A Novel High-Frequency Ultrasonic Approach for Evaluation of Homogeneity and Measurement of Sprayed Coating Thickness

A high-frequency ultrasonic approach for testing and evaluating sprayed coating thickness is proposed in this paper. This technique is based on the maximum frequency interval method of the magnitude spectrum of the acoustic pressure reflection coefficient that adopts Welch spectrum estimation. The acoustic propagation model was set up at normal incidence, and the relationship between the maximum frequency interval by the Welch power spectrum and the coating thickness was established to provide the principle for determining coating thickness. According to this principle, the thickness of a series of stainless steel coatings and ZrO2–Y2O3 (yttria-stabilized zirconia (YSZ)) coatings were detected by scanning acoustic microscopy. The relative error was less than 4% with the microscope method, indicating that the proposed ultrasonic method provides a reliable nondestructive way to measure sprayed coating thickness. The uniformity of the sprayed coating thickness could be intuitively observed from C-scan images by programming.