Calibration of Raman Spectroscopy in the Stress Measurement of Air-Plasma-Sprayed Yttria-Stabilized Zirconia

Thermal barrier coatings (TBC) are used widely on a range of components that operate at high temperatures. We report measurement of the factor that is required to convert the Raman shift to stress for air plasma sprayed yttria (7 wt %) stabilized tetragonal zirconia (ZrO₂) (YSZ) thermal barrier coatings. The factor is evaluated for the as-coated condition and also following a heat treatment at 1000 °C for 1050 h. Two Raman bands at 608 cm⁻¹ and 640 cm⁻¹ have been investigated in a diamond anvil cell under hydrostatic pressure up to ~24 GPa. In the range of zero to ~1.6 GPa, a linear behavior was observed in terms of the shifts of these two Raman bands with a gradient similar to dense bulk tetragonal ZrO₂. From these measurements the factors to convert wavenumber shift to stress have been derived. The application of these conversion factors to stress measurement in TBC coated test specimens and components is discussed.