Topcoat thickness measurement of thermal barrier coating using grating laser acoustic spectrum method

The thickness of top coating is a crucial factor to characterize the performance of thermal barrier coating. Aiming at the difficulty of thickness measurement with conventional ultrasonic method, a noncontact method based on grating laser ultrasonic acoustic spectrum is proposed. Firstly, the dispersion curve of surface acoustic waves in thermal barrier coating was obtained. The numerical simulation of the established three-layer media model based on finite element method was then performed. Experiments with thermal barrier coating specimens in different thicknesses of top coating were conducted. The theoretical results and simulative results were corrected by ultrasound attenuation theory to fit experimental results. It is found that experimental results show great agreement with the theoretical curve and numerical simulation results after correction, which illustrates the usefulness and potential of the proposed method when applied to the thickness measurement of top coating in service.