The concept and development of emission spectroscopy for the non-destructive evaluation (NDE) of the failure of thermal barrier coatings

An emission spectroscopy non-destructive evaluation (NDE) method was proposed and developed for in situ monitoring of the degradation of plasma-sprayed thermal barrier coatings (TBCs). Lithium oxide (Li2O) was chosen as the emission spectroscopic marker material doped in the yttria-stabilized zirconia (YSZ) layer in TBC system. The lithium spectral response was examined in flame in terms of lithium oxide concentration, temperature, exposed area of the doped inner layer and distance from collection port to lithium excitation source. The possible viability of emission spectroscopy as a NDE method for the TBC failure inspection was demonstrated. The Li2O concentration in YSZ was optimized based on the thermal cycling test for the Li2O-doped TBCs with different structural configurations. And the durable Li2O-doped plasma-sprayed TBC structure was generated with the optimized Li2O concentration and make it potentially applicable in industry.