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 (≈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, σ¯tbcU, and Raman peak shift, Δν  , on the freestanding TBC layer follows: Δν=Π¯σ¯tbcU(Π¯=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.