Influence of oxidation temperature and time on stresses in thermal barrier coated aerofoil sections

Abstract

The influence of temperature and time of thermal exposure on the residual stresses developed within a thermal barrier coating (TBC) and the underlying thermally grown oxide (TGO) are investigated. Stress measurements on the TBC and the TGO for specimens with aerofoil geometry features were made at positions of fixed curvature using Raman spectroscopy and photo-stimulated piezoluminescence spectroscopy. The Raman shifts were converted to stress via a factor measured using a diamond anvil cell (DAC). The acquired stresses were shown to be tensile at all positions measured in the as-coated specimens, and change progressively from tensile to compressive with thermal exposure. Residual stresses within the TGO were found to be a function of the ageing temperature and time, substrate geometry and thickness of the TBC. The results are discussed with respect to the long term integrity of the coatings.