Non-destructive thickness measurement of thermal barrier coatings by Terahertz three-dimensional synthetic aperture imaging method

The thermal barrier coating thickness of hot end components is directly related to the working performance of aeroengines in high-temperature environments. In this work, we report a non-destructive evaluation method for measuring the thermal barrier coating thickness by three-dimensional synthetic aperture imaging based on a terahertz time-domain spectroscopy system. The method is demonstrated by numerical simulations and experimental measurements. The coating thickness and surface shape measured by the method proposed in this work are in good agreement with those measured by a coordinate measuring machine. The simulation results show that the relative error of the coating thickness of the samples with curved surfaces acquired by the proposed method with respect to its true value is within 3%. The relative errors of the coating thickness and surface shape measured by the terahertz imaging method with respect to those measured by a coordinate measurement machine are within 3.5% and 5.8 μm, respectively. Unlike the existing terahertz technologies, this method can acquire the surface shape and coating thickness simultaneously without any prior knowledge of the surface structures of the thermal barrier coatings of the samples.