Ultrasonic Thickness Measurement Method for Thermal Barrier Coatings Based on Acoustic Velocity-Amplitude Mapping and Damping Attenuation Model

The thermal insulation performance of thermal barrier coatings (TBCs) depends significantly on the ceramic topcoat (TC) thickness, necessitating precise measurement. The uneven and complicated porose microstructure of TC brings a big challenge for accurate and reliable thickness measurement due to the resultant change of acoustic velocity. This paper proposes an ultrasonic thickness measurement method for the TC based on the acoustic velocity-amplitude mapping and damping attenuation model. First, the longitudinal wave transmission equation is derived from interface boundary conditions and attenuation effects, establishing a correlation between acoustic velocity and echo amplitude to characterize the coating’s acoustic properties. Then, a damping attenuation model describes signal decay in the TC, yielding an equation with acoustic velocity as the variable to estimate the required attenuation coefficient in the mapping relationship online. By solving these equations simultaneously, the acoustic velocity is determined online. Experimental results show the proposed method achieves a maximum relative error below 6.49 %, outperforming conventional fixed acoustic velocity approaches.