The application of photoluminescence piezospectroscopy for residual stresses measurement in thermally sprayed TBCs

Photoluminescence piezospectroscopy (PLPS) was used as a non-destructive technique for the measurement of residual stresses within the thermally grown oxide (TGO) layer beneath plasma-spray thermal barrier coatings (TBC). The technique has proved to be very effective for such measurements in YSZ thermal barrier coatings applied by EB-PVD but its application to thermal sprayed coatings has been hindered by optical scattering in plasma sprayed coatings of usual thicknesses. PLPS experiments were performed on TBCs with cold sprayed bond coatings and several different ceramic layer thicknesses after thermal cycling. The results are discussed as a function of the coating characteristics like bond coat spraying process, thickness of both bond and top coat, microstructural features, and damage accumulation.