainless steel substrate. The uniaxial stress, sigma(U)(thc) and Raman peak shift, Delta nu, on the freestanding TBC layer follows: Delta v = Pi sigma(U)(thc)(Pi = 25 cm(-1) GPA(-1)). The average in-plane residual stress in this layer is smaller than that obtained from thermal stress, although the trend of measured values versus thickness follows the estimated thermal stress-substrate thickness relation. This experimental evidence suggests that measurement by micro-Raman spectroscopy is an effective tool to determine local and average residual stress in the Y2O3 stabilized ZrO2 TBC layer