An Advanced Methodology for Nondestructive Measurement of Thermal Barrier Coating Thickness via Point Cloud Processing

The thickness of the thermal barrier coating (TBC) has an important impact on the thermal insulation performance and in-service life. The TBC consists of multiple coatings layers in which the metallic bond coat has similar characteristics to the alloy substrate, and therefore, most thickness measurement techniques are difficult to measure the thickness of the metallic bond coat. For this reason, this paper proposes a vision-based nondestructive measurement method that can exclude the influence of the material and internal structure of the coating when measuring the coating thickness. The method in this paper uses a line laser sensor to acquire a point cloud of the blade before and after spraying. Then, the point cloud is processed using several algorithms such as point cloud preprocessing, surface reconstruction, point cloud registration, and point cloud distance calculation to estimate the coating thickness. We employed this method to measure the thickness of the metallic bond coat, which ranged from 50 to 250 mu m. The results indicate that the relative error of thickness measurement is below 5% within a measurement area of 0.01 mm2. Compared to current nondestructive testing (NDT) techniques, the proposed method has many advantages such as having no special requirements for coating materials, insensitivity to the internal structure of the coating, ease to use, high measurement resolution, and fast measurement speed. In addition, the proposed method can enhance existing spray processes because the point cloud obtained in the method can be used to calibrate and plan the spray path.