Detection of a marker layer in a 7YSZ thermal barrier coating by femtosecond laser-induced breakdown spectroscopy

A new technique for detection of thickness loss in thermal barrier coatings caused by erosion or foreign/domestic object damage has been demonstrated for a 7YSZ thermal barrier coating. The thickness loss was assessed via femtosecond laser-induced breakdown spectroscopy (fs-LIBS) inspection for a marker layer of gadolinium zirconate, embedded at a critical depth within the 7YSZ coating. Spectroscopic detection of the marker layer was possible at fluence levels as low as 18 J cm− 2, which is about 11 times the ablation threshold fluence for 7YSZ. The surface damage caused by the laser pulses was minimal and consisted of extremely small individual circular craters with approximate diameter of 30 μm. Further, the laser action also did not cause any cracking in the 7YSZ layer. The minimal collateral damage associated with fs-laser pulses is one of the major advantages of fs-LIBS for spectroscopic characterization of thermal barrier coatings.