Laser ultrasonic imaging of debonding in TBCs based on spatial gradient energy characteristics at 1200°C

Thermal Barrier Coatings (TBCs) are crucial for ensuring the structural integrity and fatigue life of turbine blades in extreme high-temperature environments. However, the Thermally Grown Oxide (TGO) layer formed at high temperatures will inevitably compromise the interfacial bond strength. The absence of a non-destructive testing method at 1200 °C has motivated this study to propose a laser ultrasonic imaging method for debonding defects in TBCs based on Lamb wave energy leakage and spatial gradient energy characteristics. Through simulations and experiments, Rayleigh-Lamb wave mode conversion mechanisms were identified at TBC debonding area. This work introduces for the first time the Lamb wave energy leakage mechanism into TBC structures. By characterizing Lamb wave energy leakage via spatial gradient energy features, high-precision non-contact optoacoustic imaging of debonding defects was achieved. The study demonstrates that the spatial gradient energy of Lamb waves in debonded regions increases progressively with rising temperature. Under 25 °C and 1200 °C environments, the relative errors in imaging area for 3 mm-diameter debonding defects in TBCs were 4.32% and 4.88%, respectively. This methodology provides detection and monitoring technology for coating damage and failure on high-pressure turbine blades under ultra-high-temperature conditions.