Land based gas turbines and aero engines have blades with surfaces of varying curvature. In the present case aerofoil specimens with electron beam physical vapor deposited thermal barrier coatings (EBPVD-TBC) have been sectioned from the first stage jet engine turbine blades. The aerofoil specimens have been oxidised from 900°C to 1,050°C for 1,000 hrs up to 10,000 hrs in laboratory air. The instability of the coating system has been evaluated in terms of the residual stress distributions in thermal barrier coating (TBC) and thermally grown oxide (TGO) formed below the TBC. Non-destructive residual stress measurements in the TBC and TGO have been conducted by Raman spectroscopy and photo-stimulated piezo-spectroscopy respectively. It was found that the residual stress in the TBC decreases from tension to compression with extended thermal exposure whereas that in the TGO increases in compression. A systematic change of residual stress was found with respect to substrate curvature. The results are discussed in terms of the evaluation of the overall integrity of these coatings.
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