Ultrasonic Examination of Thermal Sprayed Coatings with Frequency Analysis

摘要

Thermal sprayed coating is presently being applied to surfaces of structuressuch as boiler components to prevent erosion and/or corrosion. Methods forthe nondestructive evaluation of degradation and damage, such as decline inadhesive strength and decrease in coating thickness should thus beestablished. This paper proposes nondestructive methods for evaluatingadhesive strength of thermal sprayed coating and measuring coating thicknessby ultrasonic testing. Adhesive strength was evaluated based on spectralintensity at a certain frequency band of ultrasonic waveform. Spectralintensity at a certain frequency band increases with adhesive strengthcorrespondingly. In coating thickness measurement, to enhance signal-tonoiseratio of ultrasonic waveforms, the wavelet transform was used toanalyze the ultrasonic waveform. The echo from the boundary between thecoating and base metal could be readily determined.