An accurate interface detection of TBCs coated blades by double pulse femtosecond laser-induced breakdown spectroscopy

To control the laser machining process of cooling holes on thermal barrier coatings (TBCs) deposited on turbine blades, we implemented interface detection in the depth direction by employing femtosecond-laser-induced breakdown spectroscopy (fs-LIBS). With the plasma reheating and reionization effects of double pulses, a maximum spectral enhancement factors of 12.5 was obtained. The signal-to-noise ratio of the spectrum was improved with decreasing the ablation volume. As a result, accurate detection of the interfaces between the yttria-stabilized zirconia (YSZ) coating, Ni-based superalloy substrate and glass slide was achieved. The comparison of the LIBS results with the energy-dispersive X-ray spectroscopy (EDS) confirmed the effectiveness of the detection method, which exhibited a minimum ablation rate of 255 nm per pulse. Furthermore, a practical online detection approach was proposed for depth profiling and breakdown detection during the machining process of multilayer materials with a maximum detection depth of 273 μm.